(5) inject the epoxy resin adhesive under pressure through 

 the first nipple (lowest in the case of a vertical or diagonal 

 crack] until the level of adhesive reaches the next nipple 

 (see Fig. 20] ; 



Figure 20. Concrete structure showing nipples through 

 which epoxy resin is injected. 



(6) using an inert gas, maintain a pressure of 620 kilopascals 

 (90 pounds per square inch] for about 1 minute to force the 

 adhesive into any interior microcracks adjoining the crack under 

 repair; 



(7) release the pressure and then pump more adhesive through 

 the same nipple until the next nipple overflows, then disconnect 

 the hose and cap the nipple; 



(8) follow the procedure until the entire crack is filled and 

 all nipples are capped; and 



(9] cut off the protruding ends of the capped nipples flush 

 with the concrete surface, plugging the resultant exposed openings 

 with epoxy resin sealant. 



g. Repair of Joints . Much experience of poor sealant performance and 

 resulting damage to a wide variety of structures exists. Concern with 

 such problems spurred the development and introduction in the last decade 

 of higher class sealants, both field-molded and preformed. Failures have 

 continued to occur, however, often within days and weeks rather than 

 months or years, for five, main reasons: 



(1) The joint as designed was of an impossible width, shape 

 or potential movement to seal successfully, yet an attempt was 

 made to seal it; 



136 



