Experimental evaluation of strength performance of autogenous self-healing concrete under the effect of microsilica addition

The repairing and maintenance of damaged concrete have high expenses on the construction field. In this regard, it is important to increase the potential self-healing capacity of concrete by adding pozzolanic material. But there is still insufficient knowledge about how the amount of microsilica affects the healing capacity of damaged concrete under different water-to-cement ratios and damage conditions. Hence, the primary purpose of this study is to evaluate the influence of the partial substitution of cement with microsilica, along with determining the optimal replacement ratio that will result in maximum strength recovery under preloading. For reaching this aim, 324 cubic specimens with dimensions of 10 × 10 × 10 cm were designed with 12 mix designs and water-to-cement ratios of 0.45 and 0.65 with different ratios of microsilica replacement including 0%, 5%, 7.5%, 10%, 12.5%, and 15%. These specimens were cured in lime saturated water for 7 days, preloaded at 0%, 30%, and 60% of their strength and cured again for 28 and 90 days. In order to study the Autogenous self-healing ability of microsilica-containing concrete, experiments on compressive strength and UPV, and microstructural analyses of SEM-EDS were conducted. According to the experimental data, adding 10% microsilica showed the most excellent self-healing capability. Concrete samples with 0.45 w/c ratio and preloaded by 60% recovered their compressive strength to 93.5% after 90 days, which is higher than the recovery ratio of the control sample to 76.9%. Similarly, for specimens with w/c = 0.65, recovery ratios are 90.1% and 80.4% for the sample with 10% microsilica and the control sample, respectively. In terms of microstructure analysis, the creation of secondary hydration products and pore refinements such as C–S–H gels formed by pozzolanic reaction and continued hydration of cement contributed significantly to enhancing self-healing properties of concrete. In conclusion, the partial replacement of cement with 10% microsilica can lead to a denser concrete microstructure and improve the recovery of the lost compressive strength induced by preloading-related damage.