On the processes causing the alteration of cement-based materials while drying: Differential scanning calorimetry as a reliable tool for indirect microstructural analysis

Selecting the proper drying method is one of the critical choices that must be made before conducting experimental research on cement-based materials. Rapid drying might generate additional stress in the solid matrix, leading to the alteration of the pore structure. The size and connectivity of pores determine many physical properties such as permeability, gas diffusivity, heat conductivity, etc. Different techniques of drying have been analysed in the paper: oven drying at 105 degrees C, 60 degrees C, 30 degrees C, vacuum drying, and the isopropanol solution exchange method. Differential scanning calorimetry was applied to investigate the microstructure of the material. Knowing the relationship between the growing ice content and temperature decrease allows one to conclude about the pore size distribution of the material. The biggest advantage of the method is that calorimetric tests might be performed on the untreated sample. The information obtained for the virgin sample serves as the reference for the experimental results received for the samples exposed to various drying procedures. Experimental measurements have been performed on cement pastes prepared with a CEM I with water-to-cement ratio of 0.4, 0.5 and 0.6. The internal pore structure has been additionally investigated by means of the mercury intrusion porosimetry. The samples dried using the solution exchange method are characterized by the highest gel porosity. The other methods, especially drying at high temperatures, induce the collapse of the gel porosity and higher threshold and critical pore diameter values.