Effect of silicate-modified calcium oxide-based expansive agent on engineering properties and self-healing of ultra-high-strength concrete

Abstract

At an early age, ultra-high-strength concrete (UHSC) exhibits a large autogenous shrinkage, which easily leads to matrix shrinkage and cracking. This poses a significant threat to the service life of a building structure. In this study, the effects of silicate-modified calcium oxide-based expansive agents (SCEAs) on the engineering performance and self-healing of UHSC were systematically investigated. SCEA was used as a self-healing promoter for early cracked UHSC, and the compressive strength, ultrasonic pulse velocity, and surface resistivity were determined. Moreover, the water permeability of the cracked samples and the healing degree of the surface cracks were tested. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy, and other microscopic analyses were used to characterize the chemical composition of the healing compounds. The experimental results showed that the compressive strength, ultrasonic pulse velocity, and surface resistivity of UHSC showed decreasing trends with an increase in SCEA doping. Furthermore, inductively coupled plasma optical emission spectroscopy tests showed that the addition of SCEA increased the amount of calcium ion penetration into the UHSC during the healing process. The UHSC doped with SCEA showed more visible crack width healing than the control group, and the reductions in permeability were especially obvious. The results of X-ray diffraction, FTIR, and other microscopic analyses indicated that the main composition of the UHSC healing compounds was a mixture of calcium (aluminate) silicate hydrate, calcium hydroxide, and calcite.