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How to repair concrete cracks?

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Concrete cracks are common issues that we see around. Various methods are adopted generally for repairing of concrete cracks depends on the type of cracks.

Most of the concrete cracks are due to shrinkage, heat, foundation failure, design failure, earth movements, Earthquake, over dead loading conditions and movements caused by external factors, lack of expansion and contraction joints, climate conditions, poor quality of materials, poor quality of workmanship, inadequate quality control, inappropriate methodology

.Care should be taken to following items

  1. Selection of method to fix the causes
  2. Selection of method and appropriate materials.
  3. Final inspection and assessment of repaired structure

The following methods are commonly used for repairing concrete structures. Methods are adopted based on the nature of cracks.

  1. Epoxy injection
  2. Routing and Sealing
  3. Stitching of Cracks
  4. Drilling and Plugging
  5. Grouting
  6. Hydraulic cement application
  7. Portland cement grouting
  8. Dry packing etc
  1. Epoxy Injections:
  1. Epoxy injection is an economical method of repairing non-moving cracks in concrete elements to restoring its strength.
  2. The procedure of applications will be different for locations of cracks like vertical or horizontal.
  3. In case of visibility from both ends of the concrete element, the epoxy can be injected from both ends to fill deepest end of the cracks.
  4. use a water repellent epoxy product. Concrete cracks due to corroded steel should not be repaired using the epoxy
  5. Widening the cracks to “V” shape, clean with wire brush and wash with water jet and allow to dry
  6. The epoxy is injected using the ports and the space between two ports is 200mm rest of the areas covered with epoxy paste with putty knife. Let it dry for a period of minimum 45 minutes to hold the pressure of injection.
  7. Injection shall be done from the lowest port till the epoxy coming out from the upper next port. Repeat the process till the cracks are filled with epoxy completely.

Crack Repairing procedure

Trained workers are required for injection process.

  • Start with a low-pressure injection setting and increase the pressure as per situation
  • Epoxy backflow should be verified
  • Keep the ports in position for at least 48 hours to ensure the cracks are sealed.
  • Epoxy method is not applicable for wider cracks
  • Remove the ports using a chisel, scraper or heat gun.
  • Selection of product and application of materials strictly as per manufactures’ recommendation

Some companies supply epoxy cracks injection products for architectural precast panels, underwater, low and high application temperatures, underwater  including swimming pool and salt and freshwater pier and piling repairs, water storage tanks and structures, dams, high structure temperatures, chemical and radiation resistance, large voids, narrow cracks, plate bonding, wooden (laminated) beams, concrete structures subject to vibration. For cracks where the backside cannot be sealed prior to injection.

Certain companies offer the special products with specification as follows. Not applicable to all the epoxy injection materials. Care should be taken to select the materials for the particular use.

  1. Fast strength, attain up to 5,000 psi compressive yield in less than 5 hours
  2. Vibration tolerant during cure
  3. Concrete crack injection solutions for underwater, corrosive, large void and other extreme exposures
  4. Can be used in temperatures as low as 35°F
  5. Suitable for repairing concrete cracks as narrow as 0.05mm wide
  6. Restores cracked concrete and structural members including beams and columns to original monolithic strength
  7. Stops water leakage through foundations
  8. Prevents corrosion of embedded reinforcing steel
  9. Can be used in damp, wet and underwater applications

Generally, Epoxy injection method is not applicable in the following cases

  1. active cracks
  2. Cracks greater than or equal to 0.05mm
  3. Water leakage is active
  4. Area is wet
  5. Epoxy loses strength at higher temperature

2) Routing and Sealing:

  1. Not applicable for structural cracks.
  2. Very common method
  3. Suitable for inactive cracks
  4. Make the V-shaped groove with 6mm width and 6 to 25 mm depth
  5. Clean the area with wire brush and wash the groove with pressure jet and allow it to dry.
  6. Fill the gaps with appropriate sealants like polysulphide sealants, hot tar, etc
  7. Care should be taken to the bonding of the filling materials to the surfaces of the concrete. Primer may be used.
  8. Products usually flexible to accommodate expansion and contraction
  9. Different category of materials like epoxies, Urethane, silicones, Polysulphide, polymer mortars, asphalt materials, etc

The material used as the sealant can be of any material that can balance cyclic expansion and contraction and which does not become brittle with time, including epoxies, urethanes, silicones, polysulfides, asphaltic materials, or polymer mortars. Cement grouts should be used for this purpose

3). Stitching for Structural Concrete Repair

The cracks can be formed in concrete due to various reasons like change in temperature, poor sub structure compaction, entry of water, corrosion of reinforcements, change in water table, change in use, design failure, poor quality materials, poor supervision, no quality controls, lack of clear specification etc.

