Microencapsulation of Calcium Nitrate for Concrete Applications

Abstract

The use of encapsulating healing agents that allow the self-healing of concrete has emerged as a potential solution to the current decay and costly maintenance of concrete infrastructure; however, many healing agents are expensive. The objectives of this study were to develop a procedure for the production of urea–formaldehyde microcapsules of calcium nitrate and to evaluate the effects of the microcapsules on self-healing efficiency in concrete. Calcium nitrate was selected for microencapsulation, given its low cost and its effect on acceleration of the setting of unhydrated cement. The results indicated that the agitation rate and the temperature had a linear correlation with the microcapsule diameter and the shell wall thickness, respectively. A higher agitation rate resulted in a smaller microcapsule diameter, whereas a higher temperature resulted in a thinner shell wall. The morphology of all microcapsules synthesized was virtually the same throughout the experimental matrix, with the shell walls of all the microcapsules observed having a smooth exterior surface and a rough interior surface. All microcapsules produced were also observed to have a broad particle size distribution. This characteristic was attributed to the type of surfactant used in the process. Analysis of the effects of the microcapsules on the self-healing efficiency of concrete showed that the modulus of elasticity increased after healing for all concrete specimens prepared with self-healing agents. The largest increase in the modulus of elasticity was observed at a microcapsule content of 0.50%. The results also showed that concrete specimens into which microcapsules were incorporated at any concentration had greater surface resistivities than control specimens.

Evaluating the Self-Healing Efficiency of Hydrogel-Encapsulated Bacteria in Concrete

“…Interestingly, as the capsule concentration increased, the air content decreased. This trend differs from what has been reported with polymeric capsules (such as urea-formaldehyde), where larger amounts of capsules yielded higher air contents ( 29 ). This difference can be attributed to the encapsulation process, where polymeric capsules require surfactants that tend to increase the air content within the cement paste, while the calcium alginate beads were prepared without surfactants.…”

Understanding the Impacts of Healing Agents on the Properties of Fresh and Hardened Self-Healing Concrete: A Review

“…In other words, the strength recovery was greatly enhanced on the specimens with the higher amount of microcapsules. Similar findings have been found in other studies confirming the positive impacts of the micro-encapsulated healing agents on the mechanical performance after undergoing a healing scheme [43,48,[50][51][52]72]. Sidiq et al [41] found that crack width up to 122 µm was effectively healed with embedded microcapsules containing sodium silicate and the crack healing ratio achieved up to 60%.…”

“…In general, thin-walled microcapsules would fail during the production process and concrete mixing, while thick-walled microcapsules are reluctant to break as the propagated crack will hardly penetrate [17]. The morphology, size and shape of prepared microcapsules are dependent on numerous factors including temperature, pH and agitation rate [17,18,42,43].…”

Evaluation of Self-Healing Efficiency of Reinforced Concrete Beams with Calcium Nitrate Microcapsules

“…Hassan et al developed a synthesis for production of ureaformaldehyde microencapsulation of calcium nitrate (9). The authors evaluated the self-healing efficiency in concrete as the modulus of elasticity increased after healing on all specimens containing microcapsules.…”