Better Roads Digital Magazine
Issue link: http://read.dmtmag.com/i/187662
HighwayContractor preferred alternative. For overlays of existing pavements (often after milling of the existing HMA surface layers), stress relief measures are included to avoid reflection cracking from cracks in the underlying layers. This can be achieved by incorporating paving fabric or placing a stress-absorbing membrane interlayer (SAMI), comparable to a rubberized chip seal. Often cracking and seating of the cement treated base (CTB) is part of the project approach to further assure reflection cracking will not occur. An essential and innovative aspect of the long-life projects is the performance test requirements in the design of the mixes. Under these designs, the produced mixes meet performance test requirements at least equal to the performance assumptions used for the pavement structural designs. This involves fatigue, shear and Hamburg wheel track testing. The top layers of the pavement structure are to be rut-resistant and durable, while the bottom layers are to be fatigue and reflection-crack resistant. This typically means the top 3 inches of the structure is a high-stability layer containing polymer-modified asphalt. In the bottom 3 inches of the bound (asphalt) layers, the fatigue resistance is obtained by increasing the asphalt binder content by 0.5 percent over the optimum binder content (OBC) from the lab mix design, and with that reducing the air-void content after compaction to less than 2 percent. In California, these pavements are capped with a sacrificial layer of asphalt-rubber open-graded porous friction course. Overall, the result is a durable structure designed for many years of service. One of the key players in the center of the Interstate 5 projects was Byron Berger, the Caltrans District 2 materials engineer. Not one to toss around praise unearned, Berger had the following observation on the two long-life asphalt pavement jobs in his district. "On a big construction job, it's rare to see such extensive collaboration between the scientists who developed the long-life design theory, at the University of California Pavement Research Center, the engineering staff that applied the design theory to the project, the Caltrans' Headquarters Pavement Program and the engineers – District 2 resident engineers Sean Shepard and John Bailey – who were in charge of overseeing construction of the project," Berger says. "These long-life projects illustrate the application of partnering at its best," he adds. "From mix-design challenges to interpretation of long-life testing data, Caltrans and the INDUSTRY LEADING CONSTRUCTION SOFTWARE THAT INTEGRATES WITH YOUR ACCOUNTING SYSTEM. Estimating Bill Farnbach with Caltrans (standing) looks over some preliminary plans for a long-life asphalt pavement design during a meeting with Rita Leahy of CalAPA (left) and Bob Humer with the Asphalt Institute. Safety GPS Job Costing Dispatching Equipment Maintenance Fuel Tracking Cloud Hosting Used by 40,000 construction professionals World-class 24/7 instant customer support Construction-friendly desktop & mobile apps Proven processes for implementation Low risk—Software comes with a 12-month money back guarantee! SIGN UP FOR DAILY WEBINARS Mobile Apps Innovative Software for the Construction Industry 800-683-3196 at www.HCSS.com/Better-Roads Text INFO to 205-289-3789 or visit www.betterroads.com/info Better Roads October 2013 25 HighwayContractor_BR1013.indd 25 9/30/13 2:10 PM