Effects of coarse aggregate morphology on concrete mechanical properties

Abstract

The morphology of coarse aggregate can significantly affect the mechanical performance of concrete. In this study, the correlation between the compressive properties of concrete and the coarse aggregate morphology was systematically explored. Three kinds of aggregates with significant morphology differences were selected: Spherical Aggregates, Flaky Aggregates, and Elongated Aggregates. Three-dimensional morphological information was obtained by 3D Structured-Light Scanner, and quantitative statistical analyses were conducted to assess the distribution of morphological characteristics for these three-types aggregates. It is found that the three-type aggregates with the same mesh size can be properly discriminated through the axis length, flatness, elongation, the product of flatness and elongation, and sphericality. The simplex-centroid design was used to build the correlation between aggregate morphology and the compressive strengths of concrete with different water-cement ratios. The concrete with 100% spherical aggregates owns the highest compressive strength, which is higher than that of concrete mixed with other two aggregates by 9.4%–36.2% and 5.2%–28.8% at the curing of 3-day and 28-day, respectively. When the ratio of spherical aggregates reaches above 50%, the strength loss caused by the elongated aggregates and flaky aggregates content is not obvious. Further, the failure mechanism of concrete with 100% spherical aggregates, 100% flaky aggregates, and 100% elongated aggregates under cyclic loadings were investigated by X-ray computed tomography scanning. It is found that the cracks inside spherical aggregates concrete mainly initiate from the edges and the core section remains almost intact before the destruction by a major oblique crack. Meanwhile, the high residual strain after cyclic loadings can originate from the generated vertical cracks under compression. The research findings in this study can serve as a solid base for the designing of concrete structures.