Shear and fracture properties and pore structure of low‐heat cement concrete under coupled temperature–humidity curing

Coupled temperature–humidity curing strongly affects the mechanical response and pore structure of low‐heat cement concrete in plateau hydraulic engineering. This study investigated concrete cured under different temperature and relative humidity (RH) conditions using direct shear tests, double‐ K fracture tests, two‐way ANOVA, and X‐ray computed tomography. Shear strength and fracture parameters at RH 40% generally first decreased and then increased with curing temperature, with relatively low values near 0°C; Shear strength increased with increasing RH, while at 20°C the fracture parameters under RH 95% were higher than those under RH 40%. Temperature, RH, and their interaction significantly affected shear strength (), accounting for 34.4%, 45.3%, and 18.1% of the total variation, respectively, while the humidity effect weakened with increasing temperature. Standard curing reduced CT‐resolvable porosity by 27.7%, whereas subzero low‐humidity and high‐temperature low‐humidity curing increased it by 26.3% and 15.2%, respectively. The two low‐humidity conditions also increased large‐pore volume, reduced pore sphericity, and promoted irregular crack‐like defects, with more severe deterioration under subzero low‐humidity curing. These results reveal a clear correspondence between shear–fracture performance and pore‐structure evolution.