Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/85910
on pavements in good condition that do not require structural rehabilitation. The HiMA binder contained 7.5 percent SBS (styrene- butadiene-styrene) polymer, more than twice as much used in conventional polymer-modified binders. While it's com- mon industry knowledge that modification of liquid as- phalt binders with polymers improves resistance to rutting and raveling of asphalt mixes, there is a practical limit to polymer concentration. Usually, as polymer concentration exceeds three percent, the viscosity of the binder increases such that the mix becomes more difficult to produce in the plant and less workable for the paving crew. However, the polymer used in the demonstration was Kraton D0243, a new SBS product manufactured by Houston-based Kraton Performance Polymers, which meets the requirements of the new regional specifications without increasing viscosity. Vermont Places HiMA Thin Lift As Vermont shares the same climate and topography as its neighbor New Hampshire, it was keen to try out the new NEPPP demonstration thin lift technology within its borders. There, within the context of a larger paving project, Pike Industries placed a 2-mile section of thin hot-asphalt overlay containing the highly polymer-modified asphalt binder on U.S. 7 near Danby. Vermont installed the HiMA-modified mix as part of the NEPPP series of field demonstration tests. The Vermont installation followed NEPPP's PMTOL specs, which allow up to 25 percent recycled asphalt pavement (RAP) to be used in the hot mix. For the 2-mile Danby demonstration, the contractor installed 1 inch of PMTOL mix containing all-virgin aggregate on the first mile, and on the second mile installed 1 inch of PMTOL mix incorporating about 25 percent RAP. "We decided to test the highly polymer-modified mix because we're constantly looking for better, high-perfor- mance pavement materials that will provide longer service life at lower lifecycle costs," says Mike Fowler, Vermont Agency of Transportation (VTrans) pavement manage- ment engineer. "For example, if we can get the same durability and same installation cost per square yard from a 1-inch-thick HiMA-modified overlay that we're getting from a conven- tional 1 1/2-inch overlay, then we're using less material and saving money over the life of the pavement," Fowler says. "And if it's a mill-and-fill operation, then we don't have to mill off as much existing pavement, which gives us further savings." Fowler pointed out that he had learned of the HiMA field demonstrations project through VTrans' role as one of 14 state transportation agencies belonging to NEPPP. Pike Industries' Terex Cedarapids and Cat AP-1055D pavers place highly modified asphalt (HiMA) mix on U.S. 7 in Danby, Vt. Minnesota Follows Vermont States beyond the NEPPP territory learned of the field demos through memberships in the sister re- gional groups. Two of these, MnDOT, a member of the Midwestern Pavement Preservation Partnership, and Oregon DOT, a member of the Rocky Mountain West Pavement Preservation Partnership (RMWPPP), decided to incorporate HiMA in sections of their regular mainte- nance overlay contracts. Minnesota DOT looked at HiMA to see if it could fight reflection cracking. "The 12.5-millimeter Superpave mix we've been using for our mill-and-fill operations has done a good job of reducing thermal cracking, but we need a way to reduce reflection cracks," says Jerry Geib, P.E., MnDOT research operations engineer. There, the HiMA was used on a trial section on Minnesota Trunk Hwy. 100, substituting HiMA binder for the regular PG 64-28 binder. The HiMA binder for the MnDOT test was produced by Midwest Industrial Asphalt of Onalaska, Wis., a major supplier of conventional and polymer-modified bitumen products. In addition, MTE Services, a sister company, supported Midwest Asphalt's operation to produce the proper blending of D0243 polymer with the selected liq- uid asphalt binder. For the trial, Hardrives Inc., of Rogers, Minn., employed a Wirtgen W200 cold planer to mill off existing pave- ment, a Cat AP-1055D paver to install the HiMA overlay, and two rollers operating in vibratory mode, a Dynapac steel drum breakdown roller and a Hamm HD+140 tan- dem finish roller. According to Geib, the paving crew said there was no difference between handling HiMA mix and MNDOT's usual 12.5mm Superpave mix. Information for this article was provided by Kraton Performance Polymers, Inc. Paul Fournier, an out- sourced writer, contributed editorial material for this article. Better Roads February 2012 35