Influence of basalt fiber and flexural load on carbonation resistance of shotcrete: Experimental study and predictive model

Abstract

The interior of tunnels presents a high-temperature, high-humidity, and high-concentration CO₂ environment, which makes the surface of shotcrete highly susceptible to carbonation. Additionally, shotcrete endures substantial surrounding rock stress during service. This study focuses on the service environment of tunnel structures to investigate the carbonation resistance of shotcrete, analyzing the effects of flexural load and basalt fiber content on carbonation depth. The results show that incorporating an appropriate amount of basalt fiber can reduce the carbonation depth of shotcrete, with the optimal carbonation resistance achieved at a basalt fiber content of 0.2 %. However, excessive basalt fiber content negatively impacts carbonation resistance. Flexural tensile stress consistently accelerates the carbonation process. When the basalt fiber content is within 0.2 %, compressive stress shows an inhibitory effect on carbonation. At a basalt fiber content of 0.3 %, both tensile and compressive stress adversely affect the carbonation resistance of shotcrete. Microstructural analysis reveals that a moderate amount of basalt fiber reduces large pore sizes in the concrete and increases the number of smaller pores, while excessive fiber content diminishes this effect. Tensile stress increases the total pore volume, reducing the density of the specimen. Conversely, compressive stress compresses existing cracks and large pores, causing medium-sized pores to collapse into smaller ones, thereby enhancing the density of the concrete. A prediction model for the carbonation depth of shotcrete under flexural load was established based on basalt fiber content, with fitting correlation coefficients exceeding 0.95. In conclusion, the findings of this study provide theoretical support for evaluating the durability of shotcrete and predicting the service life of tunnel linings.