Effects of Fly Ash on the properties of

Alkali Activated Slag Concrete

Ankit Kothari

Civil Engineering, masters level (120 credits)

2017

Luleå University of Technology

Department of Civil, Environmental and Natural Resources Engineering

Avdelningen för byggkonstruktion och -produktion

Institutionen för samhällsbyggnad och naturresurser

Luleå tekniska universitet

971 87 Luleå

MASTER THESIS

Effects of Fly Ash on the properties of Alkali

Activated Slag Concrete

Ankit Kothari

Civil Engineering, master’s level

Luleå - 2017

Supervisor: Andrzej Cwirzen – Professor,

Department of Civil, Environmental and Natural Resources Engineering

Luleå University of Technology

Co-Supervisor: Abeer Humad – PhD student

Department of Civil, Environmental and Natural Resources Engineering

Luleå University of Technology

Foreword

This report is the final part of my 2 years education in Master Programme in Civil Engineering with

specialization in Mining and Geotechnical Engineering at Luleå University of Technology corresponding

to 30 credits.

This master thesis project was carried out at LTU, under the supervision of Prof. Andrzej Cwirzen and

PhD-student M.Sc. Abeer Humad as Co-Supervisor, in the Department of Civil, Environmental and

Natural Resources Engineering.

I would like to thank my supervisor Prof. Andrzej Cwirzen and Co-supervisor M.Sc. Abeer Humad for

their support and inspiration at every stage and also providing all the materials required for my thesis.

I would also like to thank Andreas Eitzenberger, senior lecturer at LTU under the division of Mining

and Geotechnical Engineering, for his support and motivation, to continue my studies in LTU. And last

but not the least I would like to thank all my classmates - Karl Hedgrade, Mamdouh, Daniel, Karina

Tommik, Ott Oisalu, Taavi Lohmuste and Koen Vos for supporting and guiding me in every ups and

downs of my master programme journey.

Luleå, May 2017

Ankit Kothari

V

Abstract

This master thesis presents the effects of fly ash on the properties of alkali activated slag concrete, com-

monly referred as Geopolymer concrete (GPC). Cement manufacturer are major producers of CO2 which

negatively affects the environment. Due to the increased construction activities and environmental con-

cern, it is necessary to introduce alternative and eco-friendly binders for concrete. Slag and fly ash based

concrete, which is by-product from industrial waste, is probably the best replacement for OPC concrete

due to less or nil environmental issue.

Most of the researchers have already concluded that slag and fly ash can be used as binders in concrete by

activating them with alkali activator solution (e.g. by sodium silicate or sodium carbonate).

In the present work concretes were produced by varying the proportion of slag to fly ash (40:60, 50:50,

60:40 & 80:20); amount of alkali activators (5, 10 & 14) and chemical modulus of sodium silicate (Ms)

(0.25, 0.5 & 1). Setting times and compressive strength values were evaluated.

Results showed that decrease in fly ash content irrespective of % of alkali activators and alkali modulus

(Ms), the compressive strength was increasing and setting time was getting shorter. The produced con-

cretes showed increasing compressive strength with increase in % of alkali activator for Ms 0.5 and 1,

while for Ms=0.25 the strength was decreasing with increase in % of alkali activators. From this it can be

concluded that, Ms=0.5 was the optimum point below which the reaction got slower.

Based on the initial investigations, mix S8:F2-SS10(1) and S8:F2-SS10(0.5) showed most promising re-

sults in terms of fresh and hardened concrete properties and were easy to handle. Consequently, the above

mentioned mixture was chosen to be studied in more detail. The experimental program for these mixes

included determination of slump flow, compressive strength (7, 14, 28 days) and shrinkage (drying and

autogenous). The results shows that, strength increased with time and comparatively mix with Ms=0.5

showed higher compressive strength than mix with Ms=1, due to higher alkalinity of the pore solution.

Mix with Ms=1 showed higher drying shrinkage compared to mix with Ms=0.5, which was explained

by higher alkalinity of the solutions (Ms=0.5) leading to rapid formation of aluminosilicate gel. Autoge-

nous shrinkage appeared to be higher for mix with Ms=0.5. This was associated with lower modulus

which leads to densification of concrete microstructure at early ages. Pore diameter decrease and the

water trapped in the pores exerted increasing tensile stress resulting for higher autogenous shrinkage.

Keywords: Geopolymer concrete, blast furnace slag, fly ash, alkali activators, alkali modulus (Ms),

sodium silicate, sodium hydroxide, compressive strength.

Note: S8:F2-SS10(0.5) – S8 (Slag 80%), F2 (Flay ash 20%), SS10(0.5): Sodium Silicate 10% with Ms=0.5

V

Sammanfattning

Denna masterprov presenterar effekterna av flygaska på egenskaperna hos alkaliaktiverad slaggbetong,

vanligen kallad Geopolymerbetong (GPC). Cementtillverkare är stora producenter av CO2 som påverkar

miljön negativt. På grund av ökad byggverksamhet och miljöhänsyn är det nödvändigt att införa alterna-

tiva och miljövänliga bindemedel för betong. Slag- och flygaskabaserad betong, som är biprodukt från

industriavfall, är förmodligen den bästa omplaceringen av OPC-betong på grund av mindre eller inget

miljöfrågor.

De flesta forskarna har redan dragit slutsatsen att slagg och flygaska kan användas som bindemedel i betong

genom att aktivera dem med alkaliaktivatorlösning (t ex med natriumsilikat eller natriumkarbonat).

I det föreliggande arbetet framställdes betongar genom att variera andelen slagg för att flyga aska (40:60,

50:50, 60:40 och 80:20); Mängd alkaliska aktivatorer (5, 10 & 14) och kemisk modulus av natriumsilikat

(Ms) (0,25, 0,5 & 1). Inställningstider och tryckstyrka värderades.

Resultaten visade att minskningen av flygaskahalten, oberoende av% av alkaliaktivatorerna och alkalimo-

dulusen (Ms), kompressionsstyrkan ökade och inställningstiden blev kortare. De framställda betongarna

visade ökande tryckhållfasthet med ökning i% av alkaliaktivatorn för Ms 0,5 och 1, medan för Ms = 0,25

minskade hållfastheten med ökning i% av alkaliaktivatorer. Härav kan man dra slutsatsen att Ms = 0,5 var

den optimala punkten under vilken reaktionen blev långsammare.

Baserat på de ursprungliga undersökningarna visade blandning S8: F2-SS10 (1) och S8: F2-SS10 (0,5)

mest lovande resultat när det gällde fräscha och härdade betongegenskaper och var lätta att hantera.

Följaktligen valdes den ovan nämnda blandningen för att studeras mer i detalj. Det experimentella pro-

grammet för dessa blandningar innefattar bestämning av nedgångsflöde, tryckhållfasthet (7, 14, 28 dagar)

och krympningsålder (torkning och autogen). Resultaten visar att styrkan ökat med tiden och jämförande

blandning med Ms = 0,5 visade högre tryckstyrka än blandning med Ms = 1, på grund av högre alkalinitet

i porösningen.

Blandning med Ms = 1 visade högre torkkrympning jämfört med blandning med Ms = 0,5 vilket förkla-

rades av högre alkalinitet av lösningarna som ledde till snabb bildning av aluminosilikatgel. Autogen

krympning tycktes vara högre för blandning med Ms = 0,5. Detta var förknippat med lägre modul som

ledde förtätning av betongmikrostruktur vid tidiga åldrar. Pordiametern minskar och vattnet fångat i po-

rerna utövar ökad dragspänning som resulterar i högre autogen krympning.

Nyckelord: Geopolymerbetong, masugnslagg, flygaska, alkaliaktivatorer, alkalimodul (Ms), natriumsili-

kat, natriumhydroxid, tryckhållfasthet.

