RoadScience Tutorial: Want Optimum Density? Get Smart
Intelligent Compaction (IC) comes from both intelligent machines and intelligent operation.
For both soil and asphalt rollers, today’s “intelligent compaction” (IC) uses machines that sense the degree of compaction beneath the drum, and vary compactive force to get density.
Now, this capability is combined with global positioning system (GPS) technology to create a real-time database of densities obtained anywhere on a pass, with the ability to log the number of passes and the temperature of the mat, anywhere on that mat, on any pass.
Intelligent rollers have the ability to make and execute an appropriate decision based on the analysis of collected information. They measure material stiffness data during compaction, analyze that information, and make a decision how to adjust the vibratory drum to optimize compaction.
Conversely, conventional compaction has limitations. It provides little or no feedback on the fly. Corings for density measurement are not analyzed until after compaction, and may not be representative of the entire section. Overcompaction can occur.
In the short term, intelligent compaction can improve density for better performance, improve construction efficiency for cost savings, and increase construction information for better quality control and quality assurance.
The Human Factor
But the burden of being right still falls on the operator, who must balance the demands of new mixes and equipment technologies against the variables of weather, variations in plant mix, and out of spec mixes caused by everything from plant errors to traffic jams to make a pavement meet density.
And while intelligent compaction technology now in development is changing the way rollers will operate in the future, in the quest for optimum density today, there is still no substitute for the kind of human experience that years in the operator’s station brings.
“A well-trained and experienced operator is better able to adjust to the ever-changing conditions encountered on construction projects than the computer-aided compactor,” says Dale Starry, director, strategic technologies, for Volvo Construction Equipment. “An experienced operator is more adept at adjusting the performance of the compactor to achieve needed results, especially when unpredicted construction delays are experienced.
“Just as a seasoned airplane pilot takes command from the auto pilot system when turbulence or other conditions are encountered,” Starry continues, “an experienced compactor operator is able to adjust the operating characteristics of the machine when the changing conditions of the material call on that operator to do so.”
An experienced operator reacts to jobsite variables and compensates for changes to materials that allow construction to continue on schedule, which is important on any high-volume project, Starry says. “For example, an experienced operator sees when soils are too dry or too wet and adjusts the operation of the compactor,” he says. “The experienced operator can also alert other personnel onsite that material modifications are needed.”
The intelligent compactor does not possess this ability, he says. “The computer on the machine can only react based on pre-programmed algorithms,” Starry says. “If the measured dynamic stiffness modulus for the soil is too low, the intelligent compactor will adjust itself to generate more force, or require additional passes over the material in an attempt to increase its stiffness modulus. If this soil is too wet, more compaction force and more passes only make the situation worse.”
Moreover, asphalt compaction is complicated by the abundance of new types of asphalt mixes being placed. Marshall hot-mix asphalt (HMA) designs are being supplanted by Superpave mixes, the tender zone of which is precludes compaction within an intermediate period.
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