Calcium sulfoaluminate cements

Lau, W., and Glasser, F.P. (1996) Hydration of calcium sulfoaluminate cements. Advances in Cement Research 8, 127-134. 

Park, C.-K. et al. (1997) Microstructural changes of calcium sulfoaluminate cement paste due to temperature, in Proceedings 10th ICCC, Goteborg, paper 41v068. 

Sharp, J.H., Lawrence, C.D., and Yang, R. (1999) Calcium sulfoaluminate cements — low-energy cements, special cements or what. Advances in Cement Research 11,3-13. 

Expansive calcium sulfoaluminate cement contains the phases... 

A high early strength calcium sulfoaluminate cement can be formed from the raw materials slag, clay, fly ash, silica, etc.I Hydration of the system C4 A3S-CS-C4AF was carried out by DTA to investigate the rate of conversion of ettringite (high calcium sulfoaluminate phase) to the monosulfoaluminate phase. 

Le Saout, G., B. Lothenbach, A. Hori,T.Higuchi and F. Winnefeld (2013). Hydration of Portland cement with additions of calcium sulfoaluminates . Cement and Concrete Research 43 81—94. 

Another similar application of isothermal calorimetry is the assessment of the thermal power at different curing regimes see Figure 2.11. Sealed conditions, which are the usual case in isothermal calorimetry, are compared to pastes with extra water added on top of the sample. This extra water causes an increase in cumulative heat and thus an increased hydration degree. The effect becomes more pronounced at lower w/c, where the samples tend to undergo self-desiccation. The same effect can be seen also with other types of cement, such as calcium sulfoaluminate cements. As this type of cement needs a higher w/c for complete hydration compared to Portland cement (around 0.5-0.6 instead of 0.4 see Winnefeld and Lothenbach 2010), the effect of the extra water is already very evident at a w/c of 0.7 see Figure 2.12. 

Figure 2.12 Influence of extra water on hydration ofa calcium sulfoaluminate cement at a w/c of 0.70. Sealed cured in vials saturated cured with added water on top of sample in vial. (Adapted from Lura, P. et al.. Journal of Thermal Analysis and Calorimetry, 101(3), 925-932, 2010).

Dry mix mortars often exhibit a quite complex mix composition, especially if they are rapid setting and/or rapid hardening. In the latter case, they generally contain binary or ternary binders based on calcium aluminate or calcium sulfoaluminate cements in blends with calcium sulfate without and with portland cement. Isothermal calorimetry is an efficient method to use for optimising mix designs of such mortars with respect to the hydration kinetics. As only small cement mortar or paste samples are used, the influence of the binder composition as well as of different combinations of accelerators, retarders, water reducers, plasticisers, etc. can quickly be tested. Two examples of how the amount of calcium sulfate addition is able to influence hydration kinetics are shown for blends of calcium aluminate cement with hemihydrate (Figure 2.22) and ternary binders based on port-land cement, calcium sulfoaluminate cement and anhydrite (Figure 2.23). 

Figure 2.23 Influence of the amount of anhydrite added on the hydration kinetics of ternary binders based on portland cement (PC), calcium sulfoaluminate cement (CSA) and anhydrite hydrated at 20°C and at a water-binder ratio of O.SO. Citric acid (0.27 mass% referred to binder) was added as set retarder. (Adapted from Pelletier, L. et al.. Cement and Concrete Composites, 32(7), 497-507, 2010.)...

Champenois, J. B., C. Can dit Coumes, A. Poulesquen, P. Le Bescop and D. Damidot (2013). Beneficial use of a cell coupling rheometry, conductimetry, and calorimetry to investigate the early age hydration of calcium sulfoaluminate cement . Rheologica Acta 52(2) 177-187. 

Winnefeld, F, and B. Lothenhach (2010). Hydration of calcium sulfoaluminate cements - Experimental findings and thermodynamic modelling . Cement and Concrete Research 40(8) 1239-1247. 

Figure 3.22 Chemical shrinkage as a function of cumulative heat of hydration (a) for calcium sulfoaluminate cement (CSA) and portland cement (PC) pastes and (b) for two Portland cement pastes with different w/c. The open symbols show the results of saturated (open) samples where chemical shrinkage and heat flow were measured simultaneously, while the full symbols represent the heat of hydration of samples with no water on top (sealed) (Lura et al. 2010).

Figure 4.1 XRD scans (IO°-45° 20 range) of typical industrially produced cements white Portland cement (WPC), plain portland cement (PC), calcium aluminate cement (CAC) and calcium sulfoaluminate cement (CSA). The diffraction peaks of the main phases are indicated alite (CjS M3), belite (P-CjS), aluminate (CjA), ferrite (C4AF), calcium aluminate (CA), ye elimite (Yee), anhydrite (Anh), gypsum (Gyp), gehlenite (Geh), mayenite (May) and magnetite (Mag).

Figure 8.25 Blend of calcium sulfoaluminate cement with gypsum hydrated for 14 days. (Courtesy of Julien Bizzozero.)...

ASTM C845 Type E-I (K) expansive cement manufactured ia the United States usually depends on aluminate and sulfate phases that result ia more ettriagite formation duriag hydration than ia normal Portland cements. Type K contains an anhydrous calcium sulfoaluminate, C A SI. This cement can be made either by iategraHy burning to produce the desired phase composition, or by intergrinding a special component with ordinary Portland cement clinkers and calcium sulfate. 

The most widely used single component, calcium sulfoaluminate admixture, is composed of 30% CAS, 50% CaSO and 20% CaO with small amounts of glassy phase. Particle s3ize is coarser than that of Portland cement. Larger particle size ensures that the potential expansion due to hydration is extended over a period of time. Chemical and physical properties of the most widely used proprietary product, Denka CSA, are given in Table 6.10 [74], Other CSAs include mixtures of C ASH and 2 CS (monosulfate and gypsum) and mixtures of Type I cement, liigh-aiumina cement, CaSO, 2H O, Ca(OH) and CaO [75], 4 2... 

Tetracaldum trialuminate sulfate (calcium sulfoaluminate, C4A3S) is the phase that is mainly responsible for the early strength development of the cement. For best performance the C4A3S content in non-expansive suhbbehte cements should he between 30% and 40% (Beietka et al, 1996). In the presence of iron oxide in the raw meal, a small amount of this oxide may enter into solid soluhon with the sulfoaluminate phase,... 

The ferrite phase (calcium aluminate ferrite C2(A,F)) is formed in the presence of Fc203 in the raw meal. The ferrite phase present in sulfoaluminate cements possesses a higher reactivity than in ordinary Portland cement, presumably because of its formation at a lower temperature (Sharp et al., 1999). It contributes to both the short-term strength and the ultimate strength of the cement. 

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