Advantage of Hydrodemolition on the Bond Strength of Concrete Overlay

In the repair work of concrete bridge decks, pneumatic and hydraulic breakers are the conventional tools for surface preparation. However these tools tend to cause damage to the surrounding healthy concrete and steel reinforcement. Hydrodemolition has emerged as a newer and more effective method. Yun et al.* conducted an experimental study to demonstrate the advantage of hydrodemolition on the bond strength of VES-LMC overlay.

VES-LMC is short for Very-Early Strength Latex-Modified Concrete. It has been widely used as an overlay material for concrete bridge deck repair because of its short curing time, high durability, and high bond strength. In this experimental study, VES-LMC was used as the overlay material. The concrete for the base slab was made with ordinary Portland cement and a maximum aggregate size of 25 mm, with target strength of 39 MPa. The bond strength of the VES-LMC overlay was evaluated for these three surface conditions of the base slabs: (1) treated with a spin jet; (2) treated with a pneumatic breaker; (3) untreated.

It was found that the tensile bond strength is the highest when the base slab was treated with the spin jet (1.72 MPa). It was 28 percent higher than that of the untreated surface (1.34 MPa) and 51 percent higher than that of the breaker-treated surface (1.12 MPa).

Based on visual inspection, it was found that, in the case of the untreated surface, the dominate failure mode is interface failure. But in the case of the breaker-treated surface, the dominate failure mode is substrate failure, indicating substrate damage from the breaking energy. In the case of the jet-treated surface, there is no single dominate failure mode.

* Yun, K.K., Kim, S.K., Choi, S.Y.  and  Choi, P.G. (2006) Effect of hydrodemolition on the bond strength of VES-LMC overlay, Proceedings of the 8^th Pacific Rim International Conference on Water Jet Technology, Qingdao, China, Oct. 10-12, Paper 37.