Aggregates have a variety of moisture states and these will change depending on weather and storage conditions. Aggregate moisture states include: oven-dry, partially saturated, saturated surface-dry, and over-saturated with free water on the surfaces. The moisture state of the aggregate will change the water-cement ratio of a concrete mixture unless the current state of the aggregate is measured and accounted for during the mixture. Industry practice bases free water adjustments on saturated-surface dry weights, whereas the technically correct procedure is to base adjustments on oven-dry weights. Generally the difference between these methods will be quite small, and can be neglected, however with highly absorbent aggregates or aggregates at a high moisture contents, the difference could be consequential. This presentation discusses how aggregate moisture is handled as an industry practice and the technically correct procedures for moisture adjustments.
This free presentation, Do You Really Know About Moisture Corrections?, was presented by Ally Luke at the ACI Spring 2013 Convention and is available here.