Optimization of mortar self-healing performance-based on response surface methodology: A multifactor analysis of zeolites, crystalline admixtures, and water-to-binder ratio

Abstract

To address the issue of concrete structures being prone to crack failure, this study employs the response surface method (RSM) to evaluate the impact of adding zeolites and crystalline admixture (CA) on the self-healing performance of mortar. Initially, zeolite amount, CA amount, and the water-to-binder ratio (W/B) are considered as response factors, using ultrasonic pulse velocity (UPV), electrical resistivity, and the self-healing rate as the response target values. UPV and electrical resistivity are used to monitor self-healing process, while self-healing rate quantifies healing of cracks. Subsequently, through designing experiments with RSM, a regression model is established, achieving multi-objective optimization of the mortar self-healing rate, and experimental validation is carried out for the optimized combinations. Finally, the mechanical properties of mortar specimens are studied, and scanning electron microscopy (SEM) and X-ray diffraction (XRD) are used to analyze the microstructure and crystal phase composition of the crack healing fillers. The quadratic polynomial model has a high degree of fit, and the error between the measured and predicted values is less than 10%, indicating the reliability of RSM in determining the optimal mix parameters for mortar self-healing. The SEM and XRD results further confirm that the moisture released by zeolites promotes the activation reaction of CA, generating a larger amount and more densely structured calcium silicate hydrate (C-S-H) gel. Moreover, the research results show that although incorporation zeolites diminishes mortar specimens' strength, incorporation zeolites promotes the generation of C-S-H gel within the cracks, attributable to activation reaction of CA, ultimately promoting crack healing and improving the strength of the mortar. Based on optimization analysis, the optimal amounts of zeolites, CA, and W/B were determined to be 20%, 4%, and 0.45, respectively.