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2015WinterShotcreteEMag

2014 Honorable Mention Long Prairie Digester Rehabilitation Project By David Graham Tprocess wastewater generated by food pro- 12 ft (3.7 m).The tanks were originally constructed withis 21 x 21 ft (6.4 x 6.4 m) with a wall height ofhe Long Prairie Digester is a wastewatertreatment facility constructed in 2012 to cessing operations. The facility includes four cast-in-place concrete slab-on-ground floors, reinforced concrete process tanks and one open- 18 in. (450 mm) thick insulated concrete form top receiving tank. (ICF) walls, and topped with a precast concrete The enclosed process tanks vary in size. Two roof system. A polyurea lining material was of the tanks measure 282 x 39 ft (86 x 12 m); one sprayed over the interior wall insulation and the is 59 x 24 ft (18 x 7.3 m); and the other is 87 x underside of the precast roof (Fig. 1). 24 ft (26 x 7.3 m). The wall height of the enclosed tanks is 22 ft (6.7 m). The open-top receiving tank The Problem After original construction, the tanks were tested for watertightness. During the testing phase, the tank walls exhibited extensive leaking (Fig. 2 and 3). The insulated form wall system made it impos- sible to determine where the leaks originated. It was immediately evident that removal of all interior insulation would be necessary to properly inspect tank walls, expansion, and construction joints. After removal of interior insulation, the exposed walls revealed extreme honeycombed areas resulting from poor consolidation during original construction. Also, the ICF wall ties used consisted of a hollow tie without a waterstop feature; thus, water could be leaking from any- where in the walls through existing voids or through any of the thousands of hollow ties. The Repair Solution The plan provided for repair of structurally deficient areas and protection of carbon steel wall ties while providing a smooth, level surface to receive a final protective lining system. Due to the high volume and severity of poorly consolidated areas, it was determined that the tank walls required repair prior to final lining applica- tion. Honeycomb areas were chipped back to sound concrete and brought back with shotcrete to orig- inal wall plane using King Packaged Materials MS-W1 with poly fibers. These areas were not troweled and were left with a natural gun finish. After repair of honeycombed areas, 6 x 6 in. W1.4 x W1.4 (152 x 152 mm W9.1 x 9.1) welded wire reinforcement was securely anchored to all Fig. 1: Tank before repair wall surfaces. Wall surfaces were washed with 40 Shotcrete • Winter 2015


2015WinterShotcreteEMag
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