Assessment of thermal cracking and damage in concrete by ultrasonic velocity and Vp/Vs ratio

The velocity properties of concrete are highly sensitive to the changes of concrete structure after high temperatures. Experimental and theoretical data indicate a reduction in velocities and a decrease in the V_p/V_s ratio with temperature. After the heated concrete is saturated with water, the dependence of velocities on temperature shows a different trend compared with the dry specimen. The V_p/V_s ratio increases significantly with the heating temperature. Based on the effective medium theory and the crack model, velocities of cracked concrete were presented, exhibiting a high degree of agreement with the experimental results. The influence of the secondary hydration process on the matrix of saturated concrete should be considered, as this can account for the discrepancy between the experimental and the theoretical results under the saturated condition. This study provides a framework for the detection of thermal damage in concrete, especially for the detection of water content in the concrete.