mix design by various methods

A Project Report on

Submitted ByRAHUL DAS BISWAS(CE- 20105040)

MIX DESIGN OF CONCRETE BY VARIOUS METHODS

A Project ReportSubmitted ByRAHUL DAS BISWASIn partial fulfillment for the award of the degreeOfBACHELOR OF ENGINEEREINGINCIVIL ENGINEERING

Under The Guidance ofProf. SANTOSH KUMAR DAS

Department of Civil EngineeringUNIVERSITY INSTITUTE OF TECHNOLOGYBURDWAN UNIVERSITYSESSION: 2010-2014

CERTIFICATE

This is to certify that the project entitled Mix Design of Concrete by Various Methods is the bonafide work carried out by Rahul Das Biswas, student of University Institute of Technology, Burdwan University, under my supervision and guidance in partial fulfillment of the requirements for the award of the Degree of Bachelor of Engineering in Civil Engineering.

_____________________________ _______________________________ Prof. Aparna Roy Prof. Santosh Kumar Das Head of the Department, (Project Guide) Department of Civil Engineering, Department of Civil Engineering,University Institute of Technology, University Institute of Technology, Burdwan University Burdwan University

ACKNOWLEDGEMENT

We deem it a pleasure to acknowledge our sense of gratitude to our project guide Prof. Santosh Kumar Das, Department of Civil Engineering,University Institute of Technology,Burdwan University, under whom we have carried out the project work. His incisive and objective guidance and timely advice encouraged us with constant flow of energy to continue the work.

I would like to place on record my deep sense of gratitude to Prof. Aparna Roy, Head of the Department,Department of Civil Engineering,University Institute of Technology,Burdwan University, for his generous guidance, help and useful suggestions.

I would like to thank my group co-workersfor their support and contributions during the period of project work.

__________________________ (Rahul Das Biswas)

TABLE OF CONTENTS

Introduction Literature Review Concrete Mix Design According to IS: 10262-1982 Introduction Basic Data required for Mix Design Standard deviation (s) of compressive strength of concrete Degree of quality control expected under different site conditions Procedure Trial Mix Concrete Mix Design According to IS: 10262-2009 Introduction Scope Standard deviation Selection of mix proportions Trial mixes Steps for design American Concrete Institute(ACI) 211.1-91 Method of Mix-Design Introduction Assumptions Design procedure Road Note No. 4 Method DOE Method of Concrete Mix Design Mix Design of Concrete by IS: 10262-1982 M-25 Grade of Concrete M-30 Grade of Concrete M-35 Grade of Concrete M-40 Grade of Concrete M-45 Grade of Concrete

Design of concrete mix using IS 10262:2009 M-25 Grade of Concrete M-30 Grade of Concrete M-35 Grade of Concrete M-40 Grade of Concrete Mix design of concrete according to ACI-211.1-1991 method M-25 Grade of Concrete M-30 Grade of Concrete M-35 Grade of Concrete M-40 Grade of Concrete M-45 Grade of Concrete Mix Design of Concrete by DOE method M-25 Grade of Concrete M-30 Grade of Concrete M-35 Grade of Concrete M-40 Grade of Concrete M-45 Grade of Concrete Comparison between the Quantities of the Design Parameters for M-25 Grade of Concrete M-30 Grade of Concrete M-35 Grade of Concrete M-40 Grade of Concrete M-45 Grade of Concrete Conclusion General Basic Data Used In Different Codes Similarities between the mix design processes Differences between the mix design processes References

Introduction

Concrete is the basic engineering material used in most of the civil engineering structures. Its popularity as basic building material in construction is because of, its economy of use, good durability and ease with which it can be manufactured at site. The ability to mould it into any shape and size, because of its plasticity in green stage and its subsequent hardening to achieve strength, is particularly useful. Generally concrete is used to build protective structures, which are subjected to several extreme stress conditions. Concrete is the most widely used construction material manufactured at the site.Like other engineering materials, concrete also needs to be designed for properties like strength, durability, workability. Concrete mix design is the science of deciding relative proportions of ingredients of concrete to achieve the desired workability with optimum strength and durability in the most economical way.

The advantages of mix design of concrete are: I. Quality: Better strength Better imperviousness and durability Dense and homogeneous concreteII. Economy: Economy in cement consumption: It is possible to save up to 15% of cement for M20 grade of concrete with the help of concrete mix design. In fact higher the grade of concrete more are the savings. Lower cement content also results in lower heat of hydration and hence reduces shrinkage cracks. Best use of available materials: Site conditions often restrict the quality and quantity of ingredient materials. Concrete mix design offers a lot of flexibility on type of aggregates to be used in mix design. Mix design can give an economical solution based on the available materials if they meet the basic IS requirements. This can lead to saving in transportation costs from longer distances. Other properties: Mix design can help us to achieve form finishes, high early strengths for early deshuttering, concrete with better flexural strengths, concrete with pump ability and concrete with lower densities.

Mix design is carried out using certain empirical relationships among design parameters, developed from the past experience. There are several codes which give empirical formula and directed some methods for the mix design of concrete.

In this context we are trying to show some of the research work results, analyzing the methods used in several codes, design mix for a grade of concrete by the codes and comparing the results, also the comparison between the codes.

Literature Review

Bruce Patterson and Keith Johnston1 have done a research work onseveral aspects of Concrete Mix Design on Federal Highway Administration at Washington D.C. 20590; at the year of 1991.This study investigates different aspects of concrete mix design. The variability of compressive strength, slump and air content from batch to batch is examined. The effect of increasing the sand content per cubic yard of concrete on the compressive strength is studied with another series of laboratory batches. Finally, the effect of the maximum coarse aggregate size on compressive strength is evaluated with a third set of laboratory batches. The differences between the mean compressive strength of batches were evaluated using statistics. Some of the findings were: 1. Variability in average 28-day compressive strength between laboratory batches of the same design is very low. 2. The average 28-day compressive strength of concrete made with a 10% increase in the sand content is higher than that of concrete made with standard mix proportions. The workability of the former as measured by the slump is lower.3. The average 28-day compressive strength of concrete made with 3/4 inch maximum size aggregate is significantly higher than concrete made with 1 inch maximum size aggregate.Proportioning and testing of concrete mixtures has followed certain procedures within the Oregon State Highway Division. They have always accepted some unexamined assumptions which were never tested for the local materials and equipments.

H. M. A. Al-Mattarneh, A. H. Hassan, M. H. Abu Hassan, B. S. Mohammed2 from university Tenaga National, at Malaysia, through investigating found an expert system for concrete mix design. According to them, Actually these systems were developed mainly for the reduction of time and wastage of material for determining optimum mixture proportion by conventional method. Our codes are based on the data gathered from experience at a certain region or place and therefore simultaneously find a limitation on being used at other places. This serious problem was eliminated by this report. This report was mainly based on design codes, technical literatures, surveys and interviews as well.

ParupalliRaghuver, K.Nagaraju, S.Chandrashekar Reddy, SpandanaMrudula3 researched on mix design entitled as Study Of Mix Design On Self Compacting Concrete Of M30 Grade, Under the guidance of V.Mallikarjuna Reddy3and submitted in the fulfillment of the requirements. This was a bonafide work carried out by them and the results embodied in this project report had been very much unique. Concrete occupies unique position among the modern construction materials, Concrete is a material used in building construction, consisting of a hard, chemically inert particulate substance, known as a aggregate (usually made for different types of sand and gravel), that is bond by cement and water. Self compacting concrete (SCC) is a high performance concrete that can flow under its own weight to completely fill the form work and self-consolidates without any mechanical vibration. Such concrete can accelerate the placement, reduce the labor requirements needed for consolidation, finishing and eliminate environmental pollution. The so called first generation SCC is used mainly for repair application and for casting concrete in restricted areas, including sections that present limited access to vibrate. Such value added construction material has been used in applications justifying the higher material and quality control cost when considering the simplified placement and handling requirements of the concrete. The successful production of self compacting concrete (SCC) for use, is depended on arriving at an appropriate balance between the yield stress and the viscosity of the paste. Specially formulated high range water reducers are used to reduce the yield stress to point to allow the designed free flowing characteristics of the concrete. However, this alone may result in segregation if the viscosity of the paste is not sufficient to support the aggregate particles in suspension. The process of selecting suitable ingredients of concrete and determining their relative amounts with an objective of producing a concrete of required strength, durability, and workability as economically as possible is termed as concrete mix design. The Mix Design for concrete M30 grade is being done as per the Indian Standard Code IS: 10262-1982.

