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Much of the U.S. exploration focused on using crushed, hardened concrete as an aggregate in fresh concrete has been in major road pavement. Work on this matter began with a major effort in the 1980s in Minnesota. Regrettably, most of the exploration focused on using recycled concrete aggregate (RCA) as a base material to the pavement. But in other areas of the world, many acknowledge RCA as a effective aggregate source when properly intregated into the mix design process. For example, Japan has used RCA for more than 20 years in structural concrete applications. RCA can be used for practical purposes 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 disputes the perception that concrete (plain or reinforced) made with RCA has inherently low-grade short- and long-term components. He supported his statement by highlighting the results enclosed in the paper, "The Key to the Design and Construction of High Quality Structural-Grade Recycled Aggregate Concrete." Razaqpur described how his team examined 14 different mix designs using RCA. They examined fresh and hardened components (slump, fresh and hardened density, elastic modulus, compressive strength, stress-strain relationship, creep, and shrinkage) and compared the results to related reinforced concrete prepared with fresh structural concrete. The outcome of his work is a novel mix-proportioning method for concrete prepared with coarse recycled concrete aggregate, in which RCA is treated as a two-phase material comprising mortar and natural aggregate. The remaining mortar in RCA is considered part of the entire mortar (fresh plus residual mortar) in the mix. "By testing an broad number of specimens, we have demonstrated that the proposed procedure would result in generating high-quality, structural-grade concrete, with predictable results," said Razaqpur. Razaqpur hopes this new approach to mix proportioning will promote using RCA in structural concrete. At the same event, Bill Palmer, senior engineer at Complete Construction Consultants, a Boulder, Col.-based consulting company, presented a number of supplementary resources for information on using recycled aggregates in concrete. He listed quite a few organizations that can give assistance and technical information: The first occasion I'd seen one, was outside a restaurant where I lived and they did a pretty first-class job, using the pieces of an old sidewalk, ingeniously. I never observed something like this before and like the majority of us know, there is a first point for everything. Building concrete stairs by means of recycled materials got me thinking regarding other things that we may perhaps construct with recycled building products. People are not just using recycled concrete for stairways, they're using them for minor retaining walls. Recycled concrete retaining walls and stairways can be built from little to large sections of damaged sidewalks and driveways. Simply position the ruined pieces into attractive designs, until you have something that functions as a flight of steps. Start from the bottom and work your way up, until you have produced a beautiful recycled concrete stairway. If you are planning on building a retaining wall out of old concrete, basically stack these materials on top of each other, until you've created the retaining wall, you envisioned. I do not suggest building retaining walls higher than twenty four inches with these types of materials.
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Recycled Concrete Reinforced Concrete
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