USACE concrete plant ensures quality, speed
April 10, 2013
Did you know the U.S. Army Corps of Engineers has a state-of-the-art concrete batch plant in Charleroi, Pa., which is within the Pittsburgh District's oversight? Well, they do.
Some people may question how the federal government can justify spending $28 million on this facility, but after getting a better understanding of the plant and its operations, they might rethink the question.
The Corps places most of its concrete under water at locks, dams and river related structures; therefore, the concrete has to be designed to last. The average age of the district's maintained locks and dams are 50 years. Over the years, sulfate found in the rivers can deteriorate concrete.
Glenn Bush, a Pittsburgh District construction representative, said the concrete produce at the Charleroi meets the high standard needed to withstand river sulfate.
"A plant like this one has capabilities that are rarely seen in the private sector, and those features yield exceptional quality concrete with every batch," Bush said.
It produces concrete at rates averaging 165 yards-per-hour, 15 yards per hour above the estimated production rate in the initial plant design. To date, the largest pour the plant produced was between 1,200 and 1,300 yards.
In 2005, the Corps contracted with Trumbull Corporation to construct the concrete batch plant for construction on four Monongahela River locks and dams as part of the lower Mon project. Trumbull used the plant until the contract expired, the Corps would take over responsibility.
In June 2005, construction of the plant was initiated with the removal of coal on the site from the previous plant. Once cleared, paving of the entire site started with a scheduled completion date of 10 weeks according to Pennsylvania Department of Environmental Protection Agency restrictions.
Construction of the plant began in October 2005. In June 2006, the plant was complete, and the first batch of concrete was produced. The plant was designed to have a production rate of 150 yards-per-hour and operates with an EPA, National Pollutant Discharge Elimination System permit, which is an industry standard all industrial concrete plants must follow.
Bush said the plant is very efficient.
"A batch plant is a complicated series of machines that must work in harmony to produce the desired product," Bush said.
The plant consists of interconnected components, working together to create a high-quality concrete mix. A roof over each aggregate bin with an overhead sprinkler system ensures constant moisture control, and ensures a better concrete mix. There are four different aggregate types used within the mix with three course: three-quarter inch ASHTO #67 small aggregate, three-quarter -- 1 1/2 railroad ballast aggregate, 1 1/2 -- three-inch ASHTO #1 large aggregate, and one fine aggregate - Georgetown sand. In addition to the aggregate, the concrete mix may also use up to five different cements at any given time depending upon projects.
The plant is able to use less cement yet it still acquires remarkable breaking strengths not only because the aggregates maintain a constant moisture rate but also because it meets the temperature requirement of 65 degrees Fahrenheit.
Another interesting feature of the plant is its ability to create a concrete mix that meets the temperature requirements during all seasons. This is accomplished by using a sand cooling system the summer and a heat exchanger during the winter. When installed, the ice cooling system was only the second one in use in North America.
It consists of a wet belt that works with an air conditioner in a sand cooler. The system eliminates the need for traditional ice houses. The rotating sand cooler moves sand through chilled air to lower its temperature. Additionally, a flooded wet belt moves coarse aggregate through a bath of 37-degrees-Fahrenheit water, lowering the aggregate's temperature.
The same system can be used in the winter to warm the raw materials with the heat exchanger, which is connected to a steam boiler. This allows continued production during the fall and winter months.
All water used on-site is taken from the river.
Trucks entering or leaving the plant are required to go through a truck wash to prevent foreign materials from entering the plant or any materials from leaving the site. All water, used for the truck wash or in the plant's two acre area site, is pumped into a water treatment facility on site. The water goes through a settling pond and then through a filtration system where the pH is tested. Once the water passes all EPA regulations, it is returned back into the river.
Additionally, there is also an on-site concrete testing facility that is shared between the government and the contractors located on the plant site.
Since it's a shared facility, all quality assurance and quality control representatives are able to do testing simultaneously. The types of testing performed include quality testing, grading, washing, absorption and specific gravity testing.
The facility is operated and maintained to meet commercial standards although not required.