Izhar Ahmed andDr S.S.Jamkar4carried out a study on Effects of Fly Ash on Properties of Concrete as Per IS: 10262-2009 on IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE).According to them, properties of concrete depend up on properties of ingredients and their relative proportion. Due to addition of mineral as well as chemical admixture in concrete design of concrete mixes has become increasingly complex. BIS has rationalized concrete mix proportioning code in Dec 2009, which is used to design standard concrete mixes using both mineral as well as chemical admixtures. By considering the code, the present work deals with the development of fly ash based concrete mix proportion. This paper presents the results of an investigation dealing with Concrete cubes of 100 mm size, to replace 0%, 5%, 10% and 15% cement with fly ash. To cover a wide range of concrete mixes water cementitious material ratio (W/C) of 0.3, 0.4 and 0.5 were used for water content of 186 kg/m3, 191.58 kg/m3 and 197.16 kg/m3 each. The effect of various parameters such as replacement of cement by fly ash, water to cementitious material ratio and water content is studied on fresh and hardened properties of concrete. The study mainly consisted of establishing relation between these parameters in the form of Graphs to specify proportioning of required fly ash based concrete. Both workability and strength aspects are considered.To analyze the behavior of concrete in fresh state, three different water content i.e. 186 kg/m3, 191.58 kg/m3 and 197.16 kg/m3 were selected for each W/C ratio. Graph 1 and Graph 2 shows the behavior of workability in terms of slump, for W/C ratio of 0.4 and 0.5.

It is observed that for a given W/C ratio and for given water content, addition of fly ash increases the workability. Workability goes on increasing with increase in percentage of fly ash from 5% to 15%. This trend is consistent for W/C ratio of 0.4 and 0.5. For W/C ratio of 0.3, mixes with and without fly ash is very low workable as per IS 456-2000. Hence a higher dosage of superplasticizer (SP) is required to achieve desired workability. The workability of fly ash based concrete is improved in following ways: a) As fly ash has lower specific weight, the resultant cement paste results in a bigger volume of cementing materials which is easy to handle and compacted.(b) The very fine particles existing in fly ash are attached by cement particles, forming a structure similar to a ball bearing, which reduces friction and improves workability.(c) The perfect spherical shaped fly ash particles are not able to interlock between themselves or with the cement particles, providing lubricating effect to fresh binder matrix. To achieve desired workability for a particular water cement ratio, water content can be selected from Graph 1 and Graph 2, for different percentages of fly ash.

The results for compressive strength for 7 days, 28 days and 56 days, obtained from the experimental investigation are represented graphically in Graph 3, Graph 4 and Graph 5 respectively.

It is seen from the graph, the mixes containing 5%, 10% and 15% fly ash, gain compressive strength more slowly as compare to reference mix (0% fly ash) up to 28 days. Beyond 28 days concrete containing fly ash will ultimately exceeds the strength.

From the above Graphs it is observed that for all W/C ratios and percentage replacement of fly ash with OPC, increase in compressive strength tremendously from 7 to 56 days. Graph 6, Graph 7 and Graph 8 shows the relation between age of concrete and compressive strength in MPa for 0.3, 0.4 and 0.5 W/C ratio respectively.

It is observed from the above Graph for all W/C ratio considered, concrete containing fly ash has very low early age compressive strength i.e. at 7 days. But at the age of 28 days the strength is increased which is nearly equals to reference concrete. Observations of 56 days compressive strength shows much better results than reference mix. Concrete containing 10 % replacement of fly ash by weight of cement gives better results than 5 % and 15 % replacement.

M.C. Nataraja and Lelin Das5 had carried out a study on Concrete mix design based on the ACI(211.1-1991) method, the old and new BIS method (IS 10262: 1982 & IS 10262: 2009) upon M-20 grade of concrete using OPC-43 grade of cement. They reported that basic differences among them depending upon the following aspects- Selection of water cement ratio Cement content Fine & coarse aggregate content Measure of workability Strength & durability Use of supplementary material such as chemical and mineral admixtures

R. Anuradha, V. Sreevidiy, R. Venkatassubramani and B.V. Rangan6 carried out an experimental study on Geo-polymer Concrete which is relevant to Indian Standard (IS 10262-2009). Two kinds of systems were considered in this study using 100% replacement of cement by ASTM class F low calcium fly ash (Sp gravity 2.3) and 100% replacement of sand by M-sand which is crushed aggregates produced from hard granite. Sodium hydroxide, Sodium silicate and alkaline liquids were also used. They used IS 10262-2009 for mix design of this concrete. This concrete was cured for 24 hours at 60oc. It is an excellent alternative solution to the CO2 producing cement concrete. The results of this study show that the workability increases with higher amount of fly ash but strength decreases. On the other hand M-sand increases the strength of concrete as compare to the river sand.

S.Yuvaraj, Dr.Sujimohankumar, N. Dinesh and Karthic7 had carried out an experimental study in the field of Nanotechnology implementation in concrete using IS 10262-2009. In order to reduce the carbon emission due to the cement manufacturing the fly ash was partially used in place of OPC cement. It was found that it not only reduces the emission of CO2 but also improves the workability, corrosion strength and long term strength of the concrete. The use of nano silica as an additive to fill up the deviation, and it is possible because the silica(S) in the sand reacts with calcium hydrate in (CH) the cement at nano scale to form C-S-H bond and its improve the strengthening factor of concrete which helps to achieve high compressive strength of concrete. The results of this study show that there is frequently use of fly ash in modern version of code to get optimum strength and durability of concrete and to reduce CO2& cost of concrete.

B. Bhattacharjee8 had carried out a study on Concrete mix design and optimization using different grades of concretes in both old and new code of Bureau of Indian Standards. They concluded that mix design is the mix proportion cement, sand, coarse aggregate, water and admixture (if necessary) to get proper strength, durability & workability. In the modified version of code the exposed conditions, air/non air content cement, surface texture (smooth or crushed) and angularity of aggregate had taken into consideration. The calculation of coarse aggregate is first calculated then the fine aggregate in new code and the selection of starting W/C ratio is also quite different from the previous one. There is provision of frequently use of fly ash in steed of cement to minimize the cost and to reduce CO2 emission.

Prince Arulraj and Sruthi Rajam9 carried out a study on Concrete mix design based on the old and the new Indian codes. They reported that Mix design is the process of determining the appropriate proportions of cement, fine aggregate, coarse aggregate, water and admixtures if any which will satisfy the requirements of compressive strength, workability and durability. IS10262-1982 is the relevant code for the design of Concrete mixes. Bureau of Indian Standards has revised this code in the year 2009. An attempt has been made to determine the effect of revision on the proportioning concrete the mixes. Concrete of grades M20, M25, M30, M30, M40 were designed by varying all the parameters as per the old and new codes.

GenadijShakhmenko and Juris Birsh10 carried out a study on Concrete mix design and optimization. They reported that determination of ingredients of aggregate mixes is an important part of concrete mix design. A concrete mix design method is used taking into account granulation parameters of aggregates. The task of concrete mix optimization implies selecting the most suitable concrete aggregates from the Data Base. The following properties are to be optimized: cost of raw materials, quality of aggregate packing, water and cement consumption. Computer programs for aggregate and concrete mix design as well as for concrete mix optimization have been worked out.MostafaA.M.Abdeen and Hossam Hodhod11 carried out a study on Analytic Formulae for Concrete Mix Design based on experimental data base and predicting the concrete behavior using ANN technique. They reported that an experimental investigation of concrete properties was made using two types of cement. Slump, compressive strength, rebound number and ultrasonic pulse velocities were investigated. The main parameters were type of cement, cement content, water content, and fine/coarse aggregate ratio. Data base was established for the mix proportions and corresponding properties. Artificial Neural Network(ANN) technique was developed in the work to simulate the concrete slump and concrete compressive strength for different mix proportions at different ages for the two types of cement and then predict the concrete behavior for different mix proportions at ages rather than those investigated in the experimental work.

