Effect of the interactions between crystal and gel hydration products on the volume change of cementitious materials

The volume change of cementitious materials is often studied based on the properties of the individual hydration product, either from the gel products causing shrinkage or the crystal products causing expansion. Previous studies of the team have theoretically revealed that the interactions between crystal and gel products produce the “micro self-stressing”, which affects the volume change of cementitious materials. This work presents theoretical and experimental studies into the impact of the interactions between crystal and gel products on the volume change of cementitious materials. Firstly, a theoretical model for the volume change of cementitious materials was proposed. Secondly, in the followed experiment, the crystallization pressure, which affects the interactions between crystal and gel products, was tailored by immersing specimens in different exchange solvents or solutions to change the solubility product. Water, isopropyl alcohol, ethanol, calcium hydroxide and calcium acetate were selected as the exchange solvents or solutions. Subsequently, cement pastes were vacuum dried. Volume changes of cement pastes were tested during the whole process. Inductively-coupled plasma mass spectrometry and ion chromatography were utilized to test the ion concentrations and calculate the crystallization pressure. Finally, the experimental results were compared with the calculated results to validate the model. Results indicated that cement pastes immersed in different solvents or solutions exhibited different volume changes. An increase in crystallization pressure by 45.3 % resulted in a 46.1 % increase in the expansion of cement paste. Moreover, the reduction in the interactions should be one of the factors contributing to the drying shrinkage of cement paste.