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Construction Technology and Management Thesis

2020

SOURCE OF MIXING WATER AND ITS

EFFECT ON COMPRESSIVE

STRENGTH OF CONCRETE THE

CASE OF BAHIR DAR

PETROS, ERMIAS

http://hdl.handle.net/123456789/11623

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BAHIR DAR UNIVERSITY

BAHIR DAR INSTITUTE OF TECHNOLOGY

SCHOOL OF RESEARCH AND GRADUATE STUDIES

FACULTY OF CIVIL AND WATER RESOURCE ENGINEERING

SOURCE OF MIXING WATER AND ITS EFFECT ON

COMPRESSIVE STRENGTH OF CONCRETE

THE CASE OF BAHIR DAR

BY

ERMIAS PETROS DEGSEW

September 2019

Bahir Dar, Ethiopia

i

SOURCE OF MIXING WATER AND ITS EFFECT ON

COMPRESSIVE STRENGTH OF CONCRETE

THE CASE OF BAHIR DAR

Ermias Petros Degsew

A thesis submitted to the School of Research and Graduate Studies of Bahir Dar

Institute of Technology, BDU in partial fulfillment of the requirements for the degree

of Master of Science in Civil Engineering (Construction Technology and Management)

in the Faculty of Civil and Water Resource Engineering.

Advisor: Kassahun Admassu (Dr- Ing.)

September 2019

Bahir Dar, Ethiopia

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© 2019

Ermias Petros Degsew

ALL RIGHTS RESERVED

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DEDICATION

Dedicated to my father Engineer Petros Degsew who was an inspiration to me and my

mother Hulugirgesh Aytenfisu.

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ACKNOWLEDGMENTS

First of all, I would like to thank God for helping me to finish my education. Then, I

would like to give my gratitude to my advisors Dr. Ing. Kassahun Admassu and Mr.

Abenezer Tariku for their expert guidance throughout this thesis.

I would like to thank Bahir Dar University, FCWRE for technical assistance and the

Ethiopian Roads Authority for giving me the opportunity to join the MSc program.

My gratitude goes to my fellow academic staff and laboratory assistants at Bahir Dar

University and my friends.

Last but not least, I am grateful to my sisters Mahider and Tihitina, my brother Natnael

for their encouragement and support.

vii

ABSTRACT

Making a good quality concrete which satisfies both strength and durability

requirements needs great care starting from ingredient selection. The ingredients

selected should fulfill the requirements stated in standards. Mixing water is one of the

ingredients used and should be suitable for making concrete. In Bahir Dar, there has

not been any research made on mixing water and it is not a common practice to test

mixing water for the purpose of concrete work. Considering this, a study focusing on

mixing water quality is undertaken on active construction projects in Bahir Dar. The

research is conducted by collecting data from construction sites using questionnaires

and field observations. The sources of water for concrete construction are identified

and water samples were collected from the water sources and were tested based on

standard lab procedures to identify the constituents. Then, tests on cement setting time

were conducted using the identified water sources and from site storages. Besides

concrete cubes for a class of concrete of C-30 were prepared using the water sources,

site stored water and were tested for compressive strength on their third, seventh and

twenty-eighth-day ages. The results of the questionnaire survey showed that there are

four main water sources used as mixing water: Abay River, municipal water (potable),

groundwater (hand-dug well), and Lake Tana. The impurities found in the water

sources were within the specified limit as per the ASTM C94. The tests conducted on

the initial and final setting time of cement using each water source and on-site stored

water showed an insignificant deviation from the control water source (municipal

water). The compressive strength test results on the seventh-day mark indicated that

concrete cubes cast using Abay River and groundwater (hand-dug well) had strength

less than 90% of the control. Also, for strength test of cubes using onsite stored water

shows all water sources had strength below 90% of the control. The compressive

strength test results at 28 days mark show that municipal water has the highest strength

with 40.6MPa followed by Abay River water with 39.28MPa, ground water 1 with

32.78 MPa, ground water 2 with 37.92 MPa, ground water 3 with 32.08 MPa and Lake

Tana water with 33.04MPa. Accordingly, the findings indicate to use municipal and

Abay River water sources for concrete construction works. The compressive strength

test results of concrete cube made using storage water on the 28th-day mark show

municipal water have the highest strength with 41.41 MPa followed by Abay River

water with 39.33 MPa, ground water 1 with 33.02 MPa, ground water 2 with 37.33

MPa, ground water 3 with 37.40 MPa and water from Lake Tana with 31.61 MPa. For

making concrete construction works in Bahir Dar City the research finding asserts to

use Abay River from the source, Abay river and municipal water sources on the

construction site for concrete production and curing for the specific projects.

Keywords: Water source, Mixing water, Impurities, Compressive strength, Concrete

viii

Table of contents

CONTENTS

DECLARATION......................................................................................................... II

DEDICATION............................................................................................................. V

ACKNOWLEDGMENTS .........................................................................................VI

ABSTRACT .............................................................................................................. VII

TABLE OF CONTENTS ...................................................................................... VIII

LIST OF TABLES ................................................................................................... XII

LIST OF FIGURES ................................................................................................ XIV

LIST OF ABBREVIATIONS ................................................................................. XV

CHAPTER ONE .......................................................................................................... 1

INTRODUCTION........................................................................................................ 1

1.1. Background to the Study ................................................................................. 1

1.2. Problem Statement .......................................................................................... 2

1.3. Objectives of the Study ................................................................................... 2

1.3.1. General Objective .................................................................................... 2

1.3.2. Specific Objectives .................................................................................. 3

1.4. Research Questions ......................................................................................... 3

1.5. Scope of the Study........................................................................................... 3

1.6. Limitation of the Study ................................................................................... 3

1.7. Significance of the Study ................................................................................ 3

1.8. Organization of the Thesis .............................................................................. 4

CHAPTER TWO ......................................................................................................... 5

LITERATURE REVIEW ........................................................................................... 5

2.1. Introduction ..................................................................................................... 5

2.2. Background to Concrete .................................................................................. 5

2.3. Constituents of Concrete ................................................................................. 7

ix

2.3.1. Aggregates ............................................................................................... 7

2.3.2. Cement ..................................................................................................... 8

2.3.3. Admixtures ............................................................................................... 9

2.4. Role of Water .................................................................................................. 9

2.5. Source of Water ............................................................................................. 11

2.6. Impure Water................................................................................................. 14

2.6.1. Common Impurities ............................................................................... 14

2.6.2. Acceptable Limit of Impurities .............................................................. 19

2.6.3. Effect of Impure Water .......................................................................... 21

2.7. Related Studies .............................................................................................. 23

2.8. Summary of the Literature Review ............................................................... 25

CHAPTER THREE ................................................................................................... 26

MATERIALS AND METHOS ................................................................................. 26

3.1. Introduction ................................................................................................... 26

3.2. Research Design ............................................................................................ 26

3.2.1. Study Area ............................................................................................. 26

3.2.2. Study Technique .................................................................................... 26

3.3. Materials ........................................................................................................ 27

3.3.1. Coarse Aggregate ................................................................................... 27

3.3.2. Sand........................................................................................................ 28

3.3.3. Cement ................................................................................................... 28

3.3.4. Water ...................................................................................................... 28

3.4. Methods ......................................................................................................... 28

3.4.1. Mix Design and Proportioning............................................................... 28

3.4.2. Mixing and Casting ................................................................................ 30

3.4.3. Curing .................................................................................................... 30

3.4.4. Testing.................................................................................................... 30

x

3.5. Methods of Data Analysis ............................................................................. 30

CHAPTER FOUR ...................................................................................................... 32

RESULTS AND DISCUSSION ................................................................................ 32

4.1. Introduction ................................................................................................... 32

4.2. Questionnaire and Field Observation Results ............................................... 32

4.2.1. Discussion of Questionnaire Results ..................................................... 32

4.2.2. Discussion of Field Observation Results ............................................... 39

4.3. Materials Test Results ................................................................................... 40

4.3.1. Aggregates ............................................................................................. 40

4.3.2. Water ...................................................................................................... 42

4.3.3. Cement ................................................................................................... 44

4.4. Testing of Concrete Cubes, Analysis and Discussion of Results .................. 45

CHAPTER FIVE ....................................................................................................... 51

CONCLUSION AND RECOMMENDATION ....................................................... 51

5.1. Conclusion ..................................................................................................... 51

5.2. Recommendation ........................................................................................... 52

5.3. Areas for Further Research ........................................................................... 52

REFERENCES ........................................................................................................... 53

APPENDICES ............................................................................................................ 57

Appendix A: Questionnaire ...................................................................................... 58

Appendix B: Materials Test Results ........................................................................ 63

B.1. Tests for Coarse Aggregate ........................................................................... 63

B.2. Tests for Fine Aggregates ............................................................................. 70

B.3. Setting Time of Hydraulic Cement by Vicat Apparatus ............................... 78

B.4. Mixing Water Test Results ........................................................................... 80

Appendix C: Mix Design ......................................................................................... 81

Appendix D: Compressive Strength Test Results .................................................... 86

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Appendix E: Photos .................................................................................................. 88

xii

LIST OF TABLES

Table 2.1 Beneficial effects of different kinds of admixtures on concrete properties ... 9

Table 2.2 Optional chemical limits for combined mixing water ................................ 19

Table 2.3 Performance requirements for questionable water sources ......................... 20

Table 2.4 Compressive strength corresponding to different water samples ................ 23

Table 4.1 Contractor’s category and level ................................................................... 32

Table 4.2 Summary of questionnaire response rates ................................................... 33

Table 4.3 Work experience of respondents.................................................................. 33

Table 4.4 Mostly produced concrete grades in the project site.................................... 33

Table 4.5 Type of cement ............................................................................................ 34

Table 4.6 Sand and coarse aggregate sources .............................................................. 34

Table 4.7 Mostly used mixing water sources of respondents ...................................... 35

Table 4.8 Alternative sources of mixing water ............................................................ 35

Table 4.9 Respondents’ level of thinking on the water quality they use ..................... 36

Table 4.10 Site water storages ..................................................................................... 36

Table 4.11 Placement of water storages on site ........................................................... 37

Table 4.12 Criteria for using water for concrete .......................................................... 37

Table 4.13 Satisfaction of respondents with the water source ..................................... 37

Table 4.14 Responses to the effect of impure water on workability of concrete......... 38

Table 4.15 Responses to the effect of impure water on strength of concrete .............. 38

Table 4.16 Responses to the effect of impure water on the durability of concrete ...... 38

Table 4.17 Result of water analysis ............................................................................. 43

Table 4.18 Setting time of cement ............................................................................... 44

Table 4.19 Setting time of cement ............................................................................... 44

Table 4.20 Deviation of setting time from the control ................................................. 45

Table 4.21 Deviation of setting time from the control made using of storage water .. 45

Table 4.22 Compressive strength test results of concrete using identified water ........ 46

Table 4.23 Compressive strength test results percentage from the control ................. 46

Table 4.24 Compressive strength test results of concrete using on site stored water .. 47

Table 4.25 Compressive strength test results from control with onsite stored water .. 47

Table B.1 Coarse aggregate gradation ......................................................................... 64

Table B.2 Observation and calculation of fineness of sand ......................................... 71

Table B.3 Calculation of fineness modulus of sand .................................................... 71

xiii

Table B.4 Setting times mixed with different sources of water ................................... 79

Table B.5 Setting times mixed with different sources of water from site storage ....... 79

Table B.5 Results from the water analysis................................................................... 80

Table D.1 Results from Cube compressive strength .................................................... 86

Table D.2 Compressive strength test results made with water from site storages ....... 87

xiv

LIST OF FIGURES

Figure 2.1 Concrete components.................................................................................... 6

Figure 2.2 Range in proportions of materials used in concrete...................................... 6

Figure 2.3 Rounded gravel (left) and crushed stone (right) ........................................... 7

Figure 2.4 Fine aggregate (sand) .................................................................................... 8

Figure 2.5 Strength development of Portland cement .................................................... 8

Figure 2.6 Distribution of earth’s water ....................................................................... 12

Figure 2.7 An atomic absorption spectrophotometer ................................................... 12

Figure 2.8 Salinity vs compressive strength ............................................................... 16

Figure 3.1 Flow chart of the method ............................................................................ 31

Figure 4.1 Lake water being pumped to a hauler vehicle ............................................ 39

Figure 4.2 Abay River water being pumped to a hauler .............................................. 39

Figure 4.3 Abay River water being transported to construction sites .......................... 40

Figure 4.4 Groundwater storage ................................................................................... 40

Figure 4.5 Coarse aggregate grading ........................................................................... 41

Figure 4.6 Gradation of fine aggregate ........................................................................ 42

Figure 4.7 Location of water sources covered by the study ......................................... 43

Figure 4.8 Compressive strength development relationship between water sources ... 48

Figure 4.9 Compressive strength development relationship among onsite stored water49

Figure B.1 Graph of grading of coarse aggregate ........................................................ 64

Figure B.2 Graph of fineness of fine aggregate ........................................................... 72

xv

LIST OF ABBREVIATIONS

ACI American Concrete Institute

ASTM American Standards and Testing Materials

BDU Bahir Dar University

FCWRE Faculty of Civil and Water Resource Engineering

FM Fineness Modulus

MOWUD Ministry of Works and Urban Development

OPC Ordinary Portland Cement

SSD Saturated Surface Dry

1

CHAPTER ONE

INTRODUCTION

1.1. Background to the Study

Water is one of the constituents of concrete and its use is for the purposes of mixing

and curing. Municipal water supply is the main source for making concrete and its prior

use is for drinking. It is developed from various sources including; aquifers, lakes,

rivers, and the sea through desalination. The water is then purified, disinfected through

chlorination. Also, it is the best preferred for making concrete.

In construction sites where municipal water supply is inaccessible water is used either

from shallow wells, ponds or rivers. When these natural sources contain significant

amounts of suspended particles such as silt, organic impurities, and algae additional

testing is necessary.

The presence of impurities in water for concrete mix leads to decreasing structural

properties of concrete such as strength and durability to a larger extent [1]. Water

quality can significantly vary from one source to another depending on geographical

location and season. Hence, the water used for mixing concrete on construction sites

should be tested to avoid structural defects; especially where large scale constructions

take place. Similarly, impurities in the water may adversely affect the time of setting,

strength development, or form stain on concrete.

In a nutshell, the selection of suitable water from different sources for concrete making

is important in order to produce quality concrete with adequate durability. Thus, other

sources besides municipal water for the purpose of making concrete should be checked

for their suitability.

2

1.2. Problem Statement

Concrete construction uses mixing water from sources that are distinct depending on

availability, suitability, and location of construction sites. Bahir Dar is located in the

northern part of Ethiopia and has different water sources such as a lake, river and

groundwater. Water from these different sources has its own constituents and

properties.

The municipal water supply (the one that is potable) is not available in some

construction sites due to the shortage of water for the City. Even though the

recommended water for concrete construction is potable, some projects use sources

other than the treated municipal water supply and yet it is not common to test the

quality. Furthermore, water source storing practice and suitability for concrete

construction is not well understood.

Impurities found in mixing water have a diverse effect on setting time and compressive

strength of concrete [2]. It is important to study the effect of the water from each source

because different concentrations of impurities could be found due to environmental

exposures. Meanwhile, in Bahir Dar researches have not been conducted on the effects

of impurities found in mixing water for construction purposes.

