Centrifugally cast fiberglass reinforced polymer mortar (CCFRPM) pipes have been utilized in more than 40 of the 50 states across the U.S. Nearly every U.S. city with a population over 100,000 has utilized CCFRPM for some sort of installation whether it is new construction or rehab.
The popularity of the pipe, due to successful installations and the increased emphasis on life cycle cost analysis, has grown in recent years. Owners and consulting engineers are designing for the long-term with tougher requirements placed on piping materials. It is not uncommon to pay a slightly higher initial price for a product that provides a much longer lifespan with minimal maintenance. This kind of decision making is not limited to the U.S.
When the largest wastewater treatment plant in Vienna, Austria was being expanded and modernized, CCFRPM pipe was chosen to be part of the renovation. Over three miles of 94 in. diameter pipe was supplied from the Hobas Rohre factory in Weitersdorf. The complete system including pipe, fittings and manhole shafts were delivered via truck more than 150 miles across the Austrian countryside to the jobsite in Vienna.
Vienna, the capitol of Austria, has been steadily growing. The plant expansion was necessary to handle the increase of sewage connections and will include upgraded biological treatment processes as well. Reasons for the expansion were also based on improvements in local water quality.
According to Hobas, the construction and operating company responsible for the purification of wastewater in Vienna, "The most important project in the context of Vienna's water protection program is being erected in an area (of nearly 50 acres). Sixty new clarification basins with a volume of (over 97 million gallons) matching an area of over 2,000 square yards will be lifting the volumetric capacity of the main sewage treatment plant to five times its previous amount. The quantity of water inside the basins could fill about 2.2 million bathtubs."
One pipe composition
The project designers evaluated the pipe alternatives with their main requirements being corrosion resistance and abrasion resistance. They believed these two properties would provide a long operational lifetime with minimal maintenance. It was a requirement of the project specifications that the same pipe material be utilized on both the direct bury and the jacking portions of the project.
The computer-controlled CCFRPM manufacturing process allows for consistent and economical designs of both direct bury and jacking pipes. Centrifugally cast pipes provide a mold smooth exterior for sealing of gasketed joints anywhere along their length. This is particularly beneficial in direct bury applications in plant environments where modifications to the planned laying direction are often required. The CCFRPM pipe has benefits in jacking as well, and has been reported to decrease jacking loads due to the mold smooth, dimensional consistent OD.
Difficult conditions
The installation has proven to be challenging due to the presence of existing structures, the construction schedule, as well as variable soil conditions. The high stiffness design of the pipes (72 psi stiffness) has proven to be valuable and works well even with the very unique trench construction. In some areas the soils were so poor, a concrete sub grade was required to be laid first. The pipes were then buried using sand/crushed rock mixture to spring line and covered with a filter fabric. The remainder of the pipe and the trench were filled with recycled native materials.
The use of CCFRPM pipes was not based solely on the performance benefits. The pipe was also a very economical choice on an installed cost basis. The planned trench width for the direct bury section could be reduced by more than 10% (or 15 inches) due to the smaller OD compared with an alternate product. The lighter weight of the 20-foot pipe sections meant less equipment was needed on site, and the push together gasketed joints saved time by increasing the daily pipe installation.
The modernization of the plant will aid water quality, decrease overflows and help achieve compliance with surface water quality directives. The expansion of Vienna's Main Sewage Treatment Plant went online in 2005.
