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NEWS (Previous News Items)

  • In September 2014, the UCPRC published the report “Improved Methodology for Mix Design of Open-Graded Friction Courses”. This study presents an improved methodology for the mix designs of open-graded friction courses (OGFC). The methodology has been enhanced by the development of an Excel macro in order to suggest revisions to California Test 368, Standard Method for Determining Optimum Binder Content (OBC) for Open-Graded Asphalt Concrete. In addition to the development of the Excel macro, one of the primary objectives of this study was to evaluate the effect that fines content has on mix performance, which cannot be identified by the “break point sieve” concept or by volumetric properties. Posted 9/30/2014.
  • The variability of On-board Sound Intensity (OBSI) testing results due to different equipment operators is an important consideration in the study of tire/pavement noise on both flexible and rigid pavements. Results of an OBSI "rodeo" conducted by the UCPRC--in partnership with Illingworth and Rodkin (Petaluma, CA)--showed that the difference among test vehicles with different operators was, at most, about 1 decibel, a finding consistent with other OBSI comparisons. Posted 9/30/2014.
  • The Inertial Profiler Certification Program is up and running. Six certifications have been performed since July 2013. The program, which is intended to ensure that qualified operators and profilers perform pavement QA testing, has certified 25 operators and 18 inertial profilers to date. Follow the links to see the lists of Certified Operators and Profilers. Posted 7/22/2014.
  • The International Symposium on Pavement LCA was held in Davis, California, on October 14-16, 2014. Information is available here. Posted 10/20/2014.
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Summer and Fall 2014 UCPRC Activities


Candidate for fully permeable shoulder retrofit validation site

Laboratory Evaluation and Accelerated Pavement Testing of Different Open-Graded Hot-Mix Asphalt Materials. This study was part of a long-term effort that started in 2005 to develop the specifications, guidelines, standardized laboratory and field test methods, and other information needed for quieter pavement research to be incorporated into standard Caltrans practice. Based on their performance in an earlier laboratory study, several open-graded friction course (OGFC) mixes were selected for further evaluation with accelerated pavement testing using the Heavy Vehicle Simulator (HVS) and laboratory testing on plant-produced materials. These selected mixes had shown good overall laboratory performance in the previous study in terms of durability and sound absorption.

The following HVS test cells were constructed for this experiment:

  • Cell A: Caltrans 3/8 inch mix with PG 76-22PM binder, average as-built thickness = 0.06 ft
  • Cell B1: #4P mix with PG 76-22PM binder, average as-built thickness = 0.06 ft
  • Cell B2: Same mix as Cell B1, average as-built thickness = 0.07 ft
  • Cell C: #4P mix with PG 64-16 binder, average as-built thickness = 0.05 ft
  • Cell D: Georgia 1/2 inch mix with PG 58-34PM, average as-built thickness = 0.15 ft

The #4P mixes had nominal maximum aggregate size of 4.75 mm (#4 sieve) with “P” indicating a coarser aggregate gradation identified in the earlier laboratory study. The five test cells included three new OGFC mixes, with the Caltrans 3/8 inch mix serving as the control mix. The study examined the performance of the selected OGFC mixes in terms of their constructability, rutting performance, moisture damage susceptibility, surface texture, permeability, clogging susceptibility, clogging and rutting mechanisms, and tire/pavement noise.

The study found that while all of the mixes are feasible for a given project, the preliminary indications with regard to differences in expected performance are:

  • The #4P mixes offer superior noise and mechanical durability compared with the control mix. They have similar skid resistance, as measured by California Test 342 (CT), and surface permeability. They have lower macrotexture than the control, but more than the dense-graded mixes. A rubberized binder may improve moisture sensitivity and rutting performance, which was better or worse than the control mix depending on the binder type.
  • The Georgia 1/2 inch mix is likely to provide superior skid resistance and rutting performance compared to the control mix, although it could not be fully investigated in this project due to difficulties in getting it produced by local plants as designed. This mix is also likely to cost more because of the lime treatment and fibers recommended by the Georgia DOT in addition to the polymer-modified binder.

Based on the results from this study, it is recommended that several pilot sections using the #4P mix be placed using a rubberized binder. For these mixes to be placed, the gradations may need to be adjusted somewhat to be producible using current crushed stone bin gradations. It is also recommended that consideration be given to increasing the minimum surface and air temperatures for paving of open-graded mixes.

Important Note for Caltrans Users: Prior to scheduling pavement preservation (preventive maintenance or CAPM) or roadway rehabilitation work on flexible pavement highway sections, the District Materials Engineer and/or the Project Manager should review this spreadsheet to ensure that the proposed project does not include sections active in the “Quieter Pavement Research” (QPR) testing program. If the proposed project is within a QPR test section, please contact Linus Motumah of the Caltrans Office of Pavement Design before scheduling the work.

To view maps that show where the sections are located, click the following link: (or copy-and-paste it into a new browser window for a slightly larger view).

For more information, contact John Harvey of the UCPRC or Linus Motumah.