The Relative Humidity Range for the Development of Irreversible Shrinkage in Hardened Cement Paste

抄録

For better understanding of irreversible shrinkage, nine hardened cement paste (hcp) samples with three different cement types and three different water to cement ratio were prepared. Four different relative humidity conditioning histories containing the first desorption, re-humidification and the second desorption are investigated for all the specimens to obtain the length change and water sorption isotherms. The irreversible shrinkage strain was developed when the specimen was dried up to less than 80% relative humidity (RH), while other previous experiments in literatures showed that the shrinkage strain between 40% RH and 11% RH is reversible. It is concluded that the irreversible shrinkage strain is developed between 80% RH and 40% RH, which is also supported by the change in water vapor BET surface area of hardened cement paste after long-term drying.