A platform for research: civil engineering, architecture and urbanism
A platform for research: civil engineering, architecture and urbanism
The fine aggregate specification for Superpave hot mix asphalt (HMA) mixtures includes a restricted zone (RZ) that forms a band through which gradations were recommended not to pass, since mixtures passing through the RZ are believed to be rut-susceptible. However, the RZ requirement has long been a contentious issue, leading to many research efforts to investigate the effects of RZ on HMA performance. A generally agreed upon conclusion from the national research is that the RZ criterion is redundant and should be eliminated from the Superpave specification. Although the elimination of the RZ requirement is suggested today, it still remains questionable, since the research conclusion has often been made for a premium mix designed with high-quality aggregates, which is not the case for low volume Nebraska pavements. Therefore, this research was undertaken to evaluate the RZ effects on rutting-associated performance particularly for low volume local-road mixes (called SP2 mix in Nebraska). In addition, mechanical impact due to fine aggregate angularity (FAA) on HMA performance was also evaluated. Five mixes (one above-RZ mix, two through-RZ mixes with different gradations, and two below-RZ mixes with different FAA values) were designed and tested by using a simple performance testing device, the asphalt pavement analyzer (APA). Based on APA performance testing results, it can be concluded that finer-graded mixes are generally similar to or better than coarser-graded mixes. Consequently, the Superpave RZ requirements may not be a factor governing HMA mix design and performance. One more interesting fact observed from this study is that insufficient FAA in coarse-graded mixes might cause more severe rut-damage in HMA. Preliminary findings from this study can be strengthened with more laboratory data and additional work. Suggested follow-up studies conclude this report.
The fine aggregate specification for Superpave hot mix asphalt (HMA) mixtures includes a restricted zone (RZ) that forms a band through which gradations were recommended not to pass, since mixtures passing through the RZ are believed to be rut-susceptible. However, the RZ requirement has long been a contentious issue, leading to many research efforts to investigate the effects of RZ on HMA performance. A generally agreed upon conclusion from the national research is that the RZ criterion is redundant and should be eliminated from the Superpave specification. Although the elimination of the RZ requirement is suggested today, it still remains questionable, since the research conclusion has often been made for a premium mix designed with high-quality aggregates, which is not the case for low volume Nebraska pavements. Therefore, this research was undertaken to evaluate the RZ effects on rutting-associated performance particularly for low volume local-road mixes (called SP2 mix in Nebraska). In addition, mechanical impact due to fine aggregate angularity (FAA) on HMA performance was also evaluated. Five mixes (one above-RZ mix, two through-RZ mixes with different gradations, and two below-RZ mixes with different FAA values) were designed and tested by using a simple performance testing device, the asphalt pavement analyzer (APA). Based on APA performance testing results, it can be concluded that finer-graded mixes are generally similar to or better than coarser-graded mixes. Consequently, the Superpave RZ requirements may not be a factor governing HMA mix design and performance. One more interesting fact observed from this study is that insufficient FAA in coarse-graded mixes might cause more severe rut-damage in HMA. Preliminary findings from this study can be strengthened with more laboratory data and additional work. Suggested follow-up studies conclude this report.
Restricted-Zone Requirements for Superpave Mixes with Local Aggregate Sources
2006
40 pages
Report
No indication
English
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