Concrete Pavement Progress www.acpa.org 18 P A V E M E N T S U S T A I N A B I L I T Y » continued from page 17 pavement already in place, and material availability in the specific area. “As more emphasis is put on resiliency and environmental effects, life cycle thinking becomes more important as it accounts for the true cost of pavement assets over time, not just upfront costs.” Environmental impact is not a new consideration for the concrete pavement industry, pointed out Wathne. “We’ve been focused on ways to reduce our environmental impact for decades, embracing the use of supplementary cementitious materials such as fly ash and slag cement, increasing recycled materials content such as recycled concrete aggregates, and reducing cement intensity by optimizing aggregate gradations,” he said. “Notably, when the 2008 recession hit, sustainable practices become less of a focus for agencies as shrinking DOT budgets moved the focus to first cost.” Concrete pavement has a number of environmental benefits that engineers, owners, and policy makers should understand, said Wathne. Not only does concrete pavement’s long life with lower maintenance requirements provide significant cost-savings and decreased use of materials and energy throughout its life, but it also provides a number of other sustainability benefits during the pavement’s “use phase.” “Because of its rigidity, concrete pavement deflects less under vehicle loading, which results in reduced vehicle fuel consumption. Concrete pavement also retains its smoothness for longer, allowing for additional vehicle fuel-saving, said Wathne. “Concrete pavements’ lighter color helps mitigate urban heat island, a strategy known as cool pavement, and can help offset global warming through a process called negative radiative forcing. Concrete also absorbs carbon dioxide throughout its life, which offsets some of the pavement’s embodied emissions.” According to the Portland Cement Association’s Roadmap to Carbon Neutrality, for all the concrete produced in theU.S. between 1990 and 2018, more than 300 million metric tons of CO2 will be absorbed and sequestered by concrete over its service life.1 In addition to environmental impact/sustainability, resiliency is becoming increasingly important to highway agencies, said Wathne. “Our conventional pavement design approach essentially assumes that the various soil and base layers immediately under the pavement will remain at or near optimum moisture forever—relying on crowns, ditches, and other drainage structures to direct and keep water away from the pavement structure. This may have been a fair engineering assumption in the past when the vast majority of flood maps were originally developed, but we know this is no longer consistent with good engineering practice,” he said. “The conditions that our pavements need to perform under in many cases has changed substantially, and we now see significant flooding of our roadway networks not only along our coastlines—for example, Carolinas, Florida, Texas, and Louisiana—but also along our major rivers like the Missouri and the Mississippi.” Pavement designers did not originally contemplate complete submergence or inundation, said Wathne. “Fundamentally, making pavements resilient to inundation involves stiffening the pavement system and/or making the layers less susceptible tomoisture-related strength loss,” he said. “Concrete overlays provide an excellent way to ‘harden’ our roadways and make them more resilient to such flooding.” He added, “To keep doing what we’re doing is simply not consistent with good engineering practice.” FHWA Promotes Data-Driven Decisions “One way to encourage sustainability and resilience in pavements is quantification and data-driven decision-making,” said Migdalia Carrion, acting Sustainable Pavements Program (SPP) Manager for the Federal Highway Administration. “Whether the focus is on greenhouse gas reductions or improving any other aspect of pavement performance, we cannot improve upon what we don’t measure and report. From the lifecycle perspective, the construction quality and long-term material performance are critical to achieving desired pavement performance at a reasonable lifecycle cost and with the lowest environmental emissions.” The SPP is working with industry to identify sustainability and resilience practices, refine the data sources needed to conduct LCA and develop EPDs (for public procurement), and develop and implement specifications to quantify the GHG emissions, says Carrion. “We are focused on educating our pavement engineers on resilience and encouraging agencies to consider resilience during the planning, design, and construction of pavements.” SPP offers tools and practices to help the reporting and collection of environmental data, as well as the standardization and alignment on how different types of analyses are conducted. Carrion recommended that contractors and industry stakeholders “engage with the FHWA SPP Staff, use our products and guidelines, and provide feedback on what works best for you.” To access tools and resources provided by FHWA, go to: www.fhwa.dot.gov/pavement/sustainability 79%
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