Pavement preservation is an indispensable component of asset management that departments of transportation use to maintain and enhance the conditions and performance of their highways. Pavement preservation treatments do not improve the structural capacity of a pavement; rather they extend pavement life through delayed pavement deterioration by sealing cracks, preventing pavement oxidation, and, in the case of surface seals, rejuvenating the existing pavement surface layers. Preservation treatments utilizing asphalt emulsions as the binder have historically been underutilized and therefore considered secondary to hot mix asphalt (HMA) technologies. As such, these treatments have not been upgraded or researched to the same extent as HMA technologies. Over the past few years, however, the AASHTO Transportation System Preservation Technical Services Program (TSP-2) Emulsion Task Force (ETF) has made a concerted effort to improve the state of the science/engineering in emulsion technology with the goal of creating national performance-based standards (specifications, test methods, design practices, etc.) that are adopted by AASHTO and are not vendor specific. All the emulsion treatments except for sand seal and ultra-thin bonded wearing course (UTBWC)treatments have or are in the process of having their construction guide specifications developed through NCHRP projects. Therefore, to close the” gap” and have a full complement of standards for all emulsion preservation treatments it is critical that these two treatments have their construction guide specification developed. Some agencies have developed construction specifications for local jurisdictions, but standardized nationwide construction guide specifications do not exist.
Sand seal is a sprayed application of asphalt emulsion followed by a covering of clean sand or fine aggregate. A pneumatic-tire roller is often used after applying the sand. Excess sand is removed from the road surface after rolling. A sand seal is used to fill existing pavement cracking and even out surface smoothness defects as either a preparatory treatment for other maintenance treatments or as a wearing course. AASHTO materials specifications and design practices exist for sand seals (AASHTO MP 34-18 for Materials, and AASHTO PP 90-18 S for Design practices).
Ultra-thin bonded wearing course (UTBWC-Nova Chip) is a preventative maintenance tool used to help extend the life of a road. This UTBWC is an open graded hot mix asphalt placed over polymer modified asphalt emulsion through a special, self-priming paver and compacted with a roller. The treatment improves skid resistance and reduces hydroplaning and noise. UTBWC can be used in pavement maintenance activities or in new construction. TSP-2 ETF has submitted to AASHTO COMP, material specifications and design guides for UTBWCs.
The objective of this project is to produce recommended construction guide specifications for the application of sand seals and ultra-thin bonded surface treatments. This will assist highway agencies in adapting these specifications to the local conditions and environments and will aid DOTs in implementing these treatments in their pavement/asset management programs. The construction guide specification will address the construction operations required, with possible adjustments for local materials and experience. Quality assurance protocols and incentive/disincentives will have to be addressed. The research will include a review of previous work in the area, including construction standards, construction specifications, and construction practices both national and internationally. Deliverable documents will be in conformance with AASHTO COMP standards format.