Having that in mind, this research tries to identify the different sources of water for

making concrete in Bahir Dar and inspect the impurities in the identified water sources.

Also, the research aims at demonstrating the differences in cement setting time and the

compressive strength of concrete test specimens by using each water source in reference

to the municipal water.

1.3. Objectives of the Study

1.3.1. General Objective

The study assesses and investigates sources of mixing water used for concrete

construction works and examines its influence on setting time of cement and

compressive strength of concrete as practiced in Bahir Dar City construction sites.

3

1.3.2. Specific Objectives

The specific objectives of this research are:

1. To assess the main sources of mixing water in the study area.

2. To identify impurities found in the water sources.

3. To investigate the effect of the water source on the cement setting time.

4. To investigate the effect of the water source on concrete compressive strength.

1.4. Research Questions

The thesis has the following research questions:

- What are the sources of water (mixing and curing) used for making concrete in

the study area?

- What type of impurities are found on those identified water sources?

- What is the effect of water source on compressive strength of concrete and

setting time of cement?

1.5. Scope of the Study

This research covers the assessment of the most common sources of mixing water used

for building construction in the City of Bahir Dar, setting time of cement and

compressive strength of a normal (C-30) concrete. Concrete making materials used in

this research are collected from commonly used sources identified within the study area.

1.6. Limitation of the Study

Due to budget and time limitations, water samples were not analyzed for seasonal

changes of constituents and the attributes to geographical locations.

1.7. Significance of the Study

The contribution of this study is to identify the most common water sources for concrete

construction works for buildings that are vastly constructed in Bahir Dar. In a similar

manner, it could develop the culture of testing water by creating awareness among

4

concerned authorities, the regulatory body, contractors and other stakeholders on the

need of selecting water sources for concrete construction.

1.8. Organization of the Thesis

The rest of the thesis is organized as follows. Chapter two presents the literature

reviewed in the area of concrete making materials. It gives brief introduction, and

effects of impure mixing water on making concrete. Different mixing sources and

concrete making materials are explained. Chapter three presents materials and methods

used for conducting experimental testing on concrete cubes. Chapter four presents the

results and discussions of the research findings. Finally, in chapter five conclusion,

recommendation and further work is presented.

5

CHAPTER TWO

LITERATURE REVIEW

2.1. Introduction

This chapter on literature review focuses on constituents of concrete, the role of mixing

water, sources of water, impurities in water and their effect on concrete properties as

viewed by related studies concerning setting time and compressive strength of concrete.

2.2. Background to Concrete

Concrete is the most widely used construction material in the world and its popularity

can be attributed to two aspects. First, concrete is used for many different structures

such as dams, pavements, building frames. Second, the amount of concrete used is

much more than any other construction material [3].

A variety of shapes and structural forms can easily be attained by using concrete. Also,

concrete can be readily prepared and fabricated owing to the fact that it is widely used

worldwide. As well, its constituents are ubiquitous and available almost anywhere in

the world [4, 5].

Preparing concrete of desirable quality requires properly selecting raw materials and

controlling each and every step of the concrete making process [6]. The major phases

in concrete production or making are batching, mixing, transporting, placing,

compacting, finishing and curing. Major constituents of concrete such as aggregate,

cementitious materials, admixture, and water should be examined in order to learn the

properties of concrete [1, 3].

According to Samson K. (2017), standardizing construction materials is crucial to

ensure the quality of concrete and the materials were not tested for quality in

construction areas of Bahir Dar. The researcher also commented that water quality and

its amount were not determined and these may affect concrete strength seriously [7].

6

Concrete is a mixture made of aggregates and paste. It is composed of coarse granular

material (the aggregate or filler) glued together by a hard matrix of material (the cement

or binder) that fills the space among the aggregate particles. Concrete components are;

cement, water, fine aggregate and coarse aggregate are shown in Figure 2.1 [2, 3].

Figure 2.1 Concrete components [2]

The paste that binds the aggregate is composed of Portland cement and water. It binds

the aggregate and hardens because of the chemical reaction between the cement and

water. Also, it comprises 25% to 40% of the total volume of concrete. The absolute

volume of cement is between 7% and 15% and the water is between 16% and 21% [2].

Figure 2.2 Range in proportions of materials used in concrete [2].

A satisfactory compressive strength and adequate durability are the primary

requirement of a good concrete in its hardened state. For making concrete one of the

major components that determines the strength and different durability parameters is

water. Almost any natural water that is drinkable and has no pronounced taste or odor

can be used as mixing water for making concrete [8, 9].

7

2.3. Constituents of Concrete

2.3.1. Aggregates

The strength of aggregate is rarely tested and generally does not influence the strength

of conventional concrete as much as the strength of the paste and the paste-aggregate

bond. Aggregates are potentially harmful if they contain compounds known to react

chemically with Portland cement concrete and produce significant volume changes of

the paste, aggregates, or both; interference with the normal hydration of cement; and

otherwise harmful byproducts. Organic impurities may delay the setting and the

hardening of concrete may reduce strength gain. Organic impurities such as peats,

hummus, and organic loam may not be as detrimental but should be avoided [8].

The aggregates are usually washed and graded at the pit or plant. Some variation in

type, quality, cleanliness, grading, moisture content, and other properties is expected.

Aggregates must be clean, hard, strong, durable particles free of absorbed chemicals,

coating of clay, and other fine materials in an amount that could affect hydration and

bond of the cement paste. Changes in the moisture content of aggregate, unless carefully

compensated for by the amount of added water, also seriously affect the strength of

concrete. To minimize these changes, stockpiles should are so that the aggregate is

allowed to drain before use; also, the mixer operator should be well trained in

maintaining constant workability of the mix [2, 9].

2.3.1.1. Coarse Aggregate

Coarse aggregates consist of a combination of gravels or crushed stone with particles

predominantly larger than 5mm and generally between 9.5mm and 37.5mm [8].

Figure 2.3 Rounded gravel (left) and crushed stone (right) [8]

8

A research conducted by Yonas T. (2018), shows concrete made using untreated

(without washing) aggregate suffered a loss of 32% to 35% in compressive strength

compared with the concrete prepared with treated aggregate with OPC and PPC cement

respectively [10].

2.3.1.2. Fine Aggregate

Fine aggregates generally consist of natural sand or crushed stone with most particles

smaller than 5mm [8].

Figure 2.4 Fine aggregate (sand) [8]

2.3.2. Cement

The properties of fresh concrete have a large influence on construction speed and

decision making. Also, properties such as hardening are direct results of hydration.

Hydration of cement is the reaction between cement particles and water, including

chemical and physical processes. And the strength development of cement constituents

varies with respect to time as shown in Figure 2.5 [3].

Figure 2.5 Strength development of Portland cement [3]

9

2.3.3. Admixtures

An admixture is defined as a material other than water, aggregates, cement, and

reinforcing fibers that are used in concrete as an ingredient and added to the batch

immediately before or during mixing. Admixtures can be roughly divided into the

following groups: air-entraining agents, chemical admixtures, mineral admixtures, and

miscellaneous admixtures and Table 2.1 shows types of admixtures and their effective

usage [3].

Table 2.1 Beneficial effects of different kinds of admixtures on concrete properties [3]

Concrete Property Admixture Type Category of Admixture

Workability Water reducers Chemical

Air-entraining agents Air entraining

Inert mineral powder Mineral

Pozzolans Mineral

Polymer latexes Miscellaneous

Set control Set accelerators Chemical

Set retarders Chemical

Strength Pozzolans Mineral

Polymer latexes Miscellaneous

Durability Air-entraining agents Air entraining

Pozzolans Mineral

Water reducers Chemical

Corrosion inhibitors Miscellaneous

Shrinkage reducer Miscellaneous

Special concrete Polymer latexes Miscellaneous

Silica fume Mineral

Expansive admixture Miscellaneous

Color pigments Miscellaneous

Gas-forming admixtures Miscellaneous

2.4. Role of Water

Water is defined as “a liquid without color, smell or taste that falls as rain is in lakes,

rivers, seas, and is used for drinking, washing, etc.”. It is a very slightly compressible

liquid oxide of hydrogen, represented as H2O, which appears bluish in thick layers.

Water, freezes at 00C and boils at 1000C, has a maximum density at 40C and a high

specific heat. Water exists in the form of solid as ice, in the form of liquid as water or

a gaseous form as vapor [11, 12].

10

Water is one component for making concrete and is involved in its whole life. It is used

for the purpose of mixing and curing of concrete where the suitability should be

considered [13].

According to Zongjin L. (2011), mixing water is free water that is added in freshly

mixed concrete and has three main functions:

- It reacts with the cement powder, consequently producing hydration products

- It acts as a lubricant, contributing to the workability of fresh mixture, and

- It secures the necessary space in the paste for the development of hydration

products

Of course, water is necessary for the hydration of cement. However, the water added in

the mix is usually much higher than what the chemical reaction needs due to the fluidity

requirement of concrete for placing. Thus, we can distinguish the three kinds of water

in cement paste according to their roles: chemically reacted water, absorbed water, and

free water.

- The chemically reacted water (H2O=H) or chemically bonded water is the water

that reacts with CaO=C, SiO2=S, Al2O3=A, Fe2O3=F, and SO3=Ṧ to form

hydration products such as C–S–H, CH, and C6A3H32=Aft (ettringite). This type

of water is difficult to remove from cement paste and a complete decomposition

happens at a temperature of about 9000C.

- The absorbed water is the water molecules inside the layers of C–S–H gel. The

loss of absorbed water causes shrinkage, and the movement or migration of

absorbed water under a constant load affects the creep.

- Free water is the water outside the C–S–H gel. It behaves as bulk water and

creates capillary pores when evaporated, and can influence the strength and

permeability of concrete [3].

To produce a good-quality concrete the total amount of water in concrete and the water-

to-cement ratio are the most critical factors. For a given water-cement ratio, one selects

a minimum amount of cement that will secure the desired workability. Too much water

reduces concrete strength, while too little makes the concrete unworkable. Plasticity

11

and fluidity of concrete mix increases as water is added but the strength decreases

because of the larger volume of voids created by free water [13].

According to Joseph F. and James H. (2006), poor quality water may adversely affect

the time of setting, the strength development or cause staining. Popular selecting criteria

of water for concrete use the classical expression “if the water is fit to drink it is all

right for making concrete” and this expression has its own paradoxes:

- Water containing a small number of sugars or citrate flavoring would be suitable

for drinking but not mixing concrete.

- Conversely, water suitable for making concrete may not necessarily be fit for

drinking.

Nearly all-natural water, fresh waters, and water treated for municipal use are

satisfactory as mixing water for concrete if they have no pronounced odor or taste. Since

very little attention is usually given to the water used in concrete, a practice that is in

contrast to the frequent checking of the admixtures, cement, and aggregate components

of the concrete mixture. In fact, most of the references appear to be outdated, but they

still represent the base of modern concrete technology with regard to water for mixing

and curing [14].

Curing is used to protect concrete from loss of moisture. It can be achieved using

sprinkling, ponding or covering with plastic film or by the use of sealing compounds

[13].

2.5. Source of Water

Water is extremely important for all known forms of life and covers 71% of the earth’s

surface. 96.5% of the planet’s crust water is found in seas and oceans, 1.7% in

groundwater, 1.7% in glaciers and the ice caps of Antarctica and Greenland and 0.001%

in the air as (vapor, clouds, and precipitation). Also, 3% of the water is fresh water and

97% of earth water is saltwater. 98.8% of the freshwater is in ice and groundwater and

less than 0.3% of the freshwater is in rivers, lakes and the atmosphere. An illustrative

diagram is in Figure 2.6 [15, 16].

12

Figure 2.6 Distribution of earth’s water [16]

According to Kosmatka et.al. (2011), the greatest volume of mixing water used for

making concrete is from the municipal water supply, municipal reclaimed water supply,

site-sourced water, or water from concrete production operation (wash water). Other

sources of batch water include Free moisture, adsorbed on the surface, and on

aggregates constitutes a substantial portion of the total mixing water. It is important to

note that the free water on the aggregate is free from harmful materials.

During hot- weather concreting, ice might be used as part of the mixing water. The ice

should be completely melted by the time mixing is completed. Water might also be

added by the truck operator at the job site. And also, water contained in admixtures

must be considered part of the mixing water if the admixture’s water content is

sufficient to affect the ratio of the water-cementitious material by 0.01 or more. An

atomic absorption spectrophotometer can be used to detect the concentration of

elements in the laboratory analysis of water and shown in Figure 2.7.

Figure 2.7 An atomic absorption spectrophotometer [8]

13

Reclaimed water is wastewater treated to remove solids and certain impurities. It is

typically used for non-potable applications uses such as irrigation, dust control, fire

suppression, concrete production, and construction. Reclaimed water use supports

sustainable efforts to extend our water supplies rather than discharging the treated

wastewater to surface waters such as rivers and oceans. Recycled water from concrete

production is primarily a mixture of water, cementitious materials (partially or

completely hydrated), and aggregate fines resulting from processing returned concrete.

Recycled water can include truck wash water and stormwater at the concrete plant [8].

Lake Tana receives inflow from streams and springs that originate from the two large

shield volcanoes and runoff from its water shade. The water quality of the lake is

characterized by relatively low salinity depending on the seasons. The Lake receives

untreated and improperly treated industrial wastes from the major industries of Bahir

Dar and Gondar and small Towns around it that are discharged into the wetlands. The

wetlands trap much of the sediment yield of the streams descending from the highland

ridges. Lacustrine deposits comprising dominantly fine silt and clay cover at the bed of

Lake Tana. These deposits have been identified from high-resolution seismic studies,

supported by extensive analysis of cores drilled up to 9.5m deep [17].

Hand-dug wells (HDWs) are a common technology employed for a rural water supply

because of its relative ease in construction, low-cost input and its familiarity to most

communities. in order to improve a well’s performance. HDWs are shallow ranging in

depths up to 20 meters and approximately 1.5 meters in diameter, which accommodates

the digging process. These wells most often are dug down to tap water stored in perched

water tables, clay or other impermeable layers on which percolated water collects above

the main water table [18].

The importance of quality water is because poor quality may interfere with the setting

of cement, may adversely affect the strength of concrete or causes staining of its

surface, and may also lead to corrosion of reinforcements [19].

14

2.6. Impure Water

Great number of impurities can be found in water and from these impurities one that

are mostly found and influence the quality of normal concrete are alkali carbonates and

bicarbonates, chlorides, sulfate, iron salts, inorganic salts (mainly found in seawater,

acid water, alkaline water, wash water, industrial wastewater), and organic impurities

(like Sugar, silt or suspended particles, oils, algae) [8].

2.6.1. Common Impurities

Some impurities can be found in different forms in mixing water used for making

concrete is overviewed as a synopsis.

2.6.1.1. Chloride

The presence of chloride ions in concrete creates a high alkaline chemical environment

and causes corrosion of reinforced steel. The acid-soluble chloride ion level at which

steel reinforcement corrosion begins in concrete is about 0.2% to 0.4% by mass of

cement. Chloride can originate into concrete from distinct mixture ingredients;

admixture, aggregates, cementitious materials and mixing water, or through exposure

to deicing salts, seawater, or salt-laden air in coastal environments. Considering this

placing an acceptable limit on chloride content for anyone ingredient, such as mixing

water, is problematic considering the variety of sources of chloride ions in concrete.

Concentrations of 20,000 ppm of sodium chloride are generally tolerable in concrete

that will be dry in service and has a low potential for corrosive reactions [2].

