Mitchell Water Treatment Plant Repair Project

Greensboro, NC

Mitchell Water Treatment Plant has the ability to produce about 24 million gallons of water per day. The filter house, sedimentation basins and mixing chambers were mainly constructed in the 1950’s with additions in the early 1960’s. The primary structural system in the filter house is reinforced concrete columns, beams and slabs and concrete encased steel beams. Exterior basins and bridges are reinforced concrete. Concrete materials distress and reinforcing steel corrosion at interior and exterior locations had become more apparent in recent years. This warranted a condition assessment to characterize distress and concrete quality for desired 30 plus years of service-life extension.

The concrete condition assessment included the filter house with current and/or previous exposures to ferric sulfate, chlorine, hypochlorite and other unknown historical substances, as well as the exterior non-air-entrained concrete basins and bridges. The evaluation incorporated strength testing and petrographic evaluation for distress characterization, exploratory excavations and embedded corrosion testing including ultrasonic steel thickness, chemical analysis (chlorides, fluorides, iodides, bromides), half-cell, cover, resistivity and pH. A multiple phase approach was selected for restoring capacity to deteriorating members and extending service life. The first phase (subject of this submittal) included structural and durability repairs at the filter house and the second phase (scheduled for 2017/2018) will include structural repairs and overlay installation at exterior bridges and basins.

Repairs at the filter house included full replacement of the heavily deteriorated structural concrete slab and beams in the hypochlorite room and surrounding areas (approx. 1100 sf) with high-performance concrete and installation of supplemental supports, galvanic anodes and coatings. Three different designers and a general contractor worked in tandem to produce an exceptional result as the concrete replacement work was conducted in conjunction with mechanical system, HVAC and operational system upgrades and enhancements.