Influence of Self-healing via Embedded Macrocapsules Filled with Polyurethane on Carbonation of High-Volume Fly Ash Mortar

During carbonation of concrete, calcium hydroxide is consumed which results in a drop of the pH which can cause steel corrosion. In uncracked cementitious materials it can take several years before the carbonation front reaches the level of the reinforcement. However, most structures are cracked allowing for a fast ingress of carbon dioxide at the cracks. Self-healing cementitious materials are able to close cracks without a manual repair intervention. Most of this research has focused on a regain in liquid tightness or strength, yet results on the influence of carbonation are scarcely reported. In the current study, High-Volume Fly Ash mortar samples were made with pre-placed glass macrocapsules filled with polyurethane. Three different series were studied: reference specimens, specimens with non-pressurized capsules and specimens with pressurized capsules. After cracking of the specimens, the self-healing efficiency was assessed via a capillary water absorption test, prior to placing the specimens in a carbonation chamber and studying the carbon dioxide ingress at the location of the crack. The specimens with non-pressurized capsules showed a sealing efficiency of more than 80% compared to only 25% for specimens with pressurized capsules. The capsules were pressurized by mixing the polyurethane with benzoyl peroxide. This most likely resulted in a premature polymerization of the polyurethane inside some capsules, preventing a good crack filling. Nevertheless, the carbonation front was less deep at the location of the crack compared to the reference series without capsules. The specimens with non-pressurized capsules had a good performance; on average the carbonation depth at the location of the crack was only half of that of reference specimens.

Automated summary

During carbonation, concrete consumes calcium hydroxide, leading to a pH drop and potential steel corrosion. Cracks in cementitious materials allow for faster carbon dioxide ingress. Self-healing cementitious materials can close cracks without manual repair but the influence of carbonation is seldom studied. In this study, High-Volume Fly Ash mortar samples with glass macrocapsules filled with polyurethane were tested. Non-pressurized capsules showed sealing efficiency of over 80%, while pressurized capsules only had a 25% efficiency. Carbonation depth was shallower at cracked locations compared to reference samples. Non-pressurized capsules performed well with carbonation depth half that of reference samples.