Concrete repairing shall be done immediately after noticing the cracks. Carbon fibre wrapping is and efficient and fast method.

  1. Straight stitching

It is an easiest and long-lasting method of repairing concrete cracks. In this method, a number of the hole drilled along the crack surface and stitched with metallic wire/bars. This metallic U-shaped wire is then passed through holes and anchored strongly in the holes with grout or an epoxy-based system. A non- shrink grout or an epoxy resin-based adhesive should be used to anchor the legs of the staples.

Drill the holes on both sides of the line of cracks at a distance of 300mm at an interval of 400mm along the cracks to accommodate 10mm dia. reinforcement or as per the engineer in charge.

Cut the groove to a width of 20 mm to depth less than the cover of the Concrete.

Make the u shape steel bar and insert into the groove with Vinyl ester resin similar to Fosroc E55 or similar materials

Fill the top portion with high tensile strength epoxy adhesives.

Dowel holes can be drilled in any direction suitable for the site conditions

Advantages:

  1. Very effective and permanent.
  2. The grout combination provides an excellent bond within the substrate. Care should be taken to select the materials
  3. Masonry remains flexible enough to accommodate the natural building movement.
  4. Non-disruptive structural stabilization with no additional stress
  5. Angular Stitching of Crack

This method is more preferable for deeper slabs, foundations, beams etc.

Drilling the holes through the cracks at an angle of 35 to 45 degrees. 14mm bar is usually used at an interval of 400mm along the cracks. The lower end of the holes shall be above the cover of the concrete. Clean the hole with an air blower or with some other means. Distance between holes and the line of cracks can be decided based on the angle of holes. Use Fosroc E55 or similar vinyl ester resin materials that shall be used to fix the reinforced steel bars. Study the manufactures recommendations carefully. Select the materials which can be used for internal-external submerged conditions.

4) Drilling and Plugging:

Drilling and Plugging

This is very simple and easy method to rectify the cracks run in straight lines.Cost effective and less time-consuming method

Procedure

Holes drilled perpendicular and through the cracks. Insert small piece of pipes into the cracks to form as an inlet to receive grout. Seal cracks with sealant and leave the pipes open.Pour/inject the liquid epoxy through the pipes

Drilling and plugging

Drilling and plugging a crack are drilling down along the length of cracks vertically down and fill with grout. Hole shall be drilled to the stem of the wall and insert perforated pvc or metal tube till the end of the hole. Care should be taken to drill the hole without cutting the reinforcement. The size of the hole shall be 50mm to 75 mm depends on the size of concrete wall. Pour the epoxy or polyurethane liquid to the perforated tube till it reaches the top surface.

This method is applicable for the cracks run in straight line and accessible. Generally, this method opts for retaining walls.All minor cracks will be closed with the application of suitable grouts before applying grout to perforated tubes.

5) Grouting Method of Crack Repair:

Portland cements grouting:

In case of gravity dam and concrete wall large-sized crack formed. They can be repaired by filling with Portland cement grout. This grouting method is effective in stopping water leaks, but it will not structurally bond cracked sections.

  1. Dry packing:

Low water content mortar is inserted by tamping or ramming of the mortar into place to make tight contact between the mortar and the existing concrete. The mixed ratio of the cement mortar plays an important role in this procedure. Bituminous paint application before and after the application of cement will give more water tightness to the cracks.

Dry pack method is not suitable or advisable for filling or repairing active cracks.Widen the cracks to 25×25 mm along the line of cracks, clean the surface to receive bitumen coating or the material suggested by the manufacturer.

Cementitious waterproof materials are more suitable for this purpose. Different construction chemical suppliers can recommend suitable materials for this purpose.Manufactures recommendations should be carefully studied before application

Gravity filling

Low viscosity resins can be used to seal cracks with surface widths of 0.03 to 2 mm by gravity filling. Clean the surface with wire brush and vacuum cleaner. Pour the monomers or resin or any product recommended by the manufactures on the surface. Use paint brush or rollers to spread the materials to the surface and it to fill the pores and minute cracks by gravity.

In case of washing the surface allow drying to time to moisture percentage less than 20. This method is not advisable for active cracks.

Portland cement grouting

This method is used in gravity dams and thick concrete walls. This method is effective in stopping water leaks. Cleaning the concrete along the crack, fixing grout nipples along the cracks. Closing all other portion of cracks with cement paste, sealant, or grout. Pressure grouting cement through the nipples. Grout mixtures shall be decided based on the size and nature of cracks.

