Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/86539
RoadScience pavement, cores from newer or even fresh pavements can reveal trouble down the road. "Early in a pavement's life we often will take a core and Forensic evaluation of pavement failure begins with simple field observations. Cores Provide Clues Pavement coring is at the heart of both virgin pavement testing and pavement forensic testing. Forensic investiga- tion studies pavement structure and materials in the event of premature deterioration, substandard materials, new materi- als for evaluations, investigation of pavement for overweight loading and proposed new techniques and methods, says the Indiana DOT. Sometimes investigators will use the cores to examine thickness of the pavement structure, or deterioration at the bottom of the structure where water may be present at the interface between pavement and sub-base, eroding pavement support. Cores will reveal if any layer of asphalt has failed to bond to the layer beneath it, or if there has been any stripping in any asphalt layer throughout the core. While pavement forensic testing likely will involve cores taken from troubled undertake lab testing or performance testing for rutting, cracking or stiffness," Clyne tells Better Roads. "We'll core a fresh pavement to check for thickness, just to verify that it's what it's supposed to be. We also will look for asphalt early aging characteristics." Coring begins with visual examination of a pavement's condition. "If you can see a problem at the surface, you can pinpoint exactly where you should take those cores," Clyne says. "We never just take one core; we take several at various locations, either along one particular crack, several cracks throughout the pavement, or from a strategic grid where we take cores throughout the grid." That being said, quite often, the failure area will be small relative to the whole pavement length, or the engineer can choose one representative area of the failure and investigate that small area, which will give him or her an indication of what's going on throughout the whole project. But testing of cores often is not needed if careful visual examination will work. "We don't always test the cores in a forensic investigation; sometimes we just take a look at the cores to give us clues to what's happening," Clyne adds. "We won't test the material properties; we will be just looking to see how the pavement's deteriorated." Visual Examination Visual examination plays a big role when actual sections – not cores – are removed from pavements. Trenches and test pits cut with pavement saws can remove a larger area of pavement – up to the entire 12-foot lane width – for large samples. Depending on the size of the sample, it may be cut into smaller sections for removal, numbered and then pieced together for review. In these applications, visual examination may suffi ce. "Your eyes will tell you the story of what's going in the pavement," Clyne says. "The simpler the better, we like to say; if a simple tape measure will do, that's what we will use." With visual analysis, investigators will be looking for signs When cores aren't enough, extensive sections of pavement may be removed for forensic analysis. 20 October 2012 Better Roads that water has been in the pavement system, and scoured or leached away materials at the bottom of the core or in the core. Are the layers bonded the way they are supposed to be? Are they the proper thickness? If a pavement is a couple of inches thinner than it should be, it's liable to crack early. Water damage is indicated by a lack of material. "Portions of the core or pavement won't be there anymore," Clyne says. "When the core is taken over a pavement crack, you can see