Effect of surface preparation and bonding agent on the concrete-to-concrete interface strength

Concrete-to-concrete interfaces are present both in new and existing structures. Two distinctive situations can be identified: (1) placing hardened concrete against hardened concrete parts, such as the case of precast members for viaducts and bridge decks; and (2) placing fresh concrete against hardened concrete parts, such as the rehabilitation and strengthening of existing structures by concrete jacketing or concrete overlay, among other techniques, as well as the use of precast members placed on site to later receive a cast-in-place concrete layer.The bond strength of the concrete-to-concrete interface is influenced by several parameters but mainly by: (1) the surface preparation; (2) the use of bonding agents; (3) the compressive strength of the weakest concrete; (4) the moisture content of the substrate; (5) the curing conditions; (6) the stress state at the interface; (7) the presence of cracking; and (8) the amount of steel reinforcement crossing the interface, among others.This paper presents an experimental study conducted to assess the influence of the surface preparation and bonding agent on the bond strength of the concrete-to-concrete interface. The contribution of the substrate moisture is also addressed. Experimental results are discussed and conclusions drawn.

► Roughness is a key parameter in the behaviour of concrete-to-concrete interfaces.
► Bonding agents are usually adopted to increase the bond strength between layers.
► Substrate moisture can lead to a major reduction in the bond strength.