THERMODYNAMIC LIMITATION OF SELF-DESICCATION

Hydration reactions of sealed portland cement paste may lower the rela tive humidity within the hardening cement paste. Powers called this ph enomenon self-desiccation and stated that self-desiccation gives rise to a bulk shrinkage, so-called autogenous shrinkage (1,2). This paper presents a thermodynamic analysis of self-desiccation in hardening cem ent paste. The thermodynamic calculations are carried out on the basis of fundamental equations of reaction for the clinker minerals. Accord ing to the calculations C2S hydration seems not to be thermodynamicall y feasible at low relative humidities. The presence of C2S in the ceme nt may contribute to limit self-desiccation of portland cement paste.