增强颗粒对混凝土斜面压剪破坏过程的影响

为提高新老混凝土黏结性能,提出了一种在自密实混凝土表面撒干石子替代混凝土表面凿毛的新工艺.将石子视为黏结面增强颗粒,利用岩石破裂过程分析系统(RFPA)软件,进行了不同黏结强度斜面压剪试件和黏结面含增强颗粒斜面压剪试件在单轴压缩荷载作用下破坏过程的数值模拟,并将自密实混凝土表面撒不同粒径干石子的斜面压剪试验结果与数值模拟结果进行对比.数值模拟分析了不同黏结强度斜面压剪试件的破坏模式以及主裂纹产生、扩展、贯通、次生裂纹产生等过程.结果表明:对强度等级高于C35的新老混凝土,当黏结面黏结强度小于30MPa时,斜面压剪强度取决于黏结面黏结强度,不同强度等级混凝土的斜面压剪强度相近;当黏结面黏结强度大于30MPa时,斜面压剪强度随混凝土强度等级增大而增大,最后稳定在混凝土轴心抗压强度附近.单增强颗粒的大小对试件弹性模量和斜面压剪强度影响较小,可以忽略;多增强颗粒的粒径越大,越有利于提高斜面压剪强度,且黏结面不再是最薄弱位置.实际试验结果与数值模拟结果吻合较好,当混凝土表面撒有粒径为5~20 mm石子时,其斜面压剪强度比表面凿毛试件提高107%.

Effect of Reinforcing Particle on Failure Process in Concrete under Slant Shear Compression

In order to improve the bond quality of new to old concrete, a new construction process of scattering dry gravels onto the surface of self compacting concrete was put forward to replace the process of roughening the surface of old concrete. The dry gravels were considered as reinforcing particle, and rock failure process analysis (RFPA) code was used to study the failure process of slant shear specimens with different adhesion strength and reinforcing particles under static loading. The results of slant shear test of scattering dry gravels onto the surface were compared with that of the numerical simulation. The numerical simulation analyzed the failure characteristics of the specimens with different bond strength. When the adhesion strength of bonding surface is less than 30MPa, the strength of slant shear specimens of concrete with different strength grades is close, and is depended on the adhesion strength. Otherwise the strength of slant shear specimens increases with the concrete strength grades, and keeps stable around the overall axial compressive strength of the same concrete specimen at last. The size of single reinforcing particle almost has no influence on the elastic modulus and strength of slant shear specimens. The larger size of multiple reinforcing particles is better to improve the strength of slant shear specimens. The bonding surface is no longer the weakest position, and compares well with the actual experimental results. Compared with the process of roughening the surface of old concrete, the process of scattering gravels with the diameters of 520mm onto old concrete surface can improve the slant shear strength by 107%.