Q: Our county water department recently announced plans to build a new facility. This high-profile project would be the perfect opportunity to present the advantages of a performance-based mix design.

What are some of the aspects we should focus on? How should we tout the benefits of performance-based mixes? And are you aware of any recent water treatment projects using such mix designs?

A:It sounds as if you are early enough in the design process to create an excellent opportunity to tout the benefits of performance based mix designs. One way to start is to educate the engineers on how performance-based specifications can be used to enhance a project. The NRMCA has posted several useful promotional tools and brochures on this subject for download on its Web site at www.nrmca.org/p2p.

Regarding any ongoing projects, we recently heard of the construction of a new wastewater treatment plant begun in February in Delphos, Ohio. The $30 million project includes about 12,000 yards of 4000 psi, low initial slump concrete, and 800 tons of rebar.

The mix design includes 25% slag of the total cementitious materials and course aggregate utilizing size 57 crushed limestone. The slump was adjusted to 8 inches with a superplasticizer, Catexol 1000 SP-MN by Axim. The caps for the wastewater treatment tanks used a double mat of rebar size #7 and #4 placed to help the concrete bridge the interior of the tank.

K&L Ready Mix transported the concrete to the construction site from its plant in nearby Kalida.

An interesting feature of this plant is its use of a membrane bioreactor (MBR), a new type of wastewater treatment technology in the United States. The MBR system will include 52,000 individual filtering membranes effectively filtering up to 12 million gallons of sewage per day.

Upon completion of the new plant in fall 2006, the previous plant will become part of the city.