Minergy, in partnership with OMNNI Associates and Northeast Asphalt, Inc., has developed hot mix asphalt (HMA) mix designs using glass aggregates produced from paper mill sludge produced at Fox Valley Glass Aggregate Plant and sediments containing PCBs that were dredged from the Lower Fox River.
The glass aggregates were incorporated into two E-1, 19 mm HMA mix designs at 10 and 22 percent of the total aggregate blend. The mix design, which used 10 percent of the FVGAP glass aggregate, was verified by Wisconsin Department of Transportation (WisDOT) Central office and has been used on WisDOT and private projects. Because of the grading and angularity of the glass aggregate, it was primarily used as a substitute for washed manufactured sand.
Test results indicate that the substitution of the washed manufactured sand with the glass aggregates generally resulted in an increase in the amount of recycled asphalt pavement (RAP) that could be included in the mixes and a decrease in the amount of natural sand needed. This is a result of the high angularity of the glass aggregate, which helps to build voids in mineral aggregate (VMA) into the mix. Increased RAP contents and general coarsening of the sand fraction of the mixes resulted in added asphalt binder contents that were up to 0.5% lower than comparable designs using washed manufactured sand. In addition, the incorporation of the glass aggregates and increased RAP contents produced HMA mix designs that contained up to 37% recycled materials.
Because the aggregates substituted into the asphalt supplier’s existing asphalt mix are considered to be glass, the possibility of an increased susceptibility to stripping was a parameter that was tested. The Tensile Strength Ratio (TSR) test is the test that is currently used by the WisDOT to predict the susceptibility of the asphalt binder to strip away from the aggregates when subjected to the presence of water and general weathering. TSR results for the mixes using the glass aggregates were essentially the same as the TSR result obtained from the mix consisting of aggregates and asphalt binder that were blended in accordance with Northeast Asphalt Inc.’s mix design report. These test results indicated that the addition of glass aggregates in the mix does not make the mixes more susceptible to stripping.
Prior to use on projects, full-scale field testing was performed in September 2003 on glass aggregate mix produced and placed by Northeast Asphalt, Inc., at Johnson Trucking, Inc., in Neenah, Wis., U.S.A. The asphalt mix was sampled and tested in general accordance with WisDOT Quality Management Program specifications for quality control testing of HMA mixtures. The average of the test results compared favorably with the warning limit specifications for a running four-test average. Nuclear density testing of the pavement was performed during paving operations to document the degree of compaction achieved by the rollers and to compare the results to the WisDOT Standard Specifications. The levels of compaction achieved were typical for an E-1, 19 mm mix produced in the area. The average percent compaction also met the compaction requirements of the WisDOT Standard Specifications. The range of mix properties determined during testing was what would be normally expected during a typical HMA paving project and met the applicable WisDOT specifications for HMA mix production and placement. Follow-up testing and observations conducted in the summer of 2004 indicated that the mix was performing well under relatively heavy truck traffic.
Subsequently, the E-1, 19 mm HMA mix design using glass aggregate from the Minergy-Neenah plant has been successfully used on WisDOT and private HMA paving projects. No unusual problems with this mix have been encountered either during or after asphalt mix production and placement.
The grading and high angularity of the glass aggregate helps to build VMA into the mix, producing an economical HMA mix of very high quality. Incorporation of these glass aggregates during HMA mix design completes the process of converting a waste disposal problem into a component of a high quality and very economical asphalt pavement. These mix designs demonstrate that the glass aggregates included in these asphalt mixes can be successfully used as an aggregate component in WisDOT verified asphalt mix designs as well as commercial asphalt mix designs.