The influence of different drying methods on cement paste microstructures as reflected by gas adsorption: Comparison between freeze-drying (F-drying), D-drying, P-drying and oven-drying methods

Drying of cement pastes is required prior to microstructure investigation by means of gas adsorption technique. An ideal drying method, which would give reproducible results that could perfectly remove only the non-bound water and, at the same time, preserve the microstructure, unfortunately does not exist. The different drying methods used affect the microstructures in different ways. However, an effective water removal and, less damaging drying method between the common methods used would be still of outstanding importance for sample preparation. Many drying methods have been investigated in the past for such a purpose, and a good agreement for the best drying method does not exist. The so-called D-drying method is being used in many laboratories as the “best” method for drying cement pastes. The surface areas and pore size distributions results of the current work confirm that D-drying (D-Drying C− t) is a relatively good preservation and effective drying method, and that Freeze-drying gives slightly better results compared to D-drying (C− t) and other methods. However the short time versions of some of these methods indicate the presence of very few “micropores”, which are not present with prolonged drying times. The outgas level is also a very important variable affecting the gas adsorption measurements especially in the case of short duration drying conditions, as indicated by the results of this work.