Dicyclopentadiene and Sodium Silicate Microencapsulation for Self-Healing of Concrete

Abstract

Considerable interest has been directed in recent years toward the use of self-healing materials in concrete. The concept of microcapsule healing is based on a healing agent being encapsulated and embedded in the concrete. The objective of this study was to evaluate the effects of preparation parameters, namely, temperature, agitation rate, and pH on the shell thickness and size (diameter) of the microcapsules as well as to evaluate the self-healing mechanism in concrete through experimental testing performed in laboratory. Two healing agents were evaluated in this study, i.e., dicyclopentadiene (DCPD) and sodium silicate. Based on the results of the experimental program, it was determined that, as the pH was increased from 3.0 to 3.7, the shell thickness increased for sodium silicate, while the shell thickness reached a minimum at a pH value of 3.4 for DCPD. Sodium silicate shell thickness was almost twice the shell thickness for DCPD. The most uniform and coherent microcapsules were produced at a temperature of 55°C for both sodium silicate and DCPD. For the DCPD microcapsules and up to 49°C, the solution remained an emulsion and no encapsulation took place. An increase in agitation rate resulted in a decrease in the average diameter of the microcapsules for DCPD. On the other hand, the diameter of the microcapsules remained constant for sodium silicate microencapsulation as the agitation rate was increased from 250 to 550 rpm. Testing of concrete specimens modified with the two healing agents (DCPD and sodium silicate microcapsules) was conducted. For sodium silicate, an improvement of 11% in the modulus of elasticity of the concrete was observed after healing for the microcapsules prepared at a pH value of 3.1 and at a content of 5.0%. At other pH values, the effect of the sodium silicate microcapsules on the concrete performance was negligible. For DCPD microcapsules, the healing agent was effective in increasing the modulus of elasticity of concrete after cracking by as much as 30% for the microcapsules prepared at a pH value of 3.1 and at a content of 0.25%.