Method for controlling the absorbed water content of recycled fine aggregates by centrifugation

Accurate determination of the absorbed water content of recycled fine aggregates (RFAs) is necessary for proper proportion cement-based mixtures. However, some current standard methods are time consuming and have high operator error. In this paper, we propose an alternative method to control the absorbed water content of RFAs by centrifugation. The rotation speed, centrifugation time, and initial water content are considered as parameters. Ten commercially available RFAs were tested by a single operator with multiple measurements by the centrifugation method, and the results were compared with those obtained by the cone and volumetric flask methods. In addition, the fluidity of the mortar with RFAs and manufactured sand were compared to evaluate the additional water required for saturation. The experimental results indicate that the pre-wetted RFAs can reach the saturated-surface-dry condition after centrifugation at 2000 rpm for 10 min when the centrifugal radius is 6-10 cm, at which the water content can be defined as absorbed water. By comparing the standard deviations with other methods, the absorbed water content can be more accurately and repeatedly controlled by the centrifugation method. The fluidity of the mortar with RFAs including additional water by centrifugation shows a good relationship with that of manufactured sand. Therefore, the centrifugation method can be used to control the absorbed water content of RFAs and applied to mixture design.