It is very important to select repair materials for underwater repair projects. The materials used for underwater repair must have the following properties:

(1) New and old materials have high strength of underwater bonding, good durability and easy construction operation.

(2) The thermal properties, shrinkage deformation properties and modulus of elasticity of repairing materials and matrix concrete materials should be basically similar or identical.

(3) The permeability of repairing materials. If the repairing material is relatively impermeable, when the moisture in the concrete inside the matrix diffuses to the surface, it will gather on the bond surface of the two materials due to the obstruction of the relatively impermeable repairing layer, which will reduce the bond strength and will be destroyed under the freeze-thaw cycle (especially in the fluctuating zone of water level). Therefore, the permeability of the repairing material and the matrix concrete should be basically the same, or the drainage measures should be set up.

(4) Material that can bind underwater should be selected so that no thermal stress can cause damage to the bond during bonding maintenance.

(5) Material that can bind and harden at low temperature should be selected to adapt to the environment where the temperature of deep water is below - 5 C. At present, there are dozens of materials available for underwater repair, including inorganic materials, organic materials, inorganic and organic composite materials. The bond strength between cement-based inorganic materials and old concrete is generally not high; the bond strength between resin-based organic materials and old concrete is very high under dry conditions, but most of them do not bond well under wet or water conditions; the composite materials based on organic polymer modified cement can change the shortcomings of the former two, but the choice of polymer is very heavy. Yes.

A large number of practices have shown that in the case of large load and temperature difference, it is better to select inorganic materials (or composite materials with inorganic materials as the main body) whose deformation properties are similar to those of matrix concrete when repairing engineering buildings with cement concrete as the matrix, which can have better durability.

Selection of grouting materials for underwater concrete cracks:

(1) It should be consistent with the purpose of crack treatment. If it is used to prevent seepage and plug leakage, the impermeability of the material should be good; if it is used to reinforce the treatment, higher strength is required. The former can choose Lw, condensation, acrylate and sodium silicate, cement and sodium silicate, while the latter can generally choose epoxy resin, methylation, polyurethane and cement slurry.

(2) Irrigability is good. In principle, grouting with crack width of 3-5mm or more, chemical slurry with low viscosity is grouted with slits (<0.05mm), and sealing materials such as mortar and oil ash can be used for large cracks and joints.

(3) It has durability. In principle, brittle materials such as ordinary epoxy slurry and cement slurry should not be used in the treatment of loops. Elastic materials such as elastic epoxy, elastic polyurethane or Lw should be chosen instead.

It should be non-toxic, non-polluting and economical. In order to improve the efficiency of repairing works, any repairing works should be strictly clear and clean inside, which is the most difficult thing to do, but it directly affects the effect and life of the repairing works, and should be paid attention to.

In order to reduce the effect of water dissolution and dilution, and to bond well to the wet saturated fracture surface, and to make the volume change rate of the adhesive very small, we should choose silica gel with strong bonding ability, and mix more and more fine fillers with strong water absorption and large surface area, such as anhydrous alumina powder, anhydrous calcium oxide powder and silica fume powder.