1 Hazard of hydraulic concrete cracks
Concrete cracks will lead to leakage of hydraulic structures. On the one hand, under the action of pressure water, cracks will gradually widen and develop; On the other hand, when water penetrates into concrete, it will first cause hydrolysis damage, which may lead to the damage of concrete structure. According to the survey, water leakage accounts for 60% of all the adverse results caused by cracks.
2 causes of cracks in hydraulic concrete structures
According to the causes of cracks, there are: cracks caused by external load; Cracks caused by deformation; Cracks caused by construction work. The main causes of cracks in hydraulic structures are as follows:
2. 1 The hydration heat of mass concrete cannot be dissipated, which leads to a large temperature difference between the inside and outside of concrete, which makes the deformation of concrete exceed the limit and causes cracks.
2.2 In the process of concrete hardening, cracks occur when the volume deformation caused by drying shrinkage is suppressed, and sometimes the width of such cracks is very large, even running through the whole component.
2.3 Cracks caused by plastic collapse of concrete with large thickness members.
3 concrete measures to control concrete cracks
3. 1 Optimal design of concrete mixture ratio. Add fly ash and choose water reducer to ensure pumping fluidity. Collect raw materials for trial mixing, reduce the cement consumption as much as possible, add grade I fly ash, control the water-binder ratio within the range allowed by the specification, and adopt secondary gradation for coarse aggregate. Adding a proper amount of fly ash has a good effect on improving the workability of concrete, reducing temperature rise, reducing shrinkage and improving corrosion resistance.
3.2 Selection of raw materials. The fineness modulus of sand should be controlled above 2.4, and the silt content should be controlled within 65438 0%. The shape of the crushed stone should be controlled within 10%, and the silt content should be controlled within 1%. Use low hydration cement as much as possible, and control the quality of raw materials to avoid shrinkage of concrete.
4 repair methods of cracks in hydraulic structures
Scholars at home and abroad divide cracks into three types: dead cracks, active cracks and growth cracks. For dead joints, rigid materials can be used to fill and repair them; Elastic materials are used to repair living joints; For growth cracks, the factors causing cracks must be eliminated. In addition to restoring waterproof and durability, crack repair should also be carried out from the perspective of structural safety and aesthetics. At present, there are three main repair methods.
4. 1 filling method For cracks with a crack width greater than 0.5mm, a "U" or "V" groove is cut along the crack, and the top width of the groove is about 10cm, and the groove is filled with sealing material. The filling materials are cement mortar, epoxy mortar, elastic epoxy mortar and polymer cement mortar. If the steel bars in the reinforced concrete structure have rusted, the concrete should be cut to the extent that the rusted steel bars can be treated, the steel bars should be derusted, and then the grooves should be filled with cement mortar or epoxy mortar.
4.2 Injection method Injection method can be divided into pressure injection method (grouting method) and vacuum suction method. Grouting method is suitable for deep and thin cracks. Vacuum grouting method is to use vacuum pump to form vacuum in cracks and inject slurry into cracks. This method is suitable for repairing various surface cracks. Grouting materials include cement slurry, ordinary epoxy slurry, elastic polyurethane slurry and water-soluble polyurethane slurry.
5 conclusion
The structural safety and seepage prevention of hydraulic structures are mainly undertaken by concrete, so the quality of concrete is extremely important. Therefore, reducing and controlling the occurrence and development of concrete cracks plays an extremely important role in improving the quality of concrete structures and thus enhancing the safety of hydraulic structures, which must be paid attention to.
I believe that after the above introduction, everyone has a certain understanding of the harm and prevention measures of concrete construction cracks in water conservancy projects. Welcome to Zhong Da for more information.
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