## 1 Introduction
One alternative was to increase the wall thickness of both glass and ceramic capsules; however, it was found that the increase of glass wall thickness from 2 mm to 3 mm enhanced the capsules' survival during mixing, but the capsules may not rupture upon crack formation [37]. One alternative was to increase the wall thickness of both glass and ceramic capsules; however, the capsules may not rupture upon crack formation [37]. [PERSON] et al. [19] heated the polymeric capsules before mixing, which transformed the capsules from a brittle to rubbery state and changed the wall thickness of the capsule. The study found an improvement in capsule survival during the mixing, but the issues were in the compatibility between the carrier's material and healing agent, where the healing agent was hardened inside the capsules. [PERSON] et al. [15] investigated the pharmaceutical and glass capsules, where both capsules were coated with epoxy resin and sand for rougher surface for more resistant during mixing. Although the coating approach gave a promising results, the approach was not cost effective. [PERSON] et al. [38] used polystyrene microcapsules with epoxy resin in cement paste samples and found that the strength of the samples decreased due to the void produced by the capsules. Generally, the treatments applied on the capsule were for high resistant during mixing and a better adhesion between capsule shell and cement matrix was also expected to be improved. Thus, this suggests that there are several challenges facing the encapsulation system despite its potential application as healing agent carriers in the autonomous self-healing of cementitious composites. The past studies also discovered that the healing efficiency depended on the amount and size of the cracks and the amount of healing agent released by the breakage of capsules. [PERSON] et al. [29] also investigated the effect of encapsulated sodium silicate using polyurethane microcapsules (40-800 \(\upmu\)m) and the results indicated that the strength recovery after 7 days curing was 26% compared to only 10% for control samples (without microcapsules). Furthermore, the study discovered that the availability of capsules did not affect the mechanical properties of concrete. The literature review reveals the common approaches in enhancing the encapsulation system for the self-healing ability of the cement-based composites are by (1) the modification of physical characteristics of the capsule and (2) surface treatment of capsule. For this reason, the study examined the compatibility of modified polystyrene capsules containing sodium silicate in cementitious composites for autonomous self-healing mechanism. Polystyrene capsule was selected due to its physical characteristics which are almost similar to the characteristics of glass; brittle enough to break under the force applied and chemically inert to the healing agent. One of the advantages of polystyrene is its survivability during concrete mixing compared to glass. Nevertheless, a low bonding strength between the capsule and cement matrix is expected due to the smooth surface of the capsule shell making it more exposed to the slipping effect. Thus, the aim of this research was twofold, which first to address the surface treatment of the capsule and the compatibility of the modified capsule for cement-based composite application. The investigations included the physical characteristic, survivability of the capsule, and the healing ability of the cementitious composite. Secondly, to assess the effect of the modifiedcapsule on the healing ability of cement-based composite. The healing performance was investigated through the mechanical test. In addition, the feasibility of the healing agent released by the modified capsule was also measured through micro analysis of cementitious composites (i.e., scanning electron microscopy, energy dispersive x-ray, and Fourier transform infrared spectroscopy).