Influence of the age and drying process on pore structure and sorption isotherms of hardened cement paste

Sorption isotherms and scanning-isotherms of hardened Portland cement paste were measured. A structure model was developed to give a theoretical interpretation for the measured sorption isotherms. In particular, the causes for hysteresis between adsorption and desorption were described. Not only the capillary effect between condensation and evaporation in the pores but also the chemical water uptake, the drying method and the chemical aging have to be considered to explain the significant hysteresis. These results are the basis of our model for the structure and the porosity change of cementitious materials. The mathematical implementation of the structure model (called IBP-method [R.M. Espinosa, Sorptionsisothermen von Zementstein und Mörtel, Dissertation Hamburg University of Technology, 2004.]) will be described in a further essay [R.M. Espinosa, L. Franke, Inkbottle Pore-Method: prediction of hygroscopic water content in hardened cement paste at variable climatic conditions, Cement and Concrete Research (2006-this issue) doi:10.1016/j.cemconres.2006.06.011].