Suppression of Segregation and Effective Utilization of Residual Concrete Containing Excess Water by Adding Paper Sludge Ash

Unused residual concrete, retaining an excess water post-washing, is typically discharged at ready-mixed concrete plants, where it undergoes segregation into concrete debris and sludge. The significant expense incurred in managing concrete sludge disposal presents a pressing challenge. This study focuses on the high water absorbency of paper sludge ash (PSA) to develop a novel technology aimed at reducing excess water content in residual concrete. This is achieved by directly adding PSA into the drum of an agitator truck and agitating, thereby minimizing segregation. Laboratory experiments conducted with simulated residual concretes demonstrate that as the PSA-to-excess-water ratio increases, there is a corresponding reduction in slump value and amount of bleeding, coupled with an increase in compressive strength. Additionally, an equation is proposed for estimating excess water content in residual concrete using a time-domain-reflectometry, facilitating the calculation of PSA amount required on-site. The efficacy of the proposed equation is substantiated through demonstration experiments conducted at a ready-mixed concrete plant, affirming the significant property enhancement facilitated by PSA in residual concrete.