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NEWS (Previous News Items)

  • New Research Report Published: Development of Improved Guidelines and Designs for Thin BCOA: Summary, Conclusions, and Recommendations. This report summarizes the investigations undertaken by the UCPRC between 2014 and 2017 to develop recommendations and guidance on the use of thin bonded concrete overlay of asphalt (BCOA) as a rehabilitation alternative for California based on the adoption of, and improvements to, the technology developed in other US states. The report summarizes, among other things, the Heavy Vehicle Simulator testing of eleven thin BCOA sections. The main conclusion from this research project is that a well-designed, well-built 6×6 thin bonded concrete overlay placed on top of an asphalt base that is in fair-to-good condition can potentially provide 20 years of good serviceability on most of California’s non-interstate roadways.
    Posted 8/19/2019.
  • Presentation Given: John Harvey made a keynote presentation in the Sustainability and Circular Economy session of the European Asphalt Technology Association (EATA) 8th Conference at the University of Granada, Spain on 3 June, 2019.
    Posted 6/4/2019.
  • Call for Abstracts: The International Symposium on Pavement, Roadway, and Bridge Life Cycle Assessment 2020, to be held in Sacramento, California on June 3-6, 2020 is now accepting abstracts. Abstracts should be submitted by June 15, 2019. To submit abstracts, you need to set up an account with EasyChair. Go to and click “create an account”. The LCA2020 Instructions for Authors document details the process of creating an EasyChair account and submitting an abstract. You only need to specify the first author at submission time (you can specify all authors if you would like) andyou can add additional authors (or remove and/or update authors) later by logging into EasyChair andupdating your submission.
    Posted 3/12/2019.
  • New Research Report Published: Laboratory Evaluation of the Mechanical Properties of Asphalt Concrete Reinforced with Aramid Synthetic Fibers. “The research project presented in this report evaluates the effects that the addition of aramid fibers has on the mechanical properties of a dense-graded mix frequently used in California, a Superpave mix with 19 mm (3/4 in.) nominal maximum aggregate size, 15 percent reclaimed asphalt pavement (RAP) content, and PG 64-10 binder. A fiber-reinforced asphalt concrete (FRAC) was prepared by adding aramid fibers at a rate of 0.013 percent of total mix weight. The mechanical properties of the two mixes, original and FRAC, were determined in the laboratory. Based on laboratory testing, adding the fibers improved fatigue resistance...”
    Posted 4/29/2019.
  • New Research Report Published: Pavement Recycling: Shrinkage Crack Mitigation in Cement-Treated Pavement Layers - Phase 1 Laboratory Testing. “The California Department of Transportation (Caltrans) has been using full-depth reclamation (FDR) as a rehabilitation strategy since 2001. Most projects to date have used a combination of foamed asphalt and portland cement as the stabilizing agent. Recently though, the fluctuating and at times high cost of asphalt binder coupled with the relatively complex mix-design procedure for mixes that include foamed asphalt has generated interest in the use of portland cement alone as an alternative stabilizing agent. However, shrinkage cracking associated with the hydration and curing...”
    Posted 12/10/2018.
  • New Research Report Published: Guidance for Selection of Unbound Pavement Layer Seasonal Stiffnesses. “One of the benefits of using mechanistic-empirical (ME) design methods for pavements is the ability to calculate pavement response to various loading and climate conditions, and then in turn to model the entire damage process that is expected to occur over the pavement lifetime. One property that is currently not accounted for within California’s ME design software (CalME) is the change in stiffness of unbound materials that may occur due to seasonal moisture patterns. The engineering properties of unbound material may change due to a variety of factors, such as fluctuations in water content, changes in suction during wetting or drying periods, changes in overburden stress, and they are also dependent on geologic setting. Before moving to develop and implement more complex relationships to model assumed changes in the properties of unbound layers due to seasonal moisture changes...”
    Posted 11/20/2018.
  • New Research Report Published: Mechanistic-Empirical (ME) Design: Mix Design Guidance for Use with Asphalt Concrete Performance-Related Specifications. “Caltrans has adopted mechanistic-empirical (ME) methods for flexible pavement design, and is using performance-related construction specifications on some projects for hot mix asphalt. Performance-related specifications are used to help ensure that as-built materials meet the performance requirements assumed in ME pavement structural designs. PRS pose new challenges for materials producers and contractors who have never had to relate volumetric mix design parameters to achievement of mechanistic parameters for fatigue life and rutting resistance based on results from performance-related laboratory tests. The objective of this project is to provide guidance to mix designers and contractors to support their decision making regarding changes to mix designs to achieve PRS requirements. The guidance presented in this report was initially developed based on past experience. To validate...”
    Posted 8/24/2018.
  • New Research Report Published: Development of Improved Guidelines and Designs for Thin Whitetopping: Design, Instrumentation, Construction and Initial Environmental Response of Full-Scale BCOA Sections. “Thin bonded concrete overlay of asphalt (BCOA) is a rehabilitation alternative consisting of a 100 to 175 mm (0.33 to 0.58 ft) thick portland cement concrete (PCC) overlay of an existing flexible or composite pavement. Fifteen BCOA sections were built at the Davis facilities of the University of California Pavement Research Center in February 2016. Eleven of these full-scale sections were tested under accelerated loading, while four of them were used for monitoring the response of BCOA to the ambient environment and cement hydration. This full-scale experiment is part of a research project whose primary goal is to develop recommendations and guidance on the use of thin BCOA as a rehabilitation alternative in California. The design and construction of these sections is presented in this report, together with results from the quality control/quality assurance testing that was conducted. This testing...”
    Posted 8/20/2018.
  • New Research Report Published: Final Report: Permeable Pavement Road Map Workshop and Proposed Road Map for Permeable Pavement. “In early 2017, the University of California Pavement Research Center (UCPRC) and the National Center for Sustainable Transportation (NCST), working with the Interlocking Concrete Pavement Institute (ICPI), identified gaps in knowledge and other barriers to wider implementation that were perceived to be holding back the full potential for deployment of pavements that can simultaneously solve transportation, stormwater quality, and flood control problems. Further discussions were held with the National Ready Mixed Concrete Association (NRMCA), the National Asphalt Pavement Association (NAPA), and the Tongji University Sponge City Project (Shanghai, China). A workshop was organized in November 2017 based on those discussions with the goal of identifying...”
    Posted 8/16/2018.
  • New Tech Memo Published: Effects of Milling and Other Repairs on Smoothness of Overlays: Additional Testing on Construction Under Profiler-Based Smoothness Specifications. “This technical memorandum provides additional information regarding smoothness on several thin asphalt overlay projects constructed soon after changes in Caltrans specifications for constructed pavement surfaces using the International Roughness Index (IRI) as the quality metric. The IRI data were collecting using inertial profilers, before and after construction, on overlaid surfaces employing one of three repairs—digouts, cold in-place recycling (CIR), mill and filling—or none. Because the data were collected after the close of the construction contract, they include the effects of any grinding that Caltrans...”
    Posted 7/17/2018.
  • Two Presentations Given: A presentation on Reducing Pavement Life Cycle Impacts Using LCA was made by UCPRC at the California Asphalt Pavement Association (CalAPA) Conference and Equipment Expo on April 25, 2018. A keynote presentation on Asphalt Pavement Life Cycle Assessment: Review and Future Outlook was given by John Harvey in Harbin, China for the International Symposium on Road Development on May 5, 2018.
    Posted 6/15/2018.
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Winter 2019 UCPRC Activities

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.