Project Description: This project included the construction of a new cast-in-place concrete wastewater storage reservoir and wet weather treatment facility.
The 160’x215’ reservoir is capable of storing 5.75 million gallons of wastewater and was constructed following the blasting/excavation of limestone rock. With the high water table, the design engineer specified the use of 596 anchors drilled and grouted 33 feet into rock to control the buoyancy of the structure. The reservoir was constructed of 3’-5’-thick base slabs with 30’ tall x 3’6”-thick walls and cast-in-place concrete deck.
The wet weather treatment facility consisted of a concrete vortex separator and disinfection contract basin to effectively treat excess combined sewage during storm events. A concrete deck was placed on the reservoir to allow the structure to be completely backfilled.
Concrete Mixture: The reservoir and wet weather treatment facility were constructed of 4,500 psi concrete with a maximum shrinkage of 0.030 percent, 4.5 lb./CY fiberous reinforcement, and 0.10 percent maximum chloride-ion content.
All concrete exceeding 3’ thickness was considered mass concrete. It was necessary that the concrete be controlled to a maximum temperature of 158 degrees F, maximum temperature differential within the center and surface of 35 degree F, and concrete temperature at placement between 40 and 70 degree F.
Sustainability: The footprint of the entire structure was landscaped and any sewage within the reservoir is not exposed to the atmosphere. In doing so, the contractor and client minimized the construction-related exposure to wildlife, the environment, and the local community.
Innovation and Teamwork: Due to the large amount of strux fiber [WR Grace] in the concrete mixture and the large amount of course aggregate to control temperature increase, pumpability was a challenge. With the project on an extremely tight completion schedule, Joseph J. Henderson, Ozinga, and Original Concrete Pumping worked out a rapid solution to resolve this issue without compromising the quality or schedule. The mix design was modified to increase the slump to 8”, and 150 lbs. of coarse aggregate was taken out to improve pumpability.
In addition, Joseph J. Henderson, Ozinga, and E&L Support Services partnered to develop and implement a thermal control plan for mass concrete placements. E&L Support Services utilized their expertise to present feasible means to control the maximum temperature and temperature differential between the core and outside. Methods included controlling the temperature at placement and protection following walls and slabs to retain the heat of hydration on the concrete surface. Ozinga was able to deliver concrete below 70 degrees F during late summer placements using ice. Joseph J. Henderson used insulating blankets and did not strip forms until the curing period was complete. Throughout this process, the temperature was monitored using Intellirock Temperature sensors embedded in the center and outside of the walls and slabs.