2.6.1.2. Sulfate

Sulfate ions are found throughout the world. Sulfates are also present in seawater, in

some industrial environments, and in sewers. Concern over a high sulfate content in

mix water is due to possible expansive reactions and deterioration by sulfate attack.

Sulfate attack can lead to loss of strength, expansion, spalling of surface layers, and

ultimately the disintegration of concrete. Also, high amounts of sulfates in soil or water

can attack and destroy a concrete that is not properly designed. Flowing water is more

aggressive than stagnant water since new sulfate ions are constantly being transported

to the concrete for a chemical reaction. Sulfates can attack concrete by reacting with

15

hydrated compounds in the hardened cement paste. Sulfate ions attack calcium

hydroxide and the hydration products of C3A, forming gypsum and ettringite in

expansive reactions. The most common form of sulfate in aggregates is gypsum

(CaSO4•2H2O) and occurs as a coating on sand and gravel or in weathered slags.

Aggregates made from recycled building materials may contain sulfates in the form of

contamination from plaster or gypsum wallboard. It is difficult to eliminate the gypsum

present. On sieving, these particles break apart, becoming part of the sand fraction [2].

According to ASTM C1602, 3000 ppm of sulfate should be considered unless special

precautions in the composition of the concrete mixture are taken [20].

2.6.1.3. Alkali Carbonate and Bicarbonate

A large concentration of the sum of dissolved salts, which exceed 1000 ppm, can reduce

concrete strength and have an effect on setting time. The presence of Carbonates and

bicarbonates of sodium and potassium causes varying effects on the setting time of

different types of cement. Sodium carbonate (Na2CO3) can cause a very rapid setting,

bicarbonates can either accelerate or retard the set depending on the chemistry of the

cement used in the concrete [2].

Per the work of Venkateswara and Vangala (2013), the effect of strong alkaline

substances, like sodium carbonate (Na2CO3) and sodium bicarbonate (NaHCO3), on

setting time and compressive strength development of concrete assessment results

under laboratory condition indicates that Na2CO3 in deionized water accelerates the

initial as well as the final setting times whereas the compound NaHCO3 retards the

initial and final setting times. Na2CO3 and NaHCO3 in deionized water decrease the

compressive and tensile strength of concrete specimens significantly at 28 days and 90

days [21].

2.6.1.4. Salts

Natural groundwaters rarely contain more than 20 ppm to 30 ppm of iron; however,

acid mine waters may carry rather large quantities. Iron salts in concentrations up to

40,000 ppm do not usually affect concrete strengths adversely. The potential for

staining should be evaluated. Salts of manganese, tin, zinc, copper, and lead in mixing

16

water can cause a significant reduction in strength and large variations in setting time.

Of these, salts of zinc, copper, and lead are the most active. Generally, concentrations

of these salts up to 500 ppm can be tolerated in mixing water. Another salt that may be

detrimental to concrete is sodium sulfide; even the presence of 100 ppm needs testing

[2].

Referring G. Sai Teja (2014), a small amount of salinity in mixing water improves the

compressive strength of concrete as shown in Figure 2.8 [22].

Figure 2.8 Salinity vs compressive strength [22]

2.6.1.5. Silt and Clay

Higher amounts of suspended clay or fine rock particles might not affect strength but

may influence other properties of some concrete mixtures. In order to reduce the

amount of silt and clay added to the mixture by way of mix water before use, the muddy

or cloudy water should be passed through setting basins or otherwise clarified. In

mixing water about 2000 ppm of these particles can be tolerated and when cement fines

are returned to the concrete in the form of reused wash water up to 50,000 ppm can be

tolerated [2].

A research finding by Habtamu L. (2015), shows that the fine aggregates in and around

Bahir Dar contain a high amount of silt and clay in it. It also shows the awareness of

the people in the construction industry on the effect of those silt and clay in the sand is

poor [23].

17

2.6.1.6. Acid Waters

Approval of acid mixing water for use is based on the concentration (in ppm) of acids

in the water and rarely the acceptance is based on PH (a log scale measure of the

hydrogen-ion concentration). Organic acids, such as tannic acid, can have a significant

effect on strength at higher concentrations. Mixing waters containing hydrochloric,

sulfuric, and other common inorganic acids in concentrations as high as 10,000 ppm

have no adverse effect on strength. Acid waters with pH values less than 3.0 may create

handling problems and should be avoided if possible [8].

Most acidic solutions will disintegrate Portland cement concrete. The rate of

disintegration will be dependent on the type and concentration of acid. weak solutions

of some acids have insignificant effects. Also, Certain acids such as oxalic acid are

harmless. Acids attack concrete by dissolving both hydrated and un-hydrated cement

compounds as well as calcareous aggregate. Siliceous aggregates are resistant to most

acids and other chemicals and are sometimes specified to improve the chemical

resistance of concrete. These aggregates should also be avoided when a strongly basic

solution, like sodium hydroxide, is present as it attacks siliceous aggregate [2].

2.6.1.7. Alkaline Waters

Potassium hydroxide in concentrations up to 1.2% by mass of cement has little effect

on the concrete strength developed by some cement, but the same concentration, when

used with other types of cement, may substantially reduce the 28-day strength. Waters

with sodium hydroxide concentrations of 0.5% by mass of cement do not greatly affect

concrete strength provided a quick set is not induced. Higher concentrations, however,

may reduce concrete strength. The possibility of increased alkali-aggregate reactivity

should be considered [2].

2.6.1.8. Industrial Waste Water

Wastewaters such as those from tanneries, paint factories, coke plants, and chemical

and galvanizing plants may contain harmful impurities. When industrial wastewater is

used as mixing water in concrete, the reduction in compressive strength is generally not

greater than 10%- 15%. Most waters carrying industrial wastes have less than 4000

18

ppm of total solids. It is best to test any wastewater that contains even a few hundred

ppm of unusual solids [2].

2.6.1.9. Harmful Substances

Organic Impurities are often of a humus nature containing tannates or tannic acid,

highly colored waters, waters with a noticeable odor, or those in which green or brown

algae are visible should be regarded with suspicion and tested accordingly. Algae in

water lead to lower strengths either by influencing cement hydration or by causing a

large amount of air to be entrained in the concrete. Water containing algae is unsuitable

for concrete because the algae can cause an excessive reduction in strength. Algae that

is present on aggregates reduce the bond between the aggregate and cement paste. A

maximum algae content of 1000 ppm is recommended. The effect of organic substances

on the setting time of Portland cement or the ultimate strength of concrete is a problem

of considerable complexity. Such substances, like surface loams, can be found in

natural waters [8].

Per the work of Kosmatka et.al. (2003), typical sewage may contain about 400 ppm of

organic matter. After the sewage is diluted in a good disposal system, the concentration

is reduced to about 20 ppm or less. This amount is too low to have any significant effect

on concrete strength. A rapid setting and considerable reduction in 28-day strength are

caused due to sugar in quantities of 0.25% or more by mass of cement. Small amounts

of sucrose, as little as 0.03% to 0.15% by mass of cement, usually retard the setting of

cement.

Oils may interfere with the action of air-entraining agents. Mineral oil (petroleum) not

mixed with animal or vegetable oils may have less effect on strength development than

other oils. However, mineral oil in concentrations greater than 2.5% by mass of cement

may reduce strength by more than 20%. When evaluating a water source for its effect

on concrete properties, it is important to also test the water with chemical admixtures

that will be used in the concrete mixture. Certain compounds that are found in mixing

water can influence the performance and efficiency of certain admixtures. For example,

the dosage of air-entraining admixture may need to be increased when used with hard

waters containing high concentrations of certain compounds or minerals [2].

19

2.6.2. Acceptable Limit of Impurities

The qualitative limits of harmful constituents in water are not known reliably and

unnecessary restriction can be economically damaging [8]. According to Neville

(2010), water that contains large quantities of chlorides causes persistent dampness and

surface efflorescence. Chloride can also lead to corrosion of embedded steel in

concrete. Some mineral waters contain alkali carbonates and bicarbonates that

contribute to alkali-silica reaction. The presence of algae results in air entrainment with

a consequent loss of strength [19].

ASTM C1602 states that an acceptable limit in the concrete depends primarily upon the

type of structure and the environment to which it is exposed during its service life.

Some impurities may have little effect on strength and setting time, yet adversely affect

durability and other properties Therefore, certain optional limits on chlorides, sulfates,

alkalis, and solids in the mixing water may be set or appropriate tests can be performed

to determine the effect the impurity has on various properties as shown in Table 2.2

[20].

Table 2.2 Optional chemical limits for combined mixing water [20]

Chemical or Type of construction Maximum

concentration,

ppm*

Test method

Chloride, as Cl ASTM C114

Pre-stressed concrete or concrete in bridge decks 500**

Other reinforced concrete in moist environments or

containing aluminum embedment or dissimilar metals

or with stay-in-place galvanized metal forms

1000**

Sulfate, as SO4 3000 ASTM C114

Alkalies, as (Na2O +0.658 K2O) 600 ASTM C114

Total solids by mass 50,000 ASTM C1603

*ppm is an abbreviation for parts per million.

**The requirements for concrete in ACI 318 shall govern when the manufacturer can

demonstrate that these limits for mixing water can be exceeded. For conditions allowing

the use of calcium chloride (CaCl2) accelerator as an admixture, the chloride limitation is

permitted to be waived by the purchaser

20

Acceptance criteria for water to be used in concrete that includes a limit on chlorides,

sulfates, and alkali are given in ASTM C1602, the standard specification for mixing

water used in the production of hydraulic cement concrete and it includes provisions

for:

1) Potable water–that which is fit for human consumption;

2) Non-potable water–other sources that are not potable, that might have an

objectionable taste or smell but not related to water generated at concrete plants.

This can represent water from wells, streams, or lakes;

3) Water from concrete production operations–process (wash)water or stormwater

collected at concrete plants; and

4) Combined water–a combination of one or more of the above-defined sources

recognizing that water sources might be blended when producing concrete. All

requirements in the standard apply to the combined water as batched into the

concrete and not to individual sources when water sources are combined [20].

For the structural use of concrete Ethiopian Building Code Standard (EBCS 2, 1995)

states that “mixing water shall be clean and free from harmful matter” [24]. And

according to an ASTM C94 acceptable criteria for water to be used in concrete states

“The mixing water shall be clear and apparently clean. If it contains quantities of

substances which discolor it or make it smell or taste unusual or objectionable or cause

suspicion, it shall not be used unless service records of concrete made with it or other

information indicates that it is not injurious to the quality of the concrete” [20]. Water

containing less than 2000 parts per million (ppm) of total dissolved solids is generally

satisfactory for use in concrete. Water containing more than 2000 ppm of dissolved

solids should be tested for its effect on strength and time of set as shown in Table 2.3

[20].

Table 2.3 Performance requirements for questionable water sources [20]

Limits Test Method

Compressive strength, the minimum % of

control at 7 days

90 ASTM C31, C39

Time of set, deviation from control, Hr: min. From 1:00 earlier to 1:30 later ASTM C403

*Comparisons must be based on fixed proportions of a concrete mix design representative

of questionable water supply and a control mix using100% potable water.

21

Curing water should generally satisfy the requirements for mixing water. As a rule,

water that contains less than 1000 PPM and potable water that contains inorganic solids

in excess of 2000 PPM is specified for many projects [8].

2.6.3. Effect of Impure Water

The impurities in water affect setting time, compressive strength, causes efflorescence,

staining, corrosion of reinforcement, volume instability, and reduces durability. It is

important to use water which has less amount of undesirable impurities in mixing water

for concrete. Hence, it is important to use water which is suitable for making concrete

at a site because impurities can weaken the strength and decrease durability [8].

Hereunder relation between water and properties of concrete such as setting time of

cement and compressive strength of concrete is presented in comparison with other

studies.

2.6.3.1. Influence on Setting Time

The properties of fresh cement paste and concrete depend on the constituents and

properties of ordinary water [25].

A concrete which can be readily compacted is said to be workable, but to say merely

that workability determines the ease of placement and the resistance to segregation is

too loose a description of this vital property of concrete. Furthermore, the desired

workability in any particular case would depend on the means of compaction available;

likewise, workability suitable for mass concrete is not necessarily sufficient for thin,

inaccessible, or heavily reinforced sections. For these reasons, workability should be

defined as a physical property of concrete alone without reference to the circumstances

of a particular type of construction [9].

According to a study by E.W. Gadzama (2015), on effects of sugar factory wastewater

as mixing water on the properties of normal strength concrete, there is a substantial

delay in the setting time of the cement mix using wastewater, the delay increases with

an increase in the percentage of mixing wastewater [26].

22

A study on the effects of strong alkaline substances in mixing water on strength and

setting properties of concrete by Venkateswara Reddy and Vangala (2013), concluded

the following points about setting time of cement:

- The presence of Na2CO3 in the water at concentrations of 6 gram/liter and 4

gram/liter accelerates significantly, the initial and final setting time of cement

respectively.

- The presence of NaHCO3 in concentrations equal to 4 gram/liter and 6

gram/liter retards significantly the initial and final setting time respectively [21].

2.6.3.2. Influence on Compressive Strength

The compressive strength of concrete is of primary importance in structural applications

because design procedures require this property [25]. Experimental results reported by

Al-Joulani and Nabil (2015), shows concrete and mortar specimens, it can be argued

that using stone slurry wastewater in concrete mixtures improved the workability,

compressive strength, splitting tensile strength and natural absorption [27].

A study on the effects of strong alkaline substances in mixing water on strength and

setting properties of concrete by Venkateswara and Vangala (2013), concluded the

following points about compressive strength and tensile strength of concrete:

- Presence of Na2CO3 in the water at a concentration equal to 6 gram/liter results

in a significant decrease in compressive strength and tensile strength of

concrete.

- Presence of NaHCO3 in a concentration equal to 10 gram/liter results in a

significant decrease in compressive strength and tensile strength.

- Strong alkaline substances under consideration (Na2CO3 and NaHCO3) in water

reduce the compressive strength and tensile strength significantly, thus

requiring caution in the use of water containing these substances [21].

23

2.7. Related Studies

A study made by ATA Olugbenga (2014), states: The effect of impurities such as salts

of sodium, manganese, tin, zinc, copper, and lead on the compressive strength of

concrete have been analyzed. The result from the study made on six river sources shows

the effect of different types of mixing water on the compressive strength of concrete

due to impurities. And from the analysis, the storage sources of water used in mixing

concrete have a significant impact on the compressive strength of the resulting concrete

[28].

Table 2.4 Compressive strength corresponding to different water samples [28]

Water

Samples

Compressive Strength in N/mm2

7 days 14 days 28 days 56 days

Sample 1 4.50 7.67 11.83 12.47

Sample 2 9.00 9.93 12.03 13.80

Sample 3 5.33 6.37 12.80 13.10

Sample 4 7.20 8.73 11.23 13.23

Sample 5 8.50 10.67 13.03 13.27

Sample 6 6.00 7.80 11.30 14.00

When there is a lack of potable water, an integrant constituent of concrete has resulted

in the search for possible alternatives that are a search for another source of water. The

quality of mixing water is related to workability, compressive strength, and durability.

And the results of saline water in the mix on the compressive strength shows that a

small amount of salinity in mixing water improves the compressive strength of

concrete. The result shows seawater can be used for making small structures near the

coastal areas [22].

