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

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 ceramsite 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 ultimate stresses 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.