Abstract
Hydration reaction of calciumsulphoaluminate type expansive additive containing excess freelime has been studied. Amounts of hydrates and hydration rates of compounds in expansive additive were examined by XRD quantitative analysis (Internal Standard Method) and TG-DTA. In the early stage of the reaction, the free-lime reacted radically, but hauyne and anhydrite hydrated slowly. The hydration products were calcium hydroxide, ettringite, gypsum and monosulphate. The presence of gel was assumed by a material balance of hydration reaction. In the case of calciumsulphoaluminate type, gel phase was consists of CaO, Al2O3, and SO3. On the other hand, in the case of free-lime type expansive additive, gel phase was consists of CaO, SiO2, and SO3. A formula of hydration reaction was estimated on the basis of the results of quantitative analysis. Formation of ettringite from hauyne was formulated by the reaction formula such as 1 molar hauyne produced about 2 molar ettringite and gel.