Chemical Grouting

The procedure for chemical grouting almost same as of other pressure grouting methods. In this case chemicals will be used foams, gels, urethane, sodium silicate and numerous new materials. This method is suitable in moist conditions and for fine and bigger cracks.

Disadvantage: Very good skill is required and strength is based on the type of materials

Control joint sealant:

Contraction joints are sealed against water, frost, debris and to handle recurrent movement using a flexible sealant like polysulphide sealants

Recurrent movement:

Seal and repair cracks in concrete using injection of either epoxy resin or polyurethane for recurrent movement due to traffic vibration, temperature variation and other causes due to structural failures.

Stop a water leak:

Use epoxy resin, polyurethane and other suitable products to stop water leakage. Immediate attention has to be provided to solve the water leakage through the structures which will promote the oxidisation of reinforcement.

Structural repair

Combination of epoxy resin and stitching are the most suitable method for low load non active cracks.

Structural reinforcement:

Different suppliers like sika provide wrap and seal materials to give additional strength to concrete members. Synthetic fabrics, carbon fibre mesh and other materials can be used as per manufactures recommendations. Some materials are stronger than TMT bars.

Surface repair:

In most cases for floor slabs cracks are occurred due to shrinkage and expansion. Application and products can be selected based on the nature of cracks.

Anchoring epoxy products: In many of the applications anchoring play important role in cracks repairing. So, the selection of anchoring epoxy or similar products are important.

Sealants

Any sealant to fill a Contraction joint and expansion joints in a slab should have the ability to bond to the sides of the joints and remain flexible over temperature and moisture changes.it has to withstand both compression and expansion as the concrete moves.

Typical concrete crack preparation for sealant with an epoxy product

  1. Sand

     (clean, dry) may be used as a filler for cracks – an easier approach if you are repairing an irregular crack in a floor. Sand should stop about 3/4″ from the top of the floor surface to give adequate volume of sealer epoxy in the crack.

Polyurea as a control joint filler or crack sealant in concrete slabs

Polyurea joint filler products are resistant to moisture and high adhesion properties with concrete and will cure very easily in very cold weather.Polyurea sealant products are useful in sealing control joints in “green” concrete.

An advantage of polyurea or polyurethane used as a crack sealant.

 Flexibility of the materials to accommodate slight seasonal or temperature-related movement.Injected polyurethane foam expands after it is injected into a crack.It is easier to fill the cracks of concrete structures.

Use of Epoxy-supported Grouts as a control joint or crack filler in concrete slabs or walls

Epoxy grouts will work fine to provide a well-bonded repair to a stable wall or floor cracks where there are no further movements due to temperature and moisture variation.

Epoxy material is stronger than concrete alone. Recommendation from Product manufacture and their support are very important. It is ideal for structural repair.

High Pressure or Low-Pressure Slab or Foundation Wall Crack Sealant Injection

Most foundation wall and floor slab cracks can be filled and sealed with low-pressure injection for both epoxy and polyurethane foam sealants. High pressure pumps of 250 psi with ports may be used for major foundation cracks.

Reasons to use an epoxy-based crack repair or sealant method

  • Structural repairs – Epoxy for inactive cracks
  • Very fine cracks need to be sealed – Inject low viscosity epoxy sealants
  • Wider cracks-Polyurethane foam injection and less expensive
  • May provide a smoother surface – seal & peel
  • No structural repairs only for sealing a crack against air or water leaks- Polyurethane foam injection.
  • Large Cracks extends through the foundation and walls- Polyurethane foam injection.
  • and is large, an epoxy sealant may simply leak out of the other side of the wall or floor slab – Polyurethane foam injection
  • cracks are actively leaking – Polyurethane foam injection (Polyurethane sealants are moisture activated.)

Hydraulic cement -This waterproof cement product is used for cracks repairing. It is cheaper than any other type of materials.

There is a chance for cracks formation due to shrinkage in bigger cracks. This can be used for active water leakage. It expands to seal the cracks in the presence of water.  A combination of mesh tape and sealant used to cover cracks in concrete before installing tile

Ceramic tiles fixed on a slab against the transmitting of slab cracks up the tile. In such cases or even on top of the plywood tile isolation membranes can be used. The repair of highly cracked slabs by strengthening mesh glued to the floor over the cracks to resist the transmission of the crack upwards through the ceramic tiles and other areas. This method is suitable for large area slabs with a high level of cracks.

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