Recent Advances in

Sulfoaluminate-Belite Cement

Research

Maria Juenger & Irvin Chen

University of Texas at Austin

SAB/CSA Cements

Also called calcium sulfoaluminate cements

Primary phases are:

C4A3$ (Ye’elemite or Klein’s compound)

C2S

Anhydrite/Gypsum

Early strength from ettringite

Late strength from C-S-H

Renewed Interest

Less lime = less CO2

Lower clinkering temperature (1250 C)

More friable = less grinding energy

High sulfate content makes it ideal for use of

waste as kiln feed

Cement Phase Lime Content (%)

C3S 73.7

C2S

C3A

C4AF

65.1

62.2

46.2

C4A3$ 36.7

History

Made in China since 1970s

Properties

Rapid setting

High early-age strength

Self stressing and shrinkage compensating

Uses

Pre-cast concrete applications and cold

environments

Challenges - Clinkering

No accurate “Bogue” equations

No defined or specified phase assemblage(s)

Unreliable analysis of phases present (in literature)

Lose sulfur during firing

Impurities in the raw materials have unknown effects on later cement properties

Difficult to create a consistent product on the large scale

Challenges - Hydration

C4A3$ + 2C$H2 + 34H → C6A$3H32 + 2AH3

C4A3$ + 8C$H2 + 6CH + 74H → 3C6A$3H32

AH3 + 3CH + 3C$H2 + 20H → C6A$3H32

Ettringite easy to quantify

AH3 is difficult to observe, even in microscopy – best way is with TGA/DTA

Ettringite may not react to form AFm in low gypsum conditions

Hydration is very dependent on w/c

Challenges – Dimensional Stability

Ettringite formation is expansive

Our research

Refinement of “Bogue” type equation for

phase prediction in clinkers

Dependence of hydration and properties on

phase composition

Optimum gypsum content and optimum SAB

cement composition

Impurities

Admixtures

Phase assemblages and Bogue

Target Compositions “Bogue” Equations

%C4AF = 3.043(%Fe2O3)

%C4A3$ = 1.995(%Al2O3) –

1.273(%Fe2O3)

%C2S = 2.867(%SiO2)

%C$ = 1.700(%SO3) –

0.445(%Al2O3) +

0.284(%Fe2O3)

#1 #2 #3 #4 #5 #6 #7

C2S 20 40 60 20 30 40 50

C4A3$ 60 40 20 50 40 30 20

C4AF 10 10 10 20 20 20 20

C$ 10 10 10 10 10 10 10

Made in a laboratory muffle furnace

with reagent grade materials

Higher C2S

Higher C4A3$

Phase Composition

Phase

TG (Target) R (Actual - Rietveld)

(weight %)

#2 #C #F

TG R TG R TG R

C2S 40 44.94 41.91 43.06 40.64 40.47

C4A3$ 40 41.96 40.16 43.87 39.43 42.40

C4AF 10 6.11 7.90 8.34 7.06 8.30

C$ 10 6.83 4.36 1.60 6.47 3.90

Periclase 0 0 2.34 1.97 0.90 2.20

C5S2$ 0 0 0 1.16 0 2.73

Lime 0 0.16 0.46 0 2.23 0

Others 0 0 2.87 0 3.28 0

Hydration – Proportioning Gypsum

Sample #2: 41.96% C4A3$

Sample C4A3$ Optimum Gypsum

#1 65.34% 25%

#2 41.96% 15%

#3 15.38% 8%

Gypsum Addition = 0.4461(%C4A3$) + 0.8403(%C4AF) – 1.000(%C$)] × 1.2645

Hydration –

Effect of Composition

Sample C4A3$ Optimum Gypsum

#1 65.34% 25%

#2 41.96% 15%

#3 15.38% 8%

Compressive Strength

Sample C4A3$ C2S Gypsum Addition

#1 65.34% 22.32% 25%

#2 41.96% 44.94% 15%

#3 15.38% 70.82% 8%

55 MPa

48 MPa

41 MPa

34 MPa

14 MPa

7 MPa

21 MPa

Dimensional Stability – In Water

Sample C4A3$ Gypsum Addition

#1 65.34% 25%

#2 41.96% 15%

#3 15.38% 8%

Dimensional Stability - Gypsum

Optimum Gypsum – High C4A3$

Sample #1: 64.92% C4A3$

18.06% C2S

6.24% C4AF

Hydration –

Waste Clinkers

Sample C4A3$ C$ Optimum Gypsum

#2 41.06% 6.83% 15%

#C 43.06% 1.60% 20%

#F 42.40% 3.90% 20%

Materials #C #F

Gray Limestone 56% 45%

Bauxite 14% 14%

Flue Gas Desulfurication Sludge 10% 6%

Class C Fly Ash 20% 0%

Fluidized Bed Ash 0% 35%

Hydration – effects of alkalis

Sample C4A3$ C$ Gypsum Addition

#2 41.06% 6.83% 15%

#C 43.06% 1.60% 20%

#F 42.40% 3.90% 20%

Sample C4A3$ C$ Gypsum Addition

#2 41.06% 6.83% 15%

#C 43.06% 1.60% 20%

#F 42.40% 3.90% 20%

Hydration - Retarders

Compressive Strength – Waste Materials55 MPa

48 MPa

41 MPa

34 MPa

14 MPa

7 MPa

Conclusions

Proportioning SAB clinkers can be done through a Bogue-type process, but must account for sulfur emissions

The optimum gypsum content can be defined as the minimum needed to have a consistent shape of the heat evolution curves and low expansion in water

High C4A3$ clinkers lack dimensional stability in water and do not have the highest long-term compressive strength

Intermediate (~40%) C4A3$ clinkers have hydration rates, compressive strength, and dimensional stability in water similar to OPC

Conclusions

Impurities from natural and waste materials

tested did not have a large effect on phase

formation during clinkering

Impurities, particularly alkalis, do have a large

effect on hydration

Admixtures can be used to control reaction

kinetics

Acknowledgements

National Science Foundation

Project No. CMMI 0448983

Portland Cement Association

Project No. F08-07