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 important 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 acceptable 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.

Keywords:
Bond strength; lightweight concrete; nails; agent material; high-strength concrete