WWW.ACPA.ORG 13 SUMMER // 2024 DIAMOND GRINDING determined that three years of maintenance neglect resulted in six times the repair cost. Five years of neglect resulted in up to eighteen times the repair cost. This relationship is due to the level of invasive work required to remediate a pavement section. For example, if a concrete pavement suffers from slab curling, the very cost-effective diamond grinding treatment can be performed using heaving machinery and minimal hand work. However, if that pavement is left to be beaten by dynamic loads for an extended period, the need for crack and full-depth repairs will be more prevalent—and drive-up costs. Reducing the International Roughness Index (IRI) before significant damage is done will mitigate this untimely wear and tear on pavements, resulting in a more efficient use of tax dollars and building materials. CASE STUDY: ASSET MANAGEMENT IN ARKANSAS The Arkansas Department of Transportation (ArDOT) collects data on interstates every year. Once data collection is complete, it is processed and a pavement condition index (PCI) summary is calculated, using a weighted average of four types of pavement metrics: environmental cracking, structural cracking, roughness and rutting. Conditions are assessed using FHWA threshold criteria for each 1/10-mile-long pavement section. The index is then used to assign a pavement condition rating, or “grade,” which describes the pavement condition of the state highway system as good, fair or poor. Pavement Preservation Efforts Maintain Rideability at a Competitive Cost Several sections of the pavement on I-40 in Arkansas are constructed of concrete, and a 4.3-mile section in Johnson County, constructed in 2002, provides one example of the advantages of pavement preservation. This portion of I-40 sees an average daily traffic (ADT) of 28,000 vehicles per day, with 36% of that traffic being trucks. The pavement is constructed of a 4-inch stone base, 4-inch treated permeable base and 12-inch jointed concrete pavement. The outside lane is 14 feet wide with an 8-foot asphalt shoulder. The cost of the 12-inch concrete pavement at the time of original construction was $24.15 per square yard in 2002 dollars, for a total of $9.4 million. At the time of construction, the pavement had an average international roughness index (IRI) of approximately 100 inches per mile. Pavement preservation was triggered in 2019 when an IRI of 112 was measured, since the department’s goal is to keep IRI measurements close to 100. No maintenance had been performed on the pavement since it was built; the only maintenance activities had been periodic asphalt shoulder patching and cleaning of edge drains. In 2020, the department performed the concrete pavement preservation (CPP) work. The existing pavement was in excellent structural condition with very few cracked slabs, so CPP consisted of patching 138 square yards—or 0.1% of the area— along with diamond grinding for smoothness and joint rehabilitation. The project was ground to an average IRI of 43 inches per mile. The cost for diamond grinding was $825,000 and the cost for joint resealing was approximately $300,000. The total cost for the project was $1.125 million, or $65,400 per lane mile. Based on the positive outcome of the original concrete construction, combined with diamond grinding and other minimal CPP at the 15- to 18-year point, ArDOT integrated additional diamond grinding and CPP into its road management efforts, notably planning their use on two large sections on I-30. Save on Fuel With more attention than ever being focused on energy conservation, vehicle fuel efficiency and new alternatives such as hybrid cars and biodiesel, few people realize the significant impact that road rehabilitation methods like diamond grinding can have on energy use. Research by the MIT Concrete Sustainability Hub concluded that roughness and deflection of pavements impact the fuel economy of vehicles that traverse the pavement. When the surface of a pavement is smooth, vehicles traverse it more efficiently, with more of the expelled energy dedicated to forward movement rather than fighting vertical bouncing movements. When highway maintenance crews reduce the IRI of a pavement by 40%, it saves truck operators about .002 gallons of diesel or about .7 cents per truck per mile, according to IGGA’s Fuel/ Carbon Savings Calculator. While this figure seems negligible, it has a significant impact when entire highway sections are evaluated. Even when considering alternative fuel vehicles, such as electric vehicles (EV), it is important to recognize that the battery of an EV traveling on a smooth, diamond ground pavement will carry the vehicle for a longer distance because it can move more efficiently. Although at this time research has not been done to show exactly how much improvement takes place, MIT researchers suggest the expected increased distance would be the same as the percent of fuel saved for their gasoline-powered counterpart. By removing faulting, slab warping, studded tire wear and unevenness resulting from patches, diamond grinding creates a smooth, uniform pavement profile. The longitudinal texture continues on page 14 »
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