The paper reviewed by J. Kucche (2015), indicates the use of impure water for concrete

mixing is seen to be favorable for strength development at early ages and reduction in

long term strength. All the impurities may not have an adverse effect on the properties

of concrete. The allowable limits of physical and chemical impurities and the test

methods of their evolution are compiled. The limits on the number of impurities as per

Indian, Australian, American and British standards are presented. From the review, it

24

is seen that the reaction between water and cement affects the setting time, compressive

strength and also leads to softening of concrete [29].

Even though storage, the effect of seawater (saline) on the compressive strength of

concrete in relation to using freshwater was studied. After casting the concrete cubes

each sample was cured using seawater and freshwater respectively. The compressive

strength test was also affected when the concrete is mixed and cured using freshwater

and seawater and vice versa. The compressive strength test of the concrete cubes shows

increment when mixed and cured with seawater [30].

According to Rakesh A. and S.K. Dubbey (2014), water samples such as tap water,

wastewater, well water, bore well water and packed drinking water were collected and

from various sources and were used to prepare concrete cubes. The cured cubes were

crushed on the 7 and 28 days for compressive strength. And the result showed that

concrete cubes made with mineral water, tap, well, wastewater increased with days and

not having much variation in the compressive strength [31].

In the research by T. James et.al. (2011), tests on different curing methods were

conducted to evaluate the compressive strength of concrete. The result showed the

average compressive strength value for 7,14, 21 and 28 days, vary with the curing

methods. Ponding had the highest compressive strength followed by wet covering,

sprinkling, then uncured for two days [32].

A research was conducted by O.A. Dauda et.al. (2018), on investigating the effect of

contaminating the water (tap water) for curing concrete on its compressive strength.

Chemical analysis was carried out to determine the PH, total dissolved solids (TDS),

chloride, hardness, alkalinity, salinity, temperature and conductivity of wastewater. The

results of the chemical analysis showed that the parameters are higher in the wastewater

than the tap water. And the compressive strength of cubes samples immersed in tap

water shows there was a progressive decrease in strength of the samples immersed in

contaminated water as the percentage of wastewater increased [33].

According to Yitayew M. (2017), the basic criteria for selecting a curing method in

Bahir Dar are the availability of water and daily laborer. The curing methods that are

exercised in the area are plastic covering, wet cloth covering and spraying. Water

25

spraying is the most commonly used followed by a wet cloth covering method. Yitayew

made a comparison of compressive strength on the different curing methods under

laboratory investigation and as practiced. The results showed concrete cubes cured by

submerging in water have the highest compressive strength followed by a plastic

covering, wet cloth covering, and spraying water [34].

2.8. Summary of the Literature Review

Water sources are potentially useful for agriculture, industrial, household, recreational

and environmental activates. Most drinking water in Ethiopia comes from groundwater.

Bahir Dar is located in the northern part of Ethiopia and has different water sources

including; lake, river, shallow wells, and rainwater [35].

In the study area, concrete making materials need great attention and tests to ensure

production of quality concrete. The coarse aggregate has to be washed before use in

order to attain a better compressive strength of concrete. There are different impurities

that are found in water sources. The presence of chloride causes corrosion on

reinforcing steel and alkali water reduces the strength of concrete. Whereas, the

presence of alkali carbonate and bicarbonate affect the strength and cement setting

times. A small amount of salinity can improve the compressive strength of concrete.

With that in the background, the suitability of water for concrete mixing and curing

purposes should be considered.

Concrete made using questionable water sources should have a minimum of 90% of the

compressive strength made with potable water at the age of 7 days.

Generally, the sources of water carry different kinds of impurities based on the

geological nature of the study area. This shows the fact that water should be tested

before making concrete. Impurities of mixing water that is used from different sources

due to their effect on setting time, compressive strength, and impacting the durability

of concrete need be identified. Therefore, the aim of this study is to examine the effect

of water quality on the setting time and strength development of concrete; for there

were no earlier studies as a concern.

26

CHAPTER THREE

MATERIALS AND METHOS

3.1. Introduction

The compressive strength of concrete is influenced by the quality of its constituents.

Sources of concrete ingredients were identified by assessing construction sites in Bahir

Dar. The laboratory investigation was carried out using the most commonly used

concrete ingredients around the study area. The research’s objective is to assess the

main sources of water for concrete construction and investigate its effect on cement

setting time and compressive strength of concrete. To achieve the objective, an

experiment was designed in such a way that one control mix (made with potable water)

and other mixes (made with identified water sources).

3.2. Research Design

The proportion of all constituents (amount of aggregates, amount of cement and amount

of water) was kept constant in all the mixes. The sources of mixing water were the only

variable in the concrete mixes. Setting times of cement and compressive strengths of

concrete at the age of 3, 7 and 28days were conducted using water from Lake Tana,

Abay River, municipal water supply, groundwater (hand-dug well) and construction

site storage (from Lake Tana, Abay River, municipal water supply and ground). A total

of 108 concrete cubes were cast and tested for compressive strength.

3.2.1. Study Area

The study area for assessing mixing water sources applicable for concrete construction

works is Bahir Dar City which is the capital of the Amhara Regional State.

3.2.2. Study Technique

The method adopted for this research is data collection using questionnaires, field

observations and laboratory experimental works; including testing of concrete

27

ingredients, water quality test for selected impurities, setting time of cement and

compressive strength of concrete. The questionnaire was designed in order to gather

information on the different sources of mixing water used for concrete production

focusing on contractors in the City of Bahir Dar. The questions are both open and close-

ended having contents that primarily focus on the source of mixing water and the

awareness of users of its effect on concrete.

Pilot Questionnaires were distributed to clarify the questions. Then questionnaires were

distributed to collect data which will help to determine the source of mixing water used

for the experiment from the actively working contractors on building projects in Bahir

Dar. In addition, field observations were made on different construction sites in the

study area to find out the sources of water mostly used by contracting companies.

Based on the different type of mixing water sources water samples were collected for

each (River Abay, Lake Tana, Municipal Water supply and Ground water) source and

concrete cubes were casted in order to identify the effect of water source on

compressive strength of concrete. Samples from Ground water was collected from three

places based on the different location on the sites. Similarly, cement setting time test

was conducted on each (River Abay, Lake Tana, Municipal Water supply and Ground

water) identified water sources.

3.3. Materials

As stated in the objective, the main aim of this research is to assess sources of mixing

water used for concrete construction works and investigate its influence on cement

setting time and compressive strength of concrete. The detailed list of materials used

for the experimental investigation and material property test results are included in

Appendix B. The feature of various materials used in the experimental investigations

are the following.

3.3.1. Coarse Aggregate

The most commonly used sources of coarse aggregate for construction works are

crushed stones from the route of Zenzelima, Adet, Bikolo Abay, Wegelsa, and Addis

28

Zemen [34, 36]. The one used for this study is crushed stone from the Zenzelima crusher

site.

3.3.2. Sand

According to Abenezer T. (2015), there are six main sources for natural sand which are

available for construction works in and around Bahir Dar [36]. Also, Yitayew’s 2017

work notes that, the most commonly used sources of fine aggregate for construction

works are from the route of Addis Zemen, Arno, Rib, Arbaya, Tana and Tis Abay [34].

While reviewing Abel’s manuscript of 2016, the most commonly used sources of fine

aggregate for construction works are from the route of Arno, Tana, Tis Abay, Addis

Zemen, Andasa and Rib [37]. Because of its common use and availability, the Arno

sand source was made use of.

3.3.3. Cement

The cement type used for the study is ordinary Portland cement (OPC) with a grade of

42.5R and manufactured by Messobo cement.

3.3.4. Water

Mixing water from Lake Tana, Abay River, municipal water supply, groundwater

(hand-dug well) and construction site storage (from Lake Tana, Abay River, municipal

water supply and ground) were used.

3.4. Methods

3.4.1. Mix Design and Proportioning

Construction materials such as cement, river sand, and coarse aggregate for concrete

specimens were prepared. Mix design for normal strength concrete 30 MPa with a target

mean strength of 38.5 MPa which has a slump between 25-50 mm and a nominal

maximum aggregate size of 19 mm was made using ACI 211.1 mix design procedure.

It is shown in detail in Appendix C. Concrete batching was carried by weight.

The mix design made using ACI 211.1 mix design procedure following is as followed.

Step 1. Choice of Slump- A slump value in the range of 25-50 mm was chosen.

29

Step 2. Choice Maximum Size of Aggregate- The choice of the maximum size of

aggregate size according to ACI should the largest size possible so long as it is

consistent to the dimension of the structure (spacing between side forms, the thickness

of the slab, and spacing of the reinforcement bars) For this case, since it is for

experiment purposes, I take a maximum size of aggregate 20mm.

Step 3. Estimation of Mixing Water and Air Content- The quantity of water per unit

volume of concrete required to produce a given slump is dependent on the maximum

aggregate size, the shape, and grading of both coarse and fine aggregate, and the amount

of entrained air. The mix is non-air entrained. For the maximum nominal aggregate size

of 20mm and for slump value of 25-50mm the required amount of mixing water is

188.16kg/m3 and Air content is 1.9%.

Step 4. Target Mean Strength- For a 28th day specified compressive strength of C-30

and for no previous control data for the range of 21-35mpa the required target mean

compressive strength is 38.5mpa.

Step 5. Selecting Water to Cement Ratio- for 38.5mpa the free-water to cement ratio

of 0.44 is used.

Step 6. Calculation of Cement Content- water content to water to cement ration will

give us the cement content which is 427 kg/m3.

Step 7. Estimation of Coarse Aggregate Content- For the nominal maximum size of

20 mm and fines modules of fine aggregate = 2.91. The bulk volume per unit volume

of concrete of a dry rodded aggregate is found by interpolation from the table is 0.63.

Coarse aggregate content is 0.63*1506.7kg/m3 = 949.22 kg/m3. The SSD weight is

949.22*1.0234 = 971.43 kg/m3.

Step 8. Estimation of Fine Aggregate Content- The estimation of fine aggregate

content by Mass (Weight) Method is 940.93 kg/m3. And the estimation by Volume

method is 943.46 kg/m3. Using the two methods i.e. the weight method and volume

method the fine content is 940.93kg/m3 and 943.46kg/m3 which is approximate value.

For mix design the value taken is 945 kg/m3.

30

Oven dry weight of Coarse aggregate is 949kg/m3 and fine aggregate content is

918.09kg/m3. Field weight of Coarse aggregate 963.3kg/m3 and fine aggregate content

is 934.87kg/m3. Water contributed aggregate moisture is 30.82 kg and adjusted water

content is 157.18kg/m3.

Final adjusted content: approximated to nearest largest 5 multiple for ease of

measurement is Cement 427kg/m3 to 430Kg/m3, Water 157.18 kg/m3 to 160L, fine

aggregate (field) 918.09kg/m3 to 920Kg/m3, and coarse aggregate 949kg/m3 to

950Kg/m3.

3.4.2. Mixing and Casting

Materials were mixed with the identified water sources and also with water from site

storages by keeping the aggregates and cement similar and cubes of 150X150X150 mm

were cast.

3.4.3. Curing

To control the influence of the curing on the compressive strength of concrete with

water sources a plastic sheet is used to cover the cube specimens until the compressive

strength test is conducted. Then cubes are cured with a plastic sheet for 3, 7 and 28

days.

3.4.4. Testing

Water samples from different sources were collected based on the questionnaire survey

results and were tested for selected parameters. Identified water sources and water from

site storages were used to determine initial and final setting times of cement.

Compressive strength test results were recorded from concrete cubes on the 3rd, 7th,

and 28th days. The test results were then analyzed and discussed using Excel and SPSS.

3.5. Methods of Data Analysis

A pilot questionnaire was first distributed to ongoing construction projects in order to

check the understandability of the questionnaire then based on the result questionnaires

were distributed, collected and analyzed using Excel and SPSS.

31

Figure 3.1 Flow chart of the method

Problem Statement

Research Objectives

Primary Data

- Questionnaire

- Field observations

Laboratory Expermental Works

Results

Secondary Data

- Literature review

Analysis and Discussion

Conclusion and Reccommendations

32

CHAPTER FOUR

RESULTS AND DISCUSSION

4.1. Introduction

In recent years, the construction of buildings has become immense and faster in the City

of Bahir Dar. Most construction contractors, especially domestic contractors, face a

strong challenge when selecting different materials for construction due to quality and

possible alternatives. In this research problems related to water for concrete work are

assessed by collecting data with the help of the chosen research instruments;

questionnaires, field observations and laboratory tests.

4.2. Questionnaire and Field Observation Results

4.2.1. Discussion of Questionnaire Results

Contractors that were actively working on building construction projects in Bahir Dar

were surveyed. Most of the active projects are managed by general and building

contractors of 1st level. Their category and level as per the information from the

Ministry of Works and Urban Development (MOWUD) of Ethiopia are shown in Table

4.1.

Table 4.1 Contractor’s category and level

Category Level Number Percentage

General contractor

1 13 41.9

3 1 3.2

5 1 3.2

6 3 9.7

Building contractor

1 11 35.5

2 1 3.2

5 1 3.2

Total 31 100

Questionnaires were distributed to ongoing building construction projects around Bahir

Dar City. The main reason for selecting these projects is to conduct field observation

on water storage. The questionnaires were distributed to 36 contractors within the study

area and 31 were collected with the response rate was 86.11% as indicated in Table 4.2.

33

Table 4.2 Summary of questionnaire response rates

No. Respondents Distributed Responded Response Rate (%)

1 For contractors on active project site 36 31 86.11

Total 36 31 86.11

Additionally, respondents have variations in their years of working experience.

Respondents status versus year of work experience is shown in Table 4.3. The profile

of the contractors shows most of them are experienced or at least have good working

experience.

Table 4.3 Work experience of respondents

Year No. of

Respondents Percent

Valid

Percent

Cumulative

Percent

1-3 7 22.6 22.6 22.6

4-7 12 38.7 38.7 61.3

8-10 5 16.1 16.1 77.4

11-15 3 9.7 9.7 87.1

>15 4 12.9 12.9 100

Total 31 100 100

Grade of concrete mostly produced on active building project sites for constructing

building structures is shown in Table 4.4. It is observed that most of the building

constructions use C30 concrete grade for constructing beams and columns whereas C25

while constructing slabs.

Table 4.4 Mostly produced concrete grades in the project site

Grade No. of Respondents Percent Valid Percent

C25 17 54.8 54.8

C30 14 45.2 45.2

Total 31 100 100

Raw materials for making concrete; cement, aggregates (sand and crushed stone), water

(mixing and curing), selected by contractors for making the specified concrete grades

34

in their project site are tabulated below. From the response to the inquiries on the source

of cement, there is a variation in the use of cement types as depicted in Table 4.5.

Table 4.5 Type of cement

Type No. of

Respondents Percent

Valid

Percent

OPC32.5N 5 16.1 16.1

OPC32.5R 3 9.7 9.7

OPC42.5N 12 38.7 38.7

OPC42.5R 6 19.4 19.4

PPC32.5N 2 6.5 6.5

PPC32.5R 3 9.7 9.7

Total 31 100 100

From the response to the inquiries on the source of aggregates, there is a variation in

the use of sand and coarse aggregate for concrete. Fine and coarse aggregates used on

project sites for the specified concrete grades are shown in Table 4.6. The result shows

the main source of coarse aggregate is similar to previous studies made in the area by

Abenezer and Yitayew [34, 36].

