Pavement Preservation Journal - Spring 2012 - (Page 41)
Ground Penetrating Radar Fills Gaps in PMS
by Dr. Ken Maser, P.E.
PHOTO CREDITS: Infrasense, Inc.
GPR involves transmitting short radio frequency pulses and receiving echoes from the boundaries between the pavement layers.
GPS-enabled survey vehicle incorporating ground penetrating radar
pavement management system (PMS) forecasts the remaining life of all pavement segments making up a network, and then projects rehabilitation activities and allocates resources based on these projections over the life cycle of the pavement. A key element in projecting the remaining life of a pavement segment is the pavement structure, that is, the thickness and type of the pavement layers. Normally this information is recorded in the as-built drawings, but these drawings, if available, are often inaccurate and do not reflect the current pavement structure. In addition, pavement segments in the PMS, which are supposed to be lengths of uniform pavement structure, are often not uniform at all. For example, some agencies have used “dynamic segmentation” which involves segmentation based on similar distress. Consequently, both the segment’s length and its starting and ending points change from year to year depending on variations in surface conditions. CORING IS COSTLY Until recently, the only means for obtaining pavement structure data was coring. Coring may have some degree of effectiveness for specific projects, but at a network level it is costly, intrusive to traffic, and provides very limited samples of the actual pavement structure. In order to ensure that pavement management systems can economically obtain accurate pavement structure data, highway agencies have been exploring and adapting ground penetrating radar (GPR) for pavement structure investigations. GPR involves transmitting short radio frequency pulses and receiving echoes from the boundaries between the pavement layers. 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 measurements, typically ranging within 3 to 10 percent of core values, has been documented in several university, state agency, and SHRP studies. A key advantage of GPR is the ability to collect data at highway speed, using non-contact equipment as shown in the figure. Typical survey coverage of 200 to 300 lane-miles per day on intercity roads makes this technology well suited for network-level pavement structure evaluation. Network-level GPR pavement structure assessments have been carried out at the statewide level, as well as by various local agencies and municipalities. At the network level, GPR is now being used for network segmentation into relatively uniform pavement structures, for data inventory input into the PMS database, and for layer thickness detail for use with network level falling weight deflectometer (FWD) evaluations. As an example, the California DOT (Caltrans) is creating a new PMS to support the planning and programming of work activities for the state highway network pavement infrastructure. The Caltrans network consists of more than 15,243 centerline miles and 50,664 lane miles. A critical component of this PMS is a pavement structure inventory database, which is being generated through a statewide GPR data collection effort. This effort seeks to create a lane-based pavement structure inventory consisting of layer thicknesses and material types for the entire state highway network. The overall approach evolved from a University of California Pavement Research Center (UCPRC) pilot study carried out in 2005 with Infrasense, Inc. to implement “fixed segmentation” using GPR thickness data. The accuracy of the GPR data was evaluated with corresponding cores (see chart), and the segmentation approach was successfully applied to 305 lane-miles of pilot study data.
Spring 2012 pavement preservation journal 41
Table of Contents for the Digital Edition of Pavement Preservation Journal - Spring 2012
National Preservation Conference: Make Plans Now
Pavement Preservation is ‘Sustainable’ Choice
Deck Micro Surfacing Cuts Accidents, Wins Award
Enhanced Fog Seals Boost Chip Retention
Sophisticated ‘Seal Coats’ Enhance Texas DOT Pavement Preservation
Rejuvenating Treatment Preserves Runway, Grooving
Fine-Mill Pavements for Smooth Thin Overlays
Puerto Rico, Southeast States Focus on Preservation
Maryland Identifies Right Fix for Right Road, Right Time
‘Thin is In’ for New Texas Center Courses
Why to Cut Back on Cutback Asphalt
Test Sections Constructed at Virginia Smart Road
Ground Penetrating Radar Fills Gaps in PMS
Pavement Preservation Journal - Spring 2012