Effect of cementitious capillary crystalline waterproofing coating on the gas permeability of mortar

This study presents an experimental investigation in the effect of cementitious capillary crystalline waterproofing (CCCW) coating on the gas permeability of mortar and the mechanism how the gas permeability is affected. The gas permeability coefficient of mortar coated with or without CCCW material was measured through modified Cembureau method. The pore structure, micromorphology and hydration products of cement paste with or without CCCW coating were analyzed by the means of mercury intrusion porosimetry (MIP), scanning electron microscopy-energy disperse spectroscopy (SEM-EDS), X-ray diffraction (XRD) and thermogravimetry-differential scanning calorimetry (TG-DSC). The results showed that under the effect of CCCW coating, the gas permeability of mortar got decreased and the pore structure changed towards smaller pore sizes. SEM-EDS results exhibited that there was a large amount of ettringite filling in the pores in the paste with CCCW coating. XRD and TG-DSC analysis indicated that there was more calcium carbonate formed in the paste with CCCW coating than blank paste. The formation of ettringite in pores and increased calcium carbonate production refines the pore size distribution and densifies the cement matrix, which induces the decrease in gas permeability of mortar coated with CCCW material.