Recycled Concrete Slab gains significance because it protects environmental resources

Much of the U.S. research focused on using crushed, hardened concrete as an aggregate in fresh concrete has been in highway paving. Work on this topic began with a major endeavor in the 1980s in Minnesota. Sorry to say, most of the research focused on using recycled concrete aggregate (RCA) as a base material to the pavement.

But in other locations of the globe, many accept RCA as a valuable aggregate source when suitably intregated into the mix design procedure. For instance, Japan has used RCA for more than 20 years in structural concrete applications.

RCA can be used successfully 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 conflicts the belief that concrete (plain or reinforced) made with RCA has inherently low-grade short- and long-term properties. He supported his allegation by highlighting the results enclosed in the article, "The Key to the Design and Manufacture 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 outcome to comparable reinforced concrete made with fresh structural concrete.

The outcome of his effort is a unique mix-proportioning method for concrete made with coarse recycled concrete aggregate, in which RCA is treated as a two-phase material comprising mortar and organic aggregate. The residual mortar in RCA is considered part of the total mortar (fresh plus residual mortar) in the mix. "By testing an extensive number of specimens, we have demonstrated that the projected technique would result in creating high-quality, structural-grade concrete, with predictable outcome," said Razaqpur.

Razaqpur hopes this new method to mix proportioning will promote using RCA in structural concrete.

At the same event, Bill Palmer, senior engineer at Total Construction Consultants, a Boulder, Col.-based consulting company, offered some additional resources for information on using recycled aggregates in concrete. He listed quite a few organizations that can present help 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, 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 regarding other things that we could build 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 built from slight to big sections of broken sidewalks and driveways.
Simply position the destroyed pieces into attractive shapes, until you have something that functions as a stairway. Start from the bottom and work your way up, until you've formed a beautiful recycled concrete stairway.

If you're planning on building a retaining wall out of second-hand concrete, merely stack these materials on top of each other, until you've produced the retaining wall, you envisioned. I do not advocate building retaining walls higher than 24 in. with these kinds of materials.

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