Table 4.6 Sand and coarse aggregate sources

Sand Coarse Aggregate

Source No. of

Respondents Source

No. of

Respondents

Arbaya 11 Zenzelma 10

Arno 6 Meshenti 5

Gelgel Beles 2 Addis Zemen 4

Bullen 4 Infranz 2

Pawi 1 Wereta 1

Zenzelma 1 Sebatamit 6

Wereta 6 Kimbaba 3

From the responses of contractors as shown in Table 4.7 the most used sources of

mixing water are: from Abay River, municipal supply (tap water), groundwater (hand-

dug well) on-site, and Lake Tana. In addition, all the respondents use the same mixing

water while constructing the different parts of building structures.

35

Table 4.7 Mostly used mixing water sources of respondents

Water Source No. of

Respondents Percent

Valid

Percent

Ground 6 19.4 19.4

Municipal water 11 35.5 35.5

Abay River 12 38.7 38.7

Lake Tana 2 6.5 6.5

Total 31 100 100

Correspondingly, the practice of using mixing water if there is a scarcity for their first

choice is shown in Table 4.8 and from their responses, the most preferred are identified

as well. The result shows if there is a scarcity of water sources most respondents use

municipal water followed by groundwater, lake water, and river.

Table 4.8 Alternative sources of mixing water

Source of Mixing Water

Mostly Used on Sites for the

Specified Concrete Grade

Source of Mixing Water if there is Scarcity

Total

Ground Tap Abay

River

Lake

Tana

Ground

Count 0 5 0 1 6

% 0 83.3 0 16.7 100

Municipal

water

Count 2 5 2 2 11

% 18.2 45.5 18.2 18.2 100

Abay River

Count 6 1 3 1 11

% 54.5 9.1 27.3 9.1 100

Lake Tana

Count 1 1 0 0 2

% 50 50 0 0 100

Total

Count 9 12 2 7 30

% 30 40 6.7 23.3 100

From the response to the inquiries of using different curing water other than the mixing

on the sites for concrete making all projects used the same water sources for mixing

and curing purposes. The main sources for curing water are Abay River, municipal

supply (tap water), groundwater (hand-dug wells), and Lake Tana. Similarly, if there is

36

a scarcity of water sources for curing most respondents use municipal water followed

by groundwater, lake water, and river.

In order to distinguish the attention given for mixing water respondents were requested

for their opinion on the quality for concrete use in general. And the responses in Table

4.9 show around 42% is of the opinion that the water is good, 39% said it is fair to use

their source, and 19% believe that the water quality used is poor and attention should

be given. Thus, the result shows that those who use sources other than the municipal

have no confidence in the water they use.

Table 4.9 Respondents’ level of thinking on the water quality they use

No. of

Respondents Percent

Valid

Percent

Poor 6 19.4 19.4

Fair 12 38.7 38.7

Good 13 41.9 41.9

Total 31 100.0 100.0

The water storages observed on the construction sites show that 90.3% of stored water

is subjected to environmental impact with open storage tanks and only 6.5% of those

are covered from above as shown in Table 4.10. Water that is kept in an open storage,

subjected to the environment, should be checked for suitability.

Table 4.10 Site water storages

No. of

Respondents Percent

Valid

Percent

Open (open from above) 28 90.3 90.3

Closed (sealed from above) 2 6.5 6.5

Other (no answer) 1 3.2 3.2

Total 31 100 100

74.2% of the construction site's storage is placed on the ground and 19.4% is placed

below the ground as shown in Table 4.11.

37

Table 4.11 Placement of water storages on site

No. of

Respondents Percent

Valid

Percent

Valid Below the ground level 6 19.4 20.7

On the ground level 23 74.2 79.3

Total 29 93.5 100

Missing No answer 2 6.5

Total 31 100

From the responses of inquiries made on the use of criteria while selecting water

sources, 36.7 % (the one which uses potable) has standards and 63.3% do not have any

criteria as shown in Table 4.12. From the responses that use standard most of them

mentioned ASTM and EBCS.

Table 4.12 Criteria for using water for concrete

Frequency Percent Valid

Percent

Valid Use standards 11 35.5 36.7

No criteria 19 61.3 63.3

Total 30 96.8 100

Missing No answer 1 3.2

Total 31 100

From the responses of inquiries made on their satisfaction of water sources, 77.4%

agree, 12.9% slightly agree and 9.7% disagree that the water they use satisfies the

requirements set for concrete production as shown in Table 4.13.

Table 4.13 Satisfaction of respondents with the water source

No. of

Respondents Percent

Valid

Percent

Agree 24 77.4 77.4

Slightly agree 4 12.9 12.9

Disagree 3 9.7 9.7

Total 31 100 100

Contractors in Bahir Dar do not check the quality or degree of impurities that are present

in mixing and curing water. Also, the respondents have different understandings of the

38

effect of impure mixing water on workability, compressive strength and durability of

concrete structures as shown in Tables 4.14 - 4.16.

Table 4.14 Responses to the effect of impure water on workability of concrete

No. of

Respondents Percent

Valid

Percent

Valid Increase 2 6.5 7.1

Decrease 22 71 78.6

Do not know 4 12.9 14.3

Total 28 90.3 100

Missing No answer 3 9.7

Total 31 100

Table 4.15 Responses to the effect of impure water on strength of concrete

No. of

Respondents Percent

Valid

Percent

Valid Increase 4 12.9 12.9

Decrease 21 67.7 67.7

Do not know 6 19.4 19.4

Total 31 100 100

Table 4.16 Responses to the effect of impure water on the durability of concrete

No. of

Respondents Percent

Valid

Percent

Valid Increase 4 12.9 14.3

Decrease 23 74.2 82.1

Do not know 1 3.2 3.6

Total 28 90.3 100

Missing No answer 3 9.7

Total 31 100

If impurities are observable on a water source it needs either treatment or avoiding the

source. From the responses to the inquiries made on observed impurities, 82.1% replied

that they will pour cement powder on the water and let it settle to reduce visible

impurities and 8.3% replied reject the source and 13.8% of the respondents have no

comment. The practice of spraying cement powder to submerge the observed impurity

shows there needs to be a quality check on the suitability of that specific water source.

39

In a nutshell, respondents are certain of the presence of impurities in mixing water that

can affect the quality of concrete. Also, they select the source of mixing water by trend

and they are certain that impure water has an effect on concrete properties even then

they agree that the water satisfies the requirements without checking its quality. The

practice of not checking water quality even while observing impurities is not a good

professionalism and it should be considered in controlling the quality of concrete.

4.2.2. Discussion of Field Observation Results

In project sites, if there is insufficient municipality water supply the contractors mostly

prefer to use water supplied by hauler vehicles from Lake Tana as shown in Figure 4.1.

The water is pumped from Lake Tana using electric motors and transported by vehicles

to storages on construction project sites.

Figure 4.1 Lake water being pumped to a hauler vehicle

Also, water from the Abay River is pumped and transported to project sites in a similar

way as Lake Tana and is shown in Figure 4.2.

Figure 4.2 Abay River water being pumped to a hauler

The water from the Abay River is also transported by plastic bags to project sites and

is shown in Figure 4.3.

40

Figure 4.3 Abay River water being transported to construction sites

The project sites that use water from hand-dug well (shallow well) pump the water

using electric water pumps and place it directly to the storage tanks. during site

observation, water-storing systems were poor. Most of the storage tankers were open

from above. Even if the projects use potable water for producing concrete the water was

stored subjected to the environment that can easily be contaminated by dust and other

impurities on the site.

Figure 4.4 Groundwater storage

4.3. Materials Test Results

4.3.1. Aggregates

4.3.1.1. Coarse Aggregate

The coarse aggregate used for this study is from the Zenzelima crusher site because of

its wide use. The aggregate was first washed and tests were made and based on the

result a mix design was prepared. The tests were made based on ASTM C33, ASTM

C127 for testing aggregates. The test results are listed below and the details are in

Appendix B.1.

- Unit weight = 1506.67 kg/m3

- Specific gravity = 2.88

41

- Absorption capacity = 2.34%

- Free moisture content = 0.65%

The aggregate which was brought from the crusher site was tested for its gradation and

found to be a gap graded. Based on ASTM C33 the gap has a significant effect on the

strength and durability of concrete. The aggregate was separated into different sizes

using sieve shaker and blended in proportions for a well-graded sample as shown

below.

Figure 4.5 Coarse aggregate grading

4.3.1.2. Fine Aggregate

Regarding fine aggregate, there are many natural sand sources available for

construction works in Bahir Dar. Because of the common use, as a major source and

availability, the fine aggregate used for this study are from Arno. Various laboratory

tests were conducted to use the sand as an input for the mix design as shown below and

indicated in Appendix B.2.

- Unit weight = 1745.33kg/m3

- Fineness modules = 2.91

- Specific gravity = 2.93

- Absorption = 5.15 %

0

20

40

60

80

100

120

37.5 25 19 12.5 9.5 4.75

Per

centa

ge

pas

sing

Aggregate size(mm)

Data

Lower limit

Upper limit

42

- Free moisture content = 4.82 %

The silt and clay in the sand were very high and it was washed to fulfill ASTM C33

requirements with a maximum of 5%. The gradation test result shows that the fine

aggregate is a little coarser and does not completely fulfill the requirement of ASTM

C33. The fine aggregate was washed then separated into different sizes with sieve

shaker and blended again for a well-graded proportion as shown in Figure 4.5.

Figure 4.6 Gradation of fine aggregate

4.3.2. Water

Based on the questionnaire survey results, samples from four water sources were

collected then tested for impurities. The samples from municipal water, Lake Tana,

Abay River, and groundwater. There was six ground water (shallow well) users and

from those three construction project sites have been selected for test of their impurities

as shown in Appendix B and are summarized in Table 4.17. Tests conducted on the

constituents portray a result that is within the limits specified in ASTM C1602.

0

20

40

60

80

100

120

9.5 4.75 2.36 1.18 0.6 0.3 0.15

Per

cen

tag

e p

ass

ing

Sieve size(mm)

Sand grading curve

Data

Upper limit

Lower limit

43

Table 4.17 Result of water analysis

Test item

Water Source ASTM C94

Requirement Abay

River

Groun

d 1

Ground

2

Ground

3

Lake

Tana

Municipal

water

pH value 7.84 8.48 8.25 8.05 7.89 7.45 -

Turbidity (ntu) 27.6 13.5 0.87 3.9 21.3 1.1 -

Total solids (ppm) 62.7 93.9 471 395 97.4 139.9 50,000

Chloride content (ppm) 4.1 3.1 36 66 2.4 3.1 1,000

Sulfate content (ppm) 18 13 86 68 13 3 3,000

Alkalinity CaCo3 (mg/l) 90 70 220 230 80 115

The relative locations of the water sources used for making concrete are illustrated in

Figure 4.7.

Figure 4.7 Location of water sources covered by the study (Source: google earth, June 2019)

Abay

River

Lake

Tana

Municipal

water

Ground

water 1

Ground

water 2

Ground

water 3

44

4.3.3. Cement

Due to the availability, the cement used for this research is Messobo OPC (42.5R) and

is purchased from the market in Bahir Dar. The initial and final setting time is recorded

by preparing cement paste using the identified water sources and tested using the Vicat

apparatus as shown in Appendix B and summarized in Table 4.18.

Table 4.18 Setting time of cement

Test item

Water Source

Abay

River

Shallow

Well 1

Shallow

Well 2

Shallow

Well 3

Lake

Tana

Municipal

water

Initial setting time (min) 102.5 113 114 116.5 112.9 112.5

Final setting time (min) 210 225 225 225 210 240

From the results, it can be observed that there is a similarity in the initial setting times

of cement made with the different water sources. But the results of the final setting time

of cement made using Abay River and Lake Tana are 15 minutes shorter than the setting

time of groundwater and 30 minutes shorter than the municipal water. This result is due

to the alkalinity of the water sources.

Also, the initial and final setting time is recorded by preparing cement paste using the

water from construction site storage and tested using the Vicat apparatus as shown in

Appendix B and summarized in Table 4.19.

Table 4.19 Setting time of cement

Test item

Water Source

Abay

River

Shallow

Well 1

Shallow

Well 2

Shallow

Well 3

Lake

Tana

Municipal

water

Initial setting time (min) 108.5 111 115 114 112.5 114.5

Final setting time (min) 212.5 222.5 225 222.5 212.5 242.5

From the results, it can be observed that there is a similarity in the initial setting times

of cement made with the different water sources. But the results of the final setting time

of cement made using Abay River and Lake Tana are nearly 15 minutes shorter than

the setting time of groundwater and 30 minutes shorter than the municipal water. This

result is due to the alkalinity of the water sources.

45

ASTM C1602 specify that questionable water source should not have more than 60

minutes of initial setting time and 90 minutes of final setting time compared with the

control (potable water). The difference in deviation of setting times from the control is

within the specified limit of ASTM C1602 as shown in Tables 4.20. The result shows

the water sources are within the limit specified as per ASTM C1602.

Table 4.20 Deviation of setting time from the control

Test Item

Water Source Deviation from the Municipal ASTM

C1602

Requirement

Abay

River

Ground

1

Ground

2

Ground

3

Lake

Tana

Municipal

water

(control)

Initial setting time (min) 6 0.5 1.5 4 0.4 0 <60

Final setting time (min) 30 20 20 20 30 0 <90

The difference in deviation of setting times using on site sourced water from the control

is within the specified limit of ASTM C1602 as shown in Tables 4.21. The result shows

the water sources are within the limit specified as per ASTM C1602.

Table 4.21 Deviation of setting time from the control made using of storage water

Test Item

Water Source Deviation from the Municipal ASTM

C1602

Requirement

Abay

River

Ground

1

Ground

2

Ground

3

Lake

Tana

Municipal

water

(control)

Initial setting time (min) 10 3.5 0.5 0.5 2 0 <60

Final setting time (min) 30 15 17.5 15 30 0 <90

4.4. Testing of Concrete Cubes, Analysis and Discussion of Results

The workability of the mixes was measured by using standard slump test and concrete

cubes were cast and tested for compressive strength on 3rd, 7th and 28th days after curing

with plastic sheet covering. Compressive strength tests on 54 standard concrete cubes

were conducted, 9 cubes for each selected mixing water source (municipal water, Lake

Tana, Abay River, and groundwater from 3 sites).

The mixture was proportioned for a target cube strength of 38.5N/mm2 and had a coarse

aggregate content of 950Kg/m3, fine aggregate content of 920Kg/m3, the cementitious

46

material content of 430Kg/m3, and water content of 0.44. The detail of the mix design

is given in Appendix C.

The compressive strength test results of cubes made using the Abay River, Lake Tana,

municipal and water from groundwater sources for the 3, 7 and 28 days are shown in

Table 4.22.

Table 4.22 Compressive strength test results of concrete using identified water

Water Source Compressive Strength (MPa)

3 Days 7 Days 28 Days

Ground water 1 21.0 24.8 32.78

Ground water 2 19.46 21.04 37.92

Ground water 3 14.51 18.61 32.08

Abay River 17.14 20.82 39.28

Lake Tana 17.43 25 33.04

Municipal 22.04 27.6 40.67

The compressive strength test results of cubes made using different water sources show

deviations on the 7th day and are summarized in Table 4.23. The deviation of average

compressive strength test results at 7 days keeping the municipal water as a control,

only Lake Tana achieved 90% of the control.

