Sorption of water on compacts of bottle‐hydrated cement. I. The sorption and length‐change isotherms

To obtain information with regard to the porous structure of hydrated cement and the extent of its interaction with water, sorption and length‐change isotherms were determined for this material. Compacts of bottle‐hydrated cement were brought to equilibrium in a high‐vacuum system at various humidities, and measurements of the changes in length and weight during this process, were made to draw the isotherms. Results showed that this system is basically similar to systems composed of other porous materials, although complicated by a discontinuity in the adsorption part of the cycle and a secondary hysteresis. It is considered that these characteristics are related and are the result of water associated with the system by a process other than physical adsorption. It is also shown that menisci exist in the system on desorption to as low as 31% R.H. and cause considerable contraction. A surface‐area calculation by a new method for estimating the zero adsorbed water yield a value of 80·6 m. 2 /g.