Opening of Quotes - The Pointe at Riverwalk Building Utility Materials Proj No 124-069M - Etna

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Z3 mance and effectiveness of the lining. When a cement -lined pipe is placed in service and filled with water, two reactions begin immediately. The first is a gradual elimination of the temperature differential between pipe and lining, thus eliminating any stresses in the lining due to this condi- tion. Secondly, the lining begins to absorb water. Water is absorbed into the pores of the cement and into the capillary channels of the calcium silicate gel. The water absorption causes the lining to swell, restoring it to inti- mate contact with the pipe wall and virtually closing any cracks present in the lining. This swelling process is relatively slow, taking up to several weeks for the lining to be restored to its maximum volume. This process has been demonstrated on a number of occa- sions to the satisfaction of customers, con- tractors and engineers by immersing a pipe or fitting in water for one or two weeks. After a period of exposure to water, not only does the lining tighten against the pipe wall and the cracks close, but finally the sur- faces of the cracks actually re -bond. This occurs by a process called autogenous heal- ing. This phenomenon, long recognized by the cement industry, has been documented by laboratory tests to occur in cement -lined ductile pipe. In one test, a 48" ductile iron pipe with severely cracked cement lining was held half full of water for several months. At the end of that period, the lining both above and below the water surface was found to be tight, with all cracks either healed com- pletely or sealed by the formation of calcium carbonate. Field inspections of lines that have been in service for many years have verified the laboratory results; cement linings do tighten and heal in service and provide the corrosion protection to the pipe and the high flow coefficients for which they were designed. Field Repair of Damaged Cement Linings Cement lining will withstand normal handling; nevertheless, pipe or fittings may be found at times to have damaged linings which need to be repaired before placing in service. 11-2 AWWA C104 provides that damaged lining may be repaired, and the following repair procedure is recommended: 1. Cut out the damaged lining to the metal. Square the edges. 2. Thoroughly wet the cut-out area and adjoining lining. 3. With the damaged area cleaned and the adjoining lining wet, spread the mortar (see recommended mix below) evenly over the area to be patched. (See Table No. 11-1, next page, for lining thicknesses.) After the lining has become firm and adheres well to the surface, finish it with a wet 3" or 4" paint brush or similar soft bristle brush. 4. The repaired lining should be kept moist by tying canvas, wet burlap, or other wrap over the ends of the pipe or fitting for at least 24 hours. As an alternative the repaired lining may be seal coated with a cut back type of asphaltic seal coating. This must be sprayed or brushed on within five to 30 minutes after lining. To maintain NSF certification, patch must be made using a NSF certified cement for 4" pipe and larger, or the patch must be topcoated with NSF certified asphalt paint. Recommended Cement Mix Cement mix by volume: 3 Parts Portland Cement; 2 Parts Clean Sand; neces- sary water for slump of 5" to 8". The sand should be free of clay and screened through a No. 20 Screen. Precautions 1. Mortar for lining should not be used after it has been mixed for more than one hour. 2. Too rapid a loss of moisture from fresh linings due to hot weather or high wind will prevent proper cure, resulting in the lin- ing being soft and powdery. To prevent this loss of moisture, (a) do not line hot castings and (b) close the ends of the castings with wet burlap. 3. Fresh linings that become frozen will not be serviceable. Avoid lining in freezing weather.