The paper considers the change of cement mortar microstructures due to sodium sulfate crystallization. The pressure generated during the crystallization, causes the deterioration of the solid skeleton of cement-based materials. The magnitude of stress induced by crystals growing in the…
The paper considers the change of cement mortar microstructures due to sodium sulfate crystallization. The pressure generated during the crystallization, causes the deterioration of the solid skeleton of cement-based materials. The magnitude of stress induced by crystals growing in the pores strongly depends on the geometry of the system. The influence of salt crystallization on the damage of internal structure was investigated for three types of cement mortar: without air- entraining admixture (AEA) and with 0.1% and 0.2% AEA. Most severe damage of cement mortar microstructure, was observed for samples without AEA. Pores of diameter 0.2-60 µm increased their volume up to 250%. The salt crystallization revealed the damage of pores, which diameter equals 0.6-30 µm, in samples containing 0.1% and 0.2% of AEA and the increase of pore volume never exceeded 155%. The additional pore volume, which appears in CM0 samples affected by salt crystallization, is created by micro-cracks generated during crystal growth. The salt crystallization significantly influence the volume and availability for water of capillary pores and therefore affect the transport properties and the durability of cement-based materials.