Equipment World Digital Magazine
Issue link: http://read.dmtmag.com/i/674536
EquipmentWorld.com | May 2016 55 D. Allen Covey, Virginia DOT T he purpose of compac- tion is to remove air voids and align the ag- gregate material in the asphalt mix so that the particles interlock, providing the stiffness and density required in a roadway. But the goal isn't to make pavement as hard as possible, as asphalt pavements need a small amount of porosity. Compacting too much can also create deforma- tions that negatively impact ride- ability, which is the entire premise of smoothness. The compaction process is really begun by the screed, as this paver component takes the head of mate- rial and forms it into the familiar shape of a pavement. But, that's only the initial compression. While the screed makes the as- phalt look nearly perfect when it's revealed behind the paver, it takes a roller to attain the higher density pavements need to achieve ultimate smoothness. Rollers compact asphalt in either one of two ways; via static compac- tion, in which the weight of the machine provides the force, or by vibratory compaction, in which the drums of the roller provide impact force on the paving surface. Equip- ment can be solely static, solely vibratory or can be manufactured with both capabilities. Static rollers are available in drum confi gurations (typically three- drums) or pneumatic tire confi gu- rations. Vibratory rollers come in dual- and single-drum layouts. A combination roller will often have a vibrating drum in front and static pneumatic tires in back. Base and production All the steps in the paving process are tightly joined in a vertically integrated mechanism – meaning each step along the way affects subsequent stages. So the work at the end, compaction, is only as good as the work at the start. "The more we think about smoothness from the beginning – what opportunities do we have to achieve smoothness, where should we put our effort for it, where's our money best spent – I think we're either going to fi nd in most cases you're really not worried about smoothness anymore other than to not screw it up," says consult- ing engineer, Mike Robinson. "If you can get to that point, then it becomes how uniform can we be, how good a density can we get, how high a quality can we get." Robinson has roughly 30 years of experience in the paving industry and has worked for multiple paving companies, in addition to the Cali- fornia Department of Transporta- tion, over that time span. Based in Nevada, he is a registered profes- A Hamm HD+ 120 roller used in the paving operation on the northern approach to the Huguenot Bridge in Virginia.