Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/86539
RoadScience On concrete, the FWD can indicate load-transfer effi - ciency across joints. For all pavements it can test the entire structural capacity of the road, or by using backcalculation, use the raw load and defl ection data to determine the stiff- ness of each of the layers in the pavement system. "The FWD will not tell you depth," Clyne says. "You either have to know that from the plans, take cores, or use ground penetrating radar." Highway Administration. The arrival time and strength of these echoes can be used to calculate pavement layer thick- ness and other properties, such as moisture content. "Coring may have some degree of effectiveness for specifi c projects, but at a network level it is costly, intrusive to traffi c, and provides very limited samples of the actual pavement structure," says Dr. Ken Maser, P.E., president of Infrasense, Arlington, Mass. "GPR involves transmitting short radio Oklahoma DOT uses GPR to reduce the number of cores required Ground penetrating radar (GPR) is a relatively new, non-invasive, nondestructive pavement testing procedure that will reveal pavement structure data. GPR is an alternate to FWD testing but also may supplement it. Antennae mounted on a moving vehicle transmit short pulses of radio wave energy into the pavement structure, and echoes are created at boundaries of dissimilar materi- als (such as the asphalt–base interface), reports the Federal frequency pulses and receiving echoes from the boundaries between the pavement layers," Maser says. "The technology has been in use for a variety of highway applications over the past 20 years, and has been adapted for routine use by a number of state agencies." The accuracy of the GPR pavement thickness measure- ments, typically ranging within 3 to 10 percent of core val- ues, has been documented in several university, state agency, and SHRP studies, Maser says. A key advantage of GPR is the ability to collect data at highway speed, using non-contact equipment; typical survey coverage of 200 to 300 lane- miles per day on intercity roads makes this technology well Write 166 on Reader Service Card or visit www.betterroads.com/info 24 October 2012 Better Roads