Anm: S8:F2-SS10(0,5) - S8 (Slag 80%), F2 (Flaskaska 20%), SS10(0,5): Natriumsilikat 10% med Ms= 0,5

VI

VII

Table of Contents

FOREWORD .......................................................................................................... IV

ABSTRACT ............................................................................................................. V

SAMMANFATTNING ............................................................................................... V

1 INTRODUCTION .............................................................................................. 9

1.1 BACKGROUND .................................................................................................................... 9

1.2 STRUCTURE OF THESIS ..................................................................................................... 10

2 LITERATURE REVIEW .................................................................................... 12

2.1 CEMENTITIOUS BINDERS .................................................................................................. 12

2.2 ALKALI ACTIVATORS ......................................................................................................... 12

2.3 HARDENING PROCESS (SOLIDIFICATION) .......................................................................... 12

2.4 PROPERTIES ...................................................................................................................... 13

2.4.1 Workability ..................................................................................................... 13

2.4.2 Curing conditions .............................................................................................. 13

2.4.3 Mechanical properties .......................................................................................... 13

2.4.4 Shrinkage ....................................................................................................... 14

2.4.5 Durability ....................................................................................................... 14

2.5 ADVANTAGES OF GEOPOLYMER CONCRETE OVER OPC CONCRETE [14]. ....................... 14

2.6 APPLICATIONS................................................................................................................... 15

3 OBJECTIVES AND RESEARCH QUESTIONS .................................................... 16

3.1 LIMITATIONS..................................................................................................................... 16

4 EXPERIMENTAL SETUP .................................................................................. 17

4.1 MATERIALS ....................................................................................................................... 17

4.1.1 Ground granulated blast furnace slag (GGBS) ........................................................... 17

4.1.2 Fly ash (FA) ................................................................................................... 17

4.1.3 Alkaline activators ............................................................................................. 17

4.1.4 Aggregates....................................................................................................... 18

4.2 EQUIPMENT AND TEST PROCEDURES ............................................................................... 19

4.2.1 Sieve analysis................................................................................................... 19

4.2.2 Concrete mixer ................................................................................................. 19

4.2.3 Workability ..................................................................................................... 20

4.2.4 Setting time ..................................................................................................... 20

4.2.5 Compressive strength (fc) ...................................................................................... 22

4.2.6 Shrinkage ....................................................................................................... 22

5 PRELIMINARY STUDIES ................................................................................. 24

5.1 MIX DESIGN ...................................................................................................................... 24

5.2 TEST RESULTS AND ANALYSIS ........................................................................................... 26

5.2.1 Setting time ..................................................................................................... 26

5.2.2 Compressive strength .......................................................................................... 27

5.3 SUMMARY OF INITIAL STUDIES ......................................................................................... 29

6 MAIN STUDIES ................................................................................................ 30

6.1 EXPERIMENTAL SETUP ...................................................................................................... 30

VIII

6.2 TEST RESULTS, ANALYSIS AND DISCUSSION....................................................................... 31

6.2.1 Workability ..................................................................................................... 31

6.2.2 Compressive strength .......................................................................................... 31

6.2.3 Shrinkage ....................................................................................................... 32

7 CONCLUSIONS AND FUTURE WORK ............................................................. 34

7.1 CONCLUSION.................................................................................................................... 34

7.2 FUTURE WORK ................................................................................................................. 35

8 REFERENCES .................................................................................................. 37

Appendix A ........................................................................................................................ A-1

Appendix B ......................................................................................................................... B-2

Appendix C ........................................................................................................................ C-3

Appendix D ........................................................................................................................ D-4

9

1 Introduction

1.1 Background

Concrete is one of the most widely used construction materials, which accompany with Portland cement

as the major component. Cement manufacturer are one of the primary producers of carbon dioxide. After

the introduction of cement at the beginning of the industrial revolution, the emission of the greenhouse

gases has increased by 40%, [42]. If the consumption of the cement would continue further, it may lead

to disastrous effects on ecosystems, biodiversity and livelihoods of people.

Because of the increased construction activities and usage of inadequate building materials, there is a need

to introduce alternative ecological cementitious binders, which are based on waste or by-product from

steel industries (Blast furnace slag), coal industries (Fly ash), these are also called as aluminosilicate waste

materials, which has a very small Greenhouse footprint when compared to conventional cement (OPC)

[14].

Combustion of coal results in production of fly ash as a by-product and efforts are being made to increase

the utilization of these by-products in the construction field and to minimize the use of OPC. According

to estimation conducted in Australia, 13 million tons of fly ash is produced annually and out of it only

11% is utilized in the construction industries and rest of it is either disposed or used as a landfill purpose

[19]

Geopolymer was first developed in late 1970s by J. Davidovits. Production of geopolymer concrete re-

quires an aluminosilicate material and alkali activator which could include for example sodium carbonate

(Na2Co3) or sodium silicate (Na2Sio3) (water glass) along with water and aggregates (Figure 1).

Figure 1: Materials to produce Geopolymer concrete. (Credit: Queen’s University Belfast) – [30]

Many investigations have been done earlier to completely or partially replace cement with geopolymer

materials. These concretes showed good properties, for example they gained strength more rapidly and

cures more rapidly than Portland based cement and also gain most of their strength within 24 hours than

concretes based on OPC, [10]. The curing process of GPC is quite different when compared to OPC

concrete as it requires in most cases heat curing at high temperatures often exceeding 60 degrees, [34].

But in most of the cases, to cure the GPC laboratory curing at ambient temperature will be adapted.

10

The chemical reaction between the alkali activating solution and aluminosilicate waste materials such as

fly ash or blast furnace slag, results in different reaction products. For instance, alkali activated fly ash,

which is rich in silica (Si) and alumina (Al) results in formation of N-A-S-H gel (Na2O-Al2O3-SiO2-

H2O), with 3D framework. Whereas, alkali activated slag, which is rich in calcium (Ca) results in for-

mation of C-S-H gel (CaO-SiO2-H2O) with low Ca/Si ratio [7].

Alkali activated concretes are superior in comparison with OPC for example in their resistance to chlo-

ride attack, fire and acid resistance and the major application is waste immobilization solutions for the

chemical and nuclear industries [14]. Unfortunately, until today there is no specific mix design procedure

for GPC, [19].

1.2 Structure of thesis

1. Introduction

This chapter gives the brief description about content of this mater thesis.

2. Literature review

This chapter contains review of research done up to date on alkali activated blast furnace slag concrete.

3. Objectives and research questions

This chapter presents the objectives and research questions formulated based on the literature preview,

and along with this limitations of the project are presented.

4. Experimental setup

This chapter describes raw materials used for the production of GPC i.e., cementitious material (slag and

fly ash), alkali activators and aggregates, as well as equipment and test procedures; sieve analysis, slump

test, initial and final setting time, compressive strength and shrinkage..

5. Preliminary studies

It deals with the procedure followed and equipment used to produce GPC for test mixes. Later setting

time and compressive strength test are conducted for different mix proportions, which is followed by test

results and analysis for the mentioned experiments.

6. Main studies

In the main studies, based on the results obtained from preliminary studies, most promising and economic

mix will be selected in order to carry out slump test, compressive strength and shrinkage for main studies.

Further, it is followed by test results analysis and discussion for the mentioned experiments.

7. Conclusion and future work

In this chapter, conclusions are presented based on the results obtained from preliminary and main studies,

which fulfil the hypothesis and research questions. Further some recommendations for future work is also

presented.

8. References

In this section name of the authors, journals, articles, books and websites are presented, which are used

as a reference in this project.

11

9. Appendix

In the appendix, detailed quantity calculations of different GPC mixes, results of setting time and com-

pressive strength are presented.

12

2 Literature review

2.1 Cementitious binders

Geopolymer concrete is the new type of concrete which completely replaces the Portland cement (OPC)

with industrial by-products, which are rich in silica (SiO2) and alumina (Al2O3) such as metakaoline or

with industrial waste or by-product such as fly ash, rice husk ash or slag, which are also called as alumi-

nosilicate material results to form a geopolymer binder.

2.2 Alkali activators

The alkaline solution are usually a soluble hydroxide, alkali silicates or carbonates (Sodium hydroxide,

NaOH; Sodium silicates, Na2SiO3; Sodium carbonate, Na2CO3) which is used to react with silica (SiO2)

and alumina (Al2O3) rich material.

2.3 Hardening process (solidification)

The chemical reaction between the aluminosilicate rich material and alkaline activators is commonly

called geopolymerisation [19]. Geopolymerisation reaction is an exothermic reaction, described by Da-

vidovits using the two stage equation shown below, [19]. The main role of the sodium silicates solution

(Na2SiO3) is to initiate the geopolymerisation process [16]

(1)

There is ongoing debate between the researches about geopolymerization reaction which is accepted

that, the reaction takes place in three stages: [9, 15 & 19]

1) Dissolution of Si and Al from the source material

2) Hydrolysis or gelation

3) Condensation forming a 3D network of silicon – aluminates (geopolymer backbones)

The hardening of the geopolymer concrete (GPC) depends on the type of alkali activators, properties of

raw materials as well as on mix design [34]. Most scientists and engineers prefer to use the term alkali

activated fly ash, when fly ash is the source of the aluminosilicates material and alkali activated slag, when

slag is the source aluminosilicates material [15, 19]. Brough, A.R. and A. Atikson (2002), investigated the

activation and hydration process in the fly ash and slag based geopolymer concrete. The researchers ob-

13

served that fly ash can be activated by alkali solutions to form an inorganic binder through a geopoly-

merisation reaction. Whereas the activation of slag leads to formation of calcium silicates hydrated (C-S-

H) gel similar to that formed in OPC [5, 34].

