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).
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