Table 4.23 Compressive strength test results percentage from the control

Water Source Average Compressive Strength (MPa)

7 Days Control % from

Control

Minimum % of

Control at 7 Days

River Abay 20.82 27.6 75.43

>90 of the municipal

Groundwater 1 24.80 27.6 89.85

Groundwater 2 21.04 27.6 76.23

Groundwater 3 18.61 27.6 67.43

Lake Tana 25.00 27.6 90.5

Municipal water 27.60 27.6 100

The compressive strength test results on the 28th-day showed concrete cubes cast using

municipal water supply attained the highest strength. Then cubes cast by using water

47

from Abay River is 96.6%, Lake Tana is 81.24%, groundwater 1 is 80.7%, groundwater

2 is 93.4%, and groundwater 3 is 79.01% of the control.

The compressive strength test results of cubes made using water from construction site

storages of Abay River, Lake Tana, municipal and water from groundwater sources for

the 3, 7 and 28 days are shown in Table 4.24.

Table 4.24 Compressive strength test results of concrete using on site stored water

Water Source Compressive Strength (MPa)

3 Days 7 Days 28 Days

Ground water 1 21.34 20.12 33.02

Ground water 2 17.4 24.33 37.33

Ground water 3 19.56 23.74 37.40

Abay River 21.98 24.33 39.33

Lake Tana 16.25 20.12 31.61

Municipal 22.04 28.84 41.41

The compressive strength test results of cubes made using different water from site

storages show different percentage on the 7th day and are summarized in Table 4.25.

The deviation of average compressive strength test results at 7 days keeping the

municipal water as a control all water does not achieve the minimum percentage from

control Lake Tana achieved 90% of the control.

Table 4.25 Compressive strength test results from control with onsite stored water

Water Source

Average Compressive Strength (MPa)

7 Days Control % from

Control

Minimum % of

Control at 7 Days

River Abay 24.03 28.84 83.32

>90 of the municipal

Groundwater 1 20.12 28.84 69.76

Groundwater 2 24.33 28.84 84.36

Groundwater 3 23.74 28.84 67.43

Lake Tana 20.12 28.84 69.76

Municipal water 28.84 28.84 100

The compressive strength test results on the 28th-day showed concrete cubes cast using

water from site storages by municipal water supply attained the highest strength. Then

48

cubes cast by using water from Abay River is 94.97%, Lake Tana is 76.33%,

groundwater 1 is 79.73%, groundwater 2 is 90.14%, and groundwater 3 is 90.31% of

the control.

Similarly, the compressive strength development relations of concrete cubes cast with

different sources of mixing water and those made with water from construction site

storage is shown in Figure 4.8 and Figure 4.9 respectively. The results of the cube

compressive strength test show variation. Overall the municipal water source shows a

better compressive strength test result at 3rd, 7th and 28th day of curing.

Figure 4.8 Compressive strength development relationship between water sources

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

0 5 10 15 20 25 30

Com

pre

ssiv

e S

tren

gth

(M

Pa)

Days of curing

River Abay Ground 1Ground 2 Ground 3Lake Tana Municipal water(control)

49

Figure 4.9 Compressive strength development relationship among onsite stored water

4.5. Summary of Result Analysis and Discussion

The questionnaire results show the sources of water that are mostly used for the

purposes of mixing and curing concrete construction work in the study area are; Abay

River, municipal water supply, ground (hand-dug well) and Lake Tana. For the fact that

the research shows that, there are other sources of mixing water than the municipal

water supply conducting a test in order to recognizing the quality of water should be

frequently made.

Water sources were tested to identify the constituents and is found to be with the limit

specified as per ASTM C94. But there should be extra research on constituent of

groundwater sources in other places.

The initial setting time tests on cement mortar prepared with all the identified sources

show insignificant deviations. Also, the final setting time test of cement mortars

prepared with the Abay River and Lake Tana show 30 minutes earlier from the control,

municipal water. And the final setting time tests of ground water 1, 2 and 3 are

15minites earlier than the control. Likewise, initial and final setting time of cement

mortar made with water from storage tank on construction sites show similar results

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

0 5 10 15 20 25 30

Co

mp

ress

ive

Str

eng

th (

MP

a)

Days of curing

River Abay Ground 1

Ground 2 Ground 3

Lake Tana Municipal water(control)

50

compared to the source. Overall, the setting times of cement mortar done using the

identified water sources are within the limits specified by ASTM C1602.

The compressive strength test results of concrete cubes on the 7th-day mark show

mixing water made with Abay River is 75.43%, ground water 1 is 89.85%, ground

water 2 is 76.23% and ground water 3 is 67.43% from the control. Abay River and

groundwater sources have a strength of less than 90% of the control as per ASTM

C1602. Whereas, the compressive strength results of mixing water from Lake Tana is

90.5%, have a slight increase over the control.

The compressive strength test results of concrete cubes on the 7th-day mark show

mixing water made with storage water from Abay River is 83.32%, ground water 1 is

69.76%, ground water 2 is 84.36%, ground water 3 is 67.43% and Lake Tana is

69.76%from the control. Abay River, groundwater sources and Lake Tana have a

strength of less than 90% of the control as per ASTM C1602.

The compressive strength test results of concrete cubes on the 28th-day mark show

municipal water have the highest strength with 40.6 MPa followed by Abay River water

with 39.28 MPa, ground water 1 with 32.78 MPa, ground water 2 with 37.92 MPa,

ground water 3 with 32.08 MPa and water from Lake Tana with 33.04 MPa.

Finally, the compressive strength test results of concrete cube made using storage water

on the 28th-day mark show municipal water have the highest strength with 41.41 MPa

followed by Abay River water with 39.33 MPa, ground water 1 with 33.02 MPa, ground

water 2 with 37.33 MPa, ground water 3 with 37.40 MPa and water from Lake Tana

with 31.61 MPa.

The study confirmed that water sources from municipal and Abay River have a better

concrete compressive strength than Lake Tana and groundwater. Thus, it is advised not

to use Lake Tana and hand-dug well water sources for concrete construction work

without first checking the quality. One reason that the compressive strength similarity

in results is related to the fact that Lake Tana receive inflow from streams and springs.

From the findings concrete construction works in Bahir Dar City the research asserts

the use of Abay River and municipal water sources for concrete production and curing.

51

CHAPTER FIVE

CONCLUSION AND RECOMMENDATION

5.1. Conclusion

Mixing water is a key element for making good quality concrete. Due to the lack of

practice in material quality test professionals are selecting materials based on

experiences. The research finding shows the sources of water that are mostly used for

the purposes of mixing and curing concrete construction work in City of Bahir Dar are

Abay River, municipal water supply, ground (hand-dug well) and Lake Tana.

Tests conducted to identify and analyze the constituents of the water sources show that

the number of impurities found was within the limits stated in ASTM C94; though it is

not a common practice to test the quality of mixing water.

The initial and final setting time tests on cement mortar prepared with all the identified

sources show insignificant deviations. Also, initial and final setting time of cement

mortar made with water from storage tank on construction sites show similar results

compared to the source. In general, the setting times of cement mortar done using the

identified water sources are within the limits specified by ASTM C1602.

The study confirmed that water sources from municipal and Abay River have a better

concrete compressive strength than Lake Tana and groundwater. But when using water

stored on the construction site only municipal water have better compressive strength.

Thus, it is advised not to use Lake Tana, hand-dug well and River Abay water sources

for concrete construction work without first checking the quality.

In developing Cities such as Bahir Dar the practice of testing mixing water needs

serious attention. Selecting source, treating, and handling water are all compounding

factors for identifying suitable water source. For making concrete construction works

in Bahir Dar City the research finding asserts to use Abay River from the source, Abay

river and municipal water sources on the construction site for concrete production and

curing for the specific projects.

52

5.2. Recommendation

Based on the findings of this research the following recommendations are forwarded.

The research shows that there are other sources of mixing water than the municipal

water supply. Furthermore, conducting a test for recognizing the quality of water should

be frequently made.

For the reason that concrete compressive strength test results made using water from

groundwater sources show variation from place to place, the constituents of

groundwater sources should be studied further.

The research used plastic sheets for curing. Due to the varying compressive strength

test results from sources of mixing water, it is advised to study more about sources of

curing water and its effect on concrete properties including durability.

5.3. Areas for Further Research

For further study the research recommends the following topics:

- Treatment of mixing water sources to attain better concrete properties.

- The durability of concrete made with different mixing water sources.

- The curing practice and its effect on strength of concrete made with different

water sources.

53

REFERENCES

[1] Akroyd T. N. W. (1962), Concrete properties and manufacture, London, New

York, Paris: Pergamon Press.

[2] Kosmatka H. Steven, Kerkhoff B. and. Panarese W. C. (2003), Design and

control of concrete mixtures, Illinois, USA: Portland cement association.

[3] URL,http://www.concrete.org.uk. concrete making materials [Accessed April

2019].

[4] URL,http://www.sustainableconcrete.org.uk. concrete construction [Accessed

April 2019].

[5] Alam M. A., Habib M. Z., Sheikh M. R. and Hasan A (2016)., "A study on the

quality control of concrete production," vol. 13, no. 3.

[6] Zongjin L.(2011), Advanced concrete technology, Canada: John Wiley & Sons,

Inc.

[7] Samson K.(2017), The effect of aggregate gradation in cement consumption for

concrete production a laboratory investigation and field survey in Bahir Dar, Bahir

Dar University.

[8] Kosmatka S. H., and Wilson M. L.(2011), Design and control of concrete

mixtures, USA: Portland cement association.

[9]

[10]

Neville A.(2011), Properties of concrete, 5th edition, British Library.

Yonas T. (2018), Handling and storage of concrete aggregate on construction

sites. In and around Woldia, Bahir Dar University.

[11] Oxford (2010), Advanced Learners Dictionary, Oxford University Press.

[12] Merriam Webster (2018), Merriam Webster Dictionary, Inc.

[13] Arthur N., Darwin, and Dolan (2004), Design of concrete structures, 13th

edition, McGraw-Hill.

54

[14] Joseph F. L. and James H. P.(2006), Significance of Tests and Properties of

concrete-Making Materials STP 169D, ASTM International.

[15] URL,http;//www.wikipedia.org. water [Accessed April 2018] [Online].

[16] URL,http;//www.ga.water.usgs.gov/earthwater.html. "USGS," [Accessed

April 2018] [Online].

[17] Hussen A. (2010), Geological framework for groundwater occurrence in lake

Tana basin, Northwestern Ethiopia, Amhara Region.

[18] Tilahun S. A., Collick A. S. and Ayele M. (2012), "Assessment of water supply

and sanitation in Amhara Region," Learning and communication research report,

Bahir Dar, Ethiopia.

[19] Neville A. and Brooks J. (2010), Concrete Technology, 2nd edition, British

Library Cataloguing.

[20] ASTMC1602, Standard specification for mixing water used in the production of

hydraulic cement concrete, United States: ASTM international.

[21] Venkateswara R. and Vangala (2013), "Effect of strong alkaline substance in

mixing water on strength and setting properties of concrete," vol. 1, no. 2.

[22] Teja G. S., Amar P., Manoj N. R., Venkatesh E. and Teaepalli P.(2014),

"Study of compressive strength of concrete made using saline water," vol.2, no. 1

[23] Habtamu L.( 2015), Assessing the extent of silt and clay effect on workability

and compressive strength of concrete, Bahir Dar University.

[24] EBCS2 (1995), Ethiopian building code standards: Structural use of concrete

(EBCS 2), Addis Ababa, Ethiopia: Ministry of Works and urban development.

[25] ASTM-STP-169D (2006), Significance of test and properties of concrete &

concrete-making materials, USA: Pielert JFLJH, 2006.

55

[26] Gadzama E. W., Ekele O. J., Anametemfiok V. E., and Abubakar A. U.

(2015), "Effect of sugar factory wastewater as mixing water on the properties of

normal strength concrete," vol. 4, no. 3.

[27] Al-Joulani and Nabil M. A. (2015), "Effect of wastewater type on concrete

properties," vol. 10, no. 19.

[28] ATA O. (2014), "Effect of different sources of water on compressive strength of

concrete: A case study of Ile-Ife," vol. 6, no. 3.

[29] Kucche K. J., Jamkar S. S. and Sadgir P. A. (2015), "Quality of water for

making concrete: A review of literature," vol. 5, no. 1, 2015.

[30] Olutoge F. A. and Amusan G. M. (2014), "The effect of seawater on compressive

strength of concrete," vol. 3, no. 7.

[31] Rakesh A. m. and Dubey S. K. (2014), "Effect of different types of water on

compressive strength of concrete," International journal of emerging

technologies, vol. VI, no. 2, pp. 40-50.

[32] James T., Malachi A., Gadzama E. and Anametemfiok V. (2011), "Effect of

curing methods on the compressive strength of concrete," Nigerian Journal of

Technology, vol. 30, no. 3, pp. 1-7.

[33] Dauda O., Akinmusuru J., Dauda A., Fayomi O. and Durotoye T. (2018),

"Effect of curing water qualities on compressive strength of concrete," Covenant

journal of engineering technology (CJET), vol. 1, no. 2, pp. 1-13.

[34] Yitayew M. (2017), The effect of curing methods and practices on concrete

compressive strength (the case of Bahir Dar), Bahir Dar University.

[35] URL,http://www.wikipedia.org "Wikipedia," [Accessed April 2018] [Online].

[36] Abenezer T. (2015), The effect of partial replacement of natural sand with crushed

rock fine on the workability, compressive strength and cost of concrete. Case

study: Bahir Dar and it's surrounding, Bahir Dar University.

56

[37] Abel F.(2016), Assessment of quality of sand sources and the effect on the

properties of concrete (The case of Bahir Dar and its vicinities), Bahir Dar

University.

57

APPENDICES

58

Appendix A: Questionnaire

Bahir Dar University

Institute of Technology

Faculty of Civil and Water Resource Engineering

Department of Civil Engineering

Master’s thesis research questionnaire

For contractors

(In Bahir Dar)

By

Ermias Petros

March 2018

59

Dear Sir/Madam,

This questionnaire forms part of an M.Sc. thesis work, which aims at assessing

mixing water sources and their effect on properties of concrete in the case of Bahir Dar

for the purpose of highlighting the critical issues on mixing water for concrete works.

It is expected that this research will help to know the conditions of mixing water and

its effect on the properties of concrete in the construction sector. I would like to invite

you to participate in this vital endeavor. Completion of the questionnaire is truly

voluntary and returning the completed questionnaire will be considered as your consent

to take part in the survey. I humanely understand that you are already busy and

participating in this survey will be another task to add to a busy schedule. Even then,

the contribution you make in providing this invaluable information is sincerely our

common responsibility to uphold the industry’s developmental mission. All data held

are purely for research purposes and will be treated as strictly confidential by all means.

Thank you for your time and valid contribution in advance.

Yours faithfully,

Ermias Petros

Post Graduate Student, Construction Technology and Management

Bahir Dar University, Bahir Dar Institute of Technology, Faculty of Civil and Water

Resource Engineering

Tel: - +251 (0)91 043 5419

E-mail: - ermy_mten@yahoo.com or ermymten1@gmail.com

Bahir Dar:

60

Part I- Profile of Company (mark √ in the box)

1. What is your contracting level/ category as per the MOWUD of Ethiopia?

Category

Level

1 2 3 4 5 6 7 8 9 10

General Contractor

Building contractor

Road contractor

2. Your year of work experience in the construction industry

1-3 4-7 8-10 11-15 >15

Part II- Research questions, (mark √ in the box)

1. Which grade(s) of concrete is (are) mostly produced/used in your project site, for

structural use?