Chris C. Ramseyer and Roozbeh Kiamanesh12 carried out a study on Optimizing concrete mix designs to produce cost effective paving mixes. The research was designed to determine the effect of the mechanically activated fly ash on fresh concrete properties and the ultimate strength of the hardened concrete. The activation of the fly ash was performed with a modified ball mill to increase the hydration reaction rate of the fly ash particles. Two primary variables were studied in this research: Grinding duration and the percentage of fly ash as a portion of cementitious material. The results of this study show that the concrete with higher proportions of fly ash has higher workability, although the strength of the samples decreases in most cases if high volume of fly ash is used.

Concrete Mix Design According to IS: 10262-1982

Introduction

The proportioning of concrete mixes consists of determination of the quantities of respective ingredients necessary to produce concrete having adequate, but not excessive, workability and strength for the particular loading and durability for the exposure to which it will be subjected. Emphasis is laid on making the most economical use of available material so as to produce concrete of the required attributes at the minimum cost.Concrete has to be of satisfactory quality in both the fresh and hardened states. The task of proportioning concrete mixes is accomplished by the use of certain established relationships which afford reasonably accurate guidance for selecting the best combination of ingredients so as to achieve the desirable properties of the fresh and hardened concrete. Out of all thePhysical characteristics of concrete, compressive strength is often taken as an index of its quality in terms of durability, impermeability and water tightness and is easily measurable. Therefore, the mix design is generally carried out for a particular compressive strength of concrete, coupled with adequate workability, so that the fresh concrete can be properly placed and compacted.The basic assumption made in mix design is that the compressive strength of workable concrete is, by and large, governed by the water-cement ratio. Another most convenient relationship applicable to normal concretes is that for a given type, shape, size and grading of aggregates, the amount of water determines its workability. However, there are various other factors which affect the properties of concrete, for example, the quality and quantity of cement, water and aggregates; batching; transportation; placing; compaction; curing; etc. Therefore, the specific relationships that are used in proportioning concrete mixes should be considered only as a basis for trial,, subject to modifications in the light of experience as well as for the particular materials used at the site in each case.

Basic Data required for Mix Design

The following basic data are required to be specified for design of a concrete mix:a) Characteristic compressive strength of concrete at 28 days (fck),b) Degree of workability desired,c) Limitations on the water-cement ratio and the minimum cement content to ensure adequate durability,d) Type and maximum size of aggregate to be used, ande) Standard deviation (s) of compressive strength of concrete.

Standard deviation (s) of compressive strength of concrete:

This is the root mean square deviation of all the results. This is denoted by s.Numerically it can be explained as,S = Where, s = Standard deviation, n = number of observations X = particular value of observationsXm= arithmetic mean.

Concrete like most other construction material having certain amount of variability in strength according to its mixing methods and proportion. And can be vary from batch to batch and some time also within the batch. If, compressive strength test cubes results in a random tests is plotted on Histrogram the results follow a bell shaped curve which is called normal distribution curve, which is shown below. (Fig-A.1)

Fig-A.1

Fig-A.2Standard deviation increases with increasing variability. The characteristics of the normal distribution curve are fixed by the average value and the standard deviation. The spread ofthe curve along the horizontal scale is governed by the standard deviation, while the position of the curve along the vertical scale is fixed by the mean value.The value of standard deviation has to be worked out from the trials conducted in lab or field but when, results of sufficient number of teats (at least 30) are notavailable, then, depending upon thedegree of quality control expected to be exercised at .the site, the value of standard deviation given in Table below (Table A.1) may be adopted for guidance.

Table: A.1Suggested values of Standard Deviation

GRADE OFCONCRETEStandard Deviation For Different Degree of Control in N/mm2

Very GoodGoodFair

M 1022.33.3

M 152.53.54.5

M 203.64.65.6

M 254.35.36.3

M 30567.0

M 355.36.37.3

M 405.66.67.6

M 456.078.0

M 506.47.48.4

M 556.77.78.7

M 606.87.88.8

DEGREE OF QUALITY CONTROL EXPECTED UNDER DIFFERENT SITE CONDITIONS

Degree of Control Conditions ofproduction

Very good Fresh cement from single source and regular tests, weighbatchingof all materials, aggregates supplied in single sizes, control of aggregate grading and moisture content, control of water added, frequent supervision, regular workability and strength tests, and field laboratory facilities.

Good Carefully stored cement and periodic tests, weigh batching of all materials, controlled water, graded aggregate supplied, occasional grading and moisture tests, periodic check of workability and strength, intermittent supervision, and experienced workers.

FairProper storage of cement, volume batching of all aggregatesallowing for bulking of sand, weigh-batching of cement, water content controlled by inspection of mix, and occasional supervision and tests.

PROCEDURE

The Bureau of Indian Standards recommended a set of procedure for design of concrete mix mainly based on the work done in national laboratories. The mix design procedures are Covered in IS 1026282. The methods given can be applied for both medium strength andhigh strength concrete. Here the method described below step by step-

(a)Target mean strength for mix design:The target mean compressive ( fck) strength at28 days is given byFck= fck+ tS

Where,Fck = characteristic compressive strength at 28 days.S= standard deviation. (As said earlier it is taken from the table given above according to IS 10262:1982)t = a statistical value depending on expected proportion of low results (risk factor).

Table: A.2VALUES OF t (risk factor)

Accepted proportions of low resultst

1 in 50.84

1 in 101.28

1 in 151.5

1 in 201.65

1 in 401.86

1 in 1002.33

According to IS: 4562000 the characteristic strength is defined as that value below which not more than 5 per cent results are expected to fall, in which case the above equation reduces toFck= fck + 1.65 S

(b) Selection of Water/Cement ratio: Various parameters like types of cement, aggregate, maximum size of aggregate, surface texture of aggregate etc. are influencing the strength of concrete, when water/cement ratio remain constant, hence it is desirable to establish a relation between concrete strength and free water cement ratio with materials and condition to be used actually at site. In absence of such relationship it is determined from the following graph.Fig: A.3

Fig: A.3Alternately, the preliminary free water-cement ratio (by mass) corresponding to the target average strength,may be selected from the relationships shown in next figure (fig. A.4) using the curve corresponding to the 28 days cement strength to be used for the purpose.

Fig- A.4

28 day Strength of cement tested according to IS: 4031-1968A= 31.9-36.8 N/mm2B = 36.8-41.7 N/ mm2C = 41.7-46.6 N/ mm2D= 46.6-51.5 N/ mm2E = 51.5-56.4 N/ mm2F =56.4-61.3 N/ mm2

(c) Estimation of Air Content: Approximate amount of entrapped air to be expected in normal (non-air-entrained) concrete is given in Table below (Table A.3).

Table: A.3APPROXIMATE AIR CONTENT

NOMINAL MAXIMUM SIZEOF AGGREGATE(mm)ENTRAPPED AIR, AS PERCENTAGE OF VOLUME OF CONCRETE

103

202

401

(d)Selection of Water Content and Fine to Total Aggregate Ratio:For the desired workability, the quantity of mixing water per unit volume of concrete and the ratio of fine aggregate to total aggregate by absolute volume are to be estimated from Table-A.4&Table-A.5 as applicable, depending upon the nominal maximum size and type of aggregates.

