Grant Julian

Performance of Asphalt Mixtures with High Recycled Contents Using Rejuvenators and Warm-Mix Additive: Field and Lab Experiments

AbstractTo improve the cracking resistance of asphalt mixtures with high recycled asphalt pavement (RAP) and reclaimed asphalt shingles (RAS) contents, one approach is to use a recycling agent (RA)...

Effects of Changing Virgin Binder Grade and Content on High Reclaimed Asphalt Pavement Mixture Properties

Most highway agencies have decades of experience with hot-mix asphalt whose percentage of reclaimed asphalt pavement (RAP) has remained low to moderate because of the general perception that RAP mixtures may be more susceptible to various modes of cracking. As the RAP proportion increases, so does the potential for an increase in mixture stiffness and a decrease in resistance to cracking. Two proposed ways to increase the durability of RAP mixtures are to (a) increase the amount of virgin binder in the asphalt mixture and (b) decrease the performance grade of the virgin binder. To assess these options, 0%, 25%, and 50% RAP mixtures at optimum asphalt content were designed with a standard PG 67-22 virgin asphalt binder. These mixtures were tested to evaluate surface cracking, reflection cracking, and rutting with the use of an energy ratio, overlay tester, and asphalt pavement analyzer, respectively. These tests also were conducted on RAP mixtures with 0.25% and 0.50% higher asphalt contents and at the optimum asphalt content with the use of a softer virgin binder. In addition, the linear amplitude sweep methodology was used to assess the fatigue properties of the blended binders. The results showed that, to improve resistance to cracking, the amount of virgin asphalt should be increased by 0.1% for every 10% of RAP binder in the mixture for up to 30% RAP binder. Once the RAP binder exceeds 30%, a softer grade of asphalt should be used to increase the mixtures resistance to cracking. All mixtures should be assessed for rutting susceptibility.

Evaluation of foamed warm mix asphalt with reclaimed asphalt pavement: field and laboratory experiments

Warm mix asphalt (WMA) technology and reclaimed asphalt pavement (RAP) materials have been increasingly used in asphalt paving mixtures due to environmental and cost benefits. Combining WMA and RAP offers more economic and environmental benefits compared to using either alone. To evaluate the combined effect of WMA and RAP, two WMA mixtures with 20% and 30% RAP were produced using water-injection plant foaming, and they were compared with two comparable hot-mix asphalt (HMA) mixtures with 20% and 30% RAP. The four mixtures were paved on I-70 near Eagle, Colorado in May 2013. Laboratory performance properties of plant-produced mixes and field performance of the four test sections after 13, 25, 38 months were evaluated. The research results showed that the effect of water foaming WMA and RAP was not significant on the laboratory performance properties, construction quality and field performance. Thus, water-injection plant foaming WMA could be used to produce WMA mixtures with 20% and 30% RAP at a lower production temperature. These sections will continue to be monitored to evaluate their long-term performance and compare with the laboratory test results.

Effect of Geosynthetic Material in Reclaimed Asphalt Pavement on Performance Properties of Asphalt Mixtures

Geosynthetic materials have been used effectively at the interface between asphalt pavement layers for waterproofing and mitigating crack propagation. When an asphalt pavement with a geosynthetic interlayer is rehabilitated, the asphalt surface layer as well as the underlying geosynthetic interlayer can be removed for new overlays. The reclaimed asphalt pavement (RAP) as well as the geosynthetic material is reused in new asphalt mixtures because the geosynthetic material cannot be removed from the RAP. This situation leads to the question of whether the presence of the geosynthetic material in RAP has a negative impact on the performance of the new asphalt mixtures. A study was conducted to answer this question. A two-layer test section with a geosynthetic layer installed at the layer interface was constructed. The sections were milled so that RAP with and without the geosynthetic material was collected. Superpave® mix designs were then produced: one with the RAP with geosynthetic material and the other with the control RAP. A variety of hot-mix asphalt (HMA) performance tests were conducted to determine whether the presence of the geosynthetic material in the RAP had an impact on the HMA performance concerning stiffness, moisture susceptibility, rutting resistance, and resistance to low-temperature cracking. The laboratory evaluation concluded that the presence of the geosynthetic material in the RAP did not have a significant impact on the RAP properties or the volumetric and performance properties of the asphalt mixture.