Evaluation of a system for measuring seal coat quality

The Texas Department of Transportation (TxDOT) spends over {dollar}250 million per year to maintain almost 200,000 miles of roadway with more than 450 million vehicle miles per day. Seal coats are very important for the Department's preventive maintenance program. Seal coats are one of the most important elements of pavement maintenance because they slow down pavement deterioration. It is less expensive to seal coat roads with low traffic volumes every few years than it is to overlay or completely replace the road. Seal coats also beatify and seal the road from water. In addition, seal coats are instrumental in maintaining and recovering skid resistance which is a major safety requirement in pavement maintenance.; The purpose of this research project is to develop an objective technique to accurately evaluate pavement distresses including raveling (loss of aggregate) and excess binder (flushing or bleeding). Current methods available to evaluate seal coat distresses are very subjective and they include visual inspection by different people. This method is subject to different interpretation by the different inspectors with different levels of knowledge and experience on pavement distresses. Currently, there is no method based on equipment measurements to scientifically evaluate the performance of seal coats and reduce the subjectiveness of seal coat performance evaluations. A methodology based on texture could be an option to measure seal coat performance as affected by flushing and raveling.; Two portable tools are available for measuring pavement texture and need to be evaluated for measuring texture of seal coats, the Circular Track Meter (CTM) (ASTM E 2157 -- 01) and the Outflow Meter (OFM) (ASTM E 2380 -- 05). The CTM and the OFM provide measurements of pavement texture that has been shown to correlate with skid resistance. The CTM would be the most feasible and practical for a TxDOT inspector to carry in his or her truck. The Outflow Meter is also simple to use and it only requires water to operate. On the other hand, the CTM is several times more expensive than the OFM; it requires the use of a laptop computer, and preferably two people to operate. The relationship between the OFM and the CTM will be presented later in this report.; A factorial table of seal coat test sections based on age and traffic was defined by this research project and pavement texture data was collected using the CTM and OFM. These data were summarized to develop CTM and OFM correlations. In addition, the research developed seal coat failure criteria based on texture and makes recommendations on how to establish a systematic procedure to evaluate seal coats.