2.4 Properties

2.4.1 Workability

K. Arbi, et al., (2015), conducted a study on the workability of alkali activated fly ash and slag based

geopolymer concrete. The research shows that with the increase in the slag content in the GPC, causes

increase of the compressive strength but workability and setting time tend to be reduced. Retarders were

used maintain the flowability, [20].

2.4.2 Curing conditions

Geopolymer concrete develops its properties more rapidly, compared to OPC concrete. Most of the

mechanical strength is gained within the first 24 hours and it is capable to make a strong chemical bond

with all kind of rock-based aggregates, [10]. Curing process of fly ash based geopolymer concrete needs

heat curing to achieve the structural integrity and while the slag based geopolymer concrete can be cured

as OPC concrete, due to the similar hydration product (C-S-H gel), [34]. Compressive strength of GPC

is affected by the curing conditions, [21 & 23]. Pithadiya, S & Naum, (2015), studied the curing regimes

of the GPC. In his experimental studies the fly ash was replaced by slag and the specimen were cured in

both ways; normal room temperature curing and oven curing at temperature of 60 to 100°C. Replace-

ment of fly ash by slag increased the compressive strength without oven curing, [21, 26].

2.4.3 Mechanical properties

Wardhono, et al., (2015), studied the strength of the alkali-activated slag/fly ash mortar blend and sug-

gested that, the initial strength is mostly related to the GGBS (slag), while the fly ash is contributing the

later strength gain. Authors also suggested that the hydration of GPC can occur following two possible

mechanisms, [34].

1) The hydration of slag and polymerization of fly ash occurred separately

2) The two reaction are occurring simultaneously

Criado, et al., (2016), studied the microstructural and mechanical properties of alkali activated Colombian

raw materials and concluded that, with increasing amount of slag in FA:BFS based geopolymer concrete,

will reduce the porosity with formation C-A-S-H gel due to reaction of slag and N-A-S-H gel formed

due to the reaction of the fly ash. These compacted matrixes showed a good mechanical strength devel-

opment, [7].

Criado, et al., (2016), GPC showed that concretes containing 80% slag and 20% fly ash have low ductility

and toughness, higher deformations, [7].

Deb, et al., (2015) showed that the increase of slag content resulted in higher compressive strength values

and the 28-day compressive strength varied between 40 to 54 MPa. The sodium silicate to sodium hy-

droxide (SS/SH) ratio was 1.5, [12].

Girawale, (2015), studied the effects of activators by varying the molarity of NaOH, and suggested that

the compressive strength of the GPC increases with increased molarity of the alkaline solution and ratio

of (Na2SiO3/NaOH) [16]. Figure 2 shows the effect of GPC for different Na2SiO3/NaOH ratio, in terms

of compressive strength and age of concrete [27]. Also Kumar, et al., (2015), studies showed that the

strength of the geopolymer concrete varies with the variation of (Na2SiO3/NaOH) ratio, molarity of

NaOH, curing temperature [21].

14

Figure2: Graph showing compressive strength of GPC, with variation of (Na2SiO3/NaOH) [Rajera-

jeswari, et al., 2013] [27]

2.4.4 Shrinkage

Deb, et al., (2015), studied the drying shrinkage of slag blended with fly ash geopolymer concrete and

compared the results with OPC concrete. The results showed that shrinkage decreases and compressive

strength increases with the increase of slag content and decrease of SS/SH ratio in geopolymer concrete

cured at room temperature. The OPC concrete showed 11% higher shrinkage value compared to GPC.

[12].

2.4.5 Durability

Wardhono, et al., (2015), research work shows that, alkali activated slag (AAS) might have durability

problems due to growth of micro-cracks. It can be overcome, due to the polymerization process of the

fly ash geopolymer, which fills the pores formed in the AAS and increase the stability of the mortar.

Simultaneously, less water will be trapped in the pores of the AAS, which lead to smaller shrinkage and

less micro-cracking [34].

The GPC made of class F fly ash showed a higher strength and better durability due to low amount of

CaO, when compared to class C fly ash. Whereas the GPC made of class C fly ash has some durability

issue and it sets quick, [13, 19].

2.5 Advantages of Geopolymer concrete over OPC concrete [14].

High compressive strength gain in some cases

Low CO2 footprint

Good corrosion resistance, particularly when mixed with PTFE filler

Fire resistance (1200°C) and no liberation of toxic fumes when heated

Geopolymer cement has the ability to make strong bond to fresh and old substrates, steel, boro-

silicate glass and ceramics at ambient temperature. [3]

Outstanding resistance to chemical attack by chloride, including sea water, various acids and

sulphate

Bleeding free, high isolation and low permeability

FA – GPC, Low shrinkage and thermal conductivity[14]

15

2.6 Applications

GPC can be effectively used in the precast concrete industry and can be transported easily with the

minimized breakage because of the high early strength. It was also suggested that GPC can replace the

OPC concrete [1]. Geopolymer concrete based on fly ash can be utilized in rehabilitation and retrofitting

of structures (Precast industries) in the extreme condition such as aggressive soil and marine environments

[21, 28].

These benefits shows that, GPC has higher potential to use in the society, for example

1) Mass construction work

2) Highway applications in cold areas subjected to have repeated freeze – thaw cycle and deicer salt

scaling, often where OPC fails and deteriorates [14]

3) Manufacture of precast railway sleepers, precast building construction materials

4) Vaults manufacturing because of fire resistance [24]

Some successful applications of GPC

1) Queensland’s University [Global Change Institute (GCI)], 3 suspended floors made from struc-

tural geopolymer concrete – Coined Earth Friendly Concrete (EFC) (Figure 3).

2) Placement of geopolymer concrete at first private airport Brisbane West Well camp - Australia,

with the usage of 40000 m3 of GPC (Figure 4).

Figure 3: Queensland’s University GCI building with 3 suspended floors made from structural geopol-

ymer concrete. (Credit: Hassel Architect and Wagners) – [17]

Figure 4: Placement of GPC at first private airport. (Credit: UNSW (University of New South

Wales)) – [32]

16

3 Objectives and research questions

The main objective of this thesis is to contribute to the research on development of a green environmen-

tally friendly concrete from industrial by-products such as slag and fly ash and which properties will be

comparable with OPC concrete.

Geopolymer concrete still has a number of problems which limit its full scale applicability, including lack

of robustness, durability, shrinkage and creep. The following research questions were formulated for this

master thesis based on the performed literature study:

1. How the increased fly ash content in blast furnace slag based alkali activated concrete will affects

the setting time and compressive strength?

2. What is the effect of the dosage of alkali activators on setting time and compressive strength?

3. What is the effect of sodium silicate alkali modulus on setting time and compressive strength?

4. How the alkaline modulus (Ms) will affect the shrinkage of GPC?

3.1 Limitations

It was decided not to use sodium carbonate as alkaline activator along with sodium silicate. Because of

the poor results (setting time and compressive strength). And also it was decided that the alkali modulus

(Ms) will not be decreases beyond 0.25. Because of higher amount of heat liberation and not so econom-

ical.

17

4 Experimental setup

4.1 Materials

4.1.1 Ground granulated blast furnace slag (GGBS)

In the current project, slag (GGBS) of merit 5000 provided from MEROX, Sweden is used. The chem-

ical composition of the slag is done with PANalytical-Zetium – XRF spectrometer and the physical data

provided from MEROX Company as shown in Table 1.

Table 1: Chemical composition of GGBS. (Credit: MEROX Company)

4.1.2 Fly ash (FA)

In the current project, Class F fly ash provided by Cementa AB, Sweden is used. The chemical compo-

sition of Class F fly ash was analyzed and provided by ALS Scandinavia Ab Company (Table 2).

Table 2: Chemical composition of Fly ash. (Credit: ALS Scandinavia Company)

4.1.3 Alkaline activators

Liquid sodium silicate (SS) was provided by PQ Corporation and had alkali modulus Ms (SiO2 ̸ Na2O)

= 2.2 with 34.37 wt% SiO2 and 15.6 wt% Na2O and solid content of 49.97 ≅ 50 wt%. Sodium silicate

was complemented with sodium hydroxide having purity 98.5% and Na2O = 75.93 wt% provided by

PQ Corporation in powder form to acquire sodium silicate with alkali modulus Ms = 1 and also adjusted

with Ms = 0.5 and 0.25. Table 3 shows the percentage by weight of solid and water content in different

alkali modulus.

