Sorption scanning curves for hardened cementitious materials

Drying of screeded floor slabs is an important issue for the building industry. However, virtually no attention is paid in prediction models to the hysteresis of sorption isotherms, mainly because of lack of data. Disregarding the hysteresis in prediction models will generate inaccurate predictions of future moisture distribution and remaining drying time. This paper presents a method for fast determination of scanning sorption isotherms and sorption isotherms by using a gravimetric vapour sorption balance. A sorption balance continuously determines the mass of a small sample subjected to a sequence of predefined vapour pressures and temperatures. Sorption isotherms and two examples of sorption scanning curves at 20 °C are presented. Results from three materials commonly used in screeded slabs are included, viz concrete W/C 0.65, concrete W/C 0.55, and a screed, Floor 4310 Fibre Flow. Absorption scanning curves obtained for concrete show a significant moisture history dependence as a consequence of the hysteresis of the desorption isotherm itself. Desorption scanning curves originating from the absorption isotherms indicate little influence of the moisture history.