<；P>；PROBLEM TO BE SOLVED: To provide a method of manufacturing a hardened body having necessary voids while holding necessary strength using a steel manufacture slag as a part of raw material when applying to a block for marine forest creation, afforestation, water purification, and the like. <；P>；SOLUTION: The method comprises: kneading the steelmaking slag composed mainly of a coarse particle steelmaking slag remaining on a sieve having a 1.2 mm opening in terms of JIS A1102 "Method of test for sieve analysis of aggregates", and a binding material exhibiting the hydraulic property, composed of a powder having a particle size of not greater than 0.1 mm, containing a fly ash and a blast furnace slag fine powder, using water； and thereafter aging the kneaded material to become a hardened body by hydration reaction, wherein the ratio a/b of a volume (a) of a paste composed of the binding material and the water to a volume (b) of the coarse particle steelmaking slag is not less than 0.08, the unit amount of the binding material is not less than 70 kg/m<；SP>；3<；/SP>；and not greater than 380 kg/m<；SP>；3<；/SP>；, and the continuous void rate of the hardened body obtained is 5-40%. <；P>；COPYRIGHT: (C)2010,JPO&INPIT
