ARTIFICIAL AGGREGATE AND ITS PRODUCTION PROCESS

摘要

PROBLEM TO BE SOLVED: To provide artificial aggregate for civil engineering and building works, which is produced by using, as its main raw material, sewage sludge incineration ash obtained by the incineration of sewage sludge and has low specific gravity in absolute dry condition and a high unconfined compressive collapse load and further, from which heavy metals such as arsenic and selenium are eluted in amounts less than their respective soil environmental quality standard vaules, and also to provide an inexpensive production process of the artificial aggregate. SOLUTION: The production process of this artificial aggregate comprises: using sewage sludge incineration ash as the main raw material; blending the raw material incineration ash with at least one agent selected from vbinders, reducing agents, foaming agents and composition control agents, in such a way that the resulting blend contains 20-80 wt.% SiO2, 5-30 wt.% Al2O3 and <=40 wt.% CaO and has an SiO2/(Al2O3+CaO) ratio of >=0.5; mixing and pulverizing the blend; adding water to the pulverized blend; forming the resulting material into formed bodies; and firing the formed bodies at >=900 deg.C to produce the objective artificial aggregate; wherein the firing temperature is optionally >=700 deg.C, provided that the CaO content is <=9 wt.%, and preferably, the reducing agent is a carbon material and the foaming agent is at least one compound selected from iron oxide and silicon carbide. The artificial aggregate thus produced has specific gravity in absolute dry condition of <=2.5 and a >=30 kgf unconfined compressive collapse load.