Shear strength and failure criterion of geopolymer coral aggregate concrete under compression-shear loading

The utilization of geopolymer and coral aggregate in concrete preparation offers cost and time savings associated with the transportation of raw materials, as well as contributes to reducing carbon emissions and resisting the sulfate ions erosion in the marine environment. Concrete structures, including deep beams, corbels, and column joints, are typically subjected to compression-shear loading. For this purpose, a total of 54 cubic specimens are cast to test the compression-shear behavior of geopolymer coral aggregate concrete (GCAC) with different normal stress ratios (k=0,0.1,0.2,0.4,0.6,and0.8) and concrete strength grades (C20, C30, and C40). Subsequently, the failure patterns, load-shear displacement curves, and normal displacement-shear displacement curves of GCAC are obtained. The shear displacement, the shear strength, and its components are also analyzed. The results reveal that coral aggregate with high brittleness and low strength leads to more spalling powder and debris to occur as k increases, and is cut off on the shear surface. With an increase in k (k≥0.6), the descending phase of the load-shear displacement curve becomes steeper due to the higher severity of failure patterns. The shear dilation angle increases with the increase of the concrete strength grade, and first raises and then falls with the increase of k, reaching a maximum value at k=0.4, the same as the percentage of shear dilation strength. Furthermore, the increase in k has a significant negative impact on the percentage of cohesive strength, but not on that contact friction strength. Finally, based on the test results, the J2−I1fc model is determined to be the most suitable for GCAC among the three failure criterion models in this study.