TABLE: A.4APPROXIMATE SAND AND WATER CONTENTS PER CUBIC METRE OF CONCRETE FOR GRADES UPTO M 35

NOMINAL MAXIMUM SIZE OF AGGREGATE(mm)WATER CONTENT PER CUBIC METER OF CONCRETESAND AS PERCENTAGE OF TOTAL VOLUME BY ABSOLUTE VOLUME

1020840

2018635

4016530

TABLE: A.5APPROXIMATE SAND AND WATER CONTENTS PER CUBIC METRE OF CONCRETE FOR GRADES ABOVE M 35

NOMINAL MAXIMUM SIZE OF AGGREGATE(mm)WATER CONTENT PER CUBIC METER OF CONCRETESAND AS PERCENTAGE OF TOTAL VOLUME BY ABSOLUTE VOLUME

1020028

2018025

N.B: Water content corresponding to saturated surface dry aggregate.If otherwise, when computing the requirement of mixing water, allowance shall be made for the free (surface) moisture contributed by the fine and coarse aggregates. The amount of mixing water obtained from Tables A.4 and A.5 shall be reduced by an amount equal to the free moisture contributed by the coarse and fine aggregates. On the other hand, if the aggregates are dry, the amount of mixing water should be increased by an amount equal to the moisture likely to be absorbed by the aggregates.

Table: A.4is to be used for concretes grade up to M 35 and is based on the following conditions:(a) Crushed (Angular) coarse aggregate, conforming to IS: 3831970.(b) Fine aggregate consisting of natural sand conforming to grading zone II of Table of 4, IS: 3831970.(c) Water-cement ratio of 0.6 (by mass), and(d) Workability corresponds to compacting factor of 0.80Table: A.5is to be used for concretes grade above M 35 and is based on the following conditions:(a) Crushed (Angular) coarse aggregate, conforming to IS: 3831970.(b) Fine aggregate consisting of natural sand conforming to grading zone II of Table of 4, IS: 3831970.(c) Water-cement ratio of 0.35 (by mass), and(d) Workability corresponds to compacting factor of 0.80

For other conditions of workability, water-cement ratio, grading of fine aggregate, and for rounded aggregates, certain adjustments in the quantity of mixing water and fine to total aggregate ratio given in Tables A.4 and A.5 are to be made, according to Table A.6 given below.

Table: A.6Adjustment of Values in Water Content and Sand Percentage for Other Conditions

Change in conditions stipulated for tablesAdjustment Required in

Water Content% Sand in Total Aggregate

For sand conforming to grade Zones I, Zone III or Zone IV of table 4, IS:383-19790+ 1.5% for Zone I-1.5% for Zone III-3% for Zone IV

Increase or decrease in the value of compacting factor by 0.1 3%0

Each 0.05 increase or decrease in water-cement ratio0 1%

For rounded aggregate-15 kg-7 %

(e) Calculation of Cement Content: The cement content per unit volume of concrete may be calculated from the free water-cement ratio and the quantity of water per unit volume of concrete. The cement content so calculated shall be checked against the minimum cement content for the requirements of durability and the greater of the two values adopted.

(f) Calculation of Aggregate Content: With the quantities of water and cement per unit volume of concrete and the ratio of fine to total aggregate already determined, the total aggregate content per unit volume of concrete may be calculated from the following equations:

Where, V = absolute volume of fresh concrete, which is equal to gross volume (m3) minus the volume of entrapped air,W = Mass of water (kg) per m3 of concrete,C = Mass of cement (kg) per m3 of concreteSc = Specific gravity of cementp = Ratio of FA to total aggregate by absolute volumefa, Ca = Total masses of FA and CA (kg) per m3 of concrete respectively andSfa, Sca = Specific gravities of saturated, surface dry fine aggregate and coarse Aggregate respectively.Trial Mix

The calculated mix proportions shall be checked by means of trial batches. Quantities of materials worked out shall comprise Trial Mix No. 1. The quantity of materials for each trial shall be sufficient for at least three 150 mm size cube concrete specimens and concrete required to carry out workability test according to IS : 1199-1959.Workability of the Trial Mix No. 1 shall be measured. The mix shall be carefully observed for freedom from segregation and bleeding and its finishing properties. If the measured workability of Trial Mix No. 1 is different from the stipulated value, the water content shall be adjusted according to Table A.6 corresponding to the required change in compacting factor. With this adjusted water content, the mix proportions shall be recalculated keeping the free water-cement ratio at the pre-selected value which will comprise Trial Mix No. 2. In addition, two more Trial Mixes No. 3 and 4 shall be made with the water content same as Trial Mix No. 2 and varying the free water cement ratio by 10 percent of the pre-selected value. For these two additional Trial Mixes No. 3 and 4, the mix proportions are to be recalculated for the altered condition of free water-cement ratio with suitable adjustments in accordance with Table A.6.Mix No. 2 to 4 normally provides sufficient information, including the relationship between compressive strength and water-cement ratio, from which the mix proportions for field trials may be arrived at. Using the relationship so obtained between the compressive strength and water-cement ratio, any change needed in the water-cement ratio to get the required target compressive strength may be easily obtained. The concrete mix proportions shall, however, be recalculated for this changed water-cement ratio, taking the water content same as that determined in Trial Mix No. 2. If the size and special requirement of the work so warrant, the trial may be extended to cover larger ranges of mix proportions as well as other variables, such as alternative sources of aggregates, maximum sizes and grading of aggregates, and different types and brands of cements.

Concrete Mix Design According to IS: 10262-2009

Introduction

Concrete has become an indispensable construction material. According to the present state of the art, concrete has bypassed the stage of mere four component system that is cement, water, coarse aggregate and fine aggregate. It can be a combination of far more number of ingredients, as many as ten to be precise. Apart from the common four ingredients, fly ash, ground granulated blast furnace slag, silica fume, rice husk ash; metakaoline and super plasticizer are the six new ingredients which are being increasingly used nowadays in concrete produced as and when required. Hence it has become quite necessary to introduce these new aspects in the concrete mix design code as these must be given their due importance as they have become an inseparable part of concrete in the present. Further, a lot more emphasis is given on IS 456:2000 and concrete mix proportioning has been done according to its norms.

Concrete is most commonly used material in civil construction work all over the country. There is hardly any major original civil construction work where structural concrete is not used. Nowadays concrete is produced in batch mixing plants located either at site of construction or away from the site in a location from where concrete is carried in transit mixers to the site. The later one is commonly called Ready MixConcrete (RMC). The proportion of various ingredients of concrete made in batch mixing plants mentioned above is usually determined in laboratory. This process is called designing (proportioning) of concrete mix and such a concrete is called design mix concrete. The designing process is a trial and error method in which right proportion of ingredients is sought to be determined so as to achieve targeted mean strength which is kept somewhat higher than the characteristic compressive strength of the concrete. Besides achieving the targeted strength, the workability and durability requirements are also required to be ensured while designing the concrete mix. All this has to be done keeping in mind the objective of achieving overall economy by reducing the content of costliest material in the concrete, i.e. the cement. The designing process in most of the major projects is usually carried out through reputed laboratories. IS 10262:2009 is the relevant Indian standard stipulating guidelines for concrete mix proportioning. In the recent past, concrete has become one of the most important construction material for buildings and other works.

In the beginning, concrete was only manufactured using ordinary Portland cement but now as time passes newer cement varieties are developing, thus leading to development of newer concrete varieties.

We know that the main objective behind concrete mixing is to make the choose the right proportion of all the ingredients that are required to make concrete ,which are practically and economically feasible to the client as well as the constructors, and which will serve the mere purpose of it without any extra burden of cost and maintenance. This is basically archived by using trial and error method, that is my making trial mixes and getting the correct result.Understanding the basic principles of mixture design is as important as the actual calculations used toestablish mix proportions. Only with proper selection of materials and mixture characteristics can the abovequalities be obtained in concrete construction. (Abrams 1918, Hover 1998 and Shilstone 1990). ACI 211.1-91, DOE 1988 and IS 10262 are the procedures widely used for proportioning concrete mix. The IS 10262 is primarily based on the basic assumption that the compressive strength of concrete is governed generally, by the water-cement ratio. The recent development of using chemical and mineral admixtures in concrete has not altered the applicability of the age-old Abrams water-cement ratio law', and the compressive strength of concrete is governed by the water-cementitious materials ratio used in concrete (S.C. Maiti 2006). The cementitious materials include cement and mineral admixtures like fly ash, granulated blast furnace slag and silica fume etc. The strength of the cementitious paste binder in concrete depends on the quality and quantity of the reacting paste components and on the degree to which the hydration reaction has progressed. Concrete becomes stronger with time as long as there is moisture and a favorable temperature available. Therefore, the strength at any particular age is both a function of the original water-cementitious material ratio and the degree to which the cementitious materials have hydrated.

