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MIXTURE DESIGN OF FLY ASH & SLAG BASED ALKALI ACTIVATED CONCRETE FOR PRECAST CONCRETE
Department of Civil EngineeringInstitute of Technology
Nirma University
Prepared By:
Prof. Sonal P ThakkarAssistant Professor
Daxesh PatelM.Tech Student
33rd National Convention of Civil Engineers, IEI
Introduction
• Davidovits proposed that an alkaline liquid which can react with thesilicon (Si ) and aluminum (Al) in a source material of geological originor in by product material can be used to produce binders.
• Alkali activated concrete constitutes of two main compounds namelysource materials and alkaline liquids. Source materials are materialslike fly ash, granulated blast furnace slag, rice husk ash, silica fume,red mud, etc.
• The alkaline liquids are from soluble alkali metals which are sodium orpotassium based. Sodium hydroxide (NaOH) or Potassium Hydroxide(KOH) and Sodium silicate or Potassium silicate are most widely usedalkaline liquid.
Introduction(continued……)
• Present investigation attempts to find parameters affecting strengthof alkali activated concrete using fly ash and slag as source material.High compressive strength in early period makes it ideal material forprecast work in construction industry as it has controlledenvironment and excellent quality control.
Material Used
Test Details Test Results Requirement as per IS 3812: 2003 [3]
Colour Light grey -Specific Surface Area 416.4 m2/kg Min. 320 m2/ kg
Loss of ignition 1.1 % Max. 5 % by massSiO2 + Al2O3 + Fe2O3 93.0 % Min. 70 % by mass
SiO2 61.4 % Min. 35 % by massReactive Silica 34.7 % Min. 20 % by mass
CaO < 5%MgO 1.4 % Max. 5 % by massSO3 0.6 % Max. 3 % by mass
Na2O 0.6 % Max.1.5 % by massTotal Chlorides 0.03 % Max. 0.05 % by mass
Retention on 45 micron sieve
21.1 % Max. 34 % by mass
Pozzolanic Activity Index
88.2 % Min. 80 % by mass
Test Details Test Results
Colour White
Specific Surface Area
379 m2/kg
Loss of ignition
0.6 %
SiO2 36.8 %Al2O3 10.1 %CaO 37.0 %
Fe2O3 0.6 %Glass Content 92.5 %Retention on
45 micron sieve
11.0 %
Pozzolanic Activity Index
90.9 %
Table 1 Chemical Composition of Fly ash Table 2 Chemical Composition of Slag
• To increase the workability of fresh concrete, naphthalene basedsuperplasticizer, Rheobuild was used.
Figure 1 Image of NaOH flakes Figure 2 Image of Na2SiO3
Mixture Design of Alkali Activated Concrete with Flyash andSlag
• In order to evaluate parameters affecting the compressive strength,density of concrete was assumed to be 2400 kg/m3 and variation wasdone in following parameters:
Amount of source material
Molarity of sodium hydroxide
Ratio of sodium hydroxide to sodium silicate
Super plasticizer Dosage
Extra water
Effect of Combination Of Source Material
Table 3 Variation of source material
Mix No. GGBS % Fly ash %
Mix 1 10 90
Mix 2 20 80
Mix 3 30 70
Mix 4 40 60
Mix 5 50 50
Mix 6 60 40
• For this particular variation following data is considered:
Ratio of alkaline liquid to fly ash and GGBS 0.4
Ratio of sodium silicate to sodium hydroxide 2.5
Concentration of sodium hydroxide solution 12M
Admixture dosage 1.5%
Curing temperature 90 ℃
Curing time 24 hours
Figure 3 Comparison of compressive strength (N/mm2) for different mixture proportions
4.57.9 9.4
16.2
27
14.2
6.4
11.1
16.4
20.9
31 30.2
0
5
10
15
20
25
30
35
Mix 1 Mix 2 Mix 3 Mix 4 Mix 5 Mix 6
Co
mp
ress
ive
Stre
ngt
h
Comparison of compressive strength (N/mm2) for different mixture proportions
7th Day Compressive Strength 28th Day Compressive Strength
Effect of Combination Of Source Material (Continued…)
• It can be observed that with increase in slag content, compressivestrength also increases when curing temperature was 90°C for 24hours.
• Higher percentage of slag content lead to decrease in workability andhence mixing became difficulty, therefore equal proportion of slagand fly ash was considered for further studies. Also it can be observedthat at equal percentage of source material at 7 days the requiredcompressive strength was obtained.
