An Experimental Study on the Bond Strength of Old and New Cementitious Materials

Due to climate change in most countries, construction tends to take less time than planned. Therefore, prompt repairs are needed to extend service life. One repair method is pouring new concrete onto the old, particularly for concrete pavement. However, the bond between them presents a significant challenge. This paper presents an experimental study on the bond strength of new and old concrete. The pull-off or direct tensile test was conducted to address this issue. Three substrate treatments were used: as-cast, connecting-hole, and steel brushing. The experimental results indicated that the bond strength between the old and new concrete in the as-cast substrate treatment was the lowest. In contrast, the connecting-hole and steel brushing treatments resulted in strengths that were 19% and 45% higher, respectively, than the as-cast treatment. The bond strength for the connecting-hole treatment was less than that of the steel brushing treatment, possibly due to the unsuitable hole size. The failure mode observed in this test was substrate fracture rather than sharp debonding of the two layers. That is, delamination between the old and new concrete layers did not occur. This confirms the feasibility of the repair method considered in this study for the old concrete pavement in the future.