A durable hard structure is demolished by a method in which one or more holes are formed in a durable hard structure, filling the holes with an aqueous slurry containing a demolition-facilitating clinker composition consisting essentially of (1) 55% by weight or more of a clinker consisting essentially of 2 to 40% by weight of a calcium-alumino-ferrite solid solution, 60 to 98% by weight of both free lime