Oxide CaO SiO2 Al2O3 Fe2O3 MgO Na2O K2O TiO2 MnO P2O5 SO3 Cl others

Compo-

sition of

GGBFS

Wt.%

48.91 24.24 7.89 0.76 6.56 0.08 0.97 5.95 1.21 0.41 2.51 0.017 0.502

Physical

data

Specific surface

cm2/ g Bulk density kg / m 3

Particle density kg /

m3 Moisture content %

Glass content

%

5000 1100 2950 0.10 97-98

Oxide CaO SiO2 Al2O3 Fe2O3 MgO Na2O K2O TiO2 MnO P2O5 SO3 Cl

Compo-

sition of

Fly ash

Wt.%

6.1 48.1 18.9 7.79 1.84 1.06 2.26 0.84 0.0729 0.437 - -

18

Table 3: Weight % of solid and water content in different Ms

4.1.4 Aggregates

Aggregates (Coarse and Fine) were provided from Jehander Heidelberg Cement group, Sweden. Their

specific gravity was of 2.7 according to ASTM C127-15 and C128-15, [36, 37]. Mix consisted of 80wt%

of fine aggregates (0-4 mm) and 20wt% of coarse aggregates (4-8 mm). Sieve analysis test results are

shown in Figure 5. The sand was classified as medium sand (FM = 2.6–2.9) based on the fineness modulus

2.9. And also the gradation pattern of the aggregate is quite similar to the Andreasen model. The exact

calculated values of the sieve analysis are presented in the Appendix A.

Figure 5: Gradation curve for aggregates

0

10

20

30

40

50

60

70

80

90

100

0,063 0,125 0,25 0,5 1 2 4 5,6 11,2 16

PA

SS

ING

-%

SIEVES Diameter (mm)

AGGREGATE GRADINGCOMBINED CURVES

Andreasen

Current GradingCurve

Alkali modulus (Ms) Solid (wt %) Water (wt %)

Ms = 2.2 50 50

Ms = 1.0 55 45

Ms = 0.5 61 39

Ms = 0.25 66 34

19

4.2 Equipment and test procedures

4.2.1 Sieve analysis

Stack of sieves including pan and cover, weighing balance and mechanical sieve shaker.

Procedure followed ASTM C136/C136M – 14 which is also commonly known as gradation test, used

to determine the particle size distribution in the sample of aggregate [38]. In connection with this fineness

modulus (FM) will be determined. Fineness modulus is a ready index of coarseness or fineness of the

material. FM is an empirical factor obtained by adding the cumulative percentages of aggregate retained

on the sieves and dividing the sum by an arbitrary number 100. Thus, the fineness modulus (FM) of fine

aggregate (sand) was around 2.9, which is within the limit as per ASTM standards (FM = 2.3 – 3.1).

Note – Higher the value of the FM, coarser the aggregate will be.

Procedure

I. Take the known weight of the sample to the nearest 0.1 gm of accuracy. Since this weight will

be utilized to check for any material loss after sample has been graded.

II. Arrange the set of different sieve size in decreasing order from top to bottom, including pan and

cover. And place the arranged sieves on the mechanical sieve shaker.

III. Known weight of aggregates is placed on the top of the first sieve. Agitate or shake the sieves by

mechanical shaker for sufficient period of time.

IV. Note down the mass of aggregate retained on each respective sieve and calculate the percentage

of fineness modulus of aggregate.

4.2.2 Concrete mixer

Mixer is a device that combines all the raw materials such as binders, aggregates and water, homogene-

ously to produce concrete. Hobart mixer of 20 liter capacity produced by Hobart Manufacturing UK,

was used for preliminary mix studies [43] (Figure 6a). While for main concrete mixes, rotating pan con-

crete mixer (Zyklos – ZZ 75 HE) produced by Pemat Company, Germany [25] was used (Figure 6b).

Figure 6: Concrete mixer (a – Hobart mixer, b – Rotating pan mixer)

20

4.2.3 Workability

Workability is defined as the ease of handling of freshly prepared concrete or mortar, with which it can

be easily transported, placed and compacted without any segregation. Slump cone test was used in this

project to assess the workability following the ASTM C143 standard, [40].

In the current project, slump of the freshly prepared concrete was determined as per ASTM C143 stand-

ards, which is accepted by both field and laboratory atmospheric conditions [40].

Apparatus

Slump cone of standard specification as shown in the figure 7, tamping steel rod (16 mm diameter and

600 mm in length), measuring device (Ruler of 300 mm length) and metal base plate of perfectly flat and

horizontal.

Procedure

I. Clean thoroughly the internal surface of the slump cone, free from earlier residues of the concrete

and place it on the metal base plate.

II. Fill the mold with concrete in three layers. After each layer, 25 strokes of uniform tamping is done

using tamping rod. At the final stage after filling the mold, excess of concrete is removed and

leveled using trowel.

III. Remove the mold immediately and carefully in vertical direction after the final stage and noted

down the slump immediately by determining the vertical difference between the deformed

concrete and slump cone using ruler as shown in the figure 7.

Figure 7: Dimensions of slump cone (Credit: Andure, 2016) – [2]

4.2.4 Setting time

Setting time is subdivided in two parts i.e., initial setting time and final setting time. By knowing the

setting time of concrete, one can pre-plan for different kinds of operations such as transportation, placing,

compacting and finishing of concrete [8]. To conduct the setting time test (initial and final setting time),

vicat needle apparatus provided by Form+Test Prüfsystemeas, Riedlingen – Germany as shown in figure

8 will be used as per IS: 4031(5)-1988, specifications and standards [41].

21

Figure 8: Vicat needle apparatus and its details (Credit: Civil Engineering, 2012) - [6].

Initial setting time is defined as the time duration between the moment of water added to the binder,

to the time when binder starts to lose its plasticity [41].

Final setting time is defined as the time duration between the moment of water added to the binder,

to the time when binder completely losses its plasticity and becomes hard [41].

Apparatus

Vicat apparatus of IS standards, Needle of 1mm2 cross section (initial setting time), Plunger of 1mm

smaller needle and 5mm outer diameter (final setting time), non-porous base plate.

Procedure

I. Take about 300gms of binder and make a nice binder paste with w/b = 0.356. Record the time

(t0) instantly when water is added. Fill the paste in the mold, which is placed over the non-porous

plate. Adjust the 1mm2 needle in such a way that it is in contact with surface of the paste and

release it quickly. Initially, needle will penetrate completely through the binder paste and the

same procedure is carried out for every 2 min until the needle penetrates a depth of 30-35mm

from top and note down the time (t11). Therefore, initial setting time (t1) = t1

1 - t0.

II. Now, to determine the final setting time replace the needle with plunger of 1mm smaller needle

and 5mm outer diameter. The binder paste is considered to be finally set when needle makes an

impression of the 1mm smaller diameter (inner circle) and fails to make an impression of 5mm

diameter (outer circle), at this point note down the time (t21). Therefore, final setting time (t2) =

t21 - t0.

22

4.2.5 Compressive strength (fc)

The compressive strength measurements were done using CTM (compressive testing machine) produced

by Toni Technik Company, Berlin – Germany as shown in the figure 9.

Figure 9: Compressive Testing Machine (CTM). (Credits: Toni Technik) – [31]

The concrete cubes/ specimen were placed in the middle of the CTM area and uniform load is applied

in vertical direction until the specimen fails to take the load. Compressive strength (fc) was calculated

using the Equation 2.

𝑓𝑐 = (𝐹

𝐴) 𝑀𝑃𝑎 (2)

Where, fc = Compressive strength (MPa)

F = Load applied (N)

A = Surface area of specimen (mm2)

4.2.6 Shrinkage

Shrinkage can be defined as decrease of volume of the hardening concrete and if it exceeds the tensile

strength of binder matrix cracking can occur. Autogenous shrinkage can be measured on concrete samples

when specimens are prevented from drying and kept at constant temperature. The change in volume

occurs due to the chemical reaction between the cementitious binder and water. Drying shrinkage occurs

due to the moisture movement between specimen and environment and consequent evaporation of water

from capillary pores of concrete and later from gel pores [4]. However, in this type of shrinkage meas-

urement, most of the shrinkage is observed during the first month after hardening [4].

In the current project, the total deformation including autogenous shrinkage and drying shrinkage was

measured. Measurements were done with manual strain gauge DEMEC type produced by Mayes Instru-

ments Limited, England, Figure 10.

23

Figure 10: DEMEC mechanical strain gauge with description. (Credit: Mayes Group Windsor Eng-

land) - [22]

In the current work, concrete cylinder samples of 200 mm height and 100mm diameter were used for

shrinkage measurement. Initially, two points were located on the surface of the concrete sample, in such

a way that, it lies straight on a vertical line and these points are attached with pre-drilled stainless steel

disc using adhesive and calibrating bar to obtain accurate positioning of disc, Figure 11(a).

