Interactions between Organic Chelation Agents and Ions in Seawater for Accelerating Self-Healing of Cracks in Cement Paste

Abstract

To improve the durability of cracked concrete structures in a marine environment by self-healing of cracks, the efficiency and speed of self-healing need to be increased. In this study, the interactions between organic chelation agents, i.e., tetrasodium ethylenediaminetetraacetic acid (EDTA-4Na), triethanolamine (TEA), and sodium hexametaphosphate (SHMP), and ions in seawater for accelerating crack self-healing were investigated. After self-healing for 1 day, the closure ratio of cracks of an initial width of 400 μm increased from 5% to 80%, 65%, and 90% when 1.5% (by weight of cement) EDTA-4Na, SHMP, and TEA were admixed, respectively. However, the distribution of self-healing products in surface cracks of specimens with organic chelation agents was nonuniform in the early stages of healing, resulting in the large scatter—in terms of the standard deviation and range—of the values of the crack closure ratio. As the self-healing products gradually formed and accumulated in surface cracks, the standard deviation and range gradually decreased. Furthermore, in specimens with 1.5% triethanolamine, after seawater immersion for 1 day, a thin about 250-μm-thick layer of Mg(OH)2 formed at the crack mouths. During self-healing for 28 days, this thin layer extended inward up to a depth of 3 mm. To investigate the accelerator mechanism, the mineralogy of the self-healing products was characterized. When EDTA-4Na and SHMP were used, the main minerals were portlandite, brucite, aragonite, and calcite, while there was no portlandite when TEA was used.