全轻页岩陶粒混凝土三轴受压试验及其破坏准则

THE TESTS AND FAILURE CRITERIA OF FULL LIGHTWEIGHT SHALE CERAMSITE CONCRETE UNDER TRUE TRIAXIAL COMPRESSION

利用大连理工大学的大型静、动真三轴试验机,对强度等级为LC30的全轻页岩陶粒混凝土进行了等比例三轴受压试验。试验中,观察了试件的破坏形态,测得了试件的三轴受压极限强度、塑性应变、峰值应变、总应变以及应力-应变曲线。结果表明,全轻页岩陶粒混凝土在三轴受压状态下,强度和变形较单轴受压有显著增大,并伴随有明显的平台流塑现象,也呈现四种破坏形态。因此,在工程设计中将应力平台流塑段强度及其对应的塑性应变作为轻骨料混凝土的设计强度和设计应变。此外,分析了中间主应力对三轴压的强度和变形影响,并通过三轴强度模型对极限应力进行了预测,其相对误差的绝对值均小于6%,说明试验结果是准确、可靠的。最后,基于八面体应力-应变空间分别建立了其相应的破坏准则,但前者试验点一致性较好,且拉、压子午线与静水压力轴在高压应力区有交叉点,其破坏曲面是闭口的;而后者离散性虽然较大,拟合度较差,但却同样可以很好地反映出破坏面向外扩展的趋势和子午线光滑、外凸的曲线特征。

The experiments of full lightweight shale ceramsite concrete LC30 were carried out under true a triaxial compressive state in proportional loading by the large-scale static and dynamic triaxial testing machine in Dalian University of Technology. The failure modes of samples were observed, and the ultimate triaxial strength, plastic strains, peak strains, total strains, and stress-strain curves were also recorded. The results show that the strength and deformation of full lightweight shale eeramsite concrete under triaxial compression are much larger than that of uniaxial ones, there is a very apparent ＇Platform of Plastic Flow （PoPF）＇ on a stress-strain curve, and also present four failure modes as normal concrete, thusly the stress and the strain corresponding to PoPF should be design strength and strain during an engineering design for lightweight aggregate concrete. Also, the effects of intermediate principal stress on strength and deformation are analyzed under triaxial compression, the ultimatestresses were predicted by triaxial strength model, and the absolute values of relative errors are all less than 6%, which proves the test results are accurate and reliable. Finally, the failure criteria of stress and strain are established based on an octahedral stress-strain space respectively. The relevance of test points and curves are better to the former; the tension-compression meridians intersects the hydrostatic pressure axis in high-pressure stress area; and the failure surface is closed; although the latter is worse than the former, which can reflect effectively the outward expansion trend for the failure surface, the characteristics of meridians are smooth and convexity.