When leakage occur, repairing from positive side most of the time is not accessible. Resin injection procedures, then, arise from the need to work on the negative side and yet place water-stop materials on the positive side.
With the problem of small size, movement, active leakage, dampness, and debris in the crack to be sealed, an engineer or contractor might well pause to consider the characteristics he should expect in the sealant he chooses. To function as a water-stop material, an ideal injection would:
1. Be thin enough to penetrate small cracks
2. Set quickly
3. Bond to wet surfaces
4. Work in and under water
5. Possess good elastic strength
Because the above criteria, polyurethane is the ideal and widely used material for crack sealing and stop water leakage. Polyurethane grouts are designed to react with water and expand in-place, forming a tight, impermeable, elastomeric seal that immediately stops the flow of water. Polyurethane seals in three ways:
1. It forms a chemical bond to the concrete surface area.
2. It forms a mechanical anchor by entering the pores and voids.
3. By expanding, it forms a compression seal within the crack, joint, or void to act as a waterstop.
Polyurethane chemical grouts consist of a polyurethane resin that reacts with water to form an expansive, closed-cell foam. It is available in both two component and single component types.
Polyurethane chemical grouts may be used to treat cracks that are 0.1 mm. and greater in width. And it is their ability to stop active leaks that makes them particularly well suited for tanks for the storage of liquids, dams, tunnels, sewers, and other water-containment structures.