Wider Use of Various HMA Mix Types. As technology continues to develop and the market continues to demand a greater variety of paving options, more and more mix designs are becoming available. Each mix type has its specific uses and idiosyncrasies when working with it, so it is essential for contractors to know what to expect from each type and how to work with each mix.
Conventional dense-graded hot mix asphalt. A more conventional mix, dense-graded HMA is used for standard paving. It features aggregate of varying sizes surrounded by fines.
Open-graded Mix. With the open graded mix, the fines are removed and the mix is placed at 1 inch thick to allow rain water to pass through maintaining weather safety.
Gap-graded Mix. Another available mix is the gap-graded mix that contains large proportions of both coarse and fine aggregates with few large voids. Contractors will continue to see the use of gap graded mixes at intersections.
Porous Pavement. With a continued push toward achieving Leadership in Energy and Environmental Design (LEED) points, contractors working on parking lots will likely encounter porous hot mix asphalt. Smith said contractors will see an increase in this open-graded pavement, but he cautioned that this type of pavement can’t be sealcoated because the sealer would fill the pavement’s pores.
Hot Mix Plants Face Issues. While most Pavement readers are not involved in producing their own hot mix, the plants contractors buy material from are undergoing changes and encountering challenges that will impact paving work. For example, as a result of environmental sensitivity fewer new plants are opening because it’s more difficult to obtain necessary permits. As a result, contractors might have to buy mix from plants located farther from a job. This not only increases haul costs but also requires a greater emphasis on planning and scheduling so there is no downtime on the job. Smith also said that existing plants are faced with monitoring dust management, fume emissions and odor management – all of which could raise the cost of hot mix.
More Night Paving. While more specifications now require fewer road closures, more and more contractors are completing work at night. In addition to requiring additional equipment such as high-intensity lighting, the impact on a paving contractor can be significant. Crew scheduling, for example, becomes much more complicated when working the occasional night job. And because temperatures drop at night crews are working with temperatures that can lead to challenges with laying down materials.
Smoothness Becomes More Important. In many cases paving contractors are seeing a growing need for smoothness in specs, especially of a bonus is paid based on smoothness testing. Smith compared direct-dump to windrow paving, emphasizing that contractors can achieve a smoother pavement with windrow paving.