Frost durability and stress–strain relationship of lining shotcrete in cold environment

Given the different hydration processes of normal concrete without accelerator, shotcrete with accelerator has not only a short setting time and high early mechanical properties, but also different hydration products and microstructures. In high latitude and altitude areas, shotcrete lining structures are subject to freeze–thaw cycles. Thus, the durability, bearing capacity, and service life of lining shotcrete is critically threatened. In this work, a freezing–thawing durability experiment was conducted using the accelerated frost method. Dynamic elastic modulus, weight, compressive and splitting tensile strength, and the stress–strain relationship of frost–damaged shotcrete were measured for a study of the durability and mechanical property degradation rules. Microstructures, through pore structure analysis and microscopic characterization, were identified for elucidating the deterioration mechanism of the mechanical properties of shotcrete. After frost damage, the volume percentage of harmless pores rapidly decreased, whereas porosity increased. Micro-cracks appeared in interfacial transition zone grew into mortars and connected to form main cracks, which accelerated the microstructure damage. Physical and mechanical properties of shotcrete decreased with prolonged freeze–thaw cycles. However, the peak stress and toughness of shotcrete decreased, whereas peak strain, initial elastic modulus, and ultimate compression strain increased. Therefore, steel fiber reinforced shotcrete had improved frost durability and reduced growth ratio of porosity under the bridging effect.