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Western Dam Engineering <br /> <br /> <br /> <br />20 <br />to achieve a good bond between the existing and new <br />material. For most small to intermediate sized <br />conduits, the conduit thickness isn’t sufficient to <br />develop reinforcement, so dowels typically are not <br />used. All surfaces to be covered with fresh concrete <br />should be moistened to saturated surface dry <br />condition and all standing water removed, leaving the <br />surface damp immediately prior to receiving concrete. <br />A high strength, 3/8-inch concrete mix is usually <br />prescribed for the repairs (pre-mixed Sika product or <br />similar). <br /> <br />Photo 4: Spalled concrete inside a conduit.2 <br /> <br />Joint Offsets and Cracked Concrete <br />Since RCPP conduits are typically made up of short <br />sections of pipe connected by gasketed bell and spigot <br />type connections, the joint locations are a common <br />place for deterioration or poor construction practices <br />to manifest. First, the cracks or joint offsets should be <br />thoroughly cleaned of any embankment material and <br />cleared of all loose or spalled concrete. For larger <br />cracks, offsets, or failed joints, grout injection helps to <br />fill any voids that may have developed behind the <br />conduit due to localized erosion at the crack or joint <br />locations. <br /> <br />Photo 5: Crack in precast concrete conduit. <br />For this method of repair, the opening should be <br />temporarily sealed, creating a bulkhead, so that grout <br />can be injected behind the conduit. Non-shrink grout <br />can be applied from the interior of the conduit to <br />develop the bulkhead and grout injection ports can be <br />installed through the grout, around the circumference <br />of the crack, at a spacing that will allow the grout to fill <br />any voids that may have developed. Generally, grout <br />injection behind the conduit should be completed so <br />that the injection pressures do not exceed about half <br />the lateral earth pressure of the embankment at the <br />location of the crack. <br /> <br />Photo 6: Grouted joint offset with grout port installed <br />for injection grouting behind conduit. <br />For large cracks, redundancy may be desired and a <br />mechanical repair can be implemented by installing a <br />seal around the inside of the conduit after injection <br />grouting has been completed. A mechanical seal <br />should span the original crack to overlap sound <br />concrete (typically 6-9 inches on either side of the <br />crack). Various products are available to create this <br />seal (Link-Pipe Grouting Sleeve, EPDM rubber seal,