Mastic is a material that varies a bit between manufacturers and applications, but it is generally a blend of high-performance asphalt binder and engineered aggregates. It can be used in a wide variety of applications to stop water infiltration and restore ride quality.
In the best constructed pavements, cracks form naturally, as internal stresses react to environmental forces such as temperature fluctuations and oxidation. Flaws in the original pavement material or its construction (e.g., segregation, insufficient compaction, extreme temperatures), as well as utility cuts and other pavement interruptions can also result in cracking.
Cracks in the pavement allow water infiltration into the supporting subbase materials and can lead to more serious pavement distresses and premature lack of ride quality as well as shortened life expectancy. Indeed, the Pavement Preservation & Recycling Alliance (PPRA, https://roadresource.org/) estimates that 75% of unsealed cracks develop into potholes within three years.
The best treatment for cracks when they are addressed early is crack sealing or crack filling. For cracks as small as 1/8” up to about ¾” (or even an inch or so), crack sealing is one of the least expensive treatments to extend the life of asphalt pavements and can reduce the life cycle cost of the pavement by extending its life at a small cost.
But when cracks are blown out, they often are much larger than they initially appear and cracks of 1-1½” or greater are poor candidates for crack sealing or filling. Mastic has become a go-to material for larger cracks, potholes, and even alligator cracking in some instances.
Just as with crack sealing, crack filling, or any other pavement treatment, cleaning and preparation of the surface is essential with mastic treatments. The cracks must be cleaned out and dry for the material to bond well and serve its function over the long term.
We had the opportunity to see mastic applied at the 2018 Roadway Management Conference (RMC, an annual effort by the Mid-Atlantic Region of LTAP and T2 Centers, including WV, VA, PA, MD, and DE) in Gettysburg, Pennsylvania. Maxwell Products applied mastic to a wide crack and an associated pothole. A short video shows the RMC demonstration.
Mastic material can be applied in a number of ways and has been used for more than just cracks. As seen in the RMC video, potholes can be addressed as well. Some local agencies have used mastic to address more advanced distresses like alligator cracking, although it should be recognized that this form of distress often suggests that subbase degradation has already advanced, and the mastic treatment may have a lesser service life. There are even applications of mastic applied broadly across a pavement, similar to a fog seal application.
Remember that all pavement preservations work best when the correct treatment is applied to the right road at the right time in its life cycle. When structural issue with the road section set in, most pavement preservations are no longer suitable. The true value of most pavement preservation tools is to extend the useful life of the pavement for a lesser cost and keep the roadway in a good condition throughout a longer period of its life.
The Delaware T2/LTAP Center’s Municipal Engineering Circuit Rider is intended to provide technical assistance and training to local agencies, so if you have pavement management questions or other transportation issues, contact Matt Carter at matheu@udel.edu or (302) 831-7236.
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