Effect of crystalline waterproofing admixture on modulus of elasticity of concrete with different W/C ratios

Crystalline waterproofing admixtures (CWA) are used to reduce permeability and provide self-healing effect. Although previous studies have investigated the effects of crystalline admixtures on strength and durability properties of concrete, the effects of these admixtures on the modulus of elasticity of concretes with different W/C ratios remains an area requiring research. In this study, the effect of self-healing provided by CWA on the permeability and mechanical properties of concrete particularly its modulus of elasticity was investigated. For this purpose, 12 concrete mixtures with three different water-to-cement ratios (0.4, 0.5, and 0.6) and four different CWA dosages (0, 0.5, 0.8, and 1.2% by weight of cement) were designed. Three series of specimens were prepared. While one series was tested at the end of 28-day curing without any additional process, second series was pre-loaded to 65% of its compressive strength to induce damage. The last series, following damage induction, underwent additional water curing for 21 days to assess self-healing capacity. To facilitate the observation of self-healing, pre-loading was applied to induce micro-damage. The results indicated that self-healing occurred in concretes containing CWA, the phenomenon verified through SEM imaging. An examination of modulus of elasticity test results revealed that the reference concretes (produced without CWA inclusion) exhibited no substantial improvements. However, CWA-bearing concretes demonstrated enhanced modulus of elasticity, with optimal CWA dosages determined as 1.2%, 0.8%, and 1.2% for W/C ratios of 0.4, 0.5, and 0.6, respectively. Furthermore, the CWA reduced water absorption and water penetration depth under pressure, while enhancing both splitting tensile and compressive strengths.