BACK TO BASICS: Controlling Stockpile Moisture In 2020, Dr. Shane Buchanan, P.E. of CRH Americas Materials Inc., wrote a member-to-member article for NAPA on “Aggregate Moisture Measurement.” Instead of writing a new article, why not update the original to include aggregate moisture impacts on environmental product declarations (EPDs) as well? Aggregate stockpile moisture content can significantly influence drying energy cost, plant production rates, and mix volumetric properties and performance. Additionally, the amount of moisture in aggregates impacts fuel usage, which, in turn, impacts the A3 factor for asphalt materials’ EPD. Along with using recycled asphalt pavement (RAP) in new mixes to control costs and lower global warming potential (GWP), moisture is perhaps the most influential production variable—its importance and impact should not be discounted. The 1–11–11 Moisture Rule The exact relationships between moisture, drying energy, and production cost vary based on plant and material conditions; however, general rules apply. A 1% increase in moisture will increase the drying energy by approximately 11% and will decrease the plant production rate by approximately 11%. The “1–11–11 Moisture Rule” is an easy way to remember this. Moisture Impact on Plant Asphalt Binder Content Addition When the aggregate blend moisture content differs from the plant moisture content setting, substantial impacts on the added binder content may result. For example, if the plant’s moisture setting is 5% and the actual moisture is 7%, the plant will add binder based on the weight of the 7% moisture aggregate, resulting in an over- asphalted mix. Likewise, if the actual moisture is 3%, the added binder will be too low, and the mix will be under-asphalted. This affects mix economics, measured AC content, mix volumetrics, and lab performance. With the adoption of Ideal CT for a cracking test, Figure 1: Stockpile Covering (Allan Myers New Kent Plant) 24 FALL/WINTER 2024
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