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Concrete Is Ubiquitous in Our World Today

Concrete is ubiquitous in our world today. According to the Cement Sustainability Initiative (CSI), concrete is second only to water as the most-consumed material on earth, and twice as much concrete is used in construction worldwide than all other building materials combined. As a result, concrete accounts for hundreds of millions of tons of construction and demolition (C&D) waste each year, and with greater environmental awareness and stricter landfill regulations, concrete recycling is becoming increasingly important.

Why recycle concrete?

There are two main environmental and financial benefits to recycling concrete: 1) landfill waste is significantly reduced; 2) use of recycled concrete aggregate reduces the need for natural materials and the associated mining and transportation costs. Recycling of C&D debris, including concrete, is worth 1-2 LEED points.

What are some of the uses for recycled concrete?

Most recycled concrete is used as aggregate base and sub-base for roadways, as it has equal or superior compaction properties as compared to primary aggregates, and is generally less expensive. Recycled concrete aggregate can be used over geotextile fabric as a soil stabilizer on construction projects to increase the load-bearing capacity of the subgrade, and can replace natural aggregate as bedding for pipes and other underground utilities. Recycled concrete can also be used as a landscaping material, in retaining walls, to control erosion, in artificial reefs, and in underpass abutment structures.

Use of recycled concrete as an aggregate for structural concrete is slowly on the rise as researchers work to improve concrete formulas and methods of aggregate processing. Currently, recycled aggregate is mainly used in ready-mix concrete.

How is demolition concrete recycled?

Concrete must be sorted on-site and separated from other C&D materials, then either processed on-site using mobile equipment, or transported to an off-site facility, which can usually produce a higher-quality aggregate. Contaminated concrete (determined through pre- or post-demolition sampling) must be segregated and handled as hazardous waste.

After concrete has been reduced to a manageable size, it is run through a crusher. Magnets or other mechanical means are used to extract metals, such as steel rebar, which is recycled as well. The crushed concrete can then be used as-is, or, for a higher grade aggregate, it can be further screened and subjected to water floatation, hand picking, air separators, and electromagnets to remove remaining dirt, metal, and foreign particles.

Source: http://goarticles.com/article/Clearing-The-Waste-Stream-With-Concrete-Recycling/8651605/
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Clearing The Waste Stream with Concrete Recycling
Topics: Machinery