Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/85910
Applications&Innovations Avoid Common T Cold Mix Patching Failures By Tina Grady Barbaccia o do something the right way, it helps to know how to do it the wrong way. Pothole patching is not an exception to the rule. Identifying the various types of distresses and the related failure mechanisms is vital for an in-depth analysis of a pot- hole problem. By identifying the mechanisms of failure, it's then pos- sible to establish a set of performance criteria that can be used to develop improved patching materials, accord- ing to Evaluation of Pothole Patching Materials (FHWA NJ 2001-020), a report conducted by the Department of Civil & Environmental Engineering Center for Advanced Infrastructure & Transportation at Rutgers University. The report was done in cooperation with the New Jersey Department of Transportation and the Federal Highway Administration. (A downloadable PDF of the report is avail- able at qprcoldpatch.com/pdf/Rutgers-Study.pdf.) According to the report, the most common in-service fail- ures in cold-mix patching materials are: • Shoving: Doing this under traffic reduces the mix's stability. Improper compaction makes the mix more susceptible to shoving, because proper compaction is required to develop aggregate interlock that is primarily responsible for the stability of the mixture. • Raveling: This is a progressive loss of aggregate from the surface of the repair. It's the product of poor ag- gregate interlock and inadequate cohesion within the mix. Poor compaction can also contribute to raveling as it reduces cohesion. • Dishing: This results from inadequate compaction, usually occurring when the mix compacts under traf- fic. The dishing mechanism can be addressed through mixture design and proper compaction. • Freeze-thaw: The delamination of the patch from the original pavement is the result of freezing water at the bottom of the repair. Freeze-thaw damage is caused by improper adhesion of the patch to the hole as a result of improper compaction, tacking or hole preparation. • Poor skid-resistance: This can result from a flushed or bleeding surface or polished aggregates. It can be controlled with an appropriate mix design. • Bleeding: This is related to excess of binder in the patching mixture. • Lack of adhesion to the side or the bottom of the repair. This is a result of poor preparation. It also happens when tack is not used or when the mix is not self-tacking. The authors of Evaluation of Pothole Patching Materials (FHWA NJ 2001-02) at Rutgers University in Piscataway, N.J., are Dr. Ali Maher, Dr. Nenad Gucunski, William Yanko and Fotina Petsi. The New Jersey Department of Transportation project manager on this report is Robert Baker. Better Roads February 2012 29