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Much of the U.S. investigation focused on using crushed, hardened concrete as an aggregate in fresh concrete has been in mainline paving. Work on this topic started with a major endeavor in the 1980s in Minnesota. Sorry to say, most of the exploration focused on using recycled concrete aggregate (RCA) as a foundation material to the pavement. But in other areas of the globe, many accept RCA as a important aggregate source when correctly intregated into the mix design development. For example, Japan has used RCA for more than 20 years in structural concrete applications. RCA can be used in effect in structural concrete. Dr. A. Ghani Razaqpur, a professor and lead of the Civil Engineering Department at McMaster University in Hamilton, Ontario, gave a presentation at the 2008 Concrete Technology Forum, sponsored by NRMCA in May in Denver. Razaqpur conflicts the perception that concrete (plain or reinforced) prepared with RCA has inherently substandard short- and long-term components. He supported his contention by highlighting the outcome enclosed in the article, "The Key to the Design and Manufacture of High Quality Structural-Grade Recycled Aggregate Concrete." Razaqpur described how his group examined 14 different mix designs using RCA. They examined fresh and hardened properties (slump, fresh and hardened density, elastic modulus, compressive strength, stress-strain relationship, creep, and shrinkage) and compared the results to alike reinforced concrete prepared with fresh structural concrete. The outcome of his work is a unique mix-proportioning procedure for concrete made with coarse recycled concrete aggregate, in which RCA is regarded as a two-phase material comprising mortar and organic aggregate. The remaining mortar in RCA is considered part of the overall mortar (fresh plus remaining mortar) in the mix. "By testing an widespread number of specimens, we have demonstrated that the proposed method would result in creating high-quality, structural-grade concrete, with predictable outcome," said Razaqpur. Razaqpur hopes this new approach to mix proportioning will support using RCA in structural concrete. At the same event, Bill Palmer, senior engineer at Complete Construction Consultants, a Boulder, Col.-based consulting company, presented some additional resources for information on using recycled aggregates in concrete. He listed several organizations that can provide help and technical information: The first occasion I'd seen one, was outside a restaurant where I lived and they did a pretty respectable job, using the pieces of an aged sidewalk, productively. I never observed anything like this before and like most of us know, there's a first point for everything. Building concrete stairs by means of recycled materials got me thinking about other things that we can construct with recycled building products. People are not just using recycled concrete for stairways, they are using them for small retaining walls. Recycled concrete retaining walls and stairways can be constructed from slight to sizeable sections of damaged sidewalks and driveways. Simply place the destroyed pieces into attractive patterns, until you have something that functions as a flight of steps. Start from the substructure and work your way up, until you have formed a beautiful recycled concrete stairway. If you're planning on building a retaining wall out of old concrete, plainly stack these materials on top of each other, until you've formed the retaining wall, you envisioned. I do not recommend building retaining walls higher than twenty four ins with these types of materials.
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Recycled Concrete Reinforced Concrete
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