Crack injecting systems polyurethane

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. 

THERMOSETTING POLYMERS IN CONSTRUCTION APPLICATIONS 4.10 Polyurethane leak sealers and crack-injection systems... 

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. 

In order to seal cracks in wet conditions hydrophobic systems are used in conjunction with a hydrophilic polyurethane resin system. These are rapid foaming and setting resins which stop the flow of water when injected into cracks in concrete in the presence of moving water, providing an effective system of crack sealing in wet conditions. As soon as the hydrophilic resin stops the flow of water, the hydrophobic resin can be reinjected to produce a permanent seal. 

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