Damage layer thickness and formation mechanism of shotcrete with and without steel fiber under sulfate corrosion of dry–wet cycles by ultrasound plane testing method

Abstract

In recent years, nondestructive testing, especially ultrasound testing method, has been increasingly used to detect concrete strength, compactness, cracks, and other aspects. In this work, the damage layer, thickness measured by ultrasound plane testing method and the formation mechanism of the damage layer were studied. Simultaneously, the damage process and microstructure of shotcrete under multiple coupling effects of sulfate attack and cyclic drying and wetting were also investigated. The results indicated that ultrasound plane testing accurately characterizes the damage layer thickness of shotcrete with and without steel fiber. The variation in performance of the original specimen was significant with increased thickness. An exponential distribution existed between the damage layer thickness and the original performances expected weight loss ratio. In the corrosion process, sulfate ions were transported into micropores and microcracks layer by layer, and velocity was slowly diffused from a distance from the surface. For ordinary shotcrete, sulfate attack is divided into three stages: ettringite action, combined ettringite and gypsum action, and gypsum action. However, for steel fiber-reinforced shotcrete, sulfate attack only occurred at the combined ettringite and gypsum action.