Arizona Water Treatment Center Repair

The Roger Road Wastewater Treatment Plant had an expensive problem; a severely deteriorated concrete splitter box needed to be repaired, but before any work on this operating structure could begin, a temporary but costly pump around facility had to be installed to handle the processed performed by the splitter box, says John Munden, Civil Engineering Manage with the Pima County Wastewater Management Department. The splitter box is used to split the floc of raw sewage and direct it to various primary clarifiers he says. The structure was to have been part of a larger product to rehabilitate other concrete structures with a calcium aluminate cement under lament and epoxy topcoat but the contractor handling that job declined to take on the splitter box, declaring that it couldn’t be fixed, says Allen Kauffman, the president of another contracting firm that subsequently did the work using a polymer concrete repair product and an epoxy Novolac lining. The covered plaster box is 8ft wide, 18 ft long, and divided into two sections of different hieghts.

Given twelve days to do the work in November 2003, Kauffman’s company began the project by power washing the splitter box at 3,500 psi (233 bar) to clean the concrete surface and remove loose material. The deteriorated areas were then abrasive blasted with copper slag. The contractor installed a new mat rebar system, securing it to concrete with drilled-in dowels or tying it to the existing rebar. The contractor then performed another power wash with an injection of a soluble salt treatment. Blowers were set up to mately two-inch (five-centimeter) thick layers, says speed drying, and six hours later, the contractor began apply-Kauffman. The concrete repair material was allowed to set ing the polymer concrete repair product by trowel. up for two hours before additional layers were applied. Working on one wall section at a time, the contractor The contractor built the walls of the concrete structure applied the polymer concrete repair product. Back to their original thicknesses, in some cases taking a 1/8-inch-thick (3 mm) area back to 10 in. (25 cm). The contractor performed adhesion tests on the concrete repair product, noting that the cementitious substrate failed before the polymer concrete repair product. The surface preparation, rebar installation, and rebuilding of the concrete took four days, says Kauffman.

Forced heat aided the cure of the concrete repair material, allowing the contractor to proceed with the lining application 12 hours later. Over two days, two coats of the chemical-resistant epoxy Novolac lining were applied by brush and roller to a total thickness between 30 and 35 mils (750 and 875 micrometers). The epoxy novolac was heat cured over the first night and then heat cured for 24 hours following the final application , says Kauffman. According to Kauffman, Pima County had an inspector on site during all working hours. The concrete splitter box rehabilitation was completed in less than 7 days, saving more money in “pump around facility” expenses than it cost to perform the work, says Kauffman. The contractor performed a follow-up inspection in March 2005, noting no signs of deterioration of the system.

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