Concrete needs to serve its purpose in its fresh and hardened state. The basic principles which govern the proportioning of the mixes are Abrams law and Lysesrule.In general, the compressive strength of concrete is taken as the index of acceptability and grades are determined in order of that only.The earlier code published in 1982 considered only basic four elements of concrete viz. cement, sand, course aggregate and water. In this code we will see that a very much wider spectrum of concrete is under radar and hence a large and relatively newer portions of this part of civil is henceforth cultured in this code

Scope

It is known that the properties of concrete depend up on properties of ingredients and their relative proportion. Due to addition of mineral as well as chemical admixture in concrete design of concrete mixes has become increasingly complex. BIS has rationalized concrete mix proportioning code in Dec 2009, which is used to design standard concrete mixes using both mineral as well as chemical admixtures.

This standard applies all the requirements of IS 456 and provides the guidelines for concrete proportioning mixes as per the requirements using the basic concrete making materials as well as other supplementary materials which are in use nowadays. This standard has been so modified that it is applicable to only ordinary and standard concrete grades only.The basic data required for concrete mix proportioning are:-1. Grade designation.2. Type of cement to be used.3. Maximum nominal size of aggregate to be used.4. Maximum and minimum cement content.5. Maximum water cement ratio.6. Workability.7. Exposure conditions.8. Maximum temperature of concrete at the time of placing.9. Method of transporting and placing10. Early age strength requirements (if required).11. About admixtures (if used).

In general we know that concrete has got two different strength criteria , the target mean strength and the characteristic mean strength, the former being higher in value than the latter always, and the design has always been done on the basis of the target mean strength which is given by the formula:-

fck= fck +1.65*s

Where, fck= target mean compressive strength at 28 days in N/mm2.fck= characteristic compressive strength at 28 days in N/mm2. S = standard deviation in N/mm2.Now a days design of concrete mixes has become increasingly complex with the addition of mineral aswell as chemical admixture in concrete. There for BIS has rationalized concrete mix proportioning code in Dec 2009. This code is now in use to design concrete mixes using both mineral as well as chemical admixtures.

Standard deviation

Standard deviation is calculated separately for each grade of concrete and it is based on test strength of the sample.Now, the total number of test strength of samples required to constitute an acceptable record for calculation of standard deviation shall not be less than 30, and attempts must be made to obtain the required number of samples as early as possible, during the time of the first mixing.The standard deviation of a particular batch of concrete needs to separately evaluated every time the batch is liable to addition of certain different items to it apart from the regular items, such as any sort of admixtures etc and it must be up to date always.Sometimes, it happens that the value of standard deviation of a particular grade of concrete is unavailable, then a value is assumed in order to solve the problem and to continue the mix proportioning until and unless the actual test results are coming, and when the actual result comes, that value is taken into account. The following table TABLE B.1 shows the assumed values of the standard deviation (according to CLAUSES 3.2.1.2, A-3 AND B-3)TABLE: B(1) FOR ASSUMED STANDARD DEVIATION

SERIAL NO.GRADE OF CONCRETEASSUMED STANDARD DEVIATION

1.M103.5

2.M153.5

3.M204.0

4.M254.0

5.M305.0

6.M355.0

7.M405.0

8.M455.0

9.M505.0

10.M555.0

Selection of mix proportions

(a) Water cement ratio:The relationship between strength and free water-cement ratio always needs to be established for the materials in use at site because even for the same water-cement ratio the strength of concrete may be different as it depends on the shape and size of aggregate, grading, surface texture etc., which may give a completely different result, far apart from what the expectation.

In the absence of data, the preliminary data may be selected which is based on the relationship according to the target strength after 28 days. If that is also not available, then the starting value of water cement ratio can be adopted from Table 5, IS 456:2000 which is based on different exposure conditions. If any separate mineral admixtures or other cementing materials are used then its calculation has to be separately made according to IS 456:2000, table 5.

The checking of the above value needs to be done for the limiting value for the durability criteria and hence the lesser value of the two will be taken into consideration. The water content in concrete mix dcpends on many factors viz. shape, size and texture of aggregates, water cement ratio, type of cement and other materials used and of course environmental conditions especially temperature.

The following table TABLE B.2 shows the maximum or limiting value of water that can be used per volume of concrete:-TABLE: B.2FOR MAXIMUM WATER CONTENT

SERIAL NO.NOMINAL MAX. SIZE OF AGGREGATE (mm)MAXIMUM WATER CONTENT(kg)

1.10208

2.20186

3.40165

According to this code, the water content can further be reduced approximately by 10 kg for sub angular aggregates, 20 kg for gravel with some crushed particles and 25 kg for fully rounded gravels, and the results are the same i.e. the workability remains the same. Now the slump value of 25 to 50 mm is considered as standard and with further increase in slump value, the water content is increased by 3 percent with every additional 25 mm slump value. Water content can also be increased or decreased confirming to IS 9103, following the use of chemical admixtures.

(b) Coarse aggregate proportions:The aggregates are also an important part of the concrete and the shape, size and texture of aggregate is responsible for many changes in the making of concrete. Hence it is always advised to maintain a standard grade of aggregate to get the required satisfactory workability.

Approximate values of the aggregate volume is given in the following table (Table B.3)

TABLE: B.3FOR MAXIMUM COARSE AGGREGATE VALUE

SERIAL NO.NOMINAL MAX. SIZE OF AGGREGATE(mm)VOLUME OF COARSE AGGREGATE PER UNIT VOLUME OF TOTAL AGGREGATE FOR DIFFERENT ZONES OF FINE AGGREGATE

ZONE IZONE IIZONE IIIZONE IV

1.100.500.480.460.44

2.200.660.640.620.60

3.400.750.730.710.69

The above given values are for a particular water cement ratio, which is 0.5, but this chart can be suitably modified for other ratios also, as and when required. If, further an increase in workability is required, then the coarse aggregate content can be further diminished up to 10 percent.The coarse aggregate shall always confirm with IS 383. In general, only one size of aggregate is not used but, a well graded range of different sizes of aggregate in certain proportions are used to ensure better strength, bonding and overall result.

(c) Fine aggregate proportions:The coarse and fine aggregate content are calculated by the following process:-(i) The absolute volume of the cementitious material, water and chemical admixture are found out.(ii) The mass of the individual items are hen divided by their respective specific gravities.(iii) The results are multiplied by a constant factor 1/1000.(iv) The summation result is subtracted from their unit volume.

The values so obtained are divided into coarse and fine aggregate fractions by volume in accordance with the coarse aggregate proportion already determined. The final coarse and fine aggregate values are obtained by multiplying the above values with their respective specific gravities and 1000.

Trial mixes

The values so obtained from the mix design shall definitely be checked by making repetitive trial mixes and any error needs to be adjusted.Workability of the first trial mix shall be measured very much carefully and all sorts of bleeding and segregation occurring in it shall be noted with care and precision, so that if the result deviates from the anticipated value then the water or admixture or both quantities are revised.The second trial mix contains the pre-selected value of the free water cement ratio. In addition a third and fourth trial mixes are also prepared with the water content kept constant but the free water cement ratio being increased and decreased by ten percent respectively.This generally provides with the required amount of information.