C20 C25 C30 C40 Other .

If you mark “other”, Specify ___________________

2. Materials for making concrete

a. What type of cement is mostly used to produce the specified concrete grade?

OPC- 32.5N 32.5R 42.5N 42.5R .

PPC- 32.5N 32.5R 42.5N 42.5R .

Other .

If you mark “other”, what is the type of cement? ___________________

b. mixing and curing water

i. Which source of mixing water is mostly used in this site for structural

members of the specified concrete grade?

Groundwater Tap water River water Lake water

Other .

If you mark “other” please specify ________________________________

61

ii. Which source of mixing water do you select if there is scarcity of the choice

from the above question in this site?

Groundwater Tap water River water Lake water

Other .

If you mark “other” please specify ________________________________

iii. Do you use water from the same source for mixing and curing of concrete?

Yes No

If No, which source do you use for curing? _____________

c. Which source of sand is mostly used for the specified concrete grade and

specify the name?

__________________

d. Which source of Coarse aggregate is mostly used for the specified concrete

grade and specify the name?

__________________

3. What do you think about the level of attention given to mixing water for making

concrete in Bahir Dar?

Poor Fair Very Good

________________________________ (any further comments regarding the

attention given)

4. Is there any variation of using sources of water while making different part of

structure?

Yes No

If yes, please specify ______________________

5. Which method of storage of water do you have on site

Open (open from above)

Closed (sealed from above)

Other

If you mark “other”, what is the type of Storage? ____________________

6. Where is the water stored on your site?

Suspended (elevated)

Below ground level

On the ground level

62

7. Are there any criteria you use to select mixing water for concrete? (any standard

or code and trend)

Yes No

If yes, please mention it _____________________________

8. a. Do you think that the water you use satisfy the requirements set for concrete

production?

agree slightly agree disagree

b. Do you check the quality of mixing water when the source is changed

Yes No

If yes, please mention it _____________________________

9. a. What do you think about the effect of mixing water with impurities?

Increase Decrease I don’t

Know

On workability of concrete

On compressive strength of concrete

On durability of concrete

b. If you observe impurities in the water you use on site, how do you treat it?

__________________________________________________________________

__________________________________________________________________

__________________

Thank you for your response!

63

Appendix B: Materials Test Results

Concrete making materials properties have been known by conducting laboratory using

the available test machines. Accordingly, the properties of coarse aggregate and fine

aggregate has been tested using the standard procedure of ACI.

B.1. Tests for Coarse Aggregate

The aggregate sample used for making the test was taken from crusher plants located

Bahir Dar – Zenzelima route.

SIEVE ANALYSIS

Objective- The objective of sieve analysis is to determine the particle size distribution

of coarse aggregate.

Theory- The grading or particle size distribution of an aggregate as determined by a

sieve analysis test in which the particles are divided into their various sizes by standard

sieves. The analysis should be made in accordance with ASTM C 136.

Apparatus

- Balance – Digital balance with an accuracy of 0.1 gram

- Sieves – ASTM standard sieves of size 37.5mm,25m,19mm,12.5 mm,9.5mm

and 4.75mm

- Shovel and Sieve brush

Sampling- Using the Quartering method, the samples were taken appropriately.

Procedure:

- Check the sample is in air-dry condition before weighing and sieving.

- Check the sieves are clean before use

- Weigh each sieve

- The sample is sieved successively on the appropriate sieves starting with the

largest size sieve using hand sieving.

- Weigh the mass retained in each sieve

Observation and Calculation:

Weight of sample taken- 1000gm

64

Table B.1 Coarse aggregate gradation

sieve

Size

Sieve

wt.

Sieve and

sample

wt.

Wt. of

sample

retained

Cum. Wt.

retained

Cum. %

retained

Cum. %

pass

ASTM limits

Min Max Remark

37.5 711.1 711.1 0.0 - - 100.0% 100% 100%

28 725.7 725.7 0.0 - 0.0% 100.0%

25 725.7 765.7 40.0 40.00 4.0% 96.0% 95% 100%

19 724 1274 550.0 590.00 58.9% 41.1%

12.5 678.6 878.6 200.0 790.00 78.9% 21.1% 25% 60%

9.5 696.1 842.8 146.7 936.70 93.6% 6.4%

4.75 730.6 790.6 60.0 996.70 99.6% 0.4% 0% 10%

2.36 730.6 730.6 0.0 996.70 99.6% 0.4% 0% 5%

Pan 408.7 413 4.3 1,001.00 100.0% 0.0%

Total 1001.0

Figure B.1 Graph of grading of coarse aggregate

Conclusion and Recommendation

The sample as shown it does not lie within the limits of ASTM gradation specification

so it is separated using sieve shaker and blended to suitable proportions to make a mix

design using this sample for the next test.

0%

20%

40%

60%

80%

100%

1 10 100

Pe

rce

nt

Pas

s

Sive Opening

ASTM max sample's gradation ASTM min

65

Bulk Unit Weight

Theory- This test is aimed in determining of the compact weight of coarse aggregate

Unit weight- The weight of a given volume of graded aggregate which also called bulk

density which considers both aggregate and the void.

Apparatus

- Balance (non-digital)

- Tamping road

- Cylindrical metal container with a capacity of 0.03 m3

Procedure

- Clean the cylindrical container

- Weigh the cylindrical container

- Fill the cylindrical container 1/3 full by using shovel uniformly along the

perimeter

- Compact 100 times for each layer

- Fill the final until it overflows and compact then avoid the surplus by rolling

the tamping rod.

- Weigh container and aggregate

Calculation

Bulk unit weight = ((weight of aggregate + container) – (Weight of container))/ volume

of container

Weight of container = 18,000 gm

Weight of container + Aggregate = 63,200gm

Volume of container = 0.03 m3

Bulk unit weight = 45.2kg/0.03m3 = 1506.67 kg/m3

Conclusion and Recommendation

According to ASTM C-33 normal weight aggregates has a bulk density of 1380kg/m3

to 1920kg/m3. So, our sample bulk density is 1507 kg/m3, which is appropriate for

making normal weight concrete.

66

Determination of Specific Gravity, Absorption Capacity

Objective- This test method is aimed at determining the bulk and apparent specific

gravity and absorption of coarse aggregate.

Theory- The specific gravity is the ratio between the weight of aggregate and that of

the same volume of water. Specific gravity calculation is based on the assumption of

aggregates are fully solid but the existence of pores which may be permeable and

closed.

Absorption: The capacity of water taking the internal void of aggregate till being

saturated surface dry state

Specific Gravity: The ratio of the mass of a unit volume of aggregate to the same

volume of water at room temperature

Apparent Specific Gravity: Ratio of the weight in air of a unit volume the

impermeable portion of aggregate to the weight in air of an equal volume of gas-free

water at room temperature

Bulk Specific Gravity: Ratio of the weight of a unit volume of aggregate in the air to

the weight of equal volume gas-free water.

Bulk Specific Gravity (SSD): Ratio of the weight in air of unit volume of aggregate to

the same volume of water weight in which the aggregate is submerged in water for 24

hours and after that the surface is rubbed to the surface dry state.

Apparatus

- Digital balance with an accuracy of 0.1gm

- Sample container

- Water tank

Sample for test

- First, I sieved the coarse aggregate using a sieve size of 4.75mm and using the

method of quartering we take a sample size of 2kg coarse aggregate.

- I have taken samples which has equal weight one is soaked the other is oven-

dried

67

Procedure

- The other oven-dried sample is measured and recorded.

- Clean sample container

- Weigh sample container

- Weigh the sample +container

- Soak in water tank for 24 hr.

- After 24 hours take out the soaked sample

- Rub each aggregate surface with an absorbent cloth until the surface is free of

the surface film.

- After, surfaces are rubbed weigh the SSD state.

- Putting the wire mesh container is immersed in the water tank container and

the weight is tarred.

- The specific gravity or the apparent specific gravity is relative density in SSD

state

Calculation

The following data are taken from the above tests

Bulk specific gravity = 𝐴

𝐵−𝐶

Where: A = weight of oven-dry sample in the air (gram)

Container + Aggregate = 2966.5

Container weight = 979.5

Oven dried weight = 2966.5-979.5 = 1987

B = weight of saturated surface dry sample in air (gram)

Container + aggregate sample = 3015.5

Container weight = 980

Aggregate weight in air = 3015.5-980 = 2035.5

C = weight of saturated sample in water (gram)

Weight of saturated sample in water = 1296.5

Bulk Specific gravity(SSD) = 2035.5

2035.5−1296.5 = 2.75

68

Apparent specific gravity = 𝐴

𝐴−𝐶

= 1989

1989−1296.5 = 2.88

Absorption capacity (%) = 𝐵−𝐴

𝐴 𝑥 100

= 2035.5−1989

1989 𝑥 100 = 2.34 %

Conclusion

The Ethiopian Standard requires that the apparent specific gravity of a normal concrete

aggregate lays between 2.4 and 3.0. The bulk specific gravity (SSD) of our sample is

2.88 which is within the standard requirement for normal-weight aggregate. The

Ethiopian Standard requires that the apparent specific gravity of a normal concrete

aggregate lays between 2.4 and 3.0.

The apparent specific gravity of our sample is in the upper range which is 3.0 which

shows our sample aggregate is manufactured a little bit higher on the upper range what

standard requires which shows rock source of the aggregate is pure basaltic.

According to the requirement of ASTM, the water absorption content of a concrete

aggregate should lie in the range of 0.2 to 4 % (ASTM C127). The sample water

absorption capacity is 2.34 % so; it is within the range of the standard requirement. This

value is below the mean of water absorption even though it is within the range and this

shows the aggregate has less permeable pores which are related to the above bulk and

apparent specific gravities values.

Determination of Moisture Content

Objective- The objective of this test is to determine the field moisture content of the

coarse aggregate.

Theory- The moisture content within the aggregate affects both the workability

requirement the strength of concrete if not determined appropriately. Aggregate which

is dried will absorb water and cause harsh mix by consuming the water for the mix and

aggregate which carries free moisture will add water to the mix and the water to cement

69

ratio will be unbalanced and the strength will not be as planned if appropriate moisture

adjustment is not made. This test of moisture content is used for this purpose.

Apparatus

- Digital balance

- Metal container

- absorbent cloth

- Oven

Procedure

- Wash the sample to avoid dust content using a sieve of 75µm.

- Clean sample metal container

- Weigh sample container

- Weigh washed sample +container

- Put in the oven for 24 hrs.

- After 24 hours take out the oven-dried sample and weight until it cools for an

hour protected from atmospheric moisture.

- Weigh the oven-dried washed + container

Calculation

Moisture Content = 𝑠𝑎𝑚𝑝𝑙𝑒 𝑤𝑒𝑖𝑔ℎ𝑡−𝑜𝑣𝑒𝑛𝑑𝑟𝑖𝑒𝑑 𝑠𝑎𝑚𝑝𝑙𝑒

𝑜𝑣𝑒𝑛 𝑑𝑟𝑖𝑒𝑑 𝑤𝑒𝑖𝑔ℎ𝑡 𝑥 100

= 2000−1987

1987 𝑥 100 = 0.65 %

Conclusion

This moisture content is the amount of water within the aggregate and an amount of

water 0.65% by SSD weight of aggregate should be considered in the mix design as

additional water supplied by aggregate.

70

B.2. Tests for Fine Aggregates

The sand source used for making this test was taken from the Arno area.

Determination of Gradation and Fineness Modulus

Objective- This test method covers the determination of particle size distribution of all

aggregates by sieving.

Theory- According to ASTM the term coarse is used to describe particles larger than

4.75mm (retained on No.4 sieve), and the term fine aggregate is used for particles

smaller than 4.75mm.

Apparatus

- Balance: Digital Balance with an accuracy of 0.1 gram

- Sieves: ASTM standard sieve size 9.5mm and 4.75mm, 2.36mm, 1.18mm,

600µm, 300 µm, 150 µm (no. 4, 8, 16, 30, 50 & 100)

- The samples were prepared with the quartering method as appropriate

Procedure

- The sieves and the pan were weighted and recorded after proper cleaning.

- The air-dry sample was weighted and sieved successively on appropriate

sieves starting with the largest sieve size care was taken to ensure that the

sieves were clean before use

- Sieving was carried out with a net of sieves and shacked with a period of at

least 10minutes

- The retained materials on successive sieves were weighted together with the

sieve and record

71

Observation and calculation

Table B.2 Observation and calculation of fineness of sand

Sieve

size

(mm)

Sieve

weight

(gm)

sieve

and

sample

weight

weight

of

sample

retained

Cum.

weight

Retained

Cum. %

Retained

Cum.

%

Pass

ASTM

Limits Remark

Min Max

9.5 697 699.1 2.1 2.10 0 100 100 100 ok

4.75 727.6 751.2 23.6 25.70 2 98 95 100 ok

2.36 734.3 850.1 115.8 141.50 9 91 80 100 ok

1.18 605.4 850.9 245.5 387.00 26 74 50 85 ok

0.6 605.3 1214.3 609 996.00 66 34 25 60 ok

0.3 580.6 938.9 358.3 1354.30 90 10 10 30 ok

0.15 558.4 660.5 102.1 1456.40 97 3 2 10 ok

0.075 550.4 563.38 12.98 1469.38 98 2 0 5 ok

Pan

19.8 1489.18 99 1

Determination of Fineness modules

Table B.3 Calculation of fineness modulus of sand

Sieve

size

(mm)

Sieve

weight

(gm)

sieve and

sample

weight

weight of

sample

retained

Cum.

weight

Retained

Cum.

%

Retained

Cum.%

Pass

9.5 697 699.1 2.1 2.10 0.14 99.86

4.75 727.6 751.2 23.6 25.70 1.71 98.29

2.36 734.3 850.1 115.8 141.50 9.43 90.57

1.18 605.4 850.9 245.5 387.00 25.80 74.20

0.6 605.3 1214.3 609 996.00 66.40 33.60

0.3 580.6 938.9 358.3 1354.30 90.29 9.71

0.15 558.4 660.5 102.1 1456.40 97.09 2.91

Pan 550.4 583.18 32.78 1489.18 290.87

F.M 2.91

Fineness modules = 𝐶𝑜𝑚𝑚𝑢𝑙𝑎𝑡𝑖𝑣𝑒 𝑅𝑒𝑡𝑎𝑖𝑛𝑒𝑑

100 =

290.87

100 =2.91

72

Figure B.2 Graph of fineness of fine aggregate

Determination of Bulk Unit Weight

Objectives- To determine the bulk density of fine aggregates

Theory- The bulk density or unit weight of fine aggregates is the mass of the aggregates

divided by the volume of particles and the voids between the particles. It is measured

by weighing a container of known volume filled with aggregate. The mass of the

container is subtracted to give the mass of the aggregate and the bulk density is the

aggregate mass divided by the volume of the container. The value will clearly depend

on the grading which will govern how the particles fit together and on how the

aggregate is compacted.

Apparatus

- a cylindrical metal container of known volume

- Balance; with an accuracy of 0.1gm and adequate capacity

Procedure

First, we measured the weight of an empty container having a volume of 0.003m3. Then

the container is filled in three layers each layer being tamped with 25 blows using

standard tamping rod. Finally, the excess layer is trimmed off and we weight it on

balance.

