围压及粗骨料对超高强混凝土抗压性能的影响

为研究围压大小和粗骨料类型对超高强混凝土抗压性能的影响,对分别含不同类型粗骨料(玄武岩、石英岩、大理岩),相同配合比的超高强混凝土试样和其基体砂浆试样在六档围压(0、5、10、20、40、70 MPa)下进行常规三轴试验.试验结果表明:粗骨料类型对超高强混凝土试样的峰值应力、弹性模量影响显著;与基体砂浆试样相比,相同轴向应力下含粗骨料超高强混凝土试样的变形明显减小;超高强混凝土的峰值点轴向应变随围压呈线性增长,破坏形态在不同围压下呈现三种类型,0围压下的劈裂破坏、5～40 MPa围压下的剪切破坏、70 MPa围压下的挤压流动破坏;峰值应力的增长速率随围压的升高逐渐变慢,含粗骨料超高强混凝土的增长速率在低围压下高于其基体砂浆试样,而在40～70 MPa围压下两者基本趋于同一速率;不同骨料对裂缝的扩展呈现不同的阻挡作用,裂缝穿越大理岩的比例远大于石英岩.分别用Mohr-Coulomb准则与Ansari准则拟合试样的抗压强度数据,结果表明Ansari准则较Mohr-Coulomb准则更精确地反映混凝土强度随围压的变化趋势.

Effect of confinement and coarse aggregate on compressive properties of ultra-high strength concrete

To study the influences of confinements and coarse aggregate types on compressive properties of ultra-high strength concrete (UHSC), UHSC specimens with different types of coarse aggregates (basalt, quartz, marble) and the same mix proportion as well as their matrix mortar specimens were investigated by conventional triaxial test under six confinements (0,5, 0,0, 0,0 MPa). Test results show that the coarse aggregate type had a significant impact on the peak stress and elastic modulus of UHSC. The deformations of UHSC specimens with coarse aggregates decreased significantly under the same axial stress compared with the matrix mortar specimens. The axial strain at the peak point of UHSC increased linearly with the confinement and the failure modes could be classified into three types under different confinements: splitting failure at 0 confinement, shear failure at 5-40 MPa confinements, and squeeze flow failure at 70 MPa confinement. The growth rate of the peak stress gradually slowed down with the increase of confinement. The strength growth rate of UHSC with coarse aggregate was higher than its matrix mortar specimen under low confinements, while their rates tended to be the same at 40-70 MPa confinements. Different aggregates had different resistance to crack propagation, and the proportion of cracks passing through marbles was much larger than quartzs. Comparison of the fitting results by using Mohr-Coulomb criterion and Ansari criterion shows that Ansari criterion was more accurate than Mohr-Coulomb criterion in reflecting the change trend of concrete strength with confinement.