This article is the third of a four-part series on paving provided by Volvo Construction Equipment
Successful asphalt paving projects don’t happen by accident. They are the result of careful planning and proper preparation. From proper paver setup to achieving optimum mat temperature and conducting the rolling pattern at just the right time — each step in the process will affect the next. And attention to detail throughout the process can mean the difference between getting a bonus and being delayed.
In the previous installments, best practices for paver setup and laying a quality mat have been addressed. After the mat has been laid, proper compaction is key to ensuring the longevity of the road. The pavement must be able to cope with unexpected loads, heavy traffic flow and, depending on location, wear and tear from harsh winter weather. Following these compaction best practices will preserve asphalt integrity, and delay the need for road maintenance and repairs.
Compaction
Compaction is an essential part of the road construction process. Without proper compaction or densification, the finished roadway will not provide the sufficient level of support needed for structures or traffic loads, and eventually a breakdown of material will occur.
There are three key factors that contribute to quality compaction:
• Mat temperature
• Mat depth or thickness
• Compactor rolling pattern
Mat Temperature
The first rule of compaction is to monitor mat temperature. Compaction must be accomplished while the mix has enough fluidity to allow aggregate particle movement in order to remove voids and excess air in the pavement structure. In some instances, the time available for compaction can be as limited as 10 minutes.
“The key is to not let the mat temperature get too low because then you can’t work with it,” said Wayne Tomlinson, compaction training specialist, Volvo Construction Equipment. “The roller operator needs to get on the mat as soon as safely possible after it is laid.”
The cooling of HMA is predictable and can be anticipated based on prior experience and current ambient conditions. A compactor operator should keep notes on projects and different types of materials to determine best temperatures.
“When you find a temperature zone that gets your best density and smoothness, that’s the zone you need to work in all day,” said Tomlinson.
Mat Depth or Thickness
Thickness is an important compaction factor. Mat depth, or thickness, is established by a project engineer who determines the estimated usage and traffic volume for the intended pavement. It is initially part of the paving crew’s responsibility to set the correct angle of attack, but compaction plays a role in the “finished” mat thickness.
“There’s a 20 to 25 percent rule of thumb when it comes to compacting the right thickness,” said Tomlinson. “So if you want a 2-inch mat, the paver would lay a 2-and-a-half-inch mat. The roller would compact it, and the finished mat is 2 inches thick.”
The Future of Intelligent Compaction
Topics surrounding intelligent compaction (IC) have gained momentum in the industry over the last decade, and for good reason. IC technology allows for better record-keeping, increased compaction uniformity, automation and increased productivity for road crews. Also, IC technology ultimately saves time on the job site, since it eliminates the need to take physical samples to determine mat stiffness — this measurement is continually recorded and monitored with an IC system. However, previous IC systems were missing a large piece of data that is critical to the integrity of the finished road, and more accurate measurement than mat stiffness alone — an exact density measurement.
Density Direct from Volvo Construction Equipment — which will launch fall of 2015 — provides this critical component to the operator through an Android-based touch-screen monitor, similar to that of a smartphone. The Density Direct interface displays a map with color-coded density readings in addition to the numerical reading for density, the number of passes and temperature. When fully calibrated, the density calculations have been shown to be accurate to within 1.5 percent of the measured value of core samples.
The ability to have such an accurate density reading is crucial for several reasons. Density Direct reduces the need for core sampling and improves productivity and quality, as operators receive real-time density calculations covering 100 percent of the compacted mat, versus the traditional option of nuclear gauge testing, which is more time-consuming and provides only “spot-check” results.
Next Up: Rolling Pattern
With a properly laid and compacted mat, the final — and especially crucial — step in the process is the rolling pattern. Stay tuned for the final installment in the Precision Asphalt Paving 101 series, which will cover best practices for rolling pattern, as well as safety considerations.
Series List:
Part 1: Precision Paving Begins With Proper Equipment Setup
Part 2: Precision Asphalt Paving 101: Laying a Quality Mat
Part 3: Precision Asphalt Paving: Best Practices for Compaction
Part 4: Precision Asphalt Paving — Rolling Pattern, Safety
Part 5: Past, Present and Future of Intelligent Compaction
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