Caltrans Reviews Rubberized Chip Seals

As technologies advance with new asphalt binder materials, Caltrans (California Department of Transportation) is studying the potential use of terminal blended rubberized asphalt binders in chips seals in comparison with field-blended asphalt rubber.

Caltrans constructed the first terminal-blended rubber modified binder chip seal pilot project on State Route (SR) 36 in a low mountain region in Tehama County in 2013. Another pilot project in Shasta County on SR 44 in a high mountain region was constructed in 2014. The projects are now three and four years old, and valuable information can be obtained by studying their performance with regard to cracking of the pavement surface, Caltrans researchers said.

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During the fall of 2017, researchers at the California Pavement Preservation Center evaluated these projects for total cracking and other pavement distresses. Both projects include multiple test sections, and within each test section, four 500 ft.-long Performance Evaluation Sections (PESs) were constructed, with post miles. Researchers evaluated the condition of each PES section in both projects before the chip seal applications and again in the fall of 2017.

Comparative cracking results for field-blended asphalt rubber chip seal showed the total cracking for SR 44 was 22 percent of the original cracking. For SR 36, the total cracking was 15 percent of the original cracking. According to Caltrans review, the field-blended chip seal is performing well in both climatic regions for retarding cracking.

The research also compared cracking results for field blended asphalt rubber with warm mix asphalt (WMA). For SR 44, the total cracking was 93 percent of the original cracking. For SR 36, the total cracking was 30 percent of the original cracking. The field blended asphalt rubber with WMA chip seal is performing much better in the low mountain region for retarding cracking, the study said.

The comparative cracking results for terminal blended rubberized asphalt rubber found that on SR 44 the total cracking was 486 percent of the original cracking. For SR 36, the total cracking was 11.4 percent of the original cracking. The terminal blended rubberized asphalt chip seal is performing much better in the low mountain region for retarding cracking but did not perform as well in the high mountain region, the report said.

For terminal blend rubberized asphalt with WMA, comparative cracking results on SR 44 found the total cracking was 53 percent of the original cracking. For SR 36, total cracking was 19.4 percent of the original cracking. The terminal blend rubberized asphalt with WMA chip seal is performing better in the low mountain for retarding cracking. However, overall, the terminal blend rubberized asphalt with WMA performed better in the high mountain region for retarding cracking.

In evaluating the field performance of both pilot projects, all of the products appeared to have good performance with retarding total cracking on the SR 36 pavements. Terminal blended rubberized asphalt chip seal had the best crack resistance with 11 percent total cracking, when compared to the pre-construction total cracking. Field blend asphalt rubber chip seal (Type 2) was a close second with only 4 percent more total cracking for a total cracking of 15 percent.

“It is clear from these pilot projects that performance, for controlling total cracking, is more difficult to obtain in the high mountain regions with most binder materials,” Caltrans researchers said. However, for SR 44, the terminal blend rubberized asphalt chip seal with WMA outperformed the same chip seal with WMA for the high mountain region.

© Scrap Tire News, April 2018