The pore water pressure in concrete can significantly increase due to volume compression. Recycled aggregate concrete (RAC) possesses a more complex microstructure compared to natural aggregate concrete (NAC). Understanding the porosity and micromechanical properties of RAC is crucial for analysing its failure mechanism under the influence of coupled confining pressure and pore water pressure. This study compares the constituent proportions and micromechanical properties of interfacial transition zones (ITZs) and the adjacent paste matrix in NAC and RAC. Compressive stress-strain curves were obtained for concrete under coupled confining pressure and pore water pressure. The results indicate that the newly formed ITZ, which bonds to old mortar, outperformed the one bonded to natural aggregate when considering the same water-cement ratio. Compressive strength, ductility, and maximum volumetric strain gradually increased with increasing confining pressure. However, when pore water pressure was removed, compressive strength decreased while elastic modulus improved. Due to the inferior microstructures of RAC compared to NAC, the supportive effect of pore water becomes more pronounced. This is evident in the gradual increase in peak strain with increased pore water pressure for the stress-strain curves of RAC (100 % replacement ratio). Finally, a failure criterion and stress-strain theoretical model considering pore water pressure are proposed, and satisfactory fitting results are obtained.

由于体积压缩，混凝土中的孔隙水压力会显着增加。与天然骨料混凝土（NAC）相比，再生骨料混凝土（RAC）具有更复杂的微观结构。了解RAC的孔隙率和微观力学特性对于分析其在围压和孔隙水压力耦合影响下的破坏机制至关重要。本研究比较了 NAC 和 RAC 中界面过渡区 (ITZ) 和相邻糊料基体的成分比例和微观机械性能。获得了混凝土在围压和孔隙水压力耦合作用下的压缩应力-应变曲线。结果表明，在考虑相同的水灰比时，与旧砂浆粘合的新形成的 ITZ 的性能优于与天然骨料粘合的 ITZ。随着围压的增加，抗压强度、延性和最大体积应变逐渐增加。然而，当去除孔隙水压力时，抗压强度下降，而弹性模量提高。由于RAC相比NAC的微观结构较差，孔隙水的支撑作用变得更加明显。对于 RAC（100% 替代率）的应力应变曲线，随着孔隙水压力的增加，峰值应变逐渐增加，这一点很明显。最后提出了考虑孔隙水压力的破坏准则和应力应变理论模型，得到了满意的拟合结果。