Later, the concrete specimens are wrapped using transparent plastic foil, in order to prevent it from

moisture contact, Figure 11b for autogenous shrinkage measurements. While drying shrinkage measure-

ments were taken for specimens exposed to atmosphere, Figure 11c.

Figure 11: Detailing of shrinkage test (a – Positioning of disc, b – Autogenous (wrapped), c – Drying)

24

5 Preliminary studies

5.1 Mix design

Used mix designs are shown in Table 4. Concretes were produced with variable contents of ground

granulated blast furnace slag (GGBS), fly ash (FA), various amounts of alkali activators. The used concrete

mixes had 450 kg/m3 of binder, 1700 kg/m3 of aggregates and a constant w/b ratio of was 0.45. In

addition to that, to activate the binder content alkali activators of different alkali modulus (Ms) and dif-

ferent percentage of activators were used. The dosage of solid alkali activators was 5, 10 and 14 wt% of

binder weight. The mix proportions of slag to fly ash content were – 80%:20%, 60%:40%, 50%:50% and

40%:60% respectively.

Firstly, the mixing procedure of binder paste specimens, for initial and final setting time was performed

as per IS: 4031(5)-1988 standards, which was discussed earlier in experimental investigation section.

While, the mixing process for GPC specimens was performed using mini Hobart mixer. The mixing

procedure includes the mixing of all the dry material for 1 minute in mini Hobart mixer. Prepared per-

centage of alkaline activator (SS) solution of respective modulus is mixed with water and left for 10–15

minutes before adding it to the dry mix material and later it is mixed for another 4 minutes. The concrete

samples were casted in alkaline resistance polymer mold of size 100*100*100 mm cube, in order to check

the compressive strength of the concrete. Vibrator table was used for 40-60 sec, to ensure that no air or

voids are present in the specimen. Immediately after casting, the samples were sealed in plastic bags for

curing i.e., sealed laboratory curing, where the sealed specimen will be kept in the laboratory environ-

ment at the temperature of 20-22 ˚C until the testing time (Note: No heat curing treatment was applied

because of lower compressive strength).

Compressive strength of the concrete cubes (100*100*100 mm3) were determined after 7 days under

CTM provided by Toni Technik Company, Berlin – Germany. The loading rate was set to 10 kN/sec

and followed ASTM C109 / C109M-16a standards [39].

25

Table 4: Mix proportion of GPC (1 cube)

Mix Id Binder (450 kg/m3) Aggregate (1.7 Kg) w/b = 0.45 Activators

Slag (gms)

Fly Ash (gms)

FA (kg) CA (kg) Water = 202.5 gms SS (gms)

S4:F6-SS5(1) 180 270 1.36 0.34 (202.5 - 18.2) = 184.3 40.5

S5:F5-SS5(1) 225 225 1.36 0.34 (202.5 - 18.2) = 184.3 40.5

S6:F4-SS5(1) 270 180 1.36 0.34 (202.5 - 18.2) = 184.3 40.5

S8:F2-SS5(1) 360 90 1.36 0.34 (202.5 - 18.2) = 184.3 40.5

S4:F6-SS10(1) 180 270 1.36 0.34 (202.5 - 36.45) = 166.05 81

S5:F5-SS10(1) 225 225 1.36 0.34 (202.5 - 36.45) = 166.05 81

S6:F4-SS10(1) 270 180 1.36 0.34 (202.5 - 36.45) = 166.05 81

S8:F2-SS10(1) 360 90 1.36 0.34 (202.5 - 36.45) = 166.05 81

S4:F6-SS14(1) 180 270 1.36 0.34 (202.5 - 51.64) = 150.86 114.75

S5:F5-SS14(1) 225 225 1.36 0.34 (202.5 - 51.64) = 150.86 114.75

S6:F4-SS14(1) 270 180 1.36 0.34 (202.5 - 51.64) = 150.86 114.75

S8:F2-SS14(1) 360 90 1.36 0.34 (202.5 - 51.64) = 150.86 114.75

S5:F5-SS5(0.5) 225 225 1.36 0.34 (202.5 - 14.4) = 188.1 36.9

S6:F4-SS5(0.5) 270 180 1.36 0.34 (202.5 - 14.4) = 188.1 36.9

S8:F2-SS5(0.5) 360 90 1.36 0.34 (202.5 - 14.4) = 188.1 36.9

S5:F5-SS10(0.5) 225 225 1.36 0.34 (202.5 - 28.8) = 173.7 73.8

S6:F4-SS10(0.5) 270 180 1.36 0.34 (202.5 - 28.8) = 173.7 73.8

S8:F2-SS10(0.5) 360 90 1.36 0.34 (202.5 - 28.8) = 173.7 73.8

S5:F5-SS14(0.5) 225 225 1.36 0.34 (202.5 - 40.5) = 162 103.5

S6:F4-SS14(0.5) 270 180 1.36 0.34 (202.5 - 40.5) = 162 103.5

S8:F2-SS14(0.5) 360 90 1.36 0.34 (202.5 - 40.5) = 162 103.5

S5:F5-SS5(0.25) 225 225 1.36 0.34 (202.5 - 11.63) = 190.87 34.2

S6:F4-SS5(0.25) 270 180 1.36 0.34 (202.5 - 11.63) = 190.87 34.2

S8:F2-SS5(0.25) 360 90 1.36 0.34 (202.5 - 11.63) = 190.87 34.2

S5:F5-SS10(0.25) 225 225 1.36 0.34 (202.5 - 23.25) = 179.25 68.4

S6:F4-SS10(0.25) 270 180 1.36 0.34 (202.5 - 23.25) = 179.25 68.4

S8:F2-SS10(0.25) 360 90 1.36 0.34 (202.5 - 23.25) = 179.25 68.4

S5:F5-SS14(0.25) 225 225 1.36 0.34 (202.5 - 32.5) = 170 95.4

S6:F4-SS14(0.25) 270 180 1.36 0.34 (202.5 - 32.5) = 170 95.5

S8:F2-SS14(0.25) 360 90 1.36 0.34 (202.5 - 32.5) = 170 95.4

Note: - FA: Fine aggregate, CA: Coarse aggregate, SS: Sodium Silicate Mix: - S8:F2-SS14(0.25): S8 (Slag 80%), F2 (Fly ash 20%), SS14(0.25): Sodium Silicate 14% with Ms = 0.25 Mix: - S5:F5-SS5(1): S5 (Slag 50%), F5 (Fly ash 50%), SS5(1): Sodium Silicate 5% with Ms = 1 and so on…..

26

5.2 Test results and analysis

5.2.1 Setting time

The initial and final setting times are important factors for execution of concrete works, especially in-

cluding transportation, placing, compacting and finishing of concrete. The setting times of different pro-

portions of geopolymer binders along with varying the quantity of alkali activators (SS) and alkali modulus

(Ms) were measured. Figure 12 shows the initial and final setting times of mixes activated with SS with

Ms = 1. It was observed that with the decreasing of the fly ash content and keeping constant proportion

of activator both setting times were getting shorter. It was also observed that increase of the amount of

alkali activator from 5%SS to 10%SS and 14%SS caused drastic shortening of both setting times. This

could be caused by the type of fly ash (class F), which has lower amount of lime (CaO) compared to class

C fly ash. This particular class of fly ash is used in order to delay the setting time in geopolymer concrete.

In the current situation, since there is decrease in fly ash content i.e., increase in the slag content which

accelerated the setting times. The increase of the amount of the activator solution resulted in faster

polymerization and hydration process with an outcome of accelerated setting time.

Figure 12: Initial and Final setting times for various proportion of Slag and Fly ash for Ms=1

Similar trends were observed for binder paste with Ms = 0.5 and 0.25, figure 13 and figure 14. The main

reason behind the sudden shortening of the setting time is the decrease of the Ms. A higher amount

NaOH will be needed to achieve the respective modulus and lot of heat will be produced resulting to

the faster reaction and shortening of the setting time. In all the three cases a comparatively longer initial

setting time was observed with 5%SS dosage of activators, whereas the longer final setting time was

observed for 5%SS dosage with Ms=1. Overall, the proportion S8:F2 (80% Slag: 20% Fly ash) Ms = 1,

0.5 and 0.25 showed the most acceptable from the practical application point of view initial and final

setting times when using 10wt% and 14wt% of alkali activator. In terms of economic, handling and

mechanical properties mix S8:F2-SS10(1) and S8:F2-SS10(0.5) are more suitable. Mix S8:F2 with acti-

vator dosage of 14%SS irrespective of Ms, and mix S8:F2-SS10(0.25) showed flash setting time and would

be also quite expensive. Detailed quantitative calculations and results of setting time measurement are

shown in Appendix B.

