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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

Caltrans Thin Bonded Concrete Overlay of Asphalt (BCOA) Pilot Project. First Caltrans thin bonded concrete overlay of asphalt (BCOA) has been recently built in SR113 at Woodland, District 3. Thin BCOA, formerly known as thin whitetopping, is a pavement rehabilitation technique that consists of placement of a 4 to 6 in. thick concrete overlay on an existing flexible or composite pavement.

Caltrans thin BCOA pilot includes two stretches of SR113: PM 11.8-12.8 and PM 14.7-17.6. The latter was paved on October-November, 2018, while the former was paved on April-May, 2019. The design section of the project includes 6 in. thick concrete overlay on the milled asphalt base, 6 ft transverse joint spacing, and widened slabs. The overlay was built with a rapid strength concrete that was designed to provide 450 psi flexural strength (requirement for opening to traffic) in 24 hours. The pilot project includes also the use of new rubberized asphalt mix as a base.

The early field performance of the thin BCOA pilot is being monitored as part of Caltrans 3.39 Partnered Pavement Research Center project. The monitoring is focused on slab cracking, longitudinal unevenness, and transverse joint faulting and load transfer efficiently. To help the monitoring process, the pavement has been instrumented with a total of 110 sensors, which will be measuring concrete and asphalt strain, concrete and asphalt temperature, and concrete internal relative humidity.

It is expected that the monitoring of the construction and the early field performance of this pilot project will help to identify best and improved practices and standards applicable to California’s climate, materials, and construction work zone practices.