5 Reasons Why your Concrete Cracks

Why does the concrete crack happen？

First we need to figure out a new concept: Concrete Curing and Sealing Procedures.

What is concrete curing & sealing?

Cement curing is “the action taken to maintain the moisture and temperature conditions in the newly placed cement mixture to allow hydraulic cement hydration and (if applicable) pozzolanic reactions to occur, thereby allowing the potential properties of the mixture to develop.”

That said, curing is what we do with fresh concrete to ensure that it does not dry out too quickly.

There are three main benefits of properly curing new concrete:

1.Predictable power gain.

2.Improve durability by put synthetic fiber in it.

3.Better applicability and appearance. Concrete slabs that allow too fast drying may have a soft surface and poor wear resistance. Proper curing can reduce dust and dirt.

Why concrete curing & sealing is related to plastic shrinkage cracking?

Incorrect curing can cause plastic shrinkage crack. This happens when moisture evaporates from the fresh concrete surface, which is faster than the release of water that seems to replace it. The stress caused by this rapid drying on the surface of the new concrete can cause short, irregular cracks called plastic shrinkage cracks. Most contractors may optimize this point by using fiber reinforcement.

How do the concrete cracks appear?

During the curing process of cement, due to temperature stress, water level changes, settlement, or deformation of the rockfill body, the cement board will appear cracks. Such cracks often cause leakage in the dam body and endanger the safety of the dam.

How to fix the concrete curing & sealing problems?

Flexible repairing method

We can adapt to some change of crack opening and closing. It is suitable for anti-seepage repair of movable joints such as temperature joints. But it can do nothing about structural cracking. Although a more efficient way for this is to put proper polypropylene fiber ( at a dosage of 900g/m³)

Slotted filling method

What to do?

1. Groove at the top of the crack. Chisel out the concrete on both sides of the crack and dispose of the dust out of it. Clean up the matters in the tank.

2. Fill the bottom of the crack with waterproof material.

3. Apply adhesive to the surface of the groove.

4. Fill the groove with flexible waterproof material. Note that the waterproof material needs to be compacted and the surface is smooth.

5. Apply adhesive on the surface of the flexible waterproof material.

6. Paste and fix the flexible waterproof sheet, and seal the waterproof sheet with sealant.

Advantages and disadvantages

This method can prevent seepage and adapt to the change of seam width, But this does not deal with the leakage channels inside the concrete. There is no reinforcement to the structure. Moreover, grooving may destroy the concrete structure, which can cause a sudden increase in leakage. There are certain security risks.

Flexible internal grouting method to prevent concrete crack

What to do?

To plug the cracks from the inside of the structure, you can grout along the cracks (or until the holes pass through the cracks); For plastic joints, water-soluble polyurethane materials like LW& HW are usually used. They have good elasticity and Malleability. This kind of material can adapt to the opening and closing of plastic joints, and this kind of material swells when exposed to water and combines well with concrete.

Advantages and disadvantages

The flexible grouting can seal cracks from inside and prevent concrete carbonation and corrosion. But it doesn’t reinforce the structure.

Rigid repairing method

The rigid repairing method can strengthen the concrete structure and stop the leakage. But it cannot apply to structural deformation, only temporary repair of stable cracks.
Surface reinforcement method

What to do?

①Cut and repair the edges vertically.

②Chisel out the loose concrete and excessively high concrete in the repairing area. Ensure that the minimum thickness of repaired concrete is not less than 50mm.

③Make anchor holes and plant anchor bars. The distance between the anchor hole and the crack should not be less than 100mm.

④ Install steel mesh, and the steel bars are arranged in two directions.

⑤ Weld the steel mesh and anchor bars as a whole;

⑥ Pour epoxy concrete.

Advantages and disadvantages

The advantage is that it can stabilize cracks, prevent leakage and reinforce concrete panels. But this method also has many shortcomings, in the following aspects:

① Reinforce only the surface layer because it can only allow the thinner anti-seepage material applied on the surface. Therefore, the effect of structural strengthening is limited;

② Other cracks other than the surface layer are not treated;

③ The grooving process will further increase the bearing capacity of the damaged panel. The impermeability is weakened, and it may even cause more serious damage to the panel. It may also lead to a sharp increase in leakage and a catastrophic safety accident.

Rigid internal grouting method

What to do with rigid intrnal grouting method?

Adopt the method of drilling and grouting across the seam (or drilling oblique holes through the seam); Use epoxy grouting materials, which have high strength, good pourability, and can perfectly bond with the concrete on both sides of the gap.

Advantages and disadvantages
Rigid grouting can seal cracks from inside the concrete. It also prevents the carbonization and dissolution of concrete.

Yet, rigid grouting also has some shortcomings, in:

① The scum ash inside the crack is difficult to clean up completely. The grouting material is not easy to adhere to the concrete on both sides of the gap.

② The grouting material can’t fill all the cracks and voids, and there will always be fish that slip through the net.

③ The pressure generated by grouting may push up some panels and make the gap wider. Especially the cracks that are at the diagonal intersection of the crack surface and the board surface are more likely to be jacked up.

④ During the construction process such as grouting and drilling, the leakage may increase.

Our trump card: Safer and stronger mending method to cure concrete crack

What to do?

① Bury the pipe along the crack, then close the crack surface. Seal the flexible grouting of cracks (note that the grouting pressure should not be too high) from the inside first. In this way, we stop leakage and avoid damage to the cushion. At the same time, it also avoids concrete dissolution and carbonation corrosion in the cracks that may be caused by leakage;

② Treat the cracked surface and surrounding panels. Paste the SR cover sheet with adhesive. The SR cover sheet isolates the first poured concrete from the part of the panel above the crack so that the repaired structure can adapt to the deformation of the structure.

③If the structural deformation is not stable yet, pour the first part of the concrete into the construction joint first.

④ Use SR cover sheet and other materials to make flexible waterproofing around the newly poured concrete;

⑤ After the structural deformation is stable, complete all concrete pouring.

⑥Close the flexible waterproof system around all concrete. The above reinforcement method and construction process show that this method will hardly cause secondary damage to the structure. Thus, this method is safer and stronger and has a better water release effect.

Advantages and disadvantages

① It will not cause secondary damage to the damaged structure;

②First use flexible materials to stop leakage. Try to slow down the leakage and damage the cushion ASAP.

③When the structural deformation is unstable, pour the first layer of the concrete. Since the SR cover sheet is pasted between the cracks, there is a flexible barrier between the first poured concrete and the original concrete, which can adapt to the deformation of the structure.

④When the structural deformation is stable, the repairing structure must be completed, and then the newly constructed reinforced concrete structure must be used to reinforce the slab. Use triple rigidity and a flexible water stop structure to eliminate leakage.

To sum up

Concrete crack with larger cracks generally damage the structure to a greater degree and pose serious safety hazards. This article provides three methods of repairing cracks, each with its advantages and disadvantages. Readers, please compare by yourself.