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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 mainline paving. Work on this matter started with a major effort in the 1980s in Minnesota. Unfortunately, the majority of the study focused on using recycled concrete aggregate (RCA) as a base material to the pavement. But in other locations of the world, many recognize RCA as a important aggregate resource when suitably intregated into the mix design development. For instance, 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 chair 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) prepared with RCA has inherently low-grade short- and long-term properties. He supported his declaration by highlighting the results contained in the paper, "The Key to the Design and Construction 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 components (slump, fresh and hardened density, elastic modulus, compressive strength, stress-strain correlation, creep, and shrinkage) and compared the results to alike reinforced concrete prepared with fresh structural concrete. The outcome of his effort is a unusual mix-proportioning method for concrete made with coarse recycled concrete aggregate, in which RCA is handled as a two-phase material comprising mortar and organic aggregate. The remaining mortar in RCA is considered part of the overall mortar (fresh plus residual mortar) in the mix. "By testing an extensive number of specimens, we have demonstrated that the projected approach would result in creating high-quality, structural-grade concrete, with predictable outcome," said Razaqpur. Razaqpur hopes this new method to mix proportioning will support using RCA in structural concrete. At the same event, Bill Palmer, senior engineer at Total Construction Consultants, a Boulder, Col.-based consulting corporation, offered some additional resources for information on using recycled aggregates in concrete. He listed a number of organizations that can provide aid and technological information: The first occasion I'd seen one, was outside a restaurant where I lived and they did a pretty respectable job, using the portions of an old sidewalk, innovatively. I never seen something like this before and like the majority of us know, there's a first time for everything. Building concrete stairs by means of recycled materials got me thinking regarding other things that we may well build with recycled building products. People are not just using recycled concrete for stairways, they are using them for minor retaining walls. Recycled concrete retaining walls and stairways can be designed from minor to big sections of ruined sidewalks and driveways. Simply place the ruined pieces into decorative designs, until you have something that functions as a flight of steps. Start from the substructure 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 second-hand concrete, just stack these materials on top of each other, until you have formed the retaining wall, you envisioned. I do not recommend 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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