Effect of Molarity of Sodium Hydroxide
Figure 4 Comparison of compressive strength(N/mm2) for different molarity
9.63
16.44
24.74
13.8
21
28.89
0
5
10
15
20
25
30
35
3 day 7 day 28 day
Co
mp
ress
ive
Stre
ngt
h
Curing Time
Compressive Strength(N/mm2) comparison for 24 hour oven cured samples
10 M
12 M
Effect of Molarity of Sodium Hydroxide (continued…..)
• Two molarities 12 M and 10 M were taken to study the effect oncompressive strength. Figure 1 shows effect of molarity oncompressive strength when curing was done for 24 hours in oven.
• Increase in molarity will lead to addition of more amount of sodiumhydroxide quantity which will lead to having more amount of alkalineactivator to react with cementitious material.
• It can be observed that with increase in molarity from 10 M to 12 Mcompressive strength increases to 29 MPa from 25 MPa at 28 days.
Effect of Alkaline Ratio
Figure 5 Comparison of compressive strength(N/mm2) for different alkaline ratio
13.8
21
28.89
15.5
20.89
29.78
0
5
10
15
20
25
30
35
3 day 7 day 28 dayCo
mp
ress
ive
Stre
ngt
h(N
/mm
2)
Curing Period
24 hours Oven Cured
Ratio 2
Ratio 2.5
Effect of Alkaline Ratio (continued…..)
• Alkaline ratio of sodium silicate to sodium hydroxide was varied as 2.0and 2.5 and specimen were subjected to one day oven curing asshown in Figure 2.
• It was observed that there is slight increase in compressive strengthwith increase in alkaline ratio.
Effect of Superplasticizer Dosage
Figure 6 Comparison of compressive strength(N/mm2) for different dosage of superplasticizer
13.8
21
28.89
16.9
25.3
32.44
0
10
20
30
40
3 day 7 day 28 dayCo
mp
ress
ive
Stre
ngt
h
Curing Period
Compressive Strength(N/mm2) comparison for diiferentdosage of superplasticizer
1% 1.50%
Effect of Superplasticizer Dosage (Continued…..)
• Two different dosage of plasticizer of 1% and 1.5% was taken toevaluate it’s effect on compressive strength. As seen in figure 3, withincrease in dosage of superplasticizer, compressive strength alsoincreases, but it was observed that beyond 2% dosage ofsuperplasticizer lead to decrease in compressive strength. Alsoincrease in super plasticizer will lead to increase in cost and hence itsdosage is restricted.
Effect of Extra Water
15.1
23.9
30.96
17.3
25.19
32.15
0
5
10
15
20
25
30
35
3 day 7 day 28 day
Co
mp
ress
ive
Stre
ngt
h
Curing Period10% extra water added
Extra Water Content
24h
48h
Figure 7 Comparison of compressive strength for 10% extra water for 24 and 48 hours
Effect of Extra Water (continued…..)
• In order to increase workability of concrete, extra water was added.Similar to water cement ratio, addition of more water in concrete willlead to decrease in compressive strength.
• Lesser addition of water leads to difficulty in compacting and therebydecreases strength. As workability increases with extra water,increase in compressive strength to a certain extent was achieved.
Conclusion
• It can be concluded that when oven curing for 24 hours was doneapproximately strength of 30 MPa could be achieved andapproximately 25 MPa to 27 MPa strength could be achieved at 7days depending upon parameters of mix design.
• Also increase in molarity and alkaline solution ratio leads to increasein compressive strength.
• Increase in dosage of super plasticizer and water content has directeffect on workability parameter and hence strength increases.
Precast Productsand
Road footpath
References:
• Malhotra V. M.(2002) ,“ Introduction: Sustainable development andconcrete technology”, ACI Concrete International, 24(7).
• Davidovits J.,(1994),“ Properties of geopolymer cements”, Firstinternational conference on alkaline cement and concretes, Ukrain,page:131-149.
• IS: 3812 –2003, Specification for fly ash for use as pozzolana andadmixture, Bureau of Indian standards, New Delhi.
• IS: 383-1970, Specification for coarse and fine aggregate from naturalsources of concrete Bureau of Indian Standards, New Delhi
• Hardjito D., Rangan B.V.(2005)“ Development and properties of low-calcium fly ash based geopolymer concrete”, Research Report GC1,Faculty of engineering, Curtain University, Perth, Australia.
Thankyou
