Candidate for fully permeable shoulder retrofit validation site
UCPRC conducts research on partial- and full-depth recycling, RHMA-G strategies, with a big assist from CalAPA members. This past May, the UCPRC—with major assistance from members of the California Asphalt Pavement Association (CalAPA)—continued with the next phases of two comprehensive research studies into the use of recycled materials in pavements being conducted for the California Department of Transportation (Caltrans). The work covered the construction of a four-lane test track with 10 different sections. Two lanes are dedicated to investigating cold central plant recycled materials and two lanes focus on rubberized asphalt concrete. The sections will be subjected to accelerated pavement testing in conjunction with laboratory testing with the aim of increasing the use of recycled/reclaimed materials, improving pavement life, and reducing costs.
The test sections are currently being tested to answer two sets of questions:
- How do Cold Central Plant Recycled (CCPR) materials prepared with different methods stabilizers perform mechanistically?
- These test results will be compared with results from earlier testing of different full-depth reclamation (FDR) stabilization approaches and with data from field performance monitoring of projects rehabilitated using cold in-place recycling strategies.
- What are the effects of different thicknesses and nominal maximum aggregate sizes on the rutting performance of gap-graded rubberized hot mix asphalt (RHMA-G)?
CCPR practice processes 100 percent reclaimed asphalt pavement (RAP) stabilized with either foamed asphalt or asphalt emulsion and an active filler in a mobile plant at or close to the construction project. The processed material is placed with a paver and then compacted before it is surfaced with a thin layer of asphalt concrete. The accelerated pavement testing will provide information about this material’s long-term mechanistic behavior under traffic loading and different environmental conditions.
The RHMA-G experiment includes thicker layers of the material than are typically used—which can potentially result in more scrap tires being recycled into pavement—to evaluate their rutting performance under heavy loads and high temperatures. In addition, the thicker layers will also provide a look at the effects that different aggregate sizes in the RHMA-G have on rutting performance, and address Industry’s interest in using smaller maximum aggregate sizes to facilitate construction compaction and to meet smoothness requirements. A third aspect of this testing focuses on the use of small amounts of RAP in RHMA-G, primarily to replace aggregate to help reduce the RHMA-G cost without reducing the number of tires included in the mixes.
The findings of both studies will be used to refine pavement design, mix design, specification language, and performance expectations for these materials, and to provide confidence to highway engineers who design rehabilitation projects. The accelerated pavement testing results are also used with extensive laboratory testing to improve models for future pavement rehabilitation designs.
The UCPRC acknowledges the interest and support of the following organizations who assisted with the construction of the test track. Pavement Recycling Systems provided materials and equipment, processed all CCPR materials, and did the paving and compaction. They also placed and compacted the RHMA-G surface layers. Pacific Northwest Oil, Albina Asphalt, and Ergon Asphalt and Emulsions provided the binders for the CCPR materials. Asphalt Pavement and Recycling Technologies (APART) did the CCPR mix designs. George Reed did the RHMA-G mix designs and provided all the RHMA-G mixes. Aragon Geotechechnical, Graniterock, Surface Systems and Instruments, and Humboldt manufacturing assisted with quality control during construction.