Pavement Preservation Journal, Spring 2015, Vol. 8, No. 1
By Manuel Trevino, Ph.D.
Thin overlays are non-structural preventive maintenance HMA mixes used for the routine maintenance and rehabilitation of existing pavements.
These overlays are commonly placed in thin lifts of about 1 in. thick, and are mainly used to preserve pavements exhibiting surface distresses such as raveling, aging, bleeding, minor cracking, minor disintegration, texture loss, and skid resistance loss.
Thin HMA overlays enhance pavement performance and extend pavement service life, including functional characteristics such as improved user serviceability (i.e., smoothness, comfort, and quiet ride), skid resistance, splash and spray reduction, and noise reduction.
STUDYING NOISE MITIGATION
The noise mitigating properties of some of these mixes have been studied in the field in Austin, Tex., by The University of Texas Center for Transportation Research, and the results show that these surfaces are even quieter than some permeable [or open-graded] friction courses, which are commonly regarded as the quietest asphalt mixes.
Research has shown some of the advantages of using thin lift asphalt mixtures include:
• Improved ride quality
• Reduced noise levels
• Reduced life cycle costs
• No loose stones, and
• No curing time required.
Most asphalt maintenance is needed to address functional issues, and not structural issues. Therefore, increasing the thickness of the pavement is not always necessary, and thin overlays are often sufficient to improve the surface smoothness and quality.