Better Roads Digital Magazine
Issue link: http://read.dmtmag.com/i/325401
Better Roads June 2014 7 estimate the level of compaction of the pavement, but the use of these in the quality control of subgrade compaction is still under investigation, the authors write. "Existing IC technology provides a measure of stiffness in terms of a Roller Measure- ment Value (RMV)," they say. "Research is still underway to establish good correlations between RMV [their term for the ICMV] and the stiffness estimated by the conventionally avail- able equipment such as falling weight deflectometers and dy- namic cone penetrometers and laboratory resilient modulus." In work supported by Volvo Construction Equipment; Shippensburg, Pennsylvania; and the Oklahoma Transporta- tion Center, the ability of the Oklahoma University-developed Intelligent Asphalt Compaction Analyzer [IACA] in evaluating the resilient modulus of subgrade compaction was investigated. Two full-depth asphalt pavement construction projects were considered and the use of the IACA during the com- paction of stabilized subgrade was studied. In both these projects, it was verified IACA can predict subgrade resilient modulus with a reasonable accuracy. While the IACA was designed to estimate the density/ dynamic modulus of asphalt pavements during compaction, the present study showed that the IACA could be used to determine resilient modulus of stabilized subgrade soils with minimal modification. "While the results are promising, it's prudent to point out that the tests so far have focused on cementitiously stabilized subgrades," Barman, Nazari, Imran, Commuri, Zaman, Beainy and Singh say. "Additional tests for different soil types and ad- ditives are required to fully validate this technology. Research is underway to verify the ability of the IACA to identify and rectify under compacted regions on the prepared subgrade." MDP alternative to accelerometers The Cat Compaction Control system is featured on new Cat soil compactors, tandem vibratory compactors and pneumatic rollers, and is one element of a suite of intelligent compac- tion technologies. For soil compactors, the basic system provides compaction measurement using either compaction meter value (CMV) or machine drive power (MDP) technology, with the ability to boost the system with GPS mapping capability. For tandem vibratory rollers and pneumatic compactors, the system pro- vides pass-count information and GPS mapping. MDP, a machine-integrated soil compaction measurement technology, is available on new Cat B-Series soil compac- tors, and is unique in that it measures compaction with the vibe system on or off. MDP measures rolling resistance as an indication of soil stiffness, Cat says. It measures closer to the depth that the machines are able to compact. It also measures closer to lift thickness. The measurements are less impacted by the dampening effect of cohesive soils, so it can be used on padfoot machines. Machine drive power is a not a break- through in how machines compact, the maker says. Instead, MDP evaluates the rolling resistance without an accelerom- eter. "It gives an indication of soil stiffness by measuring the rolling resistance on the drum," says Loïc Le Bellec, regional sales support consultant for Caterpillar Paving Products. "It correlates the fact that the looser the material is, the harder it is for the drum to roll over the pile of material in front it." That resistance provides an indication of soil stiffness and load-bearing strength, and whether compaction is adequate to hold the road, parking lot, building or whatever is planned for the site. In Iowa, an on-off ramp in Altoona proved a great testing ground for intelligent compaction and MDP, demonstrating the ease of preventive measures, compared with costly post- construction repairs. Operator Eddy Butler went to work on the ramp, viewing real-time results on an easy-to-use monitor display on the Cat CS74B soil compactor, outfitted with Cat Compaction Control, including MDP. A green area on the display meant the area had been covered and the targets had been met. A RoadScience In-cab HCQ Tablet PC shows exact location of passes and degree of com- paction reached in color-coded format. Photo courtesy of Wirtgen America Inc. RoadScience_BR0614.indd 7 6/2/14 1:14 PM