Tensile-Splitting Behaviors of Compound Concrete Containing Demolished Concrete Lumps

To reuse concrete waste in an effective and simple way, compound concrete made of fresh concrete (FC) and coarsely crushed demolished concrete lumps (DCLs) distinctly larger than conventional recycled aggregates has been studied and adopted in actual structural members in recent years. The existing research results focus mainly on the compressive behaviors of compound concrete. In contrast to the previous studies, this paper investigates the tensile-splitting behaviors of the compound concrete. Two series of tests were conducted. In the first series, 24 300-mm cubic specimens with different replacement ratios of DCLs (0, 20, and 30%) were fabricated using normal-strength DCLs and two kinds of FC (normal-strength FC, and high-strength FC), and the tensile-splitting behaviors of the cubes were experimentally studied. In the second series of tests, 64 cubic specimens containing normal-strength DCLs and two kinds of FC with different cube dimensions (150, 200, 300, 400, and 500mm) and various characteristic sizes of DCLs (50, 67, 100, 133, and 167mm) were fabricated, and the size effect on the tensile-splitting behaviors of the cubes was experimentally examined. On the basis of the test data, a formula was presented to predict the combined tensile-splitting strength of the compound concrete. It was found that (1)the adverse effect of the DCLs on the combined tensile-splitting strength of the compound concrete did not increase significantly with the increase in the difference between the compressive strength of the fresh concrete and that of the demolished concrete; (2)for the compound concrete containing normal-strength FC, the ratio of the combined tensile-splitting strength to the combined compressive strength was generally close to that for conventional normal-strength concrete, but for compound concrete containing high-strength FC the ratio was approximately 1.1 times that for conventional high-strength concrete; (3)the influence of the characteristic size of the DCLs on the combined tensile-splitting strength of the compound concrete could generally be ignored; and (4)the combined tensile-splitting strength of the compound concrete decreased gradually with the increase in the cube dimension, and the size effect on the combined tensile-splitting strength was similar to that on the tensile-splitting strength of conventional normal-strength concrete. (C) 2018 American Society of Civil Engineers.