82

5

72

0

47

5

36

5

73

70

62

3045

35

25

20

0

200

400

600

800

1000

S4:F6 S5:F5 S6:F4 S8:F2

Tim

e (M

inu

tes)

Mix

Initial setting time (Ms=1)

5%SS 10%SS 14%SS

35

10

30

40

13

90

16

65

16

20

15

32

99

0

70

0

57

0

54

0

44

0

0

1000

2000

3000

4000

S4:F6 S5:F5 S6:F4 S8:F2

Tim

e (M

inu

tes)

Mix

Final setting time (Ms=1)

5%SS 10%SS 14%SS

27

Figure 13: Initial and Final setting times for various proportion of Slag and Fly ash for Ms=0.5

Figure14: Initial and Final setting times for various proportion of Slag and Fly ash for Ms=0.25

5.2.2 Compressive strength

The compressive strength development of slag/fly ash based geopolymer concrete for different alkali

modulus (Ms) = 1, 0.5 and 0.25 measured at 7 days is shown in figure 15, 16 and 17 respectively. Com-

pressive strength increased with increase in slag content, irrespective of alkali activator dosage and mod-

ulus (Ms). Two major different reaction takes place with slag/ fly ash based GPC i.e., calcium silicate

hydrate with Al in its structure (C-A-S-H gel) and sodium aluminosilicate hydrate (N-A-S-H gel) with

higher number of polymerized species [7].

42

0

39

0

36

5

31

5

17

0

13

0

85

68

50

43

30

20

0100200300400500

S4:F6 S5:F5 S6:F4 S8:F2Tim

e (M

inu

tes)

Mix

Initial setting time (Ms=0.5)

5%SS 10%SS 14%SS

65

60

40

35

20

15

15

1215

15

13

6

0

20

40

60

80

S4:F6 S5:F5 S6:F4 S8:F2

Tim

e (M

inu

tes)

Mix

Initial setting time (Ms=0.25)

5%SS 10%SS 14%SS

15

75

12

10

10

10

97

513

10

11

20

78

0

54

097

5

93

5

62

0

55

0

0

500

1000

1500

2000

S4:F6 S5:F5 S6:F4 S8:F2

Tim

e (M

inu

tes)

Mix

Final setting time (Ms=0.5)

5%SS 10%SS 14%SS

13

95

90

0

56

5

53

5

11

20

86

5

51

0

40

0

10

80

86

0

48

5

36

5

0

500

1000

1500

S4:F6 S5:F5 S6:F4 S8:F2

Tim

e (M

inu

tes)

Mix

Final setting time (Ms=0.25)

5%SS 10%SS 14%SS

28

GPC mix with Ms = 1

Initially, a concrete mix with 40% slag content showed poor results with Ms =1 and different dosage of

activators. The maximum compressive strength was about 10.85 MPa with an activator dosage of 14%SS,

caused by higher amount of fly ash compared to slag. Consequently, a higher amount of N-A-S-H gel

presumably formed. Porosity was higher and lower amount of C-A-S-H gel formation resulting to lower

compressive strength as shown in figure 15. So this particular mix (S4:F6) will be rejected for further

investigations.

Further with increase in the slag content in GPC, compressive strength increases with higher amount of

C-A-S-H gel formation and comparatively less pore formation. In this type of GPC, increasing percent-

age of activator dosage doesn’t influence much improvement in the compressive strength. In the mix

with 50% slag, the compressive strength was almost similar for 5% and 10% alkali activators, whereas for

14% dosage of alkali activator, the strength was almost twice the results of 5% and 10% alkali activators

(Figure 15). Based on the observed results, it can be concluded that with 14% dosage of alkali activator,

higher amount of gel is formed with faster reaction to obtain the higher mechanical strength. Mix S6:F4

and S8:F2 showed some improvements in their compressive strength (Figure 15) because of higher pro-

portions of slag as binder content, leads to faster hydration and polymerization producing higher amount

of C-A-S-H gel and lower amount of N-A-S-H gel. Therefore, it can be concluded that higher amount

of slag influence the higher compressive strength of concrete.

Figure 15: Influence of slag and activator dosage on the compressive strength of GPC (Ms = 1)

GPC mix with Ms = 0.5 and 0.25

Decrease in the Ms to 0.5 and 0.25, which means higher amount of NaOH is required, the reaction has

been accelerated resulting in higher 7-day compressive strength compared to mixes activated with Ms =

1 as shown in figure 16 and 17. In both the cases of Ms = 0.5 and 0.25, had similar trend of increasing

compressive strength with increasing slag content as in the case of Ms = 1. Particularly, the GPC with

Ms = 0.5 showed similar compressive strength values for the respective blend ratio but irrespective of

dosage of alkali modulus (S5:F5 ≅ 16.5 MPa, S6:F4 ≅ 20 MPa and S8:F2 ≅ 26 MPa). While the concrete

mix with Ms = 0.25, showed an adverse effect ie, with the increase in the percentage of activator dosage,

compressive strength was gradually decreasing. But for the mix S8:F2 the strength ≅ 25 MPa at an early

age of 7 days.

4,787,50 10,21

14,27

3,557,37

12,92

15,7110,85

13,15

14,50 16,10

0,00

5,00

10,00

15,00

20,00

S4:F6 S5:F5 S6:F4 S8:F2

Co

mp

ress

ive

stre

ngt

h (

MP

a)

Mix

Alkali Modulus = 1

5%SS 10%SS 14%SS

29

Figure 16: Influence of slag and activator dosage on the compressive strength of GPC (Ms = 0.5)

Figure 17: Influence of slag and activator dosage on the compressive strength of GPC (Ms = 0.25)

Overall the results obtained from the preliminary studies can be summarized by saying that Ms = 1 and

0.5 are more favorable in terms of economic and handling. While the Ms = 0.25 showed good mechanical

strength, it is more expensive due to extremely high amount of sodium hydroxide needed to produce

the respective modulus. The exact compressive strength values for different concrete mix is presented in

Appendix C.

5.3 Summary of initial studies

Based on the results obtained from setting time and compressive strength, mix S8:F2-SS10(1) and S8:F2-

SS10(0.5) were chosen for main studies.

16,9019,80

24,1517,30

20,3026,00

15,0218,96

27,05

0,00

5,00

10,00

15,00

20,00

25,00

30,00

S5:F5 S6:F4 S8:F2

Co

mp

ress

ive

stre

ngt

h (

MP

a)

Mix

Alkali Modulus = 0.5

5%SS 10%SS 14%SS

17,30

21,50 25,20

15,21

18,20

26,11

9,74

11,72

21,41

0,00

5,00

10,00

15,00

20,00

25,00

30,00

S5:F5 S6:F4 S8:F2

Co

mp

ress

ive

stre

ngt

h (

MP

a)

Mix

Alkali Modulus = 0.25

5%SS 10%SS 14%SS

30

6 Main Studies

6.1 Experimental setup

This part of the research included determination of slump, compressive strength and shrinkage. 9 cubes

of 100*100*100 mm and 3 cylinders of 200 mm height and 100 mm diameter were casted for each mix,

Figure 18.

For the production of GPC, the raw materials utilized will be similar to that of the materials used in

preliminary studies. Initially, all the dry materials are mixed for 1 minute in rotating pan concrete mixer

(Zyklos – ZZ 75 HE) produced by Pemat Company, Germany [25], figure 18. Alkaline activators along

with water were prepared 24 hours before mixing of concrete. After addition of water with alkali activa-

tors, mixing continues for another 4 minutes. Note: While preparing the water sample for the concrete

mixes, the water from the alkali activator solution was included.

Figure 18: GPC for main studies [a – Mixer, b – GPC, c - S8:F2-SS10(1), d - S8:F2-SS10(0.5)]

Compressive strength of the concrete cubes (100*100*100 mm3) were determined after 7, 14 and 28

days under CTM provided by Toni Technik Company, Berlin – Germany. The loading rate was set to

10 kN/sec and followed ASTM C109 / C109M-16a standards [39]. Shrinkage test were done as described

in section 4.2.5

31

6.2 Test results, analysis and discussion

6.2.1 Workability

Mix S8:F2-SS10(0.5) showed a slump of 120 mm, while the mix S8:F2-SS10(1) showed a slump of 175

mm (Table 5). In both the mixes, the proportion of binder content and dosage of alkali activators were

identical, but the alkali modulus (Ms) was 0.5 and 1. Mix with alkali modulus (Ms) 0.5 showed a better

workability presumably due to higher amount of NaOH and lower amount of sodium silicate. Conse-

quently it reacted faster and deformed less, compared to mix with Ms=1.

