Pooled fund study "making significant progress," other CRM research underway

The five-year federal-state pooled fund study is making significant progress in developing structural and mix design procedures for crumb rubber modified asphalt pavements, said Jim Lundy, the study's principal manager.

Lundy, a professor at Oregon State University, spoke to RPA members and guests from Caltrans districts 7, 8 and 11 at RPA's annual dinner in California. OSU has overall responsibility for coordinating the pooled fund study that is part of the extensive research funded by the Federal Highway Administration and the Department of Energy.

He said only the "wet process" is being investigated at the request of the Federal Highway Administration and the 32 participating states due to its superior field performance.

The pooled fund research team includes a number of national and international authorities on crumb rubber modifiers and asphalt. Among them are:

Ray Brown, director of the National Center for Asphalt Technology, who is responsible for the development of construction guidelines and specifications.

Carl Monismith, professor at the University of California-Berkeley, who is responsible for conducting the SHRP mixture testing on CRM-HMA.

Jon Epps, professor at the University of Nevada-Reno, who is responsible for conducting SHRP binder testing on CRM binders.

Nichols Consulting Engineers, which is responsible for identifying and collecting pre-construction and post-construction information on the 16 CRMHMA field test sites. The sites are located in Arizona, California, Florida, Illinois, Mississippi, New Hampshire, and Pennsylvania.

The test sections will also subjected to mix evaluation and condition monitoring.
Lundy said that interim construction guidelines have been prepared. Initial structural guides have already been released and mix design procedures will be available this spring.

Lundy outlined the study's status and accomplishments to date.

• Identification of all test sections.
• Collection of pre-construction and post-construction data.
• Testing at intermediate and high temperatures to determine the effect of blending time and temperature, prolonged storage, and reheating.

"The recyclability tests have indicated that there is no difference between the crumb rubber modified pavements and conventional mixes. "
J.R. Lundy

Lundy said that the standard SHRP binder protocol appears appropriate except when testing large size rubber particles. Increasingly small rubber sizes do not significantly change binder properties.

Regarding CRM-HMA design, he said the hypotheses indicate that superpave volumetric design is suitabIe and that the NCAT Drain Down test will work with open-graded CRM-HMA.

Lundy dispelled charges that CRMHMA pavements cannot be recycled. "Recycled CRM mixes do not require special mix design treatment compared to conventional recycled mixes."

He said once the final reports have been issued, any agency interested in starting a CRM-HMA program will have complete guidelines for design and construction procedures.

Meanwhile, replicate testing and low temperature testing of CRM binders is underway at the University of Nevada-Reno.

Five asphalts, two rubber particle sizes, and two rubber contents are being investigated along with basic asphalt compatibility with crumb rubber.

Early indications point to the acid content of asphalt determining compatibility.

Lundy also cited other research programs now underway. Texas A&M University and Western Research Institute in Laramie, Wyoming are working under major grants from the FHWA and the U.S. Department of Energy.

Texas A&M is studying the chemistry changes that take place when crumb rubber is added to asphalt. WRI is investigating the application of SHRP binder test procedures on CRM binders.

Caltrans and UC Berkeley are investigating the structural equivalencies of CRM-HMA using the heavy vehicle simulators. Results will be incorporated in the final structural design methodology

An industry approved "performance related" specification for asphaltrubber binder and gap- graded aggregate will be available by April 1.

Jay McQuillen, chairman of the RPA/Caltrans California industry task force, said the specification for rubberized asphalt concrete (RAC) results from an cooperative effort by representatives of the California industry and Caltrans.

The specification is based on years of field performance and laboratory research on Caltrans A-R (wet process) projects. Copies of the specification can be obtained from the RPA off ice.