Mechanical properties of compound concrete containing demolished concrete lumps after freeze-thaw cycles

The frost resistance of the compound concrete made of fresh concrete (FC) and demolished concrete lumps (DCLs) distinctly larger than conventional recycled aggregates was tested in the laboratory. Forty-eight 300 mm cubes of compound concrete and seventy-two 100 mm cubes of FC or demolished concrete alone were subjected to freeze-thaw cycling, and the compressive and splitting-loading failure strength of the frozen and thawed specimens was measured. Applicability of the linear strength assumption for the compound concrete at room temperature (i.e., the compound concrete strength is a linear combination of the strength of FC and demolished concrete) to the frozen and thawed compound concrete is examined. With an increasing number of freeze-thaw cycles, the tensile-splitting strength of the compound concrete decreases more rapidly than that of FC, but this trend is not very clear for the compressive strength. The ratio of tensile-splitting strength to compressive strength for the compound concrete was only about 78% of the ratio for FC. The linear strength assumption can still be used to predict the compressive strength of compound concrete after freeze-thaw cycling, but it cannot be used to predict the tensile-splitting strength. (C) 2017 Elsevier Ltd. All rights reserved.