Crack injecting systems epoxy

Cracks occur in concrete structures for several reasons (ACTI, 1993a Concrete Society, 1982). The purpose of crack injecting systems is to fill in the cracks. Epoxy systems are a popular choice for non-moving cracks. In cracks where some movement is anticipated, polyurethane systems are used (Table 1.3). 

Whereas epoxy crack injecting systems are applied in static cracks, polyurethane systems are suitable for cracks where some movement is anticipated. There are other applications where polymeric materials are considered as competitors to each other. For example, neutral cure silicone sealants and polyurethane sealants are both suitable for use in construction joints. The former type offers greater durability and ageing resistance. However, polyurethane sealants are widely used because of their cost-effectiveness. Furthermore, some products are preferred over their counterparts for environmental reasons. 

Polysulphides. Polysulphides are used as curing agents for epoxies in the presence of tertiary amines which accelerate the cure such cured systems exhibit good flexibility and tensile strength at ambient temperature. In a real sense they are flexibihsers for epoxy systems. Specific applications are for the crack injection system (for moving cracks) and coatings (Chapter 10). 

Epoxy crack injection systems are unfilled compositions, based on low-viscosity liquid epoxy resins and low-viscosity moisture-tolerant hardeners. The low viscosity of the system aids penetration into fine cracks and achieves the right balance of gel time (Anchor Chemicals/Air Products, undated a). Cracks as narrow as 0.05 mm can be filled with epoxy injection systems (CCA/, 1985). 

It has been mentioned in section 3.5 on epoxy crack injection systems that epoxies do not do well in wet conditions because they resist movement. Polyurethane resins are suitable for injection of cracks in concrete or masonry in dry or damp conditions. They can be successfully applied in cracks having a width in excess of 0.2 mm. On curing they form an elastic seal impermeable to water. 

Application of the product is made by standard resin-injection equipment, having a minimum injection pressure of 0.4N/mm (4 bar). The method of application is almost the same as that of an epoxy crack-injection system. 

Crack repair restores structural integrity, seals the cracks against moisture and restores appearance. Epoxy injection systems are employed to fill, fine or coarse cracks in horizontal or vertical surfaces (Figure 3.3) conventional equipment can be used. The benefits of epoxy injection systems are ... 

Figure 3.4 Repair of vertical cracks (a) injection nipples inserted along the crack (b) surface sealant applied over the crack (c) injection of epoxy system into the crack via the nipples, showing a capped nipple after injection has been completed (d) nipples have been removed...

Before the epoxy system is injected grease, dirt and dust should be removed completely by proper treatment. The following steps are used for injection into a vertical crack (such procedures may also be followed to repair horizontal cracks). 

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