全部博文（136）
2012年（136）
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2012-03-06 15:22:10
Concrete from roads, pavements, airfield runways, buildings, and other sources can be crushed for reuse. After crushing, magnets remove the steel rebar and the resulting aggregates are screened according to planned use. The crushed concrete produces hard, granular aggregates composed of inert mineral materials including sand, gravel, and aid crushed stone.
The American Concrete Pavement Association estimates that approximately 322 kilometers of concrete pavement is being recycled each year and approximately 5.440 metric tons of crushed concrete can be reclaimed from 1.6 km of concrete pavement with an average thickness. This shows that 2.6 million metric tons of reclaimed concrete is being recycled annually in the United States.
TxDOT has specifications that allow crushed concrete to be used in flex base, cement-stabilized base, and riprap. Additionally, crushed concrete can be used as coarse aggregates in Portland Cement Concrete and as fine aggregates in asphalt stabilized base.
Recycling of Portland cement stated in Europe after World War. With time and through necessity, recycled aggregates have become increasingly acceptable as road construction. It is estimated that approximately 100 million tons of concrete nibble is generated annually in the st1:country-region w:st='on' United States. Tins amount is projected to exceed 150 million by the year 2000. Landfill life will be unnecessarily shortened if this volume of nibble is dumped there; furthermore, a valuable material will be wasted if not recycled into usable aggregate products.
IN comparison with the national annual aggregate production of more that 2 billion tons, concrete nibble represents only 5 percent of the aggregate market if it is all recycled. Since some nibble is lost during demolition and some will be disposed of in landfills, recycled concrete aggregate is probably less than 3 percent of the total aggregate market. Crushed concrete, none-the-less represents significant opportunities for economic and environmental benefits.
The Center for Transportation Research (CTR) of the University of Texas at Austin conducted a study on recycled materials for TxDOT. According to its findings, Phan district had the biggest stockpile (3.624 metric tons) of old concrete. Nine of the twenty-one TxDOT districts responded to the survey already had stockpiles of crushed concrete and nineteen districts believed that old concrete could be used as road-base material. TxDOT engineers from Abilene, Atlanta, Beaumont and Dallas districts rated the performance of concrete as excellent and professional final product manufactured by Hongxing .
Recycling of old concrete pavement has become an important issue as more concrete pavement reaches the end of its functional and structural life. Currently, economic considerations are the primary thrust for the use of recycled concrete aggregate (RCA) in Portland cement concrete (PCC) pavement. However, as landfill spaces become scarcer and more expensive, environmental considerations will play an important role as well.
The section of IH10 in Houston District between Loop 610 and IH 45 is under reconstruction. The contractor decided to use 100 % of RCA in the new pavement concrete. This project is the first one in the nation where all the aggregates used for pavement concrete crushed by , both coarse and fine, are recycled with no virgin aggregates used. As such, there is not much information available regarding the performance of PCC pavement with 100% RCA.
