The effects of the alternate freezing and thawing cycles on the pore structure of cementitious composites modified by MHEC and PVA

Deterioration of mortars by weathering is usually of great importance and is brought about by the disruptive action of alternate freezing and thawing of free water within the material. As it appears that applications of methyl hydroxy ethyl cellulose (MHEC) and polyvinyl acetate (PVA) are very beneficial in improving frost resistance, special attention has been paid to observing the changes in microstructural features of polymer modified composites exposed to the destructive effects of water and low temperature. The presence of both admixtures in normally cured composites has been found to have a significant effect on their microstructure. The microstructure is mostly determined by the quantity of MHEC used, as it provides water retention. The application of PVA slightly affects the pore size distribution, significantly improving the adhesive properties of composites. The present research revealed an interrelationship between the quantity of admixtures used and the micro-structural features of composites subjected to freezing and thawing. The mercury intrusion porosimetry results suggest the significant effect of rehydration process with respect to the damage caused by the action of crystallised ice.