Aggregate Industries Northeast Region continues to monitor the results of their pervious concrete test strip installed at the Berlin, Mass. Ready Mixed Concrete plant. The test strip was placed last summer with the goal of monitoring the performance of the product over the course of the sometimes harsh freeze-thaw cycles experienced during a New England winter.
Pervious concrete is primarily used to help manage storm-water runoff and allows builders to utilize more land for development resulting from the reduction or elimination of retention ponds and drainage systems. Pervious concrete, also know as porous concrete, is a no-fines mix, produced with little or no sand or fine aggregates. The product allows water to drain down into a drainable base.
The Berlin test was designed to collect runoff from the asphalt pavement onto the pervious concrete strip, then draining down through the pervious pavement into a crush stone reservoir. The construction division was a key partner in the test, excavating a 10-ft-wide trench over 100 ft in length to a depth of 36 in. and installing a filter fabric on the bottom and sides of the trench. More than 2 ft of crushed stone was placed in the trench to create the reservoir. The trench was then filled with pervious concrete, placed by an asphalt paving machine fed by several ready-mix trucks, resulting in an 8-in. lift of pervious material in the trench. In total, the test strip used over 70 cu yd of pervious concrete.
Across the U.S., tests have been conducted by placing pervious concrete by hand or by a non-automated spreader box, but this was one of the few known tests conducted using a fully automated asphalt paver. The pervious mix design utilized 1/2-in. crushed stone, ASTM C-150 Type II cement, ASTM C-618 Class F fly ash and a special viscosity modifying additive (VMA). The 28-day strength averaged 4,100 psi. Six 4x8 plastic cylinder molds filled in one layer and crews tapped on the outside of the mold 10 times with a rubber mallet. The tops were screeded and leveled off with a trowel.
It is important to note that pervious concrete is an integral part of a storm-water management system, and important conditions like the amount of water runoff and subsurface soil conditions are important factors in the successful implementation of a storm-water management solution.
The successful testing of the pervious concrete mix design and placement technique creates a strong market opportunity, especially in light of the city of Boston's pending mandate relating to Green Building. The city’s new standards will be required before permits are issued for all projects of 50,000 sq ft or more. The goal is to make new buildings more energy efficient and environmentally friendly. Many other large cities around the U.S. have set green building standards for public buildings or publicly funded projects, but Boston would be the first to impose these conditions on privately developed properties too.