Endogenous Curing Mechanism and Self-Healing Properties of an Epoxy Resin (E-51) in Alkaline Environments of Cement-Based Materials

Regarding the issues arising from the addition of external curing agents in the application of epoxy resin in cement-based materials, this paper explores the feasibility of endogenous curing of epoxy resin in the alkaline environment of cement-based systems. It further analyzes and investigates the curing characteristics of epoxy resin without external curing agents and their impact on the performance of cement-based materials. Differential scanning calorimetry, mechanical property testing, microstructural observation, and electrochemical impedance spectroscopy were used to study the mechanism of sodium hydroxide (NaOH) catalyzing the process of bisphenol-A epoxy resin (E-51)-based curing, the influence of moisture and temperature on curing kinetics, and the performance of epoxy resins in mortar and self-healing concrete. The results showed that E-51 achieved self-curing under alkaline conditions in the absence of an external hardener. However, moisture significantly inhibited the reaction process. Elevating the temperature and reducing environmental humidity effectively promoted the curing reaction. In cement-based materials, E-51 exhibited endogenous curing by the inherent alkalinity of the system, remarkably enhancing the compressive strength of mortar. At 60 °C, mortar containing 10% E-51 (by cement mass) exhibited a 1.5-fold higher compressive strength than that of the control group without E-51 at 14 days of curing. It demonstrated higher healing efficiency in a microencapsulated self-healing concrete system than the traditional curing agent systems. Concrete specimens with damage induced by loading at 60% of their compressive strength exhibited 100% recovery of ultrasonic pulse velocity after storing indoors for 28 d. The findings of this study can provide theoretical basis and technical support for the application of epoxy resins in cement-based materials without the need for curing agents.