Effective Crack Control of Concrete by Self-Healing of Cementitious Composites Using Synthetic Fiber

Abstract

Although concrete is one of the most widely used construction materials, it is characterized by substantially low tensile strength in comparison to its compression strength, and the occurrence of cracks is unavoidable. In addition, cracks progress due to environmental conditions including damage by freezing, neutralization, and salt, etc. Moreover, detrimental damage can occur in concrete structures due to the permeation of deteriorating elements such as Cl− and CO2. Meanwhile, under an environment in which moisture is being supplied and if the width of the crack is small, a phenomenon of self-healing, in which a portion of the crack is filled in due to the rehydration of the cement particles and precipitation of CaCO3, is been confirmed. In this study, cracks in cementitious composite materials are effectively dispersed using synthetic fibers, and for cracks with a width of more than 0.1 mm, a review of the optimal self-healing conditions is conducted along with the review of a diverse range of self-healing performance factors. As a result, it was confirmed that the effective restoration of watertightness through the production of the majority of self-healing products was achieved by CaCO3 and the use of synthetic fibers with polarity, along with the effect of inducing a multiple number of hairline cracks. In addition, it was confirmed that the self-healing conditions of saturated Ca(OH)2 solution, which supplied CO2 micro-bubbles, displayed the most effective self-healing performance in the surface and internal sections of the cracks.

Control of the Polymorphism of Calcium Carbonate Produced by Self-Healing in the Cracked Part of Cementitious Materials

“…It is thought that the Ca 2+ ions in a saturated Ca(OH)2 solution can promote self-healing, and the generation of self-healing precipitated substances can be enhanced through an increase in the quantity of CO3 2− supplied by CO2 microbubbles during self-healing [26,27]. Therefore, CO3 2− ions were supplied by ultrafine bubbles to the cracked part in the cement-paste test body to increase the production of self-healing precipitates [1].…”

“…Each cycle lasted 24 h, during which curing was conducted for 20 h after the test body was moved to the tank of saturated Ca(OH)2 solution with a controlled temperature and pH; in the last 4 h of the cycle, the test body was immersed in a tank of It is thought that the Ca 2+ ions in a saturated Ca(OH) 2 solution can promote self-healing, and the generation of self-healing precipitated substances can be enhanced through an increase in the quantity of CO 3 2− supplied by CO 2 microbubbles during self-healing [26,27]. Therefore, CO 3 2− ions were supplied by ultrafine bubbles to the cracked part in the cement-paste test body to increase the production of self-healing precipitates [1]. The self-healing performance of the test bodies was evaluated as a function of individual conditions for up to seven cycles (seven days).…”

“…By combining the luminance of the CT images and the difference in the density of the cement-paste test bodies, the images appear dimmer: the lower the density, the darker the image [28]. The green, red, and blue colors on the left side (X-CT images) of the figure represent the front face, side face, and top face, respectively, in the image domain of the test bodies in the 2D images, while the histograms show the volume of the cement matrix and section with voids (voids + cracks) [1]. Since there were no marked changes in the void structures before and after self-healing, as revealed by the analysis of the 3D images in Figures 12 and 13, most of the volume reduction in the section with voids resulted from the closing of the crack by self-healing.…”

“…Many believe that it would be difficult to develop another building material that can completely replace concrete in the future [1]. Meanwhile, since concrete is a material whose tensile strength is lower than its compression strength, it is unavoidable for cracks to develop in a concrete structure.…”

“…Choi et al reported that a large amount of CaCO3 precipitate was produced in the surface layer and inside microcracks because the self-healing of cement-based composite materials generated carbon dioxide gas in micrometer-sized ultrafine bubbles, which flowed into microcracks under a continuous water supply [1,22,23]. Crystals of CaCO3 can be divided into three types: calcite, vaterite, and aragonite.…”