Synchronous multi-modal sensor measurement for shear damage characterization in shotcrete at various curing ages

Abstract Shotcrete is vital for the initial support of tunnels, yet the multi-physical characterization of its age-dependent shear damage remains understudied. This study integrates electromagnetic, thermal, and sound signal sensors to conduct synchronous direct shear measurements on C25 shotcrete at curing ages of 7, 14, and 28 d. By tracking these signals throughout the shear failure process, the research extracts age-dependent evolutionary rules and explores the mechanisms linking signal responses to hydration reactions and microcrack propagation. Experimental results demonstrate that an extended curing age leads to an increase in peak electromagnetic radiation (EMR) intensity. Older specimens also exhibit an earlier occurrence of asynchronous infrared temperature rises alongside a higher frequency of sound signal b -value drops and zero-crossing rate peaks. A quantitative shear failure characterization system is then established by applying the change-in-difference joint index for infrared data and the moving-average centerline crossing rate for EMR alongside traditional sound metrics. This work clarifies the curing age-dependent correlation between multi-physical field responses and shear damage in shotcrete, advancing the practical application of multi-modal sensing in tunnel monitoring.