Steps for design

The basic steps for designing according to IS 10262:2009 are:-

1. Stipulations for proportioning: All the general data regarding the quality of the materials are stated and hence the basic requirements of design are fulfilled.2. Test data for materials: All the materials used are tested and the data of those tests are presented in a tabular form in general.3. Target strength for mix proportioning: The basic approach of the problem ways itself through this step and hence this step is rendered as the first actual step towards the solution of the design problem.4. Selection of water-cement ratio: Another vital aspect of mix design without which the problem even cannot be started. Generally done with the help of Table 5 from IS 456:2000.5. Selection of water content: This is done with the help of Table 8 from IS 10262:2009.6. Calculation of cement content: After the content of water is known, the cement can be easily calculated. IS 456:2000 helps to determine the minimum cement content.7. Proportion of volume of coarse and fine aggregate: Both these volumes are calculated as they are very much necessary for the problem to step forward because both these items are integral part of concrete mixture.8. Mix calculations: The actual calculations are done and results are obtained.9. Mix proportions for trial one: With the above values the first trial is done to obtain the field results.10. Measurement of slump and further trials: The slump shall be measured and adjusted and accordingly further trials are done.

American Concrete Institute(ACI) 211.1-91 Method of Mix-Design

INTODUCTION

This method of mix design was first established in the year of 1944 by ACI committee 613.In the year 1954 this method was revised by the committee and the fact of entrained air was included.In 1970 the mix design procedure was handed over to the ACI committee 211 this committee had further modified the method (ACI 211.1)in the year 1991.Almost all the major multipurpose concrete structures built during 1950 have been designed by using the method of ACI committee method of mix design.

We shall now deal with the latest ACI committee 211.1 of 1991 method. It has the simplicity regarding the design procedure for rounded and flaky aggregate, to regular or light weight aggregates and to air entrained or non-air entrained concrete. In each of the cases the design procedure is same. There are few assumptions regarding the method of design. The assumptions are as follows:

ASSUMPTIONS

1.The method makes use of the established fact ,that over a considerable range of practical proportions fresh concrete of a given slump containing a reasonably well graded aggregate of given maximum size will have a constant water content regardless of variation in the water cement ratio with the variation of cement content.

2. It makes use of the relation that the dry rodded volume of the coarse aggregate per unit volume of the concrete depends upon the maximum size of the aggregate and the fineness modulus of the fine aggregate regardless of the shape of the particles. That is why the angular coarse aggregate require more mortar than the rounded coarse aggregate.

3. Irrespective of the methods of compaction, even after complete compaction is done a definite percentage of the air remains which is inversely proportional to the size of the aggregate.

4. We have to decide the maximum size of the coarse aggregate.Generally for the R.C.C. work it is 20 and for pre-stressed concrete its value is 10.

5. For the design purpose of particular type of job we have to decide the value of workability in terms of slump.ACI method has given various ranges of values of slump for various works such as range of slump in mm for reinforced foundation walls and footings is 20-80.6. The total water in kg/m3of concrete is selected as per ACI code depending upon the values of the selected slump and the selected maximum size of the aggregate.In this method of proportioning we consider the accidentally entrapped air in a non-air entraining agent.

7. From the above water content we find the cement content by dividing the water content by the water cement ratio.

8. The bulk volume of the dry rodded coarse aggregate per unit volume of the concrete is determined by using the maximum size of coarse aggregate and the fineness modulus of the coarse aggregate.

9. The weight of the coarse aggregate per unit volume of the concrete is calculated by multiplying the bulk volume with the bulk density.

10. The solid volume of the coarse aggregate in one cubic meter of concrete is calculated by knowing the specific gravity of the coarse aggregate.

11. In the similar way we can calculate the solid volume of the cement, water and the volume of the air entrapped.

12. The solid volume of the sand can be calculated by subtracting from the total volume the volume of the cement,coarse aggregate, water and entrapped air.

13. The weight of the fine aggregate can be calculated by multiplying the solid volume of the fine aggregate with its specific gravity.

DESIGN PROCEDURE AS PER ACI COMMITTEE 211.1-91 METHOD

(a) Assuming 5 per cent of results are allowed to fall below specified design strength,The mean strength,fm= fmin + ksWhere, fm is the mean strength of concretefmin is the characteristic strength of concretes is the standard deviationk is the tolerance factor

(b) Assuming it that OPC has been used, from table C.1, we have to take the w/c ratio.This w/c ratio from strength point of view is to be checked against maximum w/c ratiogiven for special exposure condition given in Table C.2 and minimum of the two istobe adopted.From exposure condition using Table C.2, we have to take the maximum w/c ratio.Table:C.1Relation between water/cement ratio and averagecompressive strength of concrete, according to ACI 211.191

Average compressive strength at 28 days(MPa)

Effective water/cement ratio(by mass)

Non-airentrained concreteAir-entrainedconcrete

450.38-

400.43-

350.480.40

300.550.46

250.620.53

20o.700.61

150.800.71

Table: C.2Requirements of ACI 318-89 for W/C ratio and Strength forSpecial Exposure Conditions

Exposure ConditionMaximum W/C ratio, normaldensity aggregate concreteMaximum design strength,low density aggregate concrete (MPa)

1.Concrete Intended to bewatertight0.5

0.4525

30

(a)Exposed to fresh water

(b)Exposed to brackish or sea water

2.Concrete exposed to freezing and thawing in a moist condition:0.45

0.50

0.4530

25

30

(a) kerbs, gutters, guard rails or thin sections

(b) other elements

(c) in presence of de-icing chemicals

(c) From Table C.3, for a given slump and maximum size of aggregate, for no air-entrained the mixing water content is to be taken per m3of concrete. Also the approximate entrappedair content is 2 percent.

Table: C.3 Approximate requirements for mixing water and air content for different workability and nominal maximum size of Aggregates according to ACI 211.1-91

Workability or air contentWater content, kg/m3 of concretefor indicated maximum aggregate size

10mm12.5mm20mm25mm40mm50mm70mm150mm

Non air-entrained concrete

Slump

30-50mm205200185180160155145125

80-100mm225215200195175170160140

150-180mm240230210205185180170-

Approximate entrapped air content per cent3.02.52.01.51.00.50.30.2

Air entrained concrete

Slump

30-50mm180175165160145140135120

80-100mm200190180175160155150135

150-180mm215205190185170165160-

Recommendedaveragetotalair content per-cent

Mild exposure4.54.03.53.02.52.01.51.0

Moderate exposure6.05.55.04.54.54.03.53.0

Extreme exposure7.57.06.06.05.55.04.54.0

(d) From Table C.4 for a given maximum size of coarse aggregate and for given fineness modulus the dry rodded bulk volume of C.A. per unit volume of concrete can be taken.

Table: C.4 Dry Bulk Volume of Coarse Aggregate per Unit Volume ofConcrete as given by ACI 211.191

Maximum size of aggregateBulk volume of dry rodded coarse aggregate of per unit volume of concrete for fineness modulus of sand

F.M.2.42.62.83.0

100.500.480.460.44

12.50.590.570.550.53

200.660.640.620.60

250.710.690.670.65

400.750.730.710.69

500.780.760.740.72

700.820.800.780.76

1500.870.850.830.81

(e) Therefore the weight of C.A. can be calculated.

(f) From Table C5, the first estimate of density of fresh concrete for the givenmaximumsize of aggregate and for non-air-entrained concrete can be adopted.

Table: C.5 First estimate of density (unit weight) of fresh concreteas given by ACI 211.1-91

Maximum size of aggregate (mm)First estimate of density (unit weight) of fresh concrete

Non air entrained (kg/m3)Air entrained(kg/m3)

1022852190

12.523152235

2023552280

2523752315

4024202355

5024452375

7024652400

15025052435

(g) The weight of all the known ingredient of concrete is calculated.The weight of the F.A. can be calculated by subtracting the weights of other ingredients from the total weight.

(h) Alternatively the weight of F.A. can also be found out by absolute volume methodwhich is more accurate.

(i)Then we have to find the proportions of all ingredients from the estimated quantities.

(j)After that the proportions are required to be adjusted as per field conditions.As per ACI 211.1-91 the fine aggregate has surface moisture of 2 percent and for C.A. absorbs 1 percent of water.On this regard the total amount of water which has to be supplied is determined.(k) Quantities of materials to be used in field duly corrected for free surface moisture in F.A and absorption characteristic of C.A.

