Effect of Coarse Aggregate Concentration on the Mechanical Properties and Bond-Slip Behavior Between the Low Strength Concrete and Plain Rebar

Reinforced concrete structures still exist with low-strength class in which plain reinforcement (rebar) is used. The coarse aggregate concentration (CAC) in such concrete may also vary significantly. Considering such structures and their reinforced concrete bearing systems, in this study, eight different mixtures with 0.9 and 1.2 water/cement ratios (W/Cm) and 4 different CACs (60%-40%-20%-0%) were produced. Total aggregate volume fraction was kept constant in all mixtures. Modulus of elasticity (MOE), compressive, and splitting tensile strength (STS) tests were performed at 28 days. Bond strength and bond-slip behavior were investigated by pull-out tests. Results showed that the compressive strength ranged from 7.9 to 23.4 MPa. While the MOE improved by about 34%, the compressive strength decreased by around 30% when the CAC was increased from 0% to 60% in the concrete with 1.2 W/Cm. With an increase in CAC, compressive strength and MOE increased in the mixtures with W/Cm of 0.9. The presence of coarse aggregate increased STS in the concrete with W/Cm of 1.2, while the mixture with CAC of 60% having W/Cm of 0.9 had the lowest STS. In terms of the bond strength and residual bond stress between the concrete and plain rebar, the mixtures without coarse aggregate have performed worst for both W/Cm. Additionally, when the CAC was increased from 0% to 40%, in the mixtures with W/Cm of 0.9, almost 60% improvement in bond strength was seen. Moreover, bond-slip behaviors of the mixtures were evaluated.