Pennsylvania's Experience in the Compaction of Asphalt Pavements

    Published: Jan 1984

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    During 1974 through 1977, premature pavement distress in the form of loss of fines (matrix) and ravelling (loss of aggregate particle larger than 6.35 mm [¼ in.]) was observed on several asphaltic concrete overlay projects in Pennsylvania. Statistically designed detailed investigations were conducted to determine the cause of this premature distress. Cores 152 mm (6 in.) in diameter were obtained at random and tested for density, air void content, mix composition, and rheological properties of the recovered asphalt. Lack of adequate compaction (high air void content) was determined to be the primary cause of distress. Nuclear control-strip techniques were used on these projects for compaction.

    The following data obtained from these investigations are included in the paper: (1) correlation of air void content with the extent of loss of fines and ravelling (rated as none, slight, moderate, and severe from field observations) and (2) correlation between the percent compaction data obtained by two methods (core density and nuclear gage density) at the same locations on the distressed pavements.

    Statistical analysis of the data from these projects indicated that (1) the percent compaction just after construction should be at least 92% of the maximum specific gravity of the mix to prevent the premature distress in the pavement and (2) the nuclear gage cannot be relied on completely by the user agency for acceptance purposes; it is most suited for compaction quality control by the contractor during construction.

    A statistical (end result) specification for compaction was developed and implemented by the Pennsylvania Department of Transportation in 1978. Density cores are obtained and tested at the central laboratory. The adoption of this compaction specification has resulted in a very significant improvement statewide in the initial compaction levels of asphalt pavements. The paper gives the outlines of this compaction specification, test procedures, and implications. The data on actual compaction levels (based on approximately 6000 core tests) achieved statewide in 1981 have been analyzed statistically for both binder and wearing courses.


    compaction, asphalt pavement, asphalt concrete, bituminous concrete, specifications, nuclear gage, pavement core

    Author Information:

    Kandhal, PS
    Bituminous testing and research engineer, and engineer of tests, Pennsylvania Department of Transportation, Harrisburg, Pa.

    Koehler, WC
    Bituminous testing and research engineer, and engineer of tests, Pennsylvania Department of Transportation, Harrisburg, Pa.

    Committee/Subcommittee: D04.40

    DOI: 10.1520/STP32503S

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