Experimental and theoretical investigation on the bond strength between high-strength and lightweight concrete

Abstract

The appropriate bond strength between the layers with different concrete strengths is considered the most import-ant concern for the layered elements. An experimental study has been approved to produce structural lightweight concrete with a compressive strength not decreasing by 18 MPa and a unit weight not increasing by 2000 kg/m3 and high-strength concrete with a compressive strength not decreasing by 60 MPa and then investigate the bond strength between new high-strength concrete and old lightweight concrete with different treatment cases and different compressive concrete strengths. Mix with 0% perlite meets the requirements of the targeted high-strength concrete, and mixes with 30%, 40%, and 50% perlite meet the requirements of the targeted structural lightweight concrete, and they can be used for testing bond strength with different treatment methods. The new concrete jackets have a concrete strength of 62.5 MPa, and the old concrete cube's strength is varied between 18.4, 21.8, and 38.08 MPa. A total of eleven bond strength test specimens were cast with different parameters. The specimen interface was arranged by different systems: roughness, agent material, and nails. The roughness techniques used were hand-wire brushing, grinding, or hand chiseling. Theoretical results were compared with the experimental data. It was concluded that using a new high-strength concrete with two times the strength of the old lightweight concrete and treating it with nails is the best technique to achieve an economic and accept-able value of bond strength. The nails achieved a good bond between the fresh and hardened concrete owing to the developed shear friction. The hand-chiseling roughness method gives the best bond strength results. The high difference in concrete strengths between the fresh high-strength jackets and the hardened lightweight cube isn’t mandatory to enhance the interface bond strength between them.