Case 1

Remedial (see also Remedial)

The following methods can be used to repair the crack [20-21].

Repair using epoxy injection

One of the most versatile, crack repair method is epoxy injection. This method can be used to repair cracks which narrow more than 0.002in [20]. This method has been successfully used in buildings, bridges, dams etc., due to following characteristics:

• Outstanding adhesive qualities to materials such as concrete and steel
• Resistance to a wide range of acids and alkalis and other chemicals, except acids such as nitric which have high oxidizing characteristics
• Rather vulnerable to organic solvents
• Low shrinkage when the compound course and changes from the liquid to the solid state
• High coefficient of thermal movement compared with concrete
• High compressive, tensile and flexural strength
• Appreciable loss of strength at temperatures over about 80oC
• High rate of gain of strength which can be varied to suit the particular application

The site conditions under which the resin will be applied must be stated to the formulator. Unless specially formulated, most epoxide resins must be applied to dry surfaces and the ambient air temperature and relative humidity during application must be kept within fairly narrow limit.

Video on Epoxy Injection – courtesy of Adhesive Technology

Repairing using crystallisation

Crystallisation method can also be used to stop water seepage. These are silicone based chemicals and when they come into contact with water, they will seal up the cracks. They are reactive pore fillers which penetrates into capillary tracts of concrete to react with free lime and water to form crystalline chain which blocks up the capillary and makes concrete water-tight.

Advantage: 

• The crystalline formed in the concrete will be able to improve the integrity of concrete by sealing up pores to prevent penetration of water and other chemical. Also it is independent of surface adhesion so it can resist high hydrostatic pressure.
• Normally, the crystallization chemical acts as a catalyst so it will last much longer than other injection material. Due to the same reason, it creates a automatic crack closure effect as long as water is present.

Limitation:

• This method can only be used to seal cracks up to a limited depth.

Video on crystalisation – courtesy of Kristol

Re-waterproofing and sealing

The following are the steps in this method:

• Repair area should be cleaned with high-pressure water jet, before starting the repair.
• Chisel grooves along major crack lines and along the suspected leaking areas.
• Apply a layer of crystal slurry on the floor. It will penetrate deeply into the capillary pores of the concrete, sealing the pores and shrinkage cracks by crystallization permanently. Allow the chemical to cure.
• Plug grooves with water seal. When it cures, it expands and locks the affected areas making a watertight seal.
• A coating of Cement Strengtheners Polymer can be applied to give a stronger bonding capability. With its waterproofing property, it is able to act as a waterproofing membrane which locks the infiltrated areas from further seepages. Allow the chemical proceedings to cure.
• Water repellent may be sprayed on the slab in order to further strengthen the waterproofing ability.

Repair using polyurethane injection

Polyurethane (PU) grouting is specially designed for providing water control in static joints or cracks in concrete structures. The grout material, when mixed with a certain amount of accelerator, will react with water or moisture and expand to form a tough, closed-cell rubber that is essentially unaffected by corrosive environment.

Polyurethanes are products of the petrochemical industry. They are very durable when exposed to external conditions and retain their gloss well. They can be obtained as elastomers, solid and rigid materials or flexible coatings. Major cracks or localized porous concrete can be repaired by this method.

In the application, PU reacts upon with the water in the slab and expands its volume and thus fills the cracks or pores in the slab. Therefore, it acts as a sealer over the cracks. The repairing process can be completed within half a day. Accelerator agents can be used to speed up the setting time of the grout. A finishing coat may be applied after the remedial work is completed.

Video on PU injection – courtesy of Nervia