Project: Nightingale Pump Station and CSO Storage Basin - Louisville, KY
Customer: MSD of Louisville and Jefferson County
Contractor: Judy Construction - Cynthiana, KY
Project obstacles and solutions: The Metropolitan Sewer District of Louisville and Jefferson County opened bids in 2014 for a new pump station and an underground CSO storage structure at their Nightingale facility. Like many large cities with combined sanitary and storm sewers, the MSD was under a consent decree from the EPA to eliminate overflow problems that polluted the river and streams in the Louisville area. The pump station was designed to move up to 33 million gallons of wastewater per day and the concrete storage basin was designed with a capacity of 7.7 million gallons. Judy Construction was awarded the contract for this project.
Any concrete structure of this size has its challenges in both delivery of concrete and meeting engineering requirements. The concrete for the floors and walls of the storage basin were delivered to the deepest parts of the site via crane and bucket. Floors were poured up to 5 feet thick and the walls were up to 35 feet tall. IMI spaced trucks to keep the crews moving during these pours. Mix design considerations were made for this type of delivery.
The size of the structures also required IMI QC/QA to consider keeping the concrete cool upon delivery. Mass concrete structures can have cracking issues when the core temperature gets too hot due to the heat created during cement hydration. When the core temperature greatly exceeds the temperature of the concrete on the surface, thermal cracking can occur. Typically mass concrete is defined as any poured concrete that has a dimension greater than 3 feet. Mass concrete was poured in the thickest parts of the floors and the pillars. IMI QC/QA designed a mix that used a Type F fly ash to reduce the cement content and lower the thermal impact of the mix without diminishing the strength. On the hottest of days, this concrete was mixed with chilled water and ice to keep the core temperatures in check.
Another issue that can occur in this type of construction is the permeability of the concrete. By its very nature, concrete is a porous material and will allow water to soak through it. When you are using structural steel in concrete, this can be a problem, as the water will deteriorate the steel. In this case, a high density mix was poured to keep the concrete water tight. IMI QC/QA used a high range water reducer to eliminate the bleed water that can open pores in concrete. They also used a hydration stabilizer to increase the performance of the mix.
In total, IMI provided 18,000 yards of concrete for the Nightingale expansion project.
For more information on pouring mass concrete or adjusting concrete mixes for different delivery methods, contact the sales representative for the concrete plan nearest your location. Click here.