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Concrete...

The Environment & Recycling

Did you know that 140 million tons of concrete are recycled each year in the United States alone?

Concrete recycling is becoming an increasingly popular way to utilize aggregate left behind when structures or roadways are demolished. In the past, this rubble was disposed of in landfills, but with more attention being paid to environmental concerns, concrete recycling allows reuse of the rubble while also keeping construction costs down.

Why Recycle Concrete?

  • It's high quality - meeting or exceeding all applicable state and federal specifications

  • It's an accepted source of aggregate into new concrete by ASTM and AASHTO

  • It's currently being used in concrete and asphalt products with better performance over comparable virgin aggregates

  • It provides for superior compaction and constructability

  • It's higher yield - recycled aggregates are lighter weight per unit of volume, which means less weight per cubic yard, resulting in reduced material costs, haul costs, and overall project costs

  • It weighs ten to fifteen percent (10%-15%) less than comparable virgin quarry products (concrete)

  • It offers a way to reduce landfill waste streams

  • It means minimization of environmental impacts in an Urban Quarry setting.

Uses of Recycled Concrete Aggregate

Aggregate base course (road base), or the untreated aggregates used as foundation for roadway pavement, is the underlying layer (under pavement surfacing) which forms a structural foundation for paving. A cross-section of pavement would show dirt, or subgrade, as the lowest of three levels, with aggregate base course at the center and pavement (whether concrete or asphalt) at the surface. This is the major market in the U.S. and can be mastered as the simplest and easiest use of recycled concrete. To date, it is also the most owner accepted use of recycled concrete by Departments of Transportation.

Other applicable uses include Ready Mix concrete, soil stabilization, pipe bedding and as a landscaping material (boulder/stacked rock walls, underpass abutment structures, erosion structures, water features, retaining walls, and more).

The Barriers

Inexperience with recycled aggregate products due to lack of exposure still remain a surmountable barrier to the recycled concrete market. In the recycled concrete aggregate industry, itís a new world since the early 1980s. The Federal Highway Administration (FHWA), Federal Aviation Administration (FAA), Army Corps of Engineers, Environmental Protection Agency (EPA), state Departments of Transportation (DOTís) and many municipalities are now using recycled aggregate to varying degrees. But not everyone is maximizing the use and advantage of recycled concrete aggregate materials.

The Benefits

  • Produce specification sized recycled aggregates at your location

  • Avoid haul-off costs and landfill disposal fees

  • Eliminate the expense of aggregate material imports and exports

  • Increase project efficiency and improve job cost - recycled concrete aggregates yield more volume by weight (up to 15%)

  • Minimize impact to community infrastructure by reducing import and export trucking

The Construction Materials Recycling Association (CMRA)

The Construction Materials Recycling Association (CMRA) has developed a website which contains all of the available information necessary to assist you and answer questions about recycling  concrete aggregate. We encourage you to visit this site and start planning for your concrete recycling future.

 

Fly Ash Facts for Highway Engineers

Coal fly ash is a coal combustion product that has numerous applications in highway construction. Since the first edition of Fly Ash Facts for Highway Engineers in 1986, the use of fly ash in highway construction has increased and new applications have been developed. This document provides basic technical information about the various uses of fly ash in highway construction.

Fly ash is used in concrete admixtures to enhance the performance of concrete. Portland cement contains about 65 percent lime. Some of this lime becomes free and available during the hydration process. When fly ash is present with free lime, it reacts chemically to form additional cementitious materials, improving many of the properties of the concrete, including.

  • Higher ultimate strength

  • Improved workability

  • Reduced bleeding

  • Reduced heat of hydration

  • Reduced permeability

  • Increased resistance to sulfate attack

  • Increased resistance to alkali-silica reactivity (ASR)

  • Lowered costs

  • Reduced shrinkage

  • Increased durability

 Read the full details here.


Tires Used as Energy Source in Cement Manufacturing

 

Did you know that 58 million tires were used as fuel in cement kilns in 2005? Those tires are removed from the waste stream permanently.

 

Tires for recyclingAn Alternative to Traditional Fossil Fuels

The Rubber Manufacturers Association (RMA) has estimated that 58 million scrap tires were used as fuel in portland cement plants in 2005 out of the 299 million tires produced that year [RMA 2006]. The United States Environmental Protection Agency (USEPA) states that tire-derived fuel (TDF) contains about the same amount of energy as oil and 25% more energy than coal [USEPA 2007b]. This means that each ton of TDF used by a portland cement plant has the potential to replace 1.25 tons of coal, and the impacts of coal mining, processing, and transporting are avoided. In energy terms, the cement industry consumed 12.6 trillion BTUs of TDF in 2006 which is approximately 3.6% of all of the non-electrical energy required by the manufacturing process [PCA 2007a].

Beneficial Effects

 

The environmental benefits of utilizing scrap tires as a supplemental fuel in the portland cement manufacturing process are multifold. When whole tires are combusted in cement kilns, the steel belting becomes a component of the clinker, replacing some or all of the iron required by the manufacturing process. In 2008, PCA member companies completed a study on the impact of TDF firing on cement kiln air emissions. The studyís data set included emission tests from 31 of the cement plants presently firing TDF. Dioxin-furan emission test results indicated that kilns firing TDF had emissions approximately one-third of those kilns firing conventional fuels Ė this difference was statistically significant.

For more information

Contact ACPA-Southwest or the Portland Cement Association at www.cement.org

 

Disclaimer:

All of the information on this page, with the except of the information on tire recycling, was provided by
The Construction Materials Recycling Association (CMRA).

   

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