Table 5: Slump test results

6.2.2 Compressive strength

Compressive strength of GPC cubes were determined at 7, 14 and 28 days as per ASTM C109 / C109M-

16a standards [39]. Figure 19 shows the compressive strength results obtained for GPC mix S8:F2-SS10(1)

and S8:F2-SS10(0.5).

Results showed increase of strength with time, Figure 19. In comparison with the two mixes, mix S8:F2-

SS10(0.5) showed almost 1.5-2 times higher compressive strength compared to mix S8:F2-SS10(1). There

are two main reasons behind the strength development of GPC. First and foremost is the higher percent-

age slag content, which influences higher compressive strength and secondly, is the gel formation which

increases with curing time and results in higher strength, [7]. Detailed test results are shown in Appendix

D.

Figure 19: Compressive strength development of GPC with curing period

When comparing these results with preliminary studies values were significantly higher. This might be

related to different preparation and mixing of alkaline activator solution with dry materials. While pre-

paring the solution for preliminary studies, the solutions was left for 10 – 15 minutes before adding it to

27

34

43

5360

65

0

10

20

30

40

50

60

70

7 14 28

Co

mp

ress

ive

stre

ngt

h (

MP

a)

Curing Period (Days)

Mix - S8:F2-SS10(1&0.5)

Ms = 1

Ms = 0.5

Mix Id Slump (mm)

S8:F2-SS10(1) 175

S8:F2-SS10(0.5) 120

32

the dry materials, whereas, in main studies the solution was left for 24 hrs. It can be predicted that, in the

instant solution the reaction within the solution was yet full completed; while the solution prepared for

main studies it was. Another possible reason is the used mixer type. For preliminary studies the mixer

used was mini Hobart mixer, while for main studies rotating pan concrete mixer was used. From this it

can be concluded that, even mixing procedure and mixer is important parameter for compressive strength

of concrete. Therefore, rotating pan concrete mixer is more efficient than mini Hobart mixer.

6.2.3 Shrinkage

Figure 20 shows the shrinkage test results (drying and autogenous) expressed in micro strain. The results

obtained for the concrete specimen which are opened to atmosphere shows combined autogenous and

drying shrinkage. The GPC mix with Ms = 1 seems has to have higher drying shrinkage while mix with

Ms = 0.5 has higher autogenous shrinkage. Further section briefly explains the mechanism involved in

drying and autogenous shrinkage with respect to alkali modulus (Ms).

Figure 20: Shrinkage measurement of GPC, for 30 days (Autogenous and Drying)

Drying shrinkage

Figure 21, shows the average measured drying shrinkage values mix S8:F2-SS10(1) and S8:F2-SS10(0.5).

The GPC mix with Ms = 1 showed higher rate of shrinkage compared to mix with Ms = 0.5. This

whole scenario of drying shrinkage can be analyzed based on the research conducted by Zheng, (2009).

From their research it was concluded that, with increase in the alkaline modulus (Ms) (SiO2/Na2O), the

alkalinity of the solution decreases because of increased amount of silica content and leads to formation

silica chain (Si-O-Si) instead of silica network [33 & 35]. While with the lower amount of silica content

and thus lower modulus and higher alkalinity the initial alkaline aluminosilicate gel is forming more rapid.

These gels densify binder matrix before hardening by structural reorganization of the unstable gel formed

and trapping water. When the concrete with lower modulus exposed to atmospheric moisture contacts

the water trapped it gets discharged leading to a lower shrinkage compared to higher modulus concrete

[33, 35].

Whereas with higher alkaline modulus, initially less densification takes place because of the formation of

Si-O-Si network instead of formation aluminosilcate gel and also due to the delay in reorganization of

the gel in the early stages which results in higher shrinkage [33, 35].

It does not mean that with increase in the alkaline modulus (Ms), densification of the GPC is delayed in

early stages leading to increasing in shrinkage because the reorganization of gel does not get delayed for

every Ms, due to optimum silica content [11 & 33].

0

0,5

1

1,5

2

2,5

3

3,5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Shri

nka

ge (

Mic

ro s

trai

n)

Days

S8:F2-SS10(0.5) (Auto) S8:F2-SS10(1) (Auto)

S8:F2-SS10(0.5) (Dry+Auto) S8:F2-SS10(1) (Dry+Auto)

33

Figure 21: Drying shrinkage measurement of GPC, for 30 days

Autogenous shrinkage

Figure 22, shows the average autogenous shrinkage readings of GPC mix S8:F2-SS10(1) and S8:F2-

SS10(0.5). It is seen that, GPC mix with Ms = 0.5 has higher rate of shrinkage compared to mix with

Ms = 1. This variation of shrinkage is because of alkalinity of the activator, for instance the activator with

Ms = 0.5 has higher alkalinity which results in densification of concrete by reducing the diameter of the

pores. As the diameter of the pores decreases, the trapped water in the pores of concrete leads to the

formation of larger radius of curvature and developing higher tensile stress, which causes higher autoge-

nous shrinkage [18]. The alkali modulus increases, the densification of concrete is slowed down with a

comparatively larger diameter of pores resulting in lower tensile stress, which causes lower autogenous

shrinkage [18 & 33].

Figure 22: Autogenous shrinkage measurement of GPC, for 30 days

0

0,5

1

1,5

2

2,5

3

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Shri

nka

ge (

Mic

ro s

trai

n)

Days

Drying Shrinkage

S8:F2-SS10(0.5) S8:F2-SS10(1)

0

0,5

1

1,5

2

2,5

3

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Shri

nka

ge (

Mic

ro s

trai

n)

Days

Autogenious Shrinkage

S8:F2-SS10(0.5) S8:F2-SS10(1)

34

7 Conclusions and future work

7.1 Conclusion

Answer to the research questions (section 3) are simplified

1. How the increased fly ash content in blast furnace slag based alkali activated concrete will affects the

setting time and compressive strength?

Increase in fly ash content causes, delayed initial and final setting time and decreasing the compressive

strength in slag based alkali activated concrete. Most probably related to a lower amount of C-A-S-H gel

formation and larger pores.

2. What is the effect of the dosage of alkali activators on setting time and compressive strength?

With increase in dosage of alkali activators (5%, 10% & 14%) – the setting time got shorter and compres-

sive strength increased with higher gel formation. But mix with Ms=0.25, showed an adverse effect ie,

with increase in dosage of activators, compressive strength was decreasing. Probably Ms=0.5 is the opti-

mum point, below which matrix of concrete structure gets loosen leading to a lower compressive

strength.

3. What is the effect of sodium silicate alkali modulus on setting time and compressive strength?

With decrease in the Ms, the pH of the solution gets higher by boosting the reaction within the alkaline

solution and resulting to higher compressive strength and shorter setting time. This scenario is applicable

for Ms = 1 & 0.5, while for Ms = 0.25 the compressive strength was comparatively lower to Ms = 0.5

4. How the alkaline modulus (Ms) will affect the shrinkage of GPC?

I. Drying shrinkage

GPC mix S8:F2-SS10(1) showed higher drying shrinkage compared to mix S8:F2-SS10(0.5), which is

explained by higher alkalinity of the solutions leading to densification of concrete and rapid formation of

aluminosilicate gel. While with increase in the Ms, the formation of gel and densification of concrete is

delayed leading to higher drying shrinkage.

II. Autogenous shrinkage

GPC mix S8:F2-SS10(0.5) showed higher autogenous shrinkage compared to mix S8:F2-SS10(1). This

is due to lower modulus leads to densify the concrete initially, resulting in decrease of diameter of pores

and mean-while the water trapped in the pores exert increasing tensile stress resulting in higher autoge-

nous shrinkage.

The following additional conclusions can be formed:

Slag:Fly Ash based geopolymer concrete is one of the best replacement for OPC based concrete,

because of the less emission of CO2 to atmosphere, comparatively good compressive strength

and also better utilization of industrial by-product rather than landfill.

Alkaline activator (sodium silicate combined with sodium hydroxide) is better binding agent to

bind slag: fly ash based AAC (alkali activated concrete).

It is to better prepare alkaline activator solution combined with water, 1 day before adding it to

the dry materials.

35

AAC with 80% slag and 20% fly ash, activated by 10% SS and Ms = 1 & 0.5 showed best results

in terms compressive strength.

Heat curing (24 hrs, 65˚C) didn’t give satisfactory results for 7 days compressive strength.

Concrete specimens cured in ambient temperature, showed higher compressive strength.

