Precision Estimates of AASHTO T283: Resistance of Compacted Hot Mix Asphalt (HMA) to Moisture-Induced Damage

This work presents an interlaboratory study (ILS) resulting in a precision and bias statement for AASHTO T283, “Resistance of Compacted Hot Mix Asphalt (HMA) to Moisture-Induced Damage.” To gain insight into the variability of the T283 test results, a micro-scale finite element analysis using X-ray images of the test specimens was conducted. The ILS included preparing and testing 6 replicate specimens according to AASHTO T283 using two different aggregate sources and two compaction methods. The two aggregate sources were selected based on their moisture susceptibility. A sandstone aggregate representing moisture susceptible and a limestone aggregate representing moisture resistance were selected for the study. Marshall and Superpave gyratory compactors were selected as means of compaction to create test specimens with different structures. The statistical analysis of the ILS results indicated that the average tensile strength ratios (TSR) of the Marshall and gyratory specimens and that of limestone and sandstone mixtures were significantly different. Despite the difference in the average TSR values, the variability of TSR of Marshall and gyratory compacted specimens of limestone and sandstone mixtures were not significantly different. In this respect, the TSR statistics of the four specimen types (two mixture types and two compaction methods) were combined to prepare the precision estimates for AASHTO T283. The simulation of moisture infiltration in the X-ray images of gyratory and compacted specimens indicated that moisture penetrates to the center of Marshall specimens much faster than to the center of gyratory specimens. The reason for this was found to be the difference in size and distribution of outside and inside pore spaces in gyratory and Marshall specimens. Additionally, the conditioning procedure, as described in the current T-283 standard was found to not represent the actual moisture infiltration time frame that produced damage in the field. This could explain the often encountered discrepancy between laboratory and field moisture performance.