Development of thermo-sensitive core-shell microcapsules fabricated by a facile vibrational melt coating method toward a heat-triggered set on demand of ordinary Portland cement

Abstract

Ordinary Portland cement (OPC) is one of the most widely used building materials, but its hydration and setting are challenging to control on demand. In this article, phase change material (PCM) was successfully coated on the surface of sodium silicate (SS) using a facile vibration coating method to fabricate thermo-sensitive SS@PCM (SP) microcapsules. The microcapsules were utilized to accelerate the hydration and setting of cement paste using heat as a trigger on demand. The results showed that PCM powder can be melted and uniformly coated on the surface of SS to form a core-shell structure, and the heat-triggering temperature of SP microcapsules reached 60 °C. Before heat triggering, the PCM acts as a barrier preventing SS from reacting with OPC so that a long setting time, high fluidity and extremely low dynamic yield stress could be realized. After heat triggering, the PCM shell disintegrated, followed by the release of SS, the accelerator. SS and residual heat accelerated the hydration of OPC, as evidenced by the rapid increase of storage modulus, the rising of loss modulus, and the decrease of loss factor in several minutes. This led to the setting time decreasing from hours to minutes, losing fluidity, and gaining high static yield stress. The PCM usage of 15 % is beneficial for early hydration within 2–4 h and early compressive strength development. A 3D printing test verified that the paste could achieve the goal of setting on demand by simple addition of SP microcapsules and application of heating.