Rubber Technology International (fka RTEK)

[timhyma]

Researcher Finds Use for Waste Tires








TEMPE, AZ, September 14, 2001 - The US each year produces about 240 million used tires and due to their physical makeup and size, disposal is sometimes problematic. In some instances, tires are accumulated in "tire piles" that can harbor vermin and mosquitoes in addition to being dangerous fire hazards. Instead of worrying about disposal of all of these tires, an Arizona State University researcher has an idea for recycling them - and if his idea is put to use, all of the used tires produced in his home state each year could be reused.

Civil and Environmental Engineering Assistant Professor Han Zhu's research has shown that rubber, when ground into one-millimeter chunks (called crumb rubber), can be added to Portland cement concrete (PCC) with good results. Although past researchers have worked with this combination in the lab without great results, Zhu has put his research into action by incorporating crumb rubber into a section of sidewalk on campus.

Past researchers were not happy with this mixture because the overall compressive strength of PCC is lowered by adding the crumb rubber, but Zhu's test has shown the benefits afforded to the concrete outweigh the losses, especially if the PCC is not being used in a loadbearing situation. These benefits include reductions in thermal expansion, drying shrinkage and brittleness caused by the hot Arizona environment. The rubber also acts to buffer the concrete from the freeze/thaw damage prevalent in colder climates. In addition, the compressive strength of the PCC can be restored by adding a small amount of gypsum to the mix.

The university test plot has been in place since 1999 and Grounds Construction Supervisor Andy Castillo said from his own observations the crumb rubber PCC appeared to avoid cracking better than its original counterpart.

According to the Arizona Cement Association, within the Phoenix metro area, some 12,000 cubic-yards of PCC are produced each day. By conservative estimates, if just 20 pounds of crumb rubber per cubic yard of fresh PCC were added, all 5 million scrap tires produced annually statewide could be recycled into stronger and more pliable PCC for use in sidewalks, parking lots and concrete floors.

In addition to Zhu's sidewalk, the Arizona Department of Transportation in May used the new PCC technology in the construction of a parking lot at its Phoenix Division site using 50-pounds of crumb rubber per cubic yard of PCC. Zhu says the outlook for that project is good.

http://sports.yahoo.com/m/environmental/news/getf/20010914/getfresearcherfindsuseforwas.html