remove all concrete which has undergone some degree of deterioration. 

 Numerous quick-setting patching materials, some of which are proprietary, 

 are available. Information on the field performance of these materials is 

 given in Federal Highway Administration (1975). 



c. Bonding Agents . Bonding agents are used to establish unity between 

 fresh concrete or mortar and the parent concrete. An enriched sand-cement 

 mortar or neat cement paste has generally been used in the past. Epoxy 

 resin is now used frequently as a bonding agent, with the expectation of 

 durable results. This material develops a bond having greater tensile, 

 compressive, and shear strength than concrete. It is waterproof and 

 highly resistant to chemical and solvent action. It is possible to have 

 acceptable results when the concrete is brought to a feather edge; however, 

 better results are obtained if a 25-millimeter-minimum thickness is main- 

 tained. 



Other types of bonding agents have recently become available. Certain 

 latexes, supplied as an emulsion or dispersion, improve the bond and have 

 good crack resistance. Polyvinyl acetates, stryrenebutadiene, and acrylic 

 are among those used. These materials, particularly the polyvinyl acetates, 

 must be properly compounded if the dried film is to be resistant to mois- 

 ture. They may be used either as a bonding layer or added to the concrete 

 or mortar mix. 



d. Appearance . Unless proper attention is given to all the factors 

 influencing the appearance of concrete repairs, they are likely to be un- 

 sightly. In concrete where appearance is important, particular care 

 should be taken to ensure that the texture and color of the repair will 

 match the surrounding concrete. A proper blend of white cement with the 

 job cement is important to come close to matching the color of the original 

 concrete. A patch on a formed concrete surface should never be finished 

 with a steel trowel, since this produces a dark color which is impossible 

 to remove . 



e. Curing . All patches (except where epoxy mortar or epoxy concrete 

 is used) must be properly cured to assure proper hydration of the cement 

 and durable concrete or mortar. 



f. Treatment of Cracks. The decision of whether a crack should be 

 repaired to restore structural integrity or merely sealed is dependent on 

 the nature of the structure and the cause of the crack, and upon its 

 location and extent. If the stresses which caused the crack have been 

 relieved by its occurrence, the structural integrity can be restored with 

 some expectation of permanency. However, in the case of working cracks 

 (such as cracks caused by foundation movements, or cracks which open and 

 close from temperature changes), the only satisfactory solution is to seal 

 them with a flexible or extensible material. 



Thorough cleaning of the crack is essential before any treatment takes 

 place. All loose concrete, oil-based joint sealant, and other foreign 

 material must be removed. The method of cleaning depends on the size of 

 the crack and the nature of the contaminants. It may include any combina- 

 tion of the following: compressed air, wire brushing, sandblasting, 

 routing, or the use of picks or similar tools. 



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