Rock Products

MAR 2013

Rock Products is the aggregates industry's leading source for market analysis and technology solutions, delivering critical content focusing on aggregates-processing equipment; operational efficiencies; management best practices; comprehensive market

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Page 23 of 99

SPECIAL REPORT RECYCLED CONCRETE AGGREGATE A SUSTAINABLE CHOICE FOR UNBOUND BASE. By Cecil Jones This article is adapted from a recently released white paper by the Construction Materials Recycling Association. It was researched and written by Cecil Jones, retired chief materials engineer at the North Carolina Department of Transportation, and is designed to provide guidelines on overcoming the objections of highway officials to using recycled aggregates as a base product. The complete document is available for free to CMRA members. ���Ed. A ggregates play a major role in the construction industry as they are the major component of roadways, bridges, airport runways, concrete buildings, drainage systems, and many other constructed facilities. Because aggregates are the major com��� ponent of much of the nation���s infra��� structure, their use is engineered to provide the necessary performance in place. For instance, concrete is approxi��� mately 75 percent aggregate, and the proportioning and properties are criti��� cal to the performance of the finished product. In the past, when concrete structures reached the end of their service life or needed to be repaired or replaced, the resulting materials were considered waste and were disposed of in em��� bankments and landfills. The costs of transporting these materials to waste areas were considered a necessary part of the replacement work. Likewise, the costs associated with the mining of new aggregates, the production of the replacement concrete, and the trans��� portation and placement at the project were also considered a necessary part of the work. Considering these costs, along with increasing tipping fees and diminishing landfill space, many trans��� portation agencies are moving toward recycling construction demolition de��� bris as an aggregate with performance characteristics equal to, if not better than, virgin aggregates. The properties of the original aggregates do not change because of being a part of a 22 ROCKproducts ��� MARCH 2013 concrete that has been crushed. Be��� cause of the existence of un���hydrated cement in the concrete, Recycled Con��� crete Aggregate (RCA)���base courses may exhibit higher strength than one with virgin aggregates. RCA offers an alternative to wasting concrete elements that are no longer in service. A State of Practice Review by the Federal Highway Administration found that RCA is a ���valuable resource��� that should not be wasted. (FHWA, 2004) The origin of the concrete from which RCA is produced includes the demolition of transportation structures such as existing concrete pavement and runways, total or partial demoli��� tion of bridge structures, curb and gut��� ter, sidewalks and drainage structures. The concrete can also be obtained from commercial sources ranging from building demolition to excess concrete returned to concrete plants that has been discharged in a waste pile and has hardened. The production of RCA from concrete demolition debris includes several processes. The concrete material is ei��� ther stockpiled on site and a mobile processing operation set up, or trans���

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