Precast Solutions - March/April 2008 - (Page 16)

RCP is much less reliant on the surrounding soils for its structural strength. Installation and inspection. Installation of RCP and HDPE pipe must be performed according to the manufacturer’s specification and be in compliance with relevant standards (ASTM C 1479 and D 2321, and AASHTO Section 30 of the highway bridge specifications). Because flexible, or HDPE, pipe transfers loading to the surrounding support soil, the type of backfill used, the width of the installation trench and the resulting soil strength must be carefully determined, approved and inspected during installation by the specifying engineer. RCP, on the other hand, is much less reliant on the surrounding soils for its structural strength. Deflection testing of HDPE pipe, usually 30 days after installation, is now required by some state transportation agencies for underground drainage piping. Mandatory mandrel testing, visual inspection, video taping and laser testing of the interiors of drainage culverts for ovality are becoming standard DOT requirements. While laser testing for deflection is a relatively new protocol, most transportation officials believe it offers the best data, especially for inspection of pipe bends and intersections. Deflections exceeding 5 percent to 7 percent usually constitute structural failure and require removal. Current research from field laser testing of HDPE pipe (see the sidebar “Research on Field Laser Testing of HDPE Pipe,” page 14) indicates that certain plastic pipe installations may result in failed ovality tests if proper installation is not performed. project’s sustainability when selecting materials for construction. The onus of responsibility to ensure that maximum sustainability is obtained for public projects is a serious professional engineering obligation that will only increase in the future. The sustainability value in specifying RCP with supplementary cementitious materials (SCMs are industrial byproducts such as fly ash, slag and silica fume) is clearly commendable. While state engineers are interested in learning more about concrete pipe with SCMs for reactive site conditions, engineers can be assured that these products are both locally available and have a record of good performance. Material competition. The U.S. Federal Highway Administration (FHWA) requires that all agencies using federal funds develop pipe selection policies that consider all available pipe products judged to be of satisfactory quality and equally acceptable on the basis of engineering and economic analysis. This means that state DOT specifying engineers must consider competing materials in selection of underground pipe. The idea of promoting product competition in the marketplace is based on the strongly held American belief that free enterprise ensures the best quality products at the lowest price for the consumer. In reality, however, this concept places even more responsibility on the specifying engineer to evaluate the total system, acknowledging that the initial costs of pipe material are only a percentage of the total cost of Sustainability. Environmental factors are now assessed in determining cost effectiveness of a structure’s service life. Engineers must consider a installing stormwater drainage. With regard to how state transportation engineers will determine the cost effectiveness and design of RCP or HDPE pipe in the 16 PRECAST SOLUTIONS | MARCH/APRIL 2008

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Precast Solutions - March/April 2008 Contents Smooth Move Riding the Waves Comparing RCP With Plastic Pipe Cost-Value Analysis of Storm Sewer Pipe Concrete Testing On a Grand Scale Building Confidence

Precast Solutions - March/April 2008

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