Research on the properties of crystalline admixtures: Self-healing healing materials for concrete from multiple perspectives

The research on the self-healing of concrete promoted by crystal admixtures provides a new direction for the green development of construction industry. In this study, three crystal admixtures, i.e., l-aspartic acid (LAA), Na₂SiO₃ and nano-silica (NS), were screened from the experimental results in terms of promotion of hydration, fast reaction, and effective filling. The three components were mixed as concrete self-healing agents, and the experimental ratio was designed by response surface method. Finally, the optimal ratio was selected according to the visual healing effect. The durability of mortar with the optimum ratio of self-healing agent was studied by the experiment of resistance to chloride ion and sulfate attack; its preliminary heat release was studied by hydration microcalorimeter. The microscopic analysis was carried out by X-ray powder diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) test and mercury injection method (MIP). The experimental results showed that the best healing effect was achieved when the dosage of LAA, Na₂SiO₃ and NS reached 0.5 %, 0.4 % and 0.15 % of the cement mass. In the process of healing, the early healing products are mainly calcium carbonate, and the late healing products are mainly ettringite and calcium silicate hydrate (CSH), and the healing agent effectively reduces the porosity and improves the pore structure, making the concrete matrix more dense.