Mechanisms Underlying Crystalline Waterproofing through Microstructural and Phase Characterization

The purpose of this study is to understand the complex mechanisms through which the active ingredients of crystalline waterproofing agents change the microstructure of cement-based materials. Microstructural and phase characterization are carried out on cement pastes modified with waterproofing agents through thermogravimetric analysis, scanning electron microscope with energy-dispersive x-ray spectroscopy, and x-ray microcomputed tomography. Two types are investigated-one that is applied onto the surface of existing concrete and another that is incorporated as an admixture into the fresh mix. Samples treated with the waterproofing agents are compared with a sample cured in sodium carbonate solution, one of the key active ingredients. Results indicate that both types of waterproofing agents lead to formation of calcium carbonate. The surface treatment type forms a dense coating, with little penetration into the matrix, whereas the admixture type leads to a measurable decrease in porosity throughout. The sample cured in sodium carbonate solution leads to an increase in porosity due to decalcification shrinkage, which underscores the importance of controlling sodium carbonate content to avoid excessive carbonation.