There is a concern that polymer flocculants used in the flocculation and settling processes of construction sludge contain a toxic unreacted monomer material. Therefore, a new intermediate treatment process is necessary to reduce the amount of polymer flocculant added while maintaining the required flocculation performance. Furthermore, at present, owing to the shortage of disposal spaces and the decrease of cement demand, paper sludge ash (i.e., PS-ash) generated from the paper production process should be reused in new applications. In order to reduce the amount of polymer flocculants to be added, PS-ash is employed as a material to assist the flocculation by combining a polymer coagulant with an inorganic coagulant during the coagulation sedimentation stage. Consequently, it was confirmed that the electric zeta potential of the clay slurry suspension was decreased by the addition of PS-ash and the aggregation performance was highly improved. In addition to this, it was confirmed that the addition of PS-ash to construction sludge reduced the elution of a fluoride material originating from the sediment.