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Stacking Up the Benefits of Pavement Preservation

Aug 21, 2023
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Stacking Up the Benefits of Pavement Preservation

When it comes to pavement preservation, there are many treatment options available that can address specific issues and ultimately extend pavement life. Crack seals, chip seals, slurry seals, micro surfacing, and thin overlays are widely used and have proven to be cost-effective solutions when selected properly. More and more, agencies are combining these treatments and obtaining increased benefits.

The National Center for Asphalt Technology (NCAT) and the Minnesota Department of Transportation Road Research Facility (MnROAD) have been studying the field performance of various pavement preservation treatments for over ten years in a research project funded by more than 20 state DOTs and industry professionals. Several treatment combinations are included as part of this effort and the long-term results have shown great promise.

As a stand-alone treatment, crack sealing is a simple way to prevent water intrusion and slow down crack progression. When combined with other treatments, it helps enhance the overall benefits and achieve longer-lasting surfaces. For example, it was found that under low traffic conditions, combining crack seal with a single layer chip seal reduced the risk of failure by 73% compared to using a chip seal1 alone. Application of crack sealing prior to micro surfacing has been able to reduce cracking by an average of 5% more than the stand-alone micro surface in pavements with moderate cracking2.

Likewise, other treatment combinations can have a similar effect. Cape seals, commonly defined as the application of a chip seal followed by a slurry seal or micro surface, have gained popularity thanks to their good performance. The chip seal layer – which can also be a scrub seal – helps address issues like weathering, raveling and minor cracking while sealing and protecting the surface. The slurry seal or micro surface partially fills the void space between the aggregate particles and provides a uniform, durable surface. These types of combinations are good options for restoring pavements that are slightly more deteriorated but still in sound structural condition and can achieve long service lives depending on climate and traffic levels. Test sections constructed as part of the NCAT-MnROAD research partnership have performed better than just the sum of the two treatments, in some cases showing minimal distresses even after ten years of service.

This approach is also popular for urban roads where leaving the chip seal layer exposed would not be acceptable due to the rougher nature of the treatment, increased noise and potential for aggregate particles becoming dislodged and causing windshield damage.

Chip seals can also be combined with thin overlays, providing an interlayer capable of reducing reflective cracking. In cold climate locations where severe transverse cracking significantly affects ride quality, these combinations help mitigate crack severity, reduce pavement roughness and delay deterioration. Test sections subjected to low traffic in Minnesota were able to reduce roughness by 22 to 46% immediately after construction and were estimated to provide a life-extending benefit between 6.3 and 8.3 years in terms of the International Roughness Index3.

Overall, there are many possible treatment combinations agencies can use to preserve their pavement networks. Research has shown that these are effective solutions that combine benefits to provide additional extended life and keep roads in a state of good repair.

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Dr. Adriana Vargas is an Associate Research Professor at NCAT, where her main areas of research are pavement preservation and pavement management. Prior to joining NCAT in 2016, she was a Researcher and Professor in the Civil Engineering department at the University of Costa Rica. Outside of academic positions, Dr. Vargas has worked for Nichols Consulting Engineers (NCE) in the San Francisco Bay Area conducting pavement management implementations and updates, designing pavement rehabilitation alternatives, and conducting forensic analyses. She is a member of the Association of Asphalt Paving Technologists, the International Society for Asphalt Pavements, and the Board of Directors of the Southeastern Pavement Preservation Partnership.

Written by Adriana Vargas-Nordcbeck, PhD

Aug 21, 2023
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