MIXTURE DESIGN OF FLY ASH & SLAG BASED ALKALI ACTIVATED CONCRETE FOR PRECAST CONCRETE

MIXTURE DESIGN OF FLY ASH & SLAG BASED ALKALI
ACTIVATED CONCRETE FOR PRECAST CONCRETE
Department of Civil Engineering
Institute of Technology
Nirma University
Prepared By:
Prof. Sonal P Thakkar
Assistant Professor
Daxesh Patel
M.Tech Student
33rd National Convention of Civil Engineers, IEI

Introduction
• Davidovits proposed that an alkaline liquid which can react with the
silicon (Si ) and aluminum (Al) in a source material of geological origin
or in by product material can be used to produce binders.
• Alkali activated concrete constitutes of two main compounds namely
source materials and alkaline liquids. Source materials are materials
like 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 or
potassium based. Sodium hydroxide (NaOH) or Potassium Hydroxide
(KOH) and Sodium silicate or Potassium silicate are most widely used
alkaline liquid.

Introduction(continued……)
• Present investigation attempts to find parameters affecting strength
of alkali activated concrete using fly ash and slag as source material.
High compressive strength in early period makes it ideal material for
precast work in construction industry as it has controlled
environment 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 mass
SiO2 + Al2O3 + Fe2O3 93.0 % Min. 70 % by mass
SiO2 61.4 % Min. 35 % by mass
Reactive Silica 34.7 % Min. 20 % by mass
CaO < 5%
MgO 1.4 % Max. 5 % by mass
SO3 0.6 % Max. 3 % by mass
Na2O 0.6 % Max.1.5 % by mass
Total 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 based
superplasticizer, Rheobuild was used.
Figure 1 Image of NaOH flakes Figure 2 Image of Na2SiO3

Mixture Design of Alkali Activated Concrete with Flyash and
Slag
• In order to evaluate parameters affecting the compressive strength,
density of concrete was assumed to be 2400 kg/m3 and variation was
done 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
4.5
7.9 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
CompressiveStrength
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, compressive
strength also increases when curing temperature was 90°C for 24
hours.
• Higher percentage of slag content lead to decrease in workability and
hence mixing became difficulty, therefore equal proportion of slag
and fly ash was considered for further studies. Also it can be observed
that at equal percentage of source material at 7 days the required
compressive 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
CompressiveStrength
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 on
compressive strength. Figure 1 shows effect of molarity on
compressive strength when curing was done for 24 hours in oven.
• Increase in molarity will lead to addition of more amount of sodium
hydroxide quantity which will lead to having more amount of alkaline
activator to react with cementitious material.
• It can be observed that with increase in molarity from 10 M to 12 M
compressive 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 day
CompressiveStrength(N/mm2)
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 2.0
and 2.5 and specimen were subjected to one day oven curing as
shown in Figure 2.
• It was observed that there is slight increase in compressive strength
with 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 day
CompressiveStrength
Curing Period
Compressive Strength(N/mm2) comparison for diiferent
dosage of superplasticizer
1% 1.50%

Effect of Superplasticizer Dosage (Continued…..)
• Two different dosage of plasticizer of 1% and 1.5% was taken to
evaluate it’s effect on compressive strength. As seen in figure 3, with
increase in dosage of superplasticizer, compressive strength also
increases, but it was observed that beyond 2% dosage of
superplasticizer lead to decrease in compressive strength. Also
increase in super plasticizer will lead to increase in cost and hence its
dosage 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
CompressiveStrength
Curing Period
10% 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 will
lead to decrease in compressive strength.
• Lesser addition of water leads to difficulty in compacting and thereby
decreases 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 done
approximately strength of 30 MPa could be achieved and
approximately 25 MPa to 27 MPa strength could be achieved at 7
days depending upon parameters of mix design.
• Also increase in molarity and alkaline solution ratio leads to increase
in compressive strength.
• Increase in dosage of super plasticizer and water content has direct
effect on workability parameter and hence strength increases.

Precast Products
and
Road footpath

References:
• Malhotra V. M.(2002) ,“ Introduction: Sustainable development and
concrete technology”, ACI Concrete International, 24(7).
• Davidovits J.,(1994),“ Properties of geopolymer cements”, First
international conference on alkaline cement and concretes, Ukrain,
page:131-149.
• IS: 3812 –2003, Specification for fly ash for use as pozzolana and
admixture, Bureau of Indian standards, New Delhi.
• IS: 383-1970, Specification for coarse and fine aggregate from natural
sources 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.

MIXTURE DESIGN OF FLY ASH & SLAG BASED ALKALI ACTIVATED CONCRETE FOR PRECAST CONCRETE

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MIXTURE DESIGN OF FLY ASH & SLAG BASED ALKALI ACTIVATED CONCRETE FOR PRECAST CONCRETE