The treatment of the concrete crack

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Introduction

In recent years, the results of the research and development of the crack repairing technology show that due to the structure and component of the crack because of the lack of the bearing capacity, cracking is just a symptom and structural response of the bearing capacity drop rather than the practical reason of the decrease of the bearing capacity. So it is impossible to fully recover its bearing capacity through simple crack repair. The effect of the crack repair can be roughly divided into three categories: protecting against the intrusion of the medium that can induce the corrosion of the rebar, extending the actual use years of the structure, keeping the structure complete through reinforcing, recovering the use function of the structure, improving the ability of its waterproofing and anti-seepagee.

Classification

The crack of concrete structure usually can be divided into three categories according to its formation:

Static crack

The crack that its shape,size and quantity have been stable and have no development. when repairing, only choose repair materials and methods in accordance with the thickness of the crack.

Active crack

Width can’t keep stable under the existing environment and working condition. The crack is easy to open or close with the stress of the structure and components or the change of the environmental temperature. When repairing, we should eliminate its causes firstly and observe for a period of time. When it is sure to be stable, we can treat with the method of the static crack.

Growing crack

Crack that its length, width or the number is still in the development, but after a period of time it will put a stop. We should repair the crack until it stops developing.

Repair methods

Usually using the following three methods selectively:

Surface sealing method

Using the micro and independent crack of concrete surface(width of crack ≤0.2mm) or repairing adhesive that its capillarity effect of reticular crack absorbing low viscosity and having good permeability to block off the way of crack. During the construction, clean the surface firstly, keep dry,using the brush to brush the low viscosity of repairing adhesive in the cracks, usually brushing three times, after besmearing every time besmearing again util touch is dry. The direction of the next besmear should be vertical. For the floor and other parts needing to be impervious, we should stick carbon fiber composite materials on the surface of concrete to enhance protection.

Injection method

Injecting the crack repairing adhesive of low viscosity and high strength into the crack cavity with certain pressure（0.1~0.3MPa).

Crack checking

For the size of crack above 0.1mm, no water seepage on the surface, we can let stand and inject adhesive.

Crack treatment

Clean up the area needing to construct , hew out the debris of surface to keep the surface clean and dry. Using alcohol or acetone to clean superficial and sealing surface.

Injection base installation

Install the base from bottom to top. plane can be from one end of the beginning. single hole can be installed one by one continuously. the distance of the installation can be about 300mm.

Crack sealing

Seal the injected crack with the dedicated sealing adhesive or other structural adhesive.

Sealing checking

Check the sealed crack to ensure having no leakage. check if it has leakage. we can smear sudsy water along the sealed crack and watch if it has soap bubbles through ventilation. yes, it has leakage and should add sealed adhesive; no, it is well-sealed and we can inject adhesive.

Adhesive mixing

Allocate the potting adhesive according to the ratio of the factory requirements. allocate the adhesive according to the actual situation. don’t prepare too much in order to avoid waste.

Adhesive injection

Inhale the allocated colloid into the syringes. install the perfusion machine on the base. the time of perfusion is usually 0.5-1 hour. actually syringes don’t outflow adhesive. the observation hole should prevail adhesive. if the syringes have finished injecting adhesive, it need to be injected adhesive again.

Remove the injector, curing and maintenance

After fulfilling we should dismantle the syringes in time. the base should be blocked with the plug. let stand for 24 hours to enhance and maintain, and then we can remove the base and the sealing parts.

Paste CFRP sheet

Demolish the base and repair with the sealing adhesive. stick carbon fiber composite materials on the concrete surface to be the function of protection and enhancement.

This method is suitable for the static and independent crack of 0.1mm≤width of crack≤1.5mm, perfoliate crack and honeycomb partial defects’ sealing and reinforcing.

Pressure grouting method

Within a period of time, press the grouting materials that is used for repairing the crack into the crack cavity at a higher pressure(with product use introduction)

Clean treatment

Check and analyze the situation of leakage carefully. determine the location and distance of grouting hole. clean up the area needing to construct. hew out the surface debris to keep the surface clean.

Holes drilling

Using electric hammer and other drilling tools to drill along the two sides of crack. bit diameter is 14mm, the angle of drill hole is ≤45°. the depth of drill hole≦two thirds of the thickness of the structure. drilling hole must be through the crack. but don't be through the structure(except for the grouting after the wall) the distance between drilling hole and crack ≦a half of the thickness of structure. the distance of the drilling hole is 20cm-60cm.

Embed the nozzle

Install grouting mouth in the drilling hole(also named stop water needle), and wrench tight with the special spanner to make no space between the grouting mouth and the drilling hole and no leakage.

Crack sealing

Using sealing adhesive to seal the crack surface. the aim is that don’t outflow when filling chemical pulp.

Adhesive grouting

Using the high pressure grouting machine to grout the chemical grouting material into the grouting hole.facade grouting order is from bottom to top. plane can be from the end of the beginning. single hole processes one by one continuously. when the close hole starts running out the pulp, keep the pressure for 3-5 minutes and then stop grouting to another close grouting hole.

Remove the nozzle

After the grouting, when the chemical grout has solidified, we can remove the exposed grouting mouth. clean up the solidified grouting slurry.

Sealing treatment

Repair and seal the grouting hole with the sealing adhesive.

Paste CFRP sheet

Sticking carbon fiber composite materials on the concrete surface to achieve the effect of protection and enhancement.

This method is suitable for handling large structural perfoliate crack, honeycomb and serious defects of mass concrete and deep and winding crack.

Conclusion

Concrete crack repair must be based on the appraisal conclusion of the structure reliability. Through field investigation and analysis, we can evaluate the cause, attribute and category of the crack. And according to the development degree, location and the environment of the crack, we can evaluate possible harms that the investigated crack may cause. According to this, we can choose the suitable repair methods for prevention and treatment.