7.2 Future work

Due to the lack of time some investigations couldn’t be accomplished such as drying and autogenous

shrinkage measurement. For future studies it is worth doing XRD (X-ray diffraction), FTIR (Fourier

transform infrared spectroscopy) and also SEM (Scanning electron microscopy) analysis to determine the

microstructural properties of alkali activated concrete.

37

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A-1

Appendix A

A1. Sieve Analysis of the Aggregates

Table 6: Sieve analysis of aggregates

Sieve size

Combined percentage passing of aggregates

Weight

retained

(gm)

Percentage

Weight re-

tained

Cumulative

percentage re-

tained

Cumulative

percentage

passing

11.2 mm 0 0 0 100

5.6 mm 443 14.76 14.76 85.24

4 mm 157 5.24 20 80

2 mm 246 8.2 28.2 71.8

1 mm 504 16.8 45 55

500µ 847 28.23 73.23 26.77

250µ 478 16 89.23 10.77

125µ 220 7.33 96.56 3.45

63µ 85 2.83 99.40 0.6

Pan 20 0.66 100 0

Total 3000

A2. Fineness Modulus calculation

Table 7: Fineness Modulus Calculation

Sieve size

Coarse Aggregates Fine Aggregate

Weight

retained

(gm)

%

Weight

retained

Cumulative

% retained

Cumulative

% passing

Weight

retained

(gm)

%

Weight

retained

Cumulative

% retained

Cumulative

% passing

11.2 mm 0 0 0 100 - - - -

5.6 mm 443 73.83 73.83 26.17 - - - -

4 mm 157 26.17 100 0 - - - -

2 mm - - - - 246 10.25 10.25 89.75

1 mm - - - - 504 21 31.25 98.75

500µ - - - - 847 35.3 66.55 33.45

250µ - - - - 478 20 86.55 13.45

125µ - - - - 220 9.16 95.71 4.29

63µ - - - - 105 4.375 - 0

Pan - - - -

Total 600 2400 FM =(290/100) =2.9

B-2

Appendix B

B1. Quantity calculation and results of setting time

Table 8: Results of Initial and Final setting time (min)

Mix Id Binder (300 gm) w/b = 0.356 Activators Initial (t1)

min

Final (t2)

min Slag Fly Ash Water (106.8) SS

S4:F6-SS5(1) 120 180

94.65

27

825 3510

S5:F5-SS5(1) 150 150 720 3040

S6:F4-SS5(1) 180 120 475 1390

S8:F2-SS5(1) 240 60 365

S4:F6-SS10(1) 120 180

82.5

54

73 1665

S5:F5-SS10(1) 150 150 70 1620

S6:F4-SS10(1) 180 120 62 1532

S8:F2-SS10(1) 240 60 30 990

S4:F6-SS14(1) 120 180

72.4

76.5

45 700

S5:F5-SS14(1) 150 150 35 570

S6:F4-SS14(1) 180 120 25 540

S8:F2-SS14(1) 240 60 20 440

S4:F6-SS5(0.5) 120 180

97.2

24.6

420 1575

S5:F5-SS5(0.5) 150 150 390 1210

S6:F4-SS5(0.5) 180 120 365 1010

S8:F2-SS5(0.5) 240 60 315 975

S4:F6-SS10(0.5) 120 180

87.6

49.2

170 1310

S5:F5-SS10(0.5) 150 150 130 1120

S6:F4-SS10(0.5) 180 120 85 780

S8:F2-SS10(0.5) 240 60 68 540

S4:F6-SS14(0.5) 120 180

80

69

50 975

S5:F5-SS14(0.5) 150 150 43 935

S6:F4-SS14(0.5) 180 120 30 620

S8:F2-SS14(0.5) 240 60 20 550

S4:F6-SS5(0.25) 120 180

99

22.8

65 1395

S5:F5-SS5(0.25) 150 150 60 900

S6:F4-SS5(0.25) 180 120 40 565

S8:F2-SS5(0.25) 240 60 35 535

S4:F6-SS10(0.25) 120 180

91.3

45.6

20 1120

S5:F5-SS10(0.25) 150 150 15 865

S6:F4-SS10(0.25) 180 120 15 510

S8:F2-SS10(0.25) 240 60 12 400

S4:F6-SS14(0.25) 120 180

85.2

63.6

15 1080

S5:F5-SS14(0.25) 150 150 15 860

S6:F4-SS14(0.25) 180 120 13 485

S8:F2-SS14(0.25) 240 60 06 365

C-3

Appendix C

C1. Preliminary compressive strength results for 7 days curing

Table 9: Compressive strength results (7 days curing)

Mix Id Weight

(Kg) Area (mm2)

Density

(Kg/m3) Load (KN)

Compressive Strength

(MPa)

S4:F6-SS5(1) 2.224 102*100 2180.40 48.80 4.78

S5:F5-SS5(1) 2.235 103*100 2170.00 77.30 7.50

S6:F4-SS5(1) 2.246 102*100 2201.20 104.10 10.21

S8:F2-SS5(1) 2.260 107*100 2112.15 152.70 14.27

S4:F6-SS10(1) 2.137 101*100 2216.00 35.90 3.55

S5:F5-SS10(1) 2.204 104*100 2119.20 76.70 7.37

S6:F4-SS10(1) 2.248 101*100 2225.74 130.50 12.92

S8:F2-SS10(1) 2.215 105*100 2109.50 165.00 15.71

S4:F6-SS14(1) 2.170 104*100 2086.53 112.80 10.85

S5:F5-SS14(1) 2.151 102*100 2108.82 134.10 13.15

S6:F4-SS14(1) 2.161 106*100 2038.70 153.50 14.50

S8:F2-SS14(1) 2.220 110*100 2018.20 177.20 16.10

S5:F5-SS5(0.5) 2.235 105*100 2128.57 177.10 16.90

S6:F4-SS5(0.5) 2.226 107*100 2080.40 212.00 19.80

S8:F2-SS5(0.5) 2.230 106*100 2104.00 256.00 24.15

S5:F5-SS10(0.5) 2.197 105*100 2092.40 181.70 17.30

S6:F4-SS10(0.5) 2.204 106*100 2079.24 215.10 20.30

S8:F2-SS10(0.5) 2.260 105*100 2152.40 273.00 26.00

S5:F5-SS14(0.5) 2.087 104*100 2006.73 156.20 15.02

S6:F4-SS14(0.5) 2.102 102*100 2060.30 193.40 18.96

S8:F2-SS14(0.5) 2.180 103*100 2116.50 278.60 27.05

S5:F5-SS5(0.25) 2.155 106*100 2033.00 183.10 17.30

S6:F4-SS5(0.25) 2.218 106*100 2092.45 227.80 21.15

S8:F2-SS5(0.25) 2.216 105*100 2110.50 264.50 25.20

S5:F5-SS10(0.25) 2.188 105*100 2083.80 159.70 15.21

S6:F4-SS10(0.25) 2.201 105*100 2096.20 190.80 18.20

S8:F2-SS10(0.25) 2.213 103*100 2149.00 268.90 26.11

S5:F5-SS14(0.25) 2.069 105*100 1970.50 102.30 9.74

S6:F4-SS14(0.25) 2.063 103*100 2002.90 120.70 11.72

S8:F2-SS14(0.25) 2.250 105*100 2143.00 224.80 21.41

D-4

Appendix D

D1. Compressive strength results for main studies with increasing curing time

Table 10: Main studies, compressive strength results

Mix Id

Curing

Period

(days)

Weight

(Kg) Area (mm2)

Density

(Kg/m3) Load (KN)

Compressive

Strength

(MPa)

Mean

Value

(MPa)

S8:F2-SS10(1) 7

2.23 100*100 2230.0 259.30 26.00

27 2.24 100*99 2262.6 269.40 27.20

2.23 100*99 2252.5 273.70 27.65

S8:F2-SS10(1) 14

2.24 100*100 2240.0 345.00 34.50

34 2.25 100*100 2250.0 344.00 34.40

2.21 100*99 2232.3 335.00 33.84

S8:F2-SS10(1) 28

2.26 100*99 2283.0 428.00 43.23

43 2.27 100*101 2245.0 423.00 42.00

2.27 100*100 2274.0 433.00 43.30

S8:F2-SS10(0.5) 7

2.26 100*100 2260.0 541.00 54.10

53 2.21 100*98 2255.0 523.00 53.40

2.24 100*99 2262.6 521.00 52.63

S8:F2-SS10(0.5) 14

2.30 100*100 2230.0 595.00 59.50

60 2.22 100*98 2265.3 581.00 59.30

2.20 100*98 2245.0 597.00 61.00

S8:F2-SS10(0.5) 28

2.24 100*99 2267.0 650.00 65.66

65 2.23 100*99 2253.0 628.00 63.43

2.23 100*100 2230.0 650.00 65.00