Use of the Hamburg Wheel-Tracking Device for Evaluating Moisture Susceptibility of Hot-Mix Asphalt

Abstract

Laboratory testing of hot-mix asphalt (HMA) to evaluate moisture susceptibility has improved over the past several decades. Within the past 8 years, the Hamburg wheel-tracking device (HWTD) has gained prominence in evaluating HMA for moisture susceptibility. There are no standard test methods or specifications established for this testing device. Laboratory repeatability of the test, testing configuration, test temperature, and capability to evaluate effects of antistripping additives in HMA were evaluated in this study. The HWTD was observed to be very repeatable where six replicate tests provided consistent test results. The device yielded repeatable results for mixtures produced with different aggregates and with test specimens fabricated by different compacting devices. The conventional testing configuration was altered so that cylindrical test specimens fabricated with a Superpave gyratory compactor could be used in lieu of rectangular slabs. Results indicate that cylindrical specimens compacted with the SGC could be used for moisture evaluation in the HWTD for comparative evaluation of materials. Typically, testing with the HWTD is performed at 50°C. Six mixtures were fabricated with and without antistripping additives and tested at 40°C and 50°C. Mixtures were modified with hydrated lime and a liquid antistripping additive and all were mixed with AC-20. Test results have indicated that mixtures with hydrated lime perform best, followed by those modified with liquid antistripping additive, and worst were those without any additive at 40°C. Inconsistent trends were observed at 50°C. The HWTD properly predicted performance of the mixtures modified with antistripping additives at 40°C.