Summary of report from the A-R 2000 Conference

C J Potgieter, Consultant, South Africa: "it is concluded that the bitumen rubber stress absorbing membrane interlayers (SAMIs) and asphalts performed above expectations. Many of these SAMIs and asphalts, paved under difficult traffic conditions and overlying severely distressed pavements, outlived their design period comfortably. The bitumen rubber overlays outperformed the conventional asphalts, under identical conditions, by a large margin. Bitumen rubber asphalts and SAMIs are especially suited for highly trafficked roads with pavements in structural distress and where overlays will eliminate reconstruction options in congested traffic situations.

Guido Van Heystraeten, Belgian Road Research Center, reported on a high traffic freeway in Brussels where a wet processed Asphalt- Rubber overlay containing 18-20% rubber in the binder lasted 18 years.

Cost Effectiveness

Studies regarding the cost effectiveness of using Asphalt-Rubber in pavements have been consistent in reporting an overall improvement in the life cycle cost benefits of these products. In man cases, the initial construction costs are even less than those that conventional solutions call for. Clearly, exact cost savings depend on local markets and the structural solutions adopted for each case. In general it can be stated that the higher oil and bitumen prices become, the more cost-effective Asphalt-Rubber solutions are in comparison. Selected extracts from A-R 2000 papers dealing with this issue are presented below.

Dr. Alex Visser, University of Pretoria, South Africa: "Bitumen-Rubber asphalt with a thickness of half that of asphalt made with conventional bitumen, provided at least the same fatigue resistance."

Dr. R G Hicks, Oregon State University: "The findings indicate that Asphalt-Rubber is cost effective in most of the applications used by the state highway agencies of Arizona, California and Texas."

George Way, ADOT, reported that, in a single project, the use of Asphalt-Rubber led to an 18 million dollar savings and four years less construction time, compared to structurally equivalent conventional solutions.

Jack Van Kirk, PE, Basic Resources, California: "It was determined through these field evaluations that the Asphalt-Rubber pavements could be significantly reduced in thickness. They provide the same fatigue life as thicker (conventional) asphalt concrete pavements. Multilayer systems using Asphalt-Rubber strategies can provide significant cost savings when compared to conventional AC pavement strategies."

Environmental Effects

One of the most widespread concerns regarding Asphalt-Rubber is associated with environmental effects during fabrication and placement, and the possibility of contamination when rubberized asphalt is recycled. These are some of the statements made during the Conference on the issues:

Rachel Turner, U. S. Environmental Protection Agency, stated "According to the information that was available at the time of the studies, there is no compelling evidence that the use of rubberized asphalt pavement increases the threat to human health or the environment, as compared to the threats associated with conventional asphalt pavements. "

Donna Carlson, Rubber Pavements Association (RPA), addressed the concerns regarding recycling of Asphalt-Rubber pavements.

"Major studies have been undertaken on the recycling of Asphalt-Rubber pavements; two that come to mind are the City of Los Angeles and the Texas Department of Transportation. . Both reported no difficulty in recycling Asphalt-Rubber pavements."

Dr. Shatnawi also corroborated this, stating that as far as the California Department of Transportation is concerned, "Asphalt- Rubber Hot Mix-Gap Graded is recyclable."

Antonio Pinelo, Portuguese National Laboratory of Civil Engineering, opened with an interesting concept in which the negative environmental effects of motorways and freeways can be offset if they are used as means of solving other environmental problems, specifically as a means of solving the scrap tire problem.

Antonio Amaro, Chairman of the Board of RECIGROUP and IPE-REGIA, brought to light "the responsibility of those in charge of highway networks is to be partners in the solution of scrap tire problems, and to see past the initial reservations towards the introduction of a new product, into the long term experience with the cost effective usage of Asphalt-Rubber."

Other Topics

Beyond papers that specifically addressed direct performance or data related to the three main topics, several papers were presented where laboratory comparisons of performance with several types of materials were reported.