C+S August 2023 Vol. 9 Issue 8 (web)

Every four years , the American Society of Civil Engineers (ASCE) issues a report card that grades America’s infrastructure. In the latest edition, the nation scored a C- on the overall assessment, indicating that while overall these systems are in fair condition, they exhibit deficiencies and increasing vulnerabilities. Roads, in particular, scored a D on the report, meaning they are, by and large, below standard and approaching the end of their service life. In an explanation of the grade, ASCE states that 43 percent of public roadways are in poor or mediocre condition. As the nation looks for ways to improve this assessment for the 2025 report card, it is important for repairs and rehabilitation projects to consider long-term resiliency as an essential feature. In doing so, these improvements will not only raise the grade in the short-term but also create infrastructure that will remain fit for the future with minimal maintenance. One way to bolster the overall resilience of a roadway is to assess the stability and quality of soil beneath it. Lightweight aggregates made from expanded shale, clay or slate (ESCS) can improve soil conditions to help roadways and bridges remain structurally viable for years to come. Likewise, ESCS can positively impact adjacent infrastructure systems that also need improvement such as energy and water (drinking, waste and storm), both of which were graded to be at risk for failure. As such, this material can be one of many “strategic investments” recommended to improve the nation’s infrastructure. Lightweight aggregates improve soil conditions ESCS lightweight aggregates are produced by heating the raw materials in a rotary kiln to temperatures over 1000 degrees Celsius. At this temperature, air bubbles form and remain as the aggregate cools to create a network of unconnected voids. These voids reduce the weight of ESCS to approximately one-half of other common fills. They also contribute to a predictably high internal friction angle, which can reduce lateral loads by more than one-half. Further, because ESCS is free draining, it can withstand erosion caused by flooding or excessive rainfall. Combined, these qualities help soft soils become more stable so they can withstand live loads without settling. Making the Grade: Why Lightweight Aggregates may be the Key to Improved Infrastructure By Jody Wall

ESCS help reduce dead loads and lateral forces by half to ensure a stable road base. Credit: Courtesy of ESCSI

The New Jersey Department of Transportation (NJDOT) understood these benefits when it started improvements to the I-295 to ROUTE 42 to I-76 direct connection in Camden County. The site needed a backfill that would minimize settlement and reduce loads in embankment areas and behind mechanically stabilized earth (MSE) walls. Further, the material used was needed to meet the New Jersey Department of Environmental Protection (NJDEP) requirements for flood hazard areas as well as freshwater and tidal wetlands. ESCS helped stabilize the soil. It is also free draining and chemically inert, so it helped this project improve soil conditions while minimizing the environmental impact of the project. Similarly, the North Carolina Department of Transportation (NCDOT) used ESCS to improve two bridge approaches by utilizing the soil stabilization capabilities of ESCS. The projects needed to improve the load bearing capabilities of the alluvial muck and loose, silty fine to coarse sand to ensure the project would stay structurally viable for future use. Because ESCS reduced the lateral forces acting on the embankments and the overall vertical loads on the soft soils beneath, it improved the bridge approaches’ ability to resist settling. Increases MSE wall performance Stabilizing poor soils is just one aspect of road improvement. ESCS can also improve the ability of MSE walls to maintain steep slopes. It does so by reducing the weight of backfill from approximately 100




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