WWW.ACPA.ORG 13 FALL // 2024 Of the state’s approximately 62,000 lane miles of roadway, about 1,800 are concrete; 820 of their 3,800 interstate lane miles are concrete. Therefore, finding an effective way to prolong concrete pavement life while improving performance is vital. When assessing its road network for needed repairs, the main indicator that Kentucky uses is pavement smoothness. Inertial profilometers are used to annually measure roughness on the interstate system and IRI values greater than 130 inches per mile will generally trigger CPP. Undertaking CPP is contingent on a situation in which there is moderate to low cracking and faulting. (Kentucky defines low faulting as onefourth to one-half an inch. Faulting greater than one-half inch generally would necessitate full restoration rather than preservation.) Similarly, if a third or more of the slabs needed replacement, full restoration typically would occur. Pavements with IRI measurements lower than 130 still could trigger CPP if it appeared that cracking and faulting were about to become a major problem; conversely, if a road is expected to require major work (such as widening) within the upcoming five to 10 years, the cabinet will not recommend it for CPP. Inherent Sustainability While new technologies and modes of transport receive a lot of attention as carbon-reducing strategies, traditional pavements—specifically, concrete pavement—also can offer sustainability benefits. Concrete’s sustainable qualities, especially when paired with diamond grinding, are numerous. Diamond ground concrete pavements require little maintenance when compared to heavily modified thin-lift asphalt treatments and are naturally sustainable with the following attributes: • Concrete pavement is produced locally, with local labor, supporting local communities, which is great for the economy. • Concrete has a high level of light reflectivity, making it safer to drive on at night. During the day, heat and light are reflected, reducing urban heat islands (UHI). • Concrete pavement increases fuel efficiency for semitrucks by resisting pavement deflection. Pavement deflection in flexible pavements results in a subtle but constant “uphill” rolling resistance. • Concrete is not petroleum based. There is no odor or stench when concrete pavement is placed or reheated daily by the sun. • Concrete is fully recyclable; more than 140 million tons of concrete are recycled and reused every year. In addition to carbon-reducing changes occurring at the materials production level, in-service concrete contributes to carbon neutrality by absorbing atmospheric carbon. This carbon capture, known as carbonation, occurs when hydrated portland cement is exposed to atmospheric CO2, which reacts with the water and calcium compounds in concrete and produces calcium carbonate. Carbonation takes place over the lifetime of a pavement; while there is a risk of the rate of carbonation slowing over the years due to the pore-blocking effect of the calcium carbonates being formed, it is possible to remove the carbonated surface and expose a fresh, uncarbonated layer. The simplest way of doing this is by diamond grinding—a technique that is commonly performed as part of pavement preservation. Diamond grinding as often as every 10 to 15 years will enable a concrete pavement to restart the carbonation process and continue offsetting the carbon emitted by concrete production. For example, Chisago County in Minnesota diamond ground 26.4 lane miles on I-35 and measured the carbon savings. Using the fuel/ carbon calculator4 available on the IGGA website, it was determined that, while the carbon dioxide released by equipment to perform the work was around 500,000 pounds, the annual carbon savings associated with improved ride quality and carbon sequestration was 152,000 pounds. That means that after only 3.5 years of service, the pavement will be carbon negative. While the cost of diamond grinding was approximately $850,000, the 10-year cost savings for users was more than $3.5 million in fuel alone—$66,000 in estimated fuel savings or 16,139 gallons per mile per year. Many engineers lean on asphalt overlays as the most effective repair method for ride quality and surface texture issues. While in extreme cases this may be the best viable solution, the mining of new materials, hauling of new materials to a job site and loss of carbon sequestration benefits make asphalt a more expensive and less environmentally conscious choice when compared to diamond grinding. While a diamond ground surface can remain effective for more than 20 years, the Asphalt Institute states on its website5 that asphalt overlays of concrete can last about 12 years when properly maintained. Twelve years of service is not enough time to offset the environmental benefit of a IGGA DIAMOND GRINDING Fig. 1—Over a time span of 50 years, concrete achieves carbonation of roughly 14,000 to 20,000 pounds per lane mile. continues on page 14 »
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