RPA President's Letter March RPA President's Letter

In recent years we have seen overwhelming growth in the use of Asphalt-Rubber binders for Open-graded and Gap-graded pavements and also as a spray binder for Chipseals, Scrub Seals and Stress Absorbing Membranes. The use of A-R Binders as SAMI's (Stress Absorbing Membrane Interlayers) under new asphalt pavement was one of material's original uses. When
combined with an A-R overlay the SAMI has provided the most cost effective alternative to complete pavement reconstruction on hundreds of projects.

A-R chipseals have also become a performance enhancing part of the Capeseal system. Capeseal is the term coined in South Africa in the 1970s to define a combination chipseal and slurry seal or microsurfacing. They were used as primary all-weather road surfacings on top of prepared aggregate road bases. Emulsions were used for both chipseal binder and in the slurry/micros. South Africa's design criteria was to use a larger than normal chip aggregate and to use a very fine emulsion slurry seal to fill in around the stone gaps to form a locked matrix in which the large chip stone protruded through the slurry seal to provide excellent skid resistance. As practiced in the United States, Capeseals generally use a smaller chip stone and completely bind it with the slurry/micro final surfacing. Life expectancies with emulsion Capeseals are between 10 and 12 years on good pavements. However, with an Asphalt-Rubber binder in the chipseal, many surfacings are lasting 15 to 18 years or more with little or no crack reflection.

The use of Asphalt-Rubber Capeseals also expands the range of projects on which a Capeseal solution can be used. The City of Phoenix has been using A-R Capeseals on both non-paved gravel roads and alley-ways. They have been used within agencies where chipseals had been previously banned due public fear of loose aggregate because a Capeseal looks and performs similarly to a new asphalt concrete surface.
Many City and County agencies have migrated to A-R Capeseals as their primary maintenance strategy for their worst distressed pavements. While this system can handle a fairly large amount of cracking effectively, it should not be used, as with any resurfacing system, where there is a high degree of deflecting pavements. Pavement failures due to deflecting pavements
should be removed and replaced with new structural sections.

We are currently witnessing many proprietary polymer and polymer-rubber binders trying to enter the rubberized asphalt market. Most with little research, no proven life cycle costs, and dubious, unsubstantiated marketing claims that they are "just as good" as Asphalt-Rubber. The one thing they all seem to have in common is that they come with greater risk and cost in the long term to the user. Asphalt-Rubber, as supported and promoted by the Rubber Pavements Association, is an Open, Non-Proprietary System and as such can be made by any contractor or hot mix producer willing to invest in the equipment. There are also many contractor blenders who have specialized in providing Asphalt-Rubber blending on a project-by-project basis to the industry.

If you have heard about Asphalt-Rubber but have never used it, the time is now.

• It is Safe ­ Our recently completed landmark Hot Plant Emissions study in the toughest Air Quality District in California proved that A-R Hotmix production is within AP42 guidelines.
• It is Recyclable ­Although, because of its long life cycle, perhaps not in ones lifetime.
• It is Cost Effective ­ A ten fold increase in tonnage placed in California to over 2.8 million tons over the last 3 years. It is the only rubber modified asphalt process to have a proven positive life cycle cost. (See the Hicks-Epps Lifecycle report at www.rubberpavements.org/library/lcca_australia/index.html).
• It is Quiet ­ Studies have shown that A-R Open-graded pavements have reduced noise levels by up to 6 Decibels or more and in some cases eliminating the need for highway sound walls.

(See Noise reports at
www.rubberpavements.org/library/sacramento_noise_study/index.html).

For further information contact the Rubber Pavements Association at
(480) 517-9944 or www.rubberpavements.org.
Jeffrey Reed jrreed@slurry.com