Alite-fluoroaluminate cement

Alite-fluoroaluminate cement, also called regirlated set cement (in the USA) or jet-cemerrt (in Japan), contains tricalciirm silicate (50-75%) and calcitrm fluoroaluminate (20-30%) as its main corrstituents. Other corrstituertts may include the ferrite phase, dicalcium silicate, and free CaO. 

To obtain alite-fluoroaluminate cement, the alite-fluoroaluminate clinker must be interground with anhydrite. The amount of anhydrite must be adjusted to the amount of fluoroaluminate present in the clinker to enable its hydration to ettringite, and is usually appreciably higher than in ordinary Portland cement. 

Upon mixing with water, alite-fluoroaluminate cement exhibits very rapid hydration. In paste hydration at ambient temperature about 40-50% of the CjjA2.CaF2 is hydrated... 

Compared with ordinary Portland cement pastes made with the same water/cement ratio, the porosity of matnre alite-fluoroaluminate cement pastes is distinctly lower, mainly because of the high combined water content of the resulting ettringite phase. 

At low temperatures the setting time of alite-fluoroaluminate cements is extended up to several horns, and the development of strength is retarded (Knofel and Wang, 1992, 1994 Jagereta/., 1993). 

Alite-fluoroaluminate cements do not exhibit expansive properties, unless the amount of interground calcium sulfate is excessively high. This absence of expansion is explained by the formation of the ettringite phase in a through-solution process, rather than in a topochemical reaction (Chvatal, 1993). 

Just like ordinary Portland cement pastes, alite-fluoroaluminate cement pastes undergo carbonation in a reaction with the CO2 in air. However, the rate of this process is slower than in similar ordinary Portland cement pastes, mainly because of lower porosity (Kim et al., 1992). X-ray diffraction studies have revealed a gradual disappearance of peaks belonging to the AFt and AFm phases, and the formation of gypsum, calcite, and vaterite (Knofel and Wang, 1994). The strength of the material is not adversely affected by carbonation (KnOfel and Wang, 1992). 

In blended alite-fluoroaluminate cements the alite-fluoroaluminate clinker is interground with granulated blast furnace slag and/or limestone, in addition to calcium sulfate (KnOfel and Wang, 1994). Such binders have similarities with blended cements on the basis of ordinary Portland clinker, but still exhibit a short setting time and a distinct short-term strength. 

Alite-fluoroaluminate cement is particularly suitable for emergency repair works, where very fast setting and short-term strength development are desired. Other possible applications include shotcrete engineering and precast concrete product production. Alite-fluoroaluminate cement must not be used for steam curing or any applications at high temperatures, because the ettringite phase is thermodynamically unstable at temperatures above about 70°C. 

Just as in alite-fluoroaluminate cements, ettringite, together with aluminum hydroxide. 

Calcium aluminate modified Portland cement is essentially a Portland cement with added dodecacalcium heptaaluminate (Cj2Ay), produced separately, and with an elevated calcium sulfate content (Chvatal, 1973 Kondo et al., 1997). The phase composition of the binder differs from that of a conventional alite-fluoroaluminate cement by the presence of tricalcium aluminate, and of instead of C,A,.CaF,. The cement... 

Belite-fluoroaluminate cement is more susceptible to carbonation than its alite-fluoroaluminate counterpart, owing to its higher ettringite conterrt, and this process may be accompanied by a moderate decline of strength (KnOfel and Wang, 1994). 

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