Determining the moisture content of pre-wetted lightweight aggregate: Assessing the variability of the paper towel and centrifuge methods

Internally cured (IC) concrete is frequently produced in North America using pre-wetted lightweight aggregate (LWA). One important aspect associated with the production of quality IC concrete is the accurate determination of the moisture content, including absorbed moisture and surface moisture of the LWA. Knowledge of the moisture content enables aggregate moisture corrections to be made for the concrete mixture, thereby enabling an accurate water-to-cement ratio to be maintained. Two methods for determining the moisture content of LWA include the specified ASTM C1761-13b "paper towel method" and a method that uses a centrifuge (Miller, Barrett, Zander, & Weiss, 2014). There are limited data available on the variability associated with either of these approaches when the test is performed by multiple users. In this study, the absorption of four commercially available LWAs was tested by a single operator in a single laboratory using the centrifuge method. In addition, the absorption of three commercially available LWAs was tested by 25 users performing both experimental methods. This article provides an estimation of precision associated with both a single operator and multiple operators performing both the paper towel method and the centrifuge method to find the absorption of pre-wetted lightweight fine aggregate.