(l) Field proportion as worked out above may not give the final answer. A trial mix is then made to study the properties of such a concrete in respect of workability,cohesiveness, finishing quality, yield and 28 days compressive strength. The mix may need grading improvement, by way of change in proportion between various fractions of C.A. or change in proportion between FA and CA. If feasible, change in the shape of C.A particularly 10 mm fraction would greatly improve the situation. If F.A and C.A are having different specific gravities, any change in their earlier calculated proportion, may affect the yield of concrete.If all the avenues do not improve the qualities of the concrete designed for the work in hand, then only, one must resort to increase in water content. If water content is increased, corresponding increase in cement content is also made so that W/C ratio remains same.When both water and cement is increased, it will affect the yield of concrete. Thereforeto keep the yield constant, both the quantities of F.A and C.A is required to be reducedcorrespondingly. All these needs a number of trials before one arrives at the final proportions.The mix designer must have sufficient experience, understanding and feel of concrete.

Road Note No. 4 Method

This method of designing concrete mix proportions is mainly based on the extensive laboratory and field experiments carried out by the Road Research Laboratory, U.K. It was first published in Road Note No 4 during 1950. They have established relationship between various properties of concrete and variable parameters. A series of standard grading curves have been established to give grading limits for all-in aggregates graded down from 20 mm and 40 mm. The procedure of mix design by Road Note No 4 is also called Grading Curve Method.This method of mix design was popular and was widely used up to 1970s all over the world. Most of our concrete roads and air field pavements were designed by this method. The Building Research Establishment of Department of Environment (DOE) U.K. has evolved another method called DOE method to replace the earlier Road Note No 4 method.

DOE Method of Concrete Mix Design

The DOE method was first published in 1975 and then revised in 1988. While Road Note No 4 or Grading Curve Method was specifically developed for concrete pavements, the DOE method is applicable to concrete for most purposes, including roads. The method can be used for concrete containing fly ash (in U.K. it is called pulverized fuel ash, PFA) or GGBFS. Since DOE method presently is the standard British method of concrete mix design, the procedure involved in this method is described instead of out dated Road Note No 4 method.

The following are the steps involved in DOE method:-

1. Find the target mean strength from the specified characteristic strength:-

Target mean strength = specified characteristic strength + (Standard deviation risk factor).

Standard deviation: The value of standard deviation has to be worked out from the trials conducted at lab or field.

Risk factor: It is the valuesbelow which not more than 5% result are expected to fall.

Fig- D.1

2. Calculate the water/cement ratio:-This is done in a rather round about method, using Table: D.1 and Fig. D.1Table: D.1gives the approximate compressive strength of concretes made with a free w/c ratio of 0.50. Using this table find out the 28 days strength for the approximate type of cement and types of C.A. Mark a point on the ordinate in Fig- D.1 equal to the compressive strength read form Table: D.1which is at a W/C ratio of 0.50.

TABLE: D.1Approximate Compressive Strength of Concrete Made witha free Water/Cement Ratio of 0.50 according to the 1988 BritishMethodDays of calculating strength

Type of cementType of C.A372891

Ordinary Portland cement(type I)Uncrushed22304249

Sulphate resisting cement(type V)Crushed27364956

Rapid hardening Portland cement(type III)Uncrushed29374854

Crushed34435561

Through this intersection point, draw a parallel dotted curve nearest to the intersection point. Using this new curve, we read off the W/C ratio as against target mean strength. This Water/Cement ratio must be compared to the W/C requirement for durability according to BS:8110:Part I:1985 Table: (1).

TABLE: D.2 [BS: 8110: Part I: 1985 Table: (1)]Condition of ExposerNominal cover of Concrete in mm

Mild2520202020

Moderate-35302520

Severe--403025

Very Severe--504030

Extreme---6050

Maximum Water / cementitious material ratio0.650.60.550.5.45

Minimum content of cementitious material in kg/m3275300325350400

Minimum grade MPa3035404550

3. Determination of water content: -To decide water content for the required workability, expressed in terms of slump or Vebe time, taking into consideration the size of aggregate and its type from Table: D.3 below-

Table: D.3Approximate Free Water Contents Required to Give Various Levels of Workability According to 1988 British method

AggregateWater content (kg/m3)

Max-sizemmTypeSlump 0-1010-3030-6060-180

Vebe>12seconds6-123-60-3

10crushed150180205225

uncrushed180205230250

20crushed135160180195


40crushed115140160175


Table: D.3.1Table for Reduction in the free water contents of Table:D.3 when using fly ash

Percentage of fly ash in cementitious materialReduction in water Content in kg/m3

Slump mm0-1010-3030-6060-180

Vebe seconds>126-123-60-3

1055510

2010101015

3015152020

4020202525

5025253030

4. Determination of cement content knowing the water/cement ratio and water content:-Cement content is calculated simply dividing the water content by W/C ratio. The cement content so calculated should be compared with the minimum cement content specified from the durability consideration as per BS: 8110: Part I: 1985 and higher of the two should be adopted. Sometime maximum cement content is also specified. The calculated cement content must be less than the specified maximum cement content.

5. Determination of the total aggregate content:-This requires an estimate of the wet density of the fully compacted concrete. This can be found out from Fig. 2 for approximate water content and specific gravity of aggregate. If sp. gr. is unknown, the value of 2.6 for uncrushed aggregate and 2.7 for crushed aggregate can be assumed.

6. Determination of proportion of fine aggregate:-The total aggregate is determined using Fig- D.3, Fig- D.4 is for 10 mm size, Fig- D.5 is for 20 mm size and Fig-D.6 is for 40 mm size coarse aggregate. The parameters involved in Figure are maximum size of coarse aggregate, the level of workability, the water/cement ratio, and the percentage of fines passing 600 sieve. Once the proportion of F.A. is obtained, fractions depending on the shape of aggregate. As a general guidance the figures given in Table D.4 can be used.Multiplying by the weight of total aggregate gives the weight of fine aggregate. Then the weight of the C.A. can be found out. Course aggregate can be further divided into different fractions depending on the shape ofaggregate. As a general guidance the figures given in Table D.4can be used.

Free water content in Kg/m3Fig- D.2Estimated wet density for fully compacted concreteTABLE: D.4Proportion of Coarse Aggregate Fractions According to the 1988 British methodTotal C.A510 mm1020 mm20-40mm

1003367-

100182755

The proportion so worked out should be tried in a trial mix and confirmed about its suitability for the given concrete structure. Table D.3.1 gives the reduction of free water contents from the figures given in Table D.3 when fly ash is used in the mix. The proportion so worked out should be tried in a trial mix and confirmed about its suitability for the given concrete structure.

Fig- D.3 [for 10mm size]

Fig- D.4 [for 10mm size]

Fig- D.5[for 20mm size]

Fig- D .6[for 40mm size]

Mix Design of M-25 Grade of Concrete by IS: 10262-1982

Table: E.1DESIGN STIPULATIONS

Characteristic compressive strength requiredin the field at 28 days25 N/mm2 (MPa)

Maximum size of aggregate20mm

Type of aggregateAngular, Crushed

Degree of workability (Compacting Factor)0.9

Degree of quality controlGood

Type of exposureMild

Table: E.2TEST DATA FOR MATERIALS

Cement usedOPC- 43

Specific gravity of cement3.15

Specific gravity of coarse aggregates2.7

Specific gravity of fine aggregates2.7

Water absorption:Coarse aggregate0.5%

Water absorption:Fine aggregate1%

Free (surface) moisture:Coarse aggregateNIL

Free (surface) moisture:Fine aggregateNIL

Sieve analysis: Coarse aggregateConforming to gradingZone III of Table 4 ofIS : 383- 1970

TARGET MEAN STRENGTH OF CONCRETE:

The target mean compressive ( Fck) strength at28 days is given byFck= fck+ tS

Where,Fck = characteristic compressive strength at 28 days = 25 MPaS= standard deviation= 4.0 MPat = a statistical value depending on expected proportion of low results (risk factor) = 1.65FCk = 25 + (4.0 X 1.65) = 31.6 MPaSELECTION OF WATER CEMENT RATIO:

According to the graph for Cement Grade of OPC-43 and for target strength of 31.6 MPa the water cement ratio is taken as 0.44.

