Surface friction measurements of fine-graded asphalt mixtures : final report, June 2008.
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Surface friction measurements of fine-graded asphalt mixtures : final report, June 2008.

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English
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  • Creators:
    Williams, Stacy G.
  • Corporate Creators:
    University of Arkansas, Fayetteville. Dept. of Civil Engineering
  • Subject/TRT Terms:
  • Publication/ Report Number:
    MBTC 2066
  • Resource Type:
    Tech Report
  • Geographical Coverage:
    Arkansas
  • Edition:
    Final report; June 2008
  • Corporate Publisher:
    University of Arkansas, Fayetteville. Dept. of Civil Engineering
  • NTL Classification:
    NTL-HIGHWAY/ROAD TRANSPORTATION-Materials;NTL-HIGHWAY/ROAD TRANSPORTATION-Pavement Management and Performance;NTL-HIGHWAY/ROAD TRANSPORTATION-Design;
  • Abstract:
    Skid resistance is generated by the development of friction between the vehicle tire and

    roadway surface, and is partially dependent upon the characteristics of the pavement

    texture. Microtexture and macrotexture are the critical components of pavement surface

    friction. Microtexture is the dominant characteristic at low speeds, and at high speeds,

    microtexture and macrotexture are both necessary. While these parameters are very

    important, neither is considered during the design of an asphalt mix.

    In this project, mixture design parameters were investigated to determine what features

    of 4.75mm hot-mix asphalt (HMA) mixtures significantly influenced skid resistance. The

    British Pendulum Test (BPT) was used to quantify microtexture, and a sand patch test

    (modified for laboratory use) was used to measure macrotexture in terms of texture

    depth. Mixture properties and aggregate properties were also analyzed in order to

    develop relationships and guidelines for producing skid resistance during the design

    phase of an HMA construction project. Additional considerations involved comparisons

    with traditional surface mixes of larger nominal maximum aggregate size, and the effects

    of aging and wear on the long-term skid resistance of 4.75mm mixtures.

    In general, mixture properties did not provide significant relationships to skid resistance

    (microtexture or macrotexture). Aggregate properties, however, did significantly

    correlate to measures of macrotexture. Specifically, the most influential variables were

    fine aggregate angularity, percent passing the #30 sieve, bulk specific gravity of the

    aggregate blend, and two-dimensional particle shape (as measured by the Aggregate

    Imaging System). Aggregate gradation was also significant in that a gap-graded

    aggregate blend appeared to increase both microtexture and macrotexture.

    When compared to 9.5mm and 12.5mm mixes, the 4.75mm mixes possessed the

    greatest levels of microtexture. Thus, it was concluded that 4.75mm mixes did provide

    adequate skid resistance for low-speed roadways. The macrotexture of 4.75mm mixes

    was significantly less than that for a more traditional 12.5mm surface mix. Thus, if

    4.75mm mixes are desired for use on high-speed roadways, the effects of roadway

    geometry on pavement drainage should be carefully considered.

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