Texas Moving up!

Much is said and written about the long history of Asphalt-Rubber use in Arizona and to some extent, California and Florida. However, in keeping with the proud tradition of Texas, we were the earliest "big time" user.

In 1979, TXDOT started using Asphalt-Rubber chip seals, not just here and there but throughout the state. Between 1979 and 1989 Texas had placed over 2,500 lane miles of Asphalt-Rubber roadway in 20 TXDOT Districts. In the same time period, seventy of the 254 counties had placed Asphalt-Rubber pavements.

Additionally eight airports, including Love Field in Dallas, Midland, San Antonio International Airport, Houston Hobby Airport, Cabannis Field, and Main Station Naval Training Area in Corpus Christi had used the material. The Stress Absorbing Membrane (SAM) on the Midland Airport, which also had Military Aircraft, had outstanding performance. At the present time the Houston Bush International Airport is using Asphalt-Rubber material.

In 1988, Russ Schnormeier, P.E., Technical Director for the RPA predecessor, the Asphalt-Rubber Producers Group, conducted a survey of the Asphalt-Rubber projects in Texas. His study included all the climatic regions, the Hot-Dry area of West Texas, the Cool-Dry Panhandle area, the Cool Wet Central and East Texas regions and the Warm-Wet Gulf Coast and the Rio Grande Valley.

Schnormeier, who was the Engineering Supervisor for the City of Phoenix, prior to joining ARPG, included studies by John A Blazienz and Arthur Geick of District 17 as well as studies by Drs. Scott Shuler and Bob Galloway. Evaluations by the Texas Transportation Institute and Texas A & M were also considered in Schnormeier's work.

Among the survey conclusions:

• Asphalt-Rubber reduces crack reflection problems inherent in conventional overlays.
• Asphalt-Rubber reduces maintenance costs by its resiliency, flexibility and ability to seal a surface.
• Asphalt-Rubber extended the life cycle of Texas roads and has used a waste product (scrap tires) that is a Texas and worldwide solid waste concern.
• This Texas investigation reveals Asphalt-Rubber as a SAM or SAMI (interlayer) has stopped all alligator cracking where used in the state.

In the early nineties, resistance to the federal mandate and a change to more reliance on hot mixes, the Asphalt-Rubber program experienced a slow down in Texas. After the repeal of the mandate and the expiration of the patents, the program started to develop again. However, with the state in a hot mix mode and it took some time for TXDOT to convert from their standard dense graded mode to the gap-graded mixes which are far more suitable for Asphalt-Rubber and allow a much higher binder content in the mix.

After two other districts experienced some less than satisfactory attempts of using Asphalt-Rubber binder in a dense graded mix in 1992-94, the Odessa district has led the way in the Asphalt-Rubber revival in Texas by successfully using gap and open graded A-R hot mix in several outstanding projects. In Texas these two mixes are called Course Matrix High Binder (CMHB similar to GG) and Porous Friction Course (PFC same as OG). One of the open graded projects received awards from the National Asphalt Paving Association as well as RPA. (See Photo) I am pleased to report Cox Paving blended the Asphalt-Rubber for this project.

Dan Dalager, Dr. K.C. Evans and the late Joe Morales led the Odessa work. It has inspired other districts to look seriously at the Porous Friction Courses (PFC) as a means of obtaining better performing pavements with respect to resistance to reflective cracking and raveling. One of the reasons for improved performance over polymer and conventional mixes cited by the district personnel is the high binder content of the rubber mixes.

ANOTHER WINNER - This Asphalt-Rubber project on US 385 in Crane County, Texas brought the TxDOT' Odessa District a Quality in Construction award from NAPA, the Highest Quality award from the RPA, and a Quality Contracting award for the Jones Bros. Dirt and Paving Contractors of Odessa and Cox Paving of Blanco. The district was also recognized by TxDOT with a Quality Initiative award and Environmental award for the use of nearly a quarter million scrap tires.

In 2000 RPA commissioned Magshoud Tahmoressi, former TXDOT Bituminous Engineer and now President of PaveTex Engineering and Testing, Inc. to conduct an evaluation of Asphalt-Rubber Pavements in Texas. The report, released in January 2001, studied 10 Asphalt-Rubber hot mix projects placed between 1992 and 1999 and 18 chip seals, all placed after the Schnormeier survey of 1990. The Tahmoressi project survey, which will serve as a benchmark for future evaluations, offers the following conclusions:

• All Asphalt-Rubber Porous Friction Courses (PFC) projects are exhibiting excellent performance properties. Resistance to cracking and raveling in Asphalt-Rubber PFC is particularly impressive. From cost and benefits standpoints, PFC is the best application for Asphalt-Rubber.
• With exception of two projects in Lufkin district, all Asphalt-Rubber hot mix projects that utilized CMHB (Course Matrix High Binder) gradation and are in satisfactory condition. The Lufkin projects showed premature distress due to base failures.
• Resistance to cracking in Asphalt-Rubber CMHB exceeds the resistance to cracking typically expected with CMHB.
• In Seal Coat projects which utilized grade 3 (5/8" maximum size) chips, resistance to cracking and chip loss was excellent. These projects typically did not exhibit bleeding. However, when smaller chip size (i.e. grade 4) was used bleeding was a common problem.
• If it is necessary to use grade 4 chips, then the Asphalt-Rubber application must be reduced to the extent possible to prevent bleeding. However, when the application rate is reduced, resistance to cracking will be reduced and chip retention will be diminished.

Our company has noted that the use of a modified grade 4 chip or even a grade 3 can be successful. One of the most recent projects completed by Cox Paving is a Stress Absorbing Membrane Interlayer with a cape seal on top.

The one thing the Texas survey does not report is the number of lane miles placed in the period between 1992 and 1999. My best Texas guess is that it is far more than Arizona or California, maybe even Florida that uses rubber in all its surface courses. What is for certain, in addition to miles of "rubber roads" Texas intends to challenges Arizona, Georgia and other top ranking states with the most rideable roads. We're not only the "biggest", we are ready for the "Smooth Move" to the best.