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?