Restoration of structural integrity across a crack has been successfully 

 accomplished using pressure and vacuum injection of low-viscosity epoxies 

 and other monomers which polymerize in situ and rebond the parent concrete. 

 Sealing of cracks without restoration of structural integrity requires the 

 use of materials and techniques similar to those used in sealing joints. 



Epoxy resin has become a common and satisfactory material for sealing 

 cracks. The U.S. Navy Civil Engineering Laboratory has developed the 

 following information on these resins. Epoxy, when mixed with a curing 

 agent, becomes epoxy resin, which is a thermosetting plastic that rapidly 

 develops adhesive strength. This synthetic organic compound is stable 

 chemically and physically; it is "durable, crack-resistant, and undergoes 

 little reduction in volume (2 to 3 percent) as the result of curing. 

 Adhesives of this type become irreversibly set as the result of exothermic 

 chemical changes initiated by the chemical changes initiated by the chemical 

 curing agent. Epoxy resins can be formulated to have specific values of 

 mechanical and physical characteristics; this is accomplished by means of 

 various hardeners, fillers, f lexibilizers, and plasticizers. 



Epoxy resin pressure-injected into the cracks of concrete can restore 

 the structure to its original strength. Cracks as narrow as 0.13 millimeter 

 (5 mils) and as wide as 6.35 millimeters (250 mils) can be repaired by 

 injecting epoxy resin. The type of resin needed depends on the width of 

 the crack, on whether the crack is working or stationary, and on the 

 particular method chosen for applying the resin. 



Repair of a working crack requires a formulation that will set up 

 rather rapidly so that the bond is not broken before the resin has developed 

 sufficient strength. Narrow cracks require a low-viscosity system to 

 ensure complete penetration of the crack. However, a more viscous system 

 can be used with high-pressure injection methods. The following is a 

 recommended method for repairing cracked concrete by injecting epoxy resin: 



(1) Clean the crack with compressed air; remove any salt, oil, 

 or grease deposits from the adjacent concrete surface and, if 

 possible, from the crack itself; 



(2) seal the exposed crack along its entire length; (the 

 sealant, which may be an epoxy resin, must be able to withstand 

 internal pressures of at least 862 kilopascals (125 pounds per 

 square inch); if applied to either vertical or overhead cracks, 

 it should be stiff enough so that it will not slough off or sag 

 before hardening; it should be able to bridge cracks as wide as 

 6.35 millimeters; alternatively, a special thermoplastic sealant 

 tape can be applied directly to the concrete surface and will 

 not deface the concrete when removed later) ; 



(3) if the sealant is an epoxy resin, drill holes about 6.35 

 millimeters in diameter and about 25.4 millimeters deep along the 

 crack, with spacing of the holes generally not less than the 

 thickness of the concrete member being repaired; 



(4) insert metallic nipples in the holes, secured in place 

 with a puttylike epoxy resin sealant, to serve as ports for 

 the epoxy resin; 



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