Town Rejuvenates High-Rap Mix for Heavy-Traffic Pavement

Asphalt Contractor, February 2016
Paul Fournier, Contributing Editor

A mill-and-fill paving project employing hot mix with high recycled asphalt pavement (RAP) content was recently carried out at a busy recycling/transfer center in Wellesley, MA, to demonstrate the effectiveness of a new asphalt rejuvenator.

Town officials and others are monitoring the performance of the 40% RAP mix that was dosed with Delta S, an asphalt rejuvenator product of Collaborative Aggregates.  The Wilmington, MA, company sponsored the project and served as general contractor.

The area chosen for the Wellesley demonstration lies within the town’s busy recycling and transfer center, where asphalt pavement has deteriorated due to the high volume of traffic, especially from heavily loaded trucks. The center experiences anywhere between 800 and 1,500 residents’ vehicles each day and about 4,000 on Saturdays. In addition, it undergoes continual traffic from the DPW’s regular 6-wheel, 35,000-pound trash collector trucks plus six to eight tractor-trailers that periodically pick up compacted refuse. Due to resulting pavement damage, the site was a good candidate for mill-and-fill and ideal for testing the new rejuvenator.

The demonstration was authorized by the Wellesley Department of Public Works, headed by Director Mike Pakstis, who has indicated they are willing to try new things if they offer cost-effective alternatives that prolong pavement service life. Recycling asphalt pavement and asphalt shingles (RAS) falls within this category, since it reduces the amounts of expensive virgin materials required for pavement construction, freeing up funds for additional roadway improvement projects.

Limits to RAP/RAS share

Despite the industry trend to increase asphalt recycling, there is a practical limit to the total amount of RAP and RAS that can be used in making hot mix asphalt for pavements due to the nature of the materials.  As the percentages of RAP or RAS in mix designs increase, the higher viscosity and lower ductility of the embedded asphalt due to long-term aging in the field stiffens the mix and thus diminishes new pavement resistance to rutting and cracking. A remedy for this is the use of asphalt rejuvenators.

Generally, rejuvenators can restore the original properties of asphalt binder such as viscosity and ductility. But traditional rejuvenators may contain lubricating oil extracts and extender oils, which may be derivatives of benzene, a substance toxic to humans and the environment. What’s more, some rejuvenators simply soften the binder but do not chemically reverse the oxidation of the aged binder in the RAP and RAS.

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