Effect of temperature and relative humidity on the development of the compressive strength of surface-layer cement mortar

•Provided a detailed record about temperature and relative humidity development with time at surface-layer concrete.•Verified and explained the quality of surface-layer concrete is lower than the center due to inadequate T and HR.•Investigated the effect of three curing methods on the surface concrete.•Proposed a modified maturity method considering the coupling effect of T and HR, which presents good evaluation accuracy. The ambient condition has a significant effect on the early strength of cement mortar, however, good curing treatment could improve the quality of surface-layer mortar. To further quantifiably study the effect, the temperature (T) and relative humidity (RH) histories in the surface layer of outdoor curing cement mortars were recorded by embedded sensors in the study. The compressive strength of mortar specimens under three curing conditions and the specimens drilled from mortar slabs with three surface curing techniques were tested. Based on the study, the current maturity formula considering only the effect of curing temperature overestimated the compressive strength of the surface-layer cement mortars. Through a proposed RH-modified maturity method, the strength of the mortars was predicted with a high accuracy comparing with the test results. The surface curing techniques were proved to have a significant effect on the strength development of the mortars, especially the surface layer. The significances of the study were to quantifiably analyze the combined effect of T and HR on the surface layer of mortar slab for it was susceptible to the curing environment that subsequently affects the hydration action and the microstructure of the mortar, and to modify the predict the strength of the mortars considering the combined effects.