Method overview

An ultrahigh pressure waterjet at a high flow rate is used to expose aggregate particles in existing concrete to form a rough surface with 10- to 20-mm irregularities. The exposed surfaces are further treated with shotblasting using steel particles cut to special shapes to achieve fine irregularity. This boosts the interlocking strength and bond area between old and new concrete, increases bond strength and completely unifies the layers. This result is a concrete overlay utilizing the strength of existing pavement and having no risk of delamination.
The Nippon Road Co., Ltd. developed the ND Waterjet System for surface treatment, a key element of the Perfect-Bond Concrete Overlay Method.

Concrete overlay with no risk of delamination

Possible delamination of concrete overlay.

Bonding of old and new concrete

Comparison of bond strengths by representative surface treatment methods

The conditions of treated surfaces of old concrete strongly affect the bond strength with new concrete. The bond strengths obtained by representative treatment methods are as shown in the figure.

Proof of concrete bond

The figure below shows typical bond strength obtained by the Perfect-Bond Concrete Overlay Method. The strength values are equivalent to tensile strength of concrete specimens without joints. The concrete layers are therefore judged as perfectly unified. These values also satisfy the interfacial bond strength specified by this method (not less than 85% of 28-day tensile strength).