When reinforcing bar corrosion and concrete separation have occurred over a wide area, an effective technique is to remove the deteriorated part and apply the spray repairing method. However, conventional wet spraying casts concrete to a thickness only of about 30 mm, and is often insufficient in terms of concrete adhesive strength and efficiency of implementation.

The Jot's Crete method (Fig. 1) adds an alkali-free quick-setting agent to the concrete at the tip of the spraying nozzle to ensure a thickness of about 100 mm in the sprayed concrete (Fig. 2). For the adhesive strength with existing concrete, push-off-type shearing tests were implemented and it is confirmed that it could get the equivalent shear strength monolithic concrete. As tunnel linings often require endurance of the sprayed concrete in sulfate environments, immersion tests ensured that concrete sprayed by this method has sufficient durability in such conditions.

This method has been registered in the New Technology Information System (NETIS) for Public Works, and has already been applied to a number of structures, in particular railway viaducts (Fig. 3).