EXPERIMENTAL STUDY ON THE DIRECT SHEAR PERFORMANCE OF COMPOUND CONCRETE MADE OF DEMOLISHED CONCRETE LUMPS AND SELF-COMPACTING CONCRETE

29 prisms of 300 mm×300 mm×600 mm made of normal strength demolished concrete lumps (DCLs) and high-strength fresh self-compacting concrete (SCC) were tested under two-sided direct shear loading and uniaxially compressive loading. The influences of the replacement ratio of the DCLs and the characteristic size of DCLs on the shear strength of the specimens were investigated. The results show that the SCC and DCLs are well bonded in self-compacting recycled lump concrete. When the strength of the SCC is higher than that of the demolished concrete, the incorporation of demolished concrete lumps will decrease the direct shear strength of the specimens. The influence of the block characteristic size on the direct shear strength and compressive strength of self-compacting recycled lump concrete can be approximately neglected when the block feature size ratio is between 0.22 and 0.44. The ratio of direct shear strength to compressive strength of concrete made of DCLs and SCC has no significant change with the replacement ratio and characteristic size of the demolished concrete lumps. Its value is approximately 0.1. Based on the test results, a formula for predicting the direct shear strength of self-compacting recycled lump concrete is presented. The relationship between the test value of direct shear strength and the calculated value of compressive strength is obtained. The calculation results are in good agreement with the test values.