The State of Maine Department of Transportation is at the forefront of research on how to improve road pavement quality and extend service life. They focus on improving both the material mixes used and how they are put down in the field. One recent addition is the use of GSSI’s PaveScan RDM which can accurately measure whether there is density uniformity throughout the pavement layer. Studies have found that op- timum pavement density is a crucial factor in increasing pavement life. Pilot tests on about a dozen projects show promising results; research- ers believe the equipment will be a powerful tool to help contractors make adjustments to ensure pavement quality. State of Maine uses a variety of methods to make the most of their road paving budgets Every state faces road paving funding restrictions. The State of Maine Department of Transportation devotes a significant portion of its bud- get to roadway and pavement improvements and needs to make the most of its limited resources. The state has a three-year $2.3 billion work plan; 2018 work included 48 miles of highway construction and rehabilitation at an estimated cost of $67.6 million; 356 miles of preservation paving estimated at $93.8 million, and 600 miles of light capital paving at a cost of about $22 million. Dale Peabody, Director of the Transportation Research Division at Maine DOT, explains that there is never enough funding to keep up with all the road pavement work needed. That’s why his team is con- stantly looking for ways to improve both the material mixes used and how they are laid in the field. On the mix side, Maine DOT uses a variety of tools to test compacted asphalt mixtures, including the Hamburg Wheel Tracking Device (HWTD), and the Asphalt Mixture Performance Tester (AMPT), a computer-controlled hydraulic testing machine that subjects samples to cyclic loading over a range of temperatures and frequencies. They also recently began using MiST (Moisture Induced Stress Tester), a new method for testing moisture damage susceptibility of asphalt mixtures. As for the materials themselves, Maine has conducted research on hot in-place recycling (HIPR); plant mixed recycled asphalt pavement (PMRAP) construction using asphalt emulsion and cement; and ultra- thin bounded wearing course (UTBWC) surface treatment, which na- tionwide research suggests reduces deterioration. They are also using Maine DOT Uses New GPR Technology to Improve Road Pavement Quality and Service Life Helps ensure optimum pavement density throughout pavement layer By Rob Sommerfeldt
Other density measurement methods offer limited sampling
thin hot-mix asphalt (HMA) overlays to extend the life of pavement still in serviceable shape. Laboratory performance test equipment is used to ensure the mixtures will last longer and be more durable. They are also working on new lab tests that will be better at measuring per- formance with regard to moisture. On the material lay down side, Maine DOT does the most it can to make sure the material is applied properly in the field. It specifies the equipment contractors must have, for example, materials transfer ve- hicles (MTVs), which ensure a more uniform and longer lasting road surface. They also include ride smoothness specifications to cut down on the undulations that would eventually lead to road performance issues. Also included are specifications for joints; thermal profiling with an infrared (IR) scanner; and use of intelligent compaction (IC) rollers, which facilitate real-time compaction monitoring and timely adjustments to the compaction process by integrating measurement, documentation, and control systems. “We began implementing quality control/quality assurance (QC/QA) practices years ago, and we have trained and certified technicians sampling material on the roadway,” said Peabody. “It’s a continuous process, in which we have gone away from fixing the worst first to aggressive preservation practices. It’s just like how drivers don’t wait until a car breaks down before changing the oil.” Uniform density throughout the pavement layer is critical According to Maine DOT’s Peabody, optimum pavement density is the crucial factor in increasing pavement life. “Optimum density reduces oxidation, reduces moisture damage, and decreases rutting potential. It also offers improved fatigue life and increased load bearing capacity.” He cites past studies relating density to pavement life – the rule of thumb is that even a 1 percent decrease below minimum density results in a 10 percent loss of pavement life. Peabody has found that segregation (separation of the coarse aggre- gate particles in the mix from the rest of the mass) is the enemy of density – and is a major cause of premature pavement failures. There are two types of segregation: mechanical (physical or gradation) and thermal. Unfortunately, segregation is often only identified visually and is a subjective value that is difficult to quantify. It may not even be apparent at the time of construction, making it very difficult to enforce contractually. In the past Maine has used nuclear density gauges to measure density but has moved away from this type of technology. Contractors now use
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csengineermag.com
october 2020
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