The application of thermal analysis to the hydration and conversión Reactions of calcium alumínate Cements

Abstract

The hydration of calcium aluminates cements is dominated by that of CA, CaAl₂O₄, which is a major constituent of all of them. At ambient temperatures, CAH₁₀ and an amorphous phase are formed initially, but these are metastable and slowly (or more rapidly if exposed to higher temperatures) transform into C₃AH₆ and gíbbsite. This conversion reaction is accompanied by and increase ín porosity, which can lead to a loss in strength and vulnerability to chemical attack. Various methods of thermal analysis have been applied as a routine test to determine the degree of conversion, and the results from these methods are critically evaluated. Thermal analysis is a useful technique for identification of the various hydrates that can form in these systems, especially at early stages of hydration when poorly crystalline phases are present. Differential thermal analysis curves showing peaks attributable to all these hydrates are presented and it is shown that overlap frequently occurs, leading to difficulties in interpretation, which can sometimes be minimized by use of a complementary technique such as X-ray diffraction.