A relatively new sheet lining system designed specifically to rehabilitate corroded concrete structures has been installed in a 36.3 MGD wet well at a City of Topeka, Kan., pumping station.
A routine inspection of the well and influent channel of the Shunga Pump Station revealed significant hydrogen sulfide (H2S) damage to the 12-inch-thick, cast-in-place concrete walls and ceilings.
Engineers from the City of Topeka and from the consulting firms of Camp Dresser McKee in Kansas City and Professional Engineering Consultants in Topeka considered several spray-on lining systems and adhered sheet vinyl systems but none provided the protection that engineers believed the project required. The general contractor, CAS Construction of Topeka, recommended the use of a sheet lining system developed in the late 1990s by Ameron Protective Lining Products.
The Arrow-Lock system was given an in depth evaluation and found to meet or exceed project specifications. Because the system had not been used in the immediate area and its relative newness in the marketplace, engineers also conducted phone interviews of previous users of the lining system before recommending it for the job.
Hoot General Construction Co. of Houston, an experienced Arrow-Lock applicator and installer, was hired to handle the relining.
The pump station wet well is 30 feet in diameter and 19 feet deep. A permanent diversion structure is located near the pump station and is used to direct flow from gravity sanitary sewer lines into the pump station or to other pump stations when the Shunga Pump Station is taken out of service. Connecting the two structures is a 65-foot channel that is six feet wide and five feet tall. Although the walls had significant H2S damage they were still structurally sound.
The pump station was taken out of service during the rehabilitation work, but the diversion structure had to remain in operation to divert the effluent. The walls and ceilings of the wet well were power washed and sand blasted to remove the defective concrete and expose sound material. Heavily damaged areas, where reinforcing steel was exposed, were patched before relining began. Gas monitoring equipment and air blowers were used to provide adequate safety protection during the project.
Hoot finished the job in three weeks, despite two work interruptions caused by effluent entering the wet well as a result of a downstream blockage in the diversion line.
The Arrow-Lock system is composed of three components: PVC liner sheets with arrowhead shaped ribs on one side, epoxy mastic and mastic primer. The primer is applied to the substrate and allowed to dry, then the A & B components of the mastic are mixed and applied to the primed substrate to a minimum thickness of 1/4 inch using a trowel. After the mastic is applied, the liner is placed in position and the arrow-ribbed side is pressed into the mastic to thoroughly embed the ribs, forming a mechanical lock to the substrate. A roller is then used to remove any trapped air bubbles from behind the sheet.
The sheeting is made from high-polymer vinyl chloride resins extruded under high temperature and pressure to form a dense and impervious liner. The mastic is 1:1 epoxy gel for filling voids and bonding to the prepared damp or dry concrete surfaces. Although the mastic bonds tightly to concrete, it is designed not to bond to the Arrow-Lock sheets. The mastic simply flows around the lining's arrow-ribs and, after curing, locks the lining permanently into place. The absence of traditional bonding allows ground water seepage to drain away without damaging the lining or the underlying concrete.
The over-lapping sheets first are heat sealed and then fused using weld strips and a hot air welding gun. The result is a smooth, impervious liner designed to protect the concrete structure against severe corrosion for decades.
