Influence of ambient temperature and humidity on the evolution of the tension softening behavior in concrete

The tension softening relationship is a crucial input parameter for modeling the crack propagation in concrete. To examine the influence of curing conditions on this parameter, fracture tests were performed on specimens kept at different temperatures and humidity levels across various ages. A best-fit maturity method for identifying optimal maturity model parameters was proposed and validated using test data. The results indicated that the area beneath the first branch of the softening curve increases, whereas the area under the tail decreases with ongoing hydration and higher humidity. The tensile strength f t and centroid coordinate 6 cg (vertical coordinate of softening curve area center) increase with rising temperatures up to 14 days, after which the trend reverses, with higher later-age f t and 6 cg observed in specimens exposed to elevated temperatures. Under high temperatures, the critical crack width w c (ultimate width at zero cohesive stress) and centroid coordinate w cg decrease. At the early stage, humidity has minimal effect on concrete softening properties. However, as the hydration progresses, the impact of decreasing humidity becomes more significant. At 60 days, f t , 6 cg , and w c are reduced by 23.3 %, 22.8 %, and 19.6 %, respectively, as humidity drops from 98 % to 30 %. The developed best-fit maturity method can predict various concrete properties with a maximum relative error within 7 %. The optimal activation energy Ea and moisture diffusion coefficient gamma vary across temperature and humidity ranges, making it unfeasible to use a single set (Ea, gamma) to predict properties under varying curing conditions.