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.
In order to reduce the cost of track maintenance, grouted ballastless tracks for existing lines where ballast voids are filled with cement grout have been developed and put into practical use. However, there is a problem that some constructed grouted ballastless tracks laid on soft roadbeds are in need of repair within only a few years after operations restart. Therefore, we have developed a method for improving grouted ballastless tracks laid on soft roadbeds and carried out construction work to verify the developed method on existing lines. The roadbed improvement thickness for construction was determined according to design flow proposed in this paper. This paper also describes the improvement method developed for grouted ballastless tracks for existing lines and its verification results.
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