86 Repair & Renovation Guide In an earthquake, there is always the possibility of microcracks forming in concrete elements. If the cracks are quite small (width = 0.1 to 1mm), the technique to restore the original tensile strength of the element is by injecting pressurized epoxy resin D-33 (p. 235). The procedure is as follows: The substrate must be free of loose spots, dust, oils, and standing water. Remove loose materials on both sides of the crack and clean the dust from the concrete with compressed air. Seal using the epoxy putty D-38 (p. 235) along the crack, and place nozzles every 25cm. Vertical cracks should be filled using the professional cartridge and ‘sausage’ barrel gun DUROSEAL 600 of DUROSTICK (p. 251). After the epoxy putty has solidified, the low viscosity epoxy resin D-33 (p. 235) is injected into the nozzle, starting from the lower part of the crack up. Seal the nozzle with a plug and continue pouring the resin to the next (nozzle) and so on. Larger cracks allow for longer distances between the nozzles, depending on the width of the concrete element. This technique is suitable for all types of structural elements, such as beams, columns, concrete walls, as well as any concrete structures in general. If a leveling coat is needed, the cracked surface is repaired with the appropriate reinforced cementitious repair mortar. EARTHQUAKE: CONCRETE ELEMENTS special subjects Small-scale and limited length repairs of cracks in concrete elements For such repairs, the necessary attention must be given: (i) In case of loss of the bond between the reinforcing bars and concrete, since the concrete that is in direct contact with the rebars is pulverized, the powder will create a barrier that will prevent proper dispersion of the epoxy resin and the saturation of this area, which is what the goal is. Therefore, before starting the repair, the area of the crack in need of repair must be cleaned properly with pressure air or water (if water is used it is necessary to wait for it to dry) before injecting the epoxy. (ii) It has been found that cracks smaller than about 0,75 mm, can hardly accept pressurized injection. As a result, this method should not be used to repair cracks of this type.
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