Two for the Price of One

Recycled concrete aggregate proves its value; but it demands an engineered approach.

By Tom Kuennen, Contributing Editor

Recycled concrete aggregate (RCA) is a valuable resource for road owners and builders, both in terms of lowering costs and in constructing a “green” highway. But RCA needs to be approached as an engineered product, with its production and reuse tailored to fit its composition and ultimate end use in a project.

Fortunately, new guidance is available that will help road owners and builders make decisions on how to use RCA, even as its utilization is growing on vast scales, for example the recently completed reconstruction and widening of I-294, the TriState Tollway in suburban Chicago.

Despite being blessed with extensive virgin aggregate sources, Texas is a strong supporter of RCA. In a September 2008 report, Recycled Concrete Aggregates Make ‘Cents’, the Texas DOT said, “In today’s environment of skyrocketing material and transportation costs encountered in road construction, recycled concrete aggregates (RCA) provide substantial savings to TxDOT and taxpayers.”

With RCA, natural resources are conserved, waste disposal is reduced, and air quality is improved due to reduced haul distances and reduced energy consumption, TxDOT said. “In many cases, allowing the use of RCA can be the most cost-effective choice for an aggregate source,” the DOT said. “This is especially true for those districts that do not have good, native aggregate sources. Using RCA can reduce time and expense of importing aggregates from other parts of the state.”

TxDOT has researched and used RCA with good success for about 17 years. In the years 2006-2008, TxDOT saved approximately 1.8 million tons of virgin aggregates by incorporating RCA in cement treated base, flexible base, continuously reinforced concrete pavement (CRCP), filter dams, gabion walls, concrete traffic barriers, flowable fill and select backfill for mechanically stabilized earth walls. “This equates to an estimated savings of $12.6 million from reduced or eliminated landfill and virgin aggregate associated costs. Savings from using RCA has the potential to increase tenfold based on current availability of RCA.”

RCA an Engineered Material

But care must be taken in specifying and using RCA in road structures and concrete mixes.

“Concrete pavement recycling is a viable, successful and proven technology,” said Mark B. Snyder, Ph.D., P.E., vice-president, Pennsylvania chapter of the American Concrete Pavement Association (ACPA), adjunct professor at the University of Pittsburgh, and 2010 president of the International Society for Concrete Pavements.