Cement/Fly Ash /Metakaolin Ternary Blends: Effects on Compressive Strengths of Mortars and Economics
Presented By: Billy Wiggins, P.E., Associate Member ACI Committee 232
Points of Discussion
Pozzolans Experiment Design Experiment Results Conclusion
Pozzolans
ACI Definition Pozzolanic Reactions Fly Ash Silica Fume Metakaolin Ternary Blends
ACI Definition
A siliceous or alumino- siliceous material that, in finely divided form and in the presence of moisture, chemically reacts with calcium hydroxide released by the hydration of Portland cement to form compounds possessing cementing properties.
Pozzolanic Reactions
2C3S + 6H C3S2H3 + 3CH
2C2S + 4H C3S2H3 + CH Hydration of Calcium Silicates Calcium Hydroxide (CH) is weak and porous
by itself Pozzolans react with CH to form C-S-H
Improved Aggregate-Cement Interface Pozzolan Acts as
Micro-filler Increases Bond Leads to Higher
Strength
Fly Ash
A By-Product from the Combustion of Pulverized Coal
Small glassy beads 10m Average Particle Diameter Cheap… $30/ton Versus Cement at $85/ton 90% still goes to Land Fill
Fly Ash Properties in Cement Improved Workability Improved Long-Term Strength Gains Price Lowers Heat of Hydration Decreases Water Demand Less Bleeding Improved Durability to ASR, Sulfate, &
Chlorides
Silica Fume
Produced from the Production of Silicon 93% SiO2
.1m Average Particle Diameter
Properties of Silica Fume
Greatly Improves Compressive Strengths Decreased Porosity Increases Water Demand (HRWR Typ.) “Sticky” finish Decreases Workability Decreases Bleeding Improved Durability to ASR, Sulfate, &
Chlorides
Metakaolin
Produced from Kaolin Crude Clays An Engineered Product 1 m in diameter Plate-Like in Shape Kaolin Mined in Middle Georgia SiO2 + Al2O3 + TiO2 +Fe2O3
Properties of Metakaolin Increased Water Demand (125%) Product “Creamy” Greatly Improves Compressive Strengths.
Comparible or Better than SF Improved Durability (ASR and Sulfate) Increases Heat of Hydration Decreases Bleeding Improved Durability to ASR, Sulfate, &
Chlorides
Ternary Blends Flyash+Cement+Metakaolin or Silica Fume Less HRWR Less Sticky Good Early Age and Increased Later-Age
Strength Lower Heat Rise Improved Durability to ASR, Sulfate, &
Chlorides – Better than Single Blends?
Improved Particle Packing
Improved Workability
Experiment Design
Data on SF + FA; Not much on MK+FA Synergy Between MK and FA ? Economics ? Standard ASTM Tests Maintained Flowability
Mix Matrix % Repalcement of Cement
Metakaolin
0 5 10
Flyash
0 0/0 0/5 0/10
1515/0 5/15 10/15
3030/0 5/30 10/30
RecipesRecipes for Cement Mortars
Mix #1 Mix #2 Mix #3 Mix #4 Mix #5 Mix #6 Mix #7 Mix #8 Mix #9
%MK 0 0 0 0.05 0.1 0.05 0.1 0.05 0.1
%FA 0 0.15 0.3 0 0 0.15 0.15 0.3 0.3
Sand (g) 2035 2035 2035 2035 2035 2035 2035 2035 2035
Cement (g) 740 629 518 703 666 592 555 481 444
Water (g) 359 345.6 332.1 363.4 368.0 350.0 354.4 336.5 341.0
Flyash (g) 0 111 222 0 0 111 111 222 222
Metakaolin (g) 0 0 0 37 74 37 74 37 74
W/(C+Pozz) Ratio 0.49 0.47 0.45 0.49 0.50 0.47 0.48 0.45 0.46
Flow % Increase 0.52 0.50 0.54 0.52 0.53 0.48 0.44 0.45 0.41
Compressive Strength vs. Curing Time
0
1000
2000
3000
4000
5000
6000
7000
8000
0 10 20 30 40 50 60
Days
PS
I
Control Mix15%FA30%FA5%MK10%MK5%MK - 15%FA10%MK - 15%FA5%MK - 30%FA10%MK - 30%FA
Cost Analysis INational Average: Ready Mix
Concrete Strength vs. Cost per CY
Information from Means Building Construction Cost Data 60thEd.
$0.00
$10.00
$20.00
$30.00
$40.00
$50.00
$60.00
$70.00
$80.00
$90.00
$100.00
2000 2500 3000 3500 4000 4500 5000 5500 6000 6500
compressive strength
cost
per
yar
d
Cost Analysis II Cost Comparison of Blends @ 28 Day Compressive Break Strengths
Mix #1(CM)
Mix #2 Mix #3 Mix #4 Mix #5 Mix #6 Mix #7 Mix #8 Mix #9
%MK 0 0 0 0.05 0.1 0.05 0.1 0.05 0.1
%FA 0 0.15 0.3 0 0 0.15 0.15 0.3 0.3
Sand 2035 2035 2035 2035 2035 2035 2035 2035 2035
Cement 740 629 518 703 666 592 555 481 444
Fly ash 0 111 222 0 0 111 111 222 222
Metakaolin 0 0 0 37 74 37 74 37 74
cost for 1 ton of mortar 32.19 30.00 27.80 37.73 43.26 35.53 41.06 33.33 38.86
28d Fc 4,652 4467 3433 5759 6128 5131 5648 4135 3839
cost of a ton of mortar/psi 6.92 6.71 8.10 6.55 7.06 6.92 7.27 8.06 10.12
Cost Analysis III
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
Mix #1(CM) Mix #2 Mix #3 Mix #4 Mix #5 Mix #6 Mix #7 Mix #8 Mix #9
Mixture
28d
Com
pres
sive
Str
engt
h (p
si)
Cost Analysis IV
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
50.00
Mix #1(CM) Mix #2 Mix #3 Mix #4 Mix #5 Mix #6 Mix #7 Mix #8 Mix #9
Mixture
Co
st f
or
1 to
n o
f M
ort
ar
Cost Analysis V
0.00
2.00
4.00
6.00
8.00
10.00
12.00
Mix #1(CM) Mix #2 Mix #3 Mix #4 Mix #5 Mix #6 Mix #7 Mix #8 Mix #9
Mixture
Co
st (
$) f
or
1 to
n o
f M
ort
ar/p
si
Conclusion Fly Ash Lowers Water Demand in Ternary
Blends. Metakaolin Has Better Compressive Strength
Properties Alone than in Ternary Blends in Mortar (24% Stronger at 28d than CM).
Metakaolin has Improved “Finishability” over control mixes.
The use of 5% Metakaolin lessens the cost of a mortar mixture 5.35% per psi.
Questions?
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