Inorganic powder encapsulated in brittle polymer particles for self-healing cement-based materials

Many types of healing agents have been investigated. These agents are processed in different ways, such as adhesive polymer in capsules or hollow fibre glasses, bacteria in porous aggregates and geo-materials directly incorporated in the cementbased materials. In this study, sodium silicate powder is encapsulated in polystyrene particles (polystyrene particle containing sodium silicate is defined as PS particle in short). The PS particles remain intact in the cement-based matrix before cracking. If water or moisture is available, the healing agent can be released into the crack provided that the crack passes through the PS particles. The dissolved sodium silicate reacts with calcium hydroxide in the matrix, and the healing products (C-S-H gel) can form in the crack. Furthermore, compared to the reference, for the cracked specimens with polystyrene particles, the recovery of flexural stiffness can be observed. Different sizes and mass fractions, i.e. sodium silicate / cement ratios, of PS particles used in engineered cementitious composite (ECC) mixture are studied to see their influence on mechanical properties as well as their healing efficiency. When the mass fraction of polystyrene particles is 4% of cement and the polystyrene particles have a proper slender shape, the ECC show good results in terms of flexural strength, flexural deflection capacity and recovery of mechanical properties. Therefore, encapsulation of healing agent in polystyrene could be regarded as a promising way for realising self-healing of cement-based materials