Compaction, in heavy construction, is the application of energy to soil, crushed rock, or asphalt to increase density by driving out air, which enables the finished, compacted material to support buildings, roadways, and other structures. Compaction is specified as a percentage of the maximum dry density determined in the lab.
During construction, compaction is most often measured using a nuclear densitometer. Other reliable methods include the use of sand cone (ASTM D-1556) and rubber balloon (ASTM D-2167) methodologies; less formal tests used in the field include soil probes (a pointed steel rod pushed into the ground to gage penetration resistance and therefore estimate compaction), proof-rolling with loaded dump trucks while observing deflection, and even boot-heels. These all are necessarily spot-checks; consistency is sought by controlling the compaction process. This requires the roller operator’s ability to track speed and passes over each section while estimating compaction, leading to both over- and under-compaction. Near-constant inspection is usually needed, and even so, compaction is a frequent source of job site disagreement.
Intelligent compaction (IC) is a system growing in use which combines on-board GPS, computers, and axle-mounted accelerometers to provide continuously-controlled compaction. The accelerometers measure stiffness, and indirect measurement of density, and feed that information to the computer, which uses GPS to produce a color-coded map of the working area; the colors are used to provide an intuitive depiction of areas already meeting specifications, and those needing more compaction. For asphalt work, IC systems (there are approximately eight US equipment vendors developing and selling IC), infrared sensors measure (and the computer maps) the asphalt temperature, a critical data set in ensuring timely compaction as the material cools.
As is normal, a test zone is compacted at the start of the overall compaction effort to determine the number of passes and speed the material requires to meet specifications. That information is entered into the on-board IC system as the baseline against which future work areas are compared and mapped. This eliminates guesswork, eliminates overwork, and improves the homogeneity of the finished product, saving money for the contractor and improving the service life of the compacted product.
Intelligent compaction, requires mobile technologies, GPS tracking and artificial intelligence to calculate all kinds of accelerometer and speed data, location and project requirements. This is another example of how the physical is meeting the digital and improving processes. You can learn more about how artificial intelligence is being integrated into field services by ClickSoftware here.
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Kevin Benedict,
Head Analyst for Social, Mobile, Analytics and Cloud (SMAC)
Cognizant
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***Full Disclosure: These are my personal opinions. No company is silly enough to claim them. I am a mobility and SMAC analyst, consultant and writer. I work with and have worked with many of the companies mentioned in my articles.
