Writer: Dan Trujillo
The Mesilla Valley's abundant supply of pecan shells may some day be used in the construction of new, low-cost homes.
Khaled Sobhan and David Jauregui, both assistant professors in New Mexico State University's Civil, Agricultural and Geological Engineering (CAGE) department, are using $25,000 of Department of Energy seed money to study whether crushed pecan shells can be used to form walls that are strong enough to support a house.
The team of NMSU researchers -- along with researchers from the U.S. Department of Energy, the University of Waterloo in Ontario, Canada, and adobe experts from Northern New Mexico Community College -- are studying a concept that stacks layers of polypropylene tubes filled with various waste materials such as crushed pecan shells, sawdust, pumice and bottom ash to build a four-wall house. The team then hopes to use a $150,000 DOE grant extension to study the walls under natural weather conditions over a period of three years.
"The test house will be what I call a Smart Building," Sobhan said. "It will be wired with sensors so we can remotely monitor the characteristics of the walls."
The polypropylene tube system is called a QuickFill wall and the DOE patents the technology, Sobhan said. "This is an attempt to develop low-cost, energy efficient residential housing."
After completing preliminary research on the engineering behavior of several candidate waste materials, the research team began construction of the first full-scale, 10-foot-by-10-foot wall using crushed pecan shells Aug. 10 in NMSU's structural testing laboratory. The building of the wall was planned and supervised by Jauregui and Arun Vohra, a DOE program manager from Washington, D.C.
"The idea is to be able to build homes that are affordable and energy efficient," Vohra said. "This area (the Mesilla Valley) has an abundant supply of pecan shells, so we want to know if they can be used in construction."
Quentin Wilson, an adobe instructor at Northern New Mexico Community College in El Rito, N.M., is the general contractor for the project. Wilson's private firm, Quentin Wilson and Associates, specializes in solar adobe design and construction.
"If walls can be made out of sand and straw, then they can probably be made out of crushed pecan shells," Wilson said.
Building walls from pecan shells is obviously new to the research team. Researchers first used a branch shredder to grind the shells down to a sand-like material and then used a blower to fill the polypropylene QuickFill bags with the crushed shells. The bags were then "dry stacked," layered horizontally, to form 8-foot walls. Preliminary tests show the pecan shell walls can handle 30 pounds per square inch of pressure. Manufactured walls are only required to test at two and a half to five PSI.
"We would like to show that dry stacking is strong enough for construction," Vohra said. Eventually, the QuickFill bags would be reinforced with pins or rebar. The walls will then undergo a series of tests that include a racking test, wind pressure test and vertical load test.
"The objectives of the research program include the construction of the single test wall and subsequent structural evaluation to assess the out-of-plane and in-plane load bearing characteristics," Jauregui said. "Ultimate long-range goals include testing and evaluation of more isolated walls, construction and long-term performance monitoring of an instrumented four-walled home, and seeking building code approval for this innovative building technology."
Jauregui said the pecan shell wall's R-value, the measure of the capacity of a material to impede heat flow, is expected to be high and will be tested at an independent laboratory.
A reliable source of pecan shells is quite possibly the easiest task the research team faces. Southern New Mexico's Mesilla Valley is home to the 180,000-tree Stahmann Farms, considered the largest pecan orchard in the world, and several thousand acres of other privately owned pecan orchards.
Other members of the research team include consultant John Straube, an assistant professor in the Department of Civil Engineering and School of Architecture at the University of Waterloo, and seven members from the Treasure Lake Job Corps stationed in Oklahoma.
Photo is available at http://kiernan.nmsu.edu/newsphoto/pecan_shell_wall.jpg
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CUTLINE: Khaled Sobhan, left, and David Jauregui, assistant professors in New Mexico State University's civil, agricultural and geological engineering department, look over the polypropylene QuickFill tubes that are used to build the pecan shell walls. (NMSU photo by Michael Kiernan)
Sept. 5, 2000
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