Spatial variability of compacted aggregate bases

This paper evaluates the construction quality of aggregate base course layers in terms of the variability and uniformity in density and modulus based measurements. Field and laboratory tests were conducted on 10 aggregate base course layers during HMA pavement construction in Wisconsin. Field tests consisted of in-place unit weight, LWD, DCP, and Stiffness Gauge measurement while laboratory tests included particle size analysis, compaction test, and repeated load triaxial test. Moreover, sensitivity analysis was conducted to assess the influence of the base course layer input parameters on the long-term performance of HMA pavements using the AASHTOWare Pavement ME Design software. Field and laboratory test results demonstrated the existence of high spatial variability in both density (relative compaction ranged from 82.6 to 109.1%, with 17% of test points having values <90%) and modulus based measurements and predictions (LWD average base layer modulus varied between 86.5 and 220.3 MPa) of the constructed base course layers variables. In addition, a pilot density-based specifications implementation phase undertaken by WisDOT demonstrated the existence of high spatial variability (including variability along the depth) in the measurement of relative compaction and water content. Only 46% of the density test results met the specified relative compaction of 95%. The various test results presented in this paper demonstrated the variability and non-uniformity of important aggregate performance parameters in base layers, which have an impact on the long-term pavement performance.