0

20

40

60

80

100

120

9.5 4.75 2.36 1.18 0.6 0.3 0.15

Per

cen

tag

e p

ass

ing

Sieve size(mm)

Original sand grading curve

Data

Upper limit

Lower limit

73

Calculation

Bulk unit weight = 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑓𝑖𝑛𝑒 𝑎𝑔𝑔𝑟𝑒𝑔𝑎𝑡𝑒

𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑐𝑜𝑛𝑡𝑎𝑖𝑛𝑒𝑟

Weight of container=2,969gm

Weight of aggregate +container=8,205gm

Volume of container=0.003m3

Bulk unit weight = (8205−2969)𝑔𝑚

0.003 m3 = 1745.33 Kg/m3

Conclusion

According to ASTM C-33, normal-weight aggregates have a bulk density of

1380kg/m3 to 1920 kg/m3. So, our sample bulk density is 1745.33 kg/m3, which is

appropriate for making normal weight concrete.

Determination of Specific Gravity

Objective- To determine the bulk and an apparent specific gravity of fine aggregate and

absorption capacity of fine aggregate.

Theory- The specific gravity is the ratio between the weight of fine aggregate and that

of the same volume of water. Specific gravity calculation is based on the assumption of

aggregates are fully solid but the existence of pores which may be permeable and

closed.

Absorption: The capacity of water taking the internal void of aggregate till being

saturated surface dry state.

Specific Gravity: The ratio of the mass of a unit volume of aggregate to the same

volume of water at room temperature.

Apparent Specific Gravity: Ratio of the weight in air of a unit volume the

impermeable portion of aggregate to the weight in air of an equal volume of gas-free

water at room temperature.

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Bulk Specific Gravity: Ratio of the weight of a unit volume of aggregate in the air to

the weight of equal volume gas-free water.

Bulk Specific Gravity (SSD): Ratio of the weight in air of unit volume of aggregate to

the same volume of water weight in which the aggregate is submerged in water for 24

hours and after that the surface is rubbed to the surface dry state.

Apparatus

- Balance

- Pycnometer

- Mold

- Tamper rod

Calculation

Bulk specific gravity (SSD) = 500

𝐵 + 500 − 𝐶

Where B = weight of pycnometer filled with water (gram) =1987

C = weight of pycnometer with sample and water to calibration

mark(gram) =2116

Apparent specific gravity = 𝐴

𝐵+𝐴−𝐶

Bulk specific gravity (SSD) = 500

1787 + 500 − 2116

Specific gravity = 2.93

Determination of Absorption Capacity

Objective- To determine the absorption capacity of fine aggregate

Theory- Absorption is a measure of the total pore volume accessible to water. To

calculate the mixing water content of concrete, the absorption of the aggregates and

their total moisture contents must be known. Absorption is computed as a percentage

by subtracting the oven-dry mass from the saturated surface-dry mass, dividing by the

oven-dry mass, and multiplying by 100. In concrete technology, aggregate moisture is

expressed as a percent of the dry weight of the aggregate.

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Apparatus

- Balance; with an accuracy of 0.1gm and adequate capacity

- Sample container: metallic pan

- Oven

Sampling- A portion of fine aggregate from the sample was taken by the use of sample

splitter. The sample was soaked in water. Then using the metallic pan, the sample was

dried at a temperature of 1050c. Then the dry sample was weighted after cooling.

Procedure

- We soaked the sample of sand that we obtained by using a sample splitter in

water

- We weighted the sand at SSD condition

- After weighting, we immediately placed the SSD test sample an oven at a

temperature of 1050c for 24hr

- Finally, we took out the sample from the oven dry and cooled it in room

temperature

Calculation

Absorption capacity (%) = (𝐴−𝐵)∗100

𝐵

Where: A=Weight of SSD sample in air=2000gm

B=Weight of oven-dry sample=1902.04gm

Absorption capacity (%) =(2000−1902.04

1902.04) ∗ 100 =5.15%

Conclusion

Absorption is a measure of total pore volume accessible to water. in this case, the

absorption of 5.15% is well within the maximum limit of 4%.

Determination of Moisture Content

Objective- The objective of this test is to determine the moisture content of fine

aggregates

Theory- Moisture content is the total amount of water present in the aggregate both

internally inside the pores and externally at the surface. Correction is needed to

compensate for moisture in the aggregates. Aggregates will contain some measurable

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amount of moisture. The free moisture content can be found as the difference between

total moisture content and absorption. The values can either be positive or negative.

Apparatus

- Balance

- Dish

- trowel

- Oven

Procedure

- A sample of fine aggregate from sample splitter was taken and weighted

- The sample was then oven-dried for 24 hours with a temperature of 105 0c.

- After 24 hours of the oven-dry sample was removed from the oven then

cooled about 1 hour without absorbing water from the atmosphere

- Then the oven-dry weight of aggregate was measured after cooling

Calculation

Moisture content = (𝐴 − 𝐵) ∗ 100

𝐵

Where: A = Weight of original sample (gram) =500gram

B = Weight of oven dry sample (gram) =477gram

Moisture content = (2000 − 477) ∗ 100

477

= 4.82%

Conclusion

It is important to maintain the water-cement ratio constant at its correct value. the

amount of added water should be adjusted to compensate for any observed

variations in the moisture content. The sample of sand is in damp condition

because it has free moisture. so, the free moisture should be subtracted from the

mix water requirement.

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Determination of Silt and Clay Content

Objective- To determine the silt content of fine aggregates sample.

Theory- It is important to use clean aggregate for concrete. if the aggregates are

coated with dirt, silt or clay it will result in poor concrete because the dirt will

prevent the cement from setting and also weaken the bond between the

aggregates and the cement paste. In the hand test, simply picking up a little sample

of sand and rubbing it between hands will show the silt content somewhat. if the

palm stays clean, the sand is alright from the cleanliness point of view. if it stained,

something is wrong silt test must be performed.

The silt content of the sand was determined using a jar test and it is 3.57%

Apparatus

- Graduated Glass Jar

- Dish

- Small size spoon

- Funnel

- Clean water

- Sodium hydroxide pills

Procedure:

- Prepare a graduated cylinder of greater than 100ml.

- Pour 30 ml sand to the cylinder

- Pour water up to a height of ¾ of the jar

- Close the cylinder

- Add sodium hydroxide

- Shake the jar about 1minute

- Leave the cylinder for 24 hours

- Measure the amount fine formed at the top

Calculation

Silt content (%) =(𝐴

𝐵) ∗ 100=(

2.5𝑚𝑚

70 𝑚𝑚) ∗ 100= 3.57%

Conclusion

ASTMC33,’’concrete aggregates, “limits the percentage of materials finer than a

75µm (no.2000) sieve to 3% of fine aggregate subjected to abrasion, 5%for the

fine aggregate used in any other concrete and the limit can be increased up to 5%

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to 7% for crushed sand if it can be proved that those particles passing 75µm are

not silt. Beyond this limit, the sand should be washed before using for concrete

making. Our sample is natural uncrushed sand and the silt content of 3.57 % not

acceptable for works subjected to abrasion and acceptable for other concrete

works since it is less than 5%.

B.3. Setting Time of Hydraulic Cement by Vicat Apparatus

Scope- These methods determine the time of hydraulic cement by means of a Vicat

needle. Two test methods are given; method A is the reference of Test Method using

the manual operated standard Vicat apparatus, while Method B permits the use of an

automatic Vicat machine that has, in accordance with the qualification requirements of

this method, demonstrated acceptable performance.

Setting times- The setting time measures the time taken for the cement paste to offer a

certain degree of resistance to the penetration of a special attachment pressed into it.

The time of setting is calculated as the difference between the time that a measurement

of 25 mm penetration is measured and the time of the initial contact between the cement

and water.

Apparatus

- Vicat apparatus with Vicat plunger

- Vicat needle and Vicat mold

- Gauging trowel, measuring jar, mixer, weighing balance, stopwatch and glass

plate.

Procedure

- A fresh cement paste of normal consistency is prepared and filled into the Vicat

mold.

- About 30 minutes after mixing, the mold resting on a plate is placed under the

rod and the needle is gently lowered and brought in contact with the surface of

the paste and quickly released. Thirty seconds after releasing the needle the

penetration is recorded. This is repeated every 15 minutes until the penetration

of 25mm or less is obtained in thirty seconds.

- The results of all penetration tests are recorded, and the time when penetration

of 35mm is obtained is determined by interpolation. The period elapsing

between the time when the water is added to the cement and the time at which

the needle penetrates 25mm is taken as the initial setting time.

- For the determination of the final setting time, the needle of the Vicat apparatus

is replaced by the needle with an annular attachment. The cement shall be

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considered as finally set when, upon applying the needle gently to the surface

of the test block, only the needle makes an impression, while the attachment

fails to do so.

Observation results

Table B.4 Setting times mixed with different sources of water

Test item

Water Source

Abay

River

Shallow

Well 1

Shallow

Well 2

Shallow

Well 3

Lake

Tana

Municipal

water

Initial setting time (min) 102.5 113 114 116.5 112.9 112.5

Final setting time (min) 210 225 225 225 210 240

Table B.5 Setting times mixed with different sources of water from site storage

Test item

Water Source

Abay

River

Shallow

Well 1

Shallow

Well 2

Shallow

Well 3

Lake

Tana

Municipal

water

Initial setting time (min) 108.5 111 115 114 112.9 114.5

Final setting time (min) 212.5 222.5 225 222.5 211.5 242.5

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B.4. Mixing Water Test Results

Table B.5 Results from the water analysis

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Appendix C: Mix Design

Mix Design- ACI 211.1

Cement - Messobo OPC (42.5R)

Coarse aggregate - Maximum nominal size = 20 mm

- Unit weight = 1506.67 kg/m3

- Specific gravity = 2.88

- Absorption capacity = 2.34%

- Free moisture content = 0.65%

Fine Aggregate - Unit weight = 1745.33kg/m3

- Fineness modules = 2.91

- Specific gravity = 2.93

- Absorption = 5.15 %

- Free moisture content = 4.82 %

Step 1. Choice of Slump

I have chosen a slump value in the range of 25-50 mm

Step 2. Choice Maximum Size of Aggregate

The choice of the maximum size of aggregate size according to ACI should the largest

size possible so long as it is consistent to the dimension of the structure (spacing

between side forms, the thickness of the slab, and spacing of the reinforcement bars)

For this case, since it is for experiment purposes, I take a maximum size of aggregate

20mm.

Step 3. Estimation of Mixing Water and Air Content

The quantity of water per unit volume of concrete required to produce a given slump is

dependent on the maximum aggregate size, the shape, and grading of both coarse and

fine aggregate, and the amount of entrained air. The mix is non-air entrained.

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For the maximum nominal aggregate size of 20mm and for slump value of 25-50mm

the required amount of mixing water is

19 mm ----------190 kg/m3

20mm------------?

25 mm…………….179 mm

𝑊𝑎𝑡𝑒𝑟 𝑐𝑜𝑛𝑡𝑒𝑛𝑡 =(20 − 19)(179 − 190)

(25 − 19)+ 190

=188.16kg/m3

Air content

19mm -------------2%

20mm--------------?

25mm -------------1.5

𝐴𝑖𝑟 𝑐𝑜𝑛𝑡𝑒𝑛𝑡 =(20−19)(2−1.5)

(25−19)+ 2

= 1.9%

Step 4. Target Mean Strength

For a 28th day specified compressive strength of C-30 and for no previous control data

for the range of 21-35mpa the required target mean compressive strength is

Fcr = fc +8.5

Where: fcr = Target mean strength

fc = specified characteristics strength which is 30mpa

Fcr = 30+8.5 =38.5mpa

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Step 5. Selecting Water to Cement Ratio

For fcr = 38.5mpa

41.4mpa ………………...0.41

38.5mpa…………………….?

34.5mpa……………………0.48

Interpolating I got a free-water to cement ratio of 0.44

Step 6. Calculation of Cement Content

Cement content =𝑤𝑎𝑡𝑒𝑟 𝑐𝑜𝑛𝑡𝑒𝑛𝑡

𝑤𝑎𝑡𝑒𝑟 𝑡𝑜 𝑐𝑒𝑚𝑒𝑛𝑡 𝑟𝑎𝑡𝑖𝑜

Cement content =188.16 𝑘𝑔/𝑚3

0.44 = 427 kg/m3

Step 7. Estimation of Coarse Aggregate Content

For the nominal maximum size of 20 mm and fines modules of fine aggregate = 2.91

The bulk volume per unit volume of concrete of a dry rodded aggregate is found by

interpolation from the table is 0.63

Coarse aggregate content = 0.63*1506.7kg/m3 = 949.22 kg/m3

The SSD weight is = 949.22*absorption capacity

= 949.22*1.0234 = 971.43 kg/m3

Step 8. Estimation of Fine Aggregate Content

a. Mass (Weight) Method

Um = 10*Ýa (100-a) +427(1- Ýa/ Ýc) + 188(1- Ýa/ Ýw)

Where: Um = unit weight of the concrete mix

Ýa = combined specific gravity of aggregate

= (2.88+2.93)/2 = 2.91

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a = air content = 1.9%

Um = 10*2.91 (100-1.9) +427(1- 2.91/3.15) +188(1-2.91)

= 2854.71+32.53 +188-547.88 = 2527.36kg/m3

Fine content = 2527.36-427-188-971.43 = 940.93 kg/m3

b. Volume method

water = 0.188/1000 = 0.188 m3

cement = 427/ (3.15*1000) = 0.135 m3

coarse aggregate = 971.43/ (2.88*1000) = 0. 337 m3

air = 0. 0175

Total = 0.678 m3

Therefore, the fine aggregate must occupy a volume of 1-0.678 = 0.322m3

Required SSd weight of fine aggregate = 0.322*2.93*1000 =943.46 kg/m3

Using the two methods i.e. the weight method and volume method the fine content is

940.93 and 943.46kg/m3 which is approximate value.

For mix design I have taken 945 kg/m3

Oven dry weight of aggregate

Coarse aggregate= 100*971.43/ (2.34+100) = 949kg/m3

Fine aggregate content= 100*945/ (102.93) = 918.09kg/m3

Field weight

Coarse aggregate = 949*(1.5067+100)/100 = 963.3kg/m3

Fine aggregate content = 918.84*(1.745+100)/100 = 934.87kg/m3

Water contributed aggregate moisture = 0. 01745*934.87 +0. 015067*963.3

= 16.31+14.51

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= 30.82 kg

Adjusted water content = 188-30.82 = 157.18kg/m3

Final adjusted content: approximated to nearest largest 5 multiple for ease of

measurement

Cement=427kg/m3 430Kg/m3

Water = 157.18 kg/m3 160L

Fine aggregate (field) = 918.09kg/m3 920Kg/m3

Coarse aggregate =949kg/m3 950Kg/m3

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Appendix D: Compressive Strength Test Results

Table D.1 Results from Cube compressive strength

87

Table D.2 Compressive strength test results made with water from site storages

88

Appendix E: Photos

Selected pictures that show the research process are shown as follows.

While Identifying Water Sources

While Collecting Water Samples

89

While Conducting Constituent Test in the Identified Water Sources

While Preparing Materials for Laboratory Investigation

90

While Conducting Setting Time Tests

91

While Casting Concrete and Testing for Compressive Strength