Better Roads

May 2014

Better Roads Digital Magazine

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Better Roads May 2014 5 G eosynthetics comprise a family of value-added products that allows bridges, highways and roads to be built faster, cheaper and to last longer. Some geosynthetics enhance pavement longevity by sepa- rating good materials from bad, while others promote water fl ow from pavement structures as they facilitate drainage. While most geosynthetics are planar or sheet-like in for- mat, 3D geogrids add structural strength to a road section, permitting reduced depths of aggregate bases and bituminous lifts. Family of geosynthetics ASTM (2006) D 4439 defi nes a geosynthetic as a "planar prod- uct manufactured from a polymeric material used with soil, rock, earth or other geotechnical-related material as an integral part of a civil engineering project, structure or system." "Geosynthetics are man-made polymeric materials used for geotechnical application," says the California Department of Transportation (Caltrans) in its Caltrans Geotechnical Manual. "They are used in lieu of conventional materials and often are more cost effective with equal or improved engineering performance." "Geosynthetics are materials that are incorporated into layers of rock or soil that can provide stabilization as well as separation of good material from lesser material," says Aaron Schlessinger, E.I.T., southwest region manager for Tensar In- ternational Corp. "Still, others enhance drainage." There are four different types of geosynthetics: • Geotextiles are either woven or nonwoven and used in civil engineering projects. Their mission is to prevent soils from migrating into drainage aggregate bases or pipes, while maintaining water fl ow through the system. They are used for fi ltration, drainage, separation, reinforcement Geosynthetics of all types speed construction allowing bridges, highways to be built faster and enhance pavement performance Down to Earth Down to Earth Photo courtesy of Tensar RoadScience by Tom Kuennen, Contributing Editor On Arizona's U.S. 89T emer- gency bypass construction in 2013, aggregate base is spread over triaxial geogrid above a graded base. The use of geogrid cut one-third of the cost of the aggregate base.

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