Mechanical behavior of recycled lump concrete containing mixed demolished concrete lumps with different sizes or/and shapes

This study explored the utilization of mixed demolished concrete lumps (DCLs) to develop recycled lump concrete (RLC) fabricated using high-strength fresh concrete. With 100 mm spherical DCLs as a benchmark, the impacts of mixed spherical DCLs of different sizes (50, 67, 100, or 133 mm), mixed 100 mm DCLs of various shapes (oblate, spherical, or slender), and mixed DCLs of both various sizes and shapes, on the compressive, flexural, and direct shear behaviors of RLC were examined. Test results show that the mixed DCLs with various sizes or diverse shapes insignificantly affects the compressive strength and elastic modulus of RLC, but reduces the flexural strength by 6%-12%. Besides, mixed-size spherical DCLs allow RLC to achieve similar direct shear strength to that of benchmark RLC, while mixed-shape 100 mm DCLs and a single shape (oblate or slender) 100 mm DCLs make RLC exhibit about 10% higher direct shear strength than that of benchmark RLC. Further investigations show that using mixed DCLs with both different sizes and various shapes has a negligible impact on the compressive, flexural, and direct shear behaviors of RLC, which manifests the great potential of simplifying the production of RLC in practical engineering. Finally, the applicability of the previously proposed prediction formulas for the strength and elastic modulus of RLC containing single shape and single size DCLs to the RLC with mixed DCLs was discussed.