A datum point for estimating the absorbed water in hydrated Portland cement

摘要

In order that it may be possible to differentiate between adsorbed water and water chemically bound in hydrated Portland cement, a study was conducted of the dimensional- change sorption characteristics at low relative vapour pressures. By use of compacts of bottle-hydrated cement fabricated at loads between 5000 and 65,000 lb., equilibrium as well as dynamic values were obtained for dimensional change and moisture change relationships below 20% R.H. The apparatus enabled experiments to be performed in high vacuum. It was concluded with supporting evidence from work on other porous materials that the datum point where the transition between the linear portions of the curve occurs, will yield a good estimate of the true value for adsorbed water and will thus approximate to the point for zero adsorbed water; it will also separate the processes of desorption and dehydration. This establishes therefore a method for determining the adsorbed water in hydrated cement. The results obtained from the compacts of bottle- hydrated cement indicate that by this method the surface area, as calculated from the B.E.T. theory, will be considerably lower than that obtained from the high value for the evaporable water.