RESUMO
In recent years, due to the advent of several additives and innovations, asphalt mix design has become more complex. The mixes meeting the volumetric mix design requirements may still fail prematurely in the field. Thus, a transition from a simplistic volumetric-based mix design to a performance-based mix design is required, which was also envisioned in the Strategic Highway Research Program (SHRP) and Superpave mix design. In addition to performance verification, asphalt mix designs should also be evaluated for the life-cycle costs and environmental impact to encourage durable as well as sustainable and cost-effective alternatives. In this study, three asphalt mixtures with different reclaimed asphalt pavement (RAP) contents and additives were evaluated for cracking and rutting performance by using different performance thresholds for asphalt mixtures that are generally used in the construction of high-volume roads in Oregon. A balanced mix design process was followed to determine the required binder content for the three mixtures. Based on the life cycle cost and environmental impact analyses, the mixture with warm mix additive (WMA) was selected as the most economically and environmentally viable asphalt mixture to be used for construction in Oregon.
RESUMO
The interest in minimising fuel consumption and greenhouse gas emissions among road specialists is increasing. Thus, methods for reducing asphalt concrete mixing and compaction temperatures by a few tens of degrees Celsius without compromising the long-term performance has become a topic of significant interest. This study is focused on the analysis of warm mix asphalt (WMA) prepared with locally available materials in order to determine the suitable technology applicable to the specific traffic and climatic conditions of Romania. WMA was prepared using different warm mix additives (organic additives, chemical additive, and synthetic zeolite) at different mixing and compaction temperatures, and bitumen blends with these additives were analysed by carrying out the dynamic shear rheometer test and evaluating the penetration index. In conclusion it was noted that most additives did not lead to a significant change of bitumen's characteristics, but the organic additive had a big influence on the bitumen's properties. The characteristics of WMA are very similar to those of HMA. The mixing and compaction temperatures could be reduced by approximately 40 °C when WMA was blended with the additives without compromising the performance of the asphalt mixture, compared to hot mix asphalt.
RESUMO
In this study a new procedure is developed to obtain core samples from field sections to assess clogging mechanisms of open graded friction course (OGFC) pavements using X-ray computed tomography (CT) imaging. The approach compared X-ray computed tomography (CT) images taken before and after: (1) rainfall simulations without trafficking to investigate particle-related clogging and (2) full-scale accelerated pavement rutting tests (APT) to investigate deformation related clogging of OGFC layers. Rainfall simulations were performed with runoff water of known total suspended solids (TSS) and particle size distributions (PSDs). Full-scale accelerated rutting tests were performed under controlled temperature and loads. Both investigations were performed for three different OGFC pavements with different layer thicknesses and mix types. The clogging of rutting test sections were also evaluated by comparing the surface permeability measurements performed before and after APT testing. The results of X-ray CT image processing revealed a significant reduction in air-void content of core samples after APT rutting tests. The highest air-void reduction was concentrated at the bottom of the OGFC layers. Permeability measurements also showed a 40%-90% reduction in permeability after APT trafficking. X-ray CT image processing of core samples tested under simulated rainfall showed that air void content reduction is concentrated in the lower part (2-6 mm from the bottom) of the OGFC layers as a result of particle accumulation. Small changes in air void contents were observed in the upper part of the OGFC layers (10-15 mm) while these reductions in air void contents were not significant to cause surface overflow and hence it is expected that the tested OGFC pavements will have sufficient permeability to infiltrate water during most average storm events.