Estimation of Air Content:

Approximate amount of entrapped air to be expected in normal is 2% of volume of concrete for nominal maximum size of aggregate of 20mm.

SELECTION OF WATER AND SAND CONTENT:

For 20 mm maximum size aggregate, sand conforming to gradingZone II, water content per cubic meter of concrete = 186 kg and sand content as percentageof total aggregate by absolute volume = 35%.

ADJUSMENT:

For change in values in water-cement ratio, compacting factor and sand belonging to Zone III, the following adjustment is required:



For sand conforming to grade Zone III of table 4, IS:383-19790-1.5%

Increase in the value of compacting factor by 0.1+ 3%0

0.16 decrease in water-cement ratio0-3.2%

Therefore, required sand content as percentage of total aggregate by absolute volume= 35 1.5 3.2 = 30.3 %Required water content = 186 + 5.58 = 191.6 kg/m3

Determination of cement content:Water-cement ratio = 0.44Water content = 191.6 ltRequired cement content = 191.6/.44 = 435.5 kg/m3

Determination of coarse and fine aggregate contents:

Our specified maximum size of aggregate of 20 mm, so the amount entrapped air in the wet concrete is 2 per cent.

We know

Where, V = absolute volume of fresh concrete, which is equal to gross volume (m3) - the volume of entrapped air = .98W = Mass of water (kg) per m3 of concrete =191.6 kg/m3C = Mass of cement (kg) per m3 of concrete = 435.5 kg/m3Sc = Specific gravity of cement = 3.15p = Ratio of FA to total aggregate by absolute volume = .303fa, Ca = Total masses of FA and CA (kg) per m3 of concrete respectively andSfa, Sca = Specific gravities of saturated, surface dry fine aggregate and coarse Aggregate respectively = 2.7So

fa = 531.9 kg/m3And,

Ca = 1223.5 kg/m3

But extra quantity of water to be added for absorption in case of CA, at 0.5 per cent mass,So, the mass of water per m3 = 191.6 + (1223.5*.5/100) = 191.6 + 6.1 = 197.7 kg/m3So, the mass of coarse aggregate per m3 = 1223.5 6.1 = 1217.4 kg/m3

Also, Extra quantity of water to be added for absorption in case of FA, at 1.0 per cent mass,So, the mass of water per m3 = 197.7 + (531.9*1.0/100) = 197.7 + 5.32 = 203.02 kg/m3So, the mass of fine aggregate per m3 = 531.9 5.32 = 526.58 kg/m3

The mix proportion then becomes:Cement: Fine aggregate: Coarse Aggregate

=435.5kg: 526.58 kg: 1217.4 kg

= 1 : 1.2 : 2.8

Actual quantities required for the mix per m3 of concrete:

Cement435.5 kg/m3

Water197.7 kg/m3

Fine Aggregate531.9 kg/m3

Coarse Aggregate1217.4kg/m3










Cement usedOPC- 43












According to the graph for target strength of 36.6 MPa the water cement ratio is taken as 0.40.





ADJUSMENT:






0.20 decrease in water-cement ratio0-4%

Therefore, required sand content as percentage of total aggregate by absolute volume= 35 1.5 4 = 29.5 %Required water content = 186 + 5.58 = 191.6 kg/m3

Determination of cement content:Water-cement ratio = 0.40Water content = 191.6 ltRequired cement content = 191.6/0.40 = 479.0 kg/m3



We know


fa = 506.84 kg/m3And,

Ca = 1211.27 kg/m3




= 479.0 kg: 501.77 kg: 1205.17 kg

= 1 : 1.05 : 2.52


Cement479.0 kg/m3

Water202.77 kg/m3

Fine Aggregate501.77kg/m3











Cement usedOPC- 43

















ADJUSMENT:











We know



Ca = 1192.5 kg/m3




= 532.2 kg: 480.0 kg: 1192.5 kg

= 1 : 0.9 : 2.24


Cement532.2 kg/m3

Water202.4 kg/m3












Cement usedOPC- 43

















ADJUSMENT:











We know



Ca = 1275.5 kg/m3




= 570.46 kg: 377.2 kg: 1269.1 kg

= 1 : 0.67 : 2.23


Cement570.46 kg/m3

Water195.61 kg/m3




DESIGN STIPULATIONS:







TEST DATA FOR MATERIALS:

Cement usedOPC- 43




Water absorption:Coarse aggregate5%







Where,fck = characteristic compressive strength at 28 days = 45 MPaS= standard deviation= 4 MPat = a statistical value depending on expected proportion of low results (risk factor) = 1.65FCk = 45 + (4 X 1.65) = 51.6 MPa

SELECTION OF WATER CEMENT RATIO:

According to the graph for Cement Grade of OPC-43 and for target strength of 51.6 MPa the water cement ratio is taken as 0.31.




For 20 mm maximum size aggregate, sand conforming to gradingZone II, water content per cubic meter of concrete = 180 kg and sand content as percentageof total aggregate by absolute volume =25 %.

ADJUSMENT:







Therefore, required sand content as percentage of total aggregate by absolute volume= 25 1.5 0.8 = 22.7%Required water content = 180 + 5.4 = 185.4 kg/m3

Determination of cement content:

Water-cement ratio = 0.31Water content =185.4ltRequired cement content = 185.4/.31 = 598.06 kg/m3



We know


fa =370.6 kg/m3And,

Ca = 1262.15kg/m3

Water absorbed by coarse aggregate 5% = 1262.15 x 5/100 = 63 kg/m3

So field weight of coarse aggregate = 1216.15-63 = 1153.15kg/m3

And water absorbed by fine aggregate 1% = 370.6 x 1/100 = 3.706kg/m3

So field weight of fine aggregate should be taken = 370.6-3.706 =366.89 kg/m3

Now the water content = 185.4+63+3.706 = 252.1 kg/m3

The mix proportion then becomesCement: Fine aggregate: Coarse Aggregate

=598.06 kg :366.89 kg:1153.15 kg

= 1 :0.6: 1.93


Cement598.06 kg/m3

Water252.1 kg/m3



Design of concrete mix of M25 grade using IS 10262:2009

1. STIPULATIONS FOR PROPORTIONING and TEST DATA FOR MATERIALS:

Grade designation- M25 Type of cement used- OPC 43 Maximum nominal size of aggregate- 20 mm Degree of quality control- Good Exposure conditions- Mild (for PCC) Specific gravity of cement- 3.15 Type of aggregate used- Angular, crushed Degree of supervision- Good Chemical admixture type- Super plasticizer (IS 9103) Workability- 100 mm slump Specific gravity of coarse aggregate- 2.7 Specific gravity of fine aggregate- 2.7 Water absorption of coarse aggregate- 0.5 percent Water absorption of fine aggregate- 1.0 percent Free surface moisture of coarse aggregate- Nil Free surface moisture of fine aggregate- Nil Zone of fine aggregate- Zone III (Table 4, IS 383) Fineness modulus of fine aggregate- 2.8 Maximum free water cement ratio- 0.55 Minimum cement content- 300 kg/m3

2. TARGET STRENGTH FOR MIX PROPORTIONING: We knowfck = fck+1.65*shere, fck= 25 Mpa or 25 N/mm2 s= 4.0 (according to Table 1 of IS 10262: 2009)therefore, fck = 25 + 1.65 * 4 = 31.6 N/mm2.

3. SELECTION OF WATER CEMENT RATIO ( first trial):According to Table 5 of IS 456: 2000 , we getThe maximum free water cement ratio= 0.55We are adopting the value as 0.5 which is less than 0.55.

4. SELECTION OF WATER CONTENT :According to Table 2 of IS 10262: 2009,for 20 mm aggregatesthe maximum water content is 186 kg, for 25 to 50 mm slump.Hence, estimated water content for 100 mm slump = (186 + 6% of 186) kg = (186 + 11.16) kg

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