As reported at the QC Manager Spring meeting on April 14, 2021, IAPA members have expressed concerns with increased Hamburg Wheel failures with the implementation of IFIT. Live polling suggested that about one-third of dense-graded mixes (polymer and polymer) and two-thirds of IL4.75 mixes have Hamburg rut depths greater than 10 mm at the required number of passes.
Potential causes include changes in sample preparation (62 mm sample changed to cutting samples from top/bottom of 160 mm gyratory), changes in void compaction (7% to 7.5%), adjustments to improve Flexibility Index, or other issues. The Department conducted a voids study over the winter with samples submitted by IAPA members. While this study did demonstrate some trends with voids, it did not identify a definite cause of Hamburg failures. Therefore, the Department has asked for IAPA members to provide more detailed information on mixes that are of concern. Members are asked to provide mix data using this spreadsheet for any design that is failing, has failed, or maybe close (>10 mm rut depth) to failing Hamburg testing in the 2020 or 2021 design season. PLease complete as much of the data fields as possible.
Please return the completed excel spreadsheet and appropriate mix design sheets for each trial by May 31, 2021. This information will only be shared with the Department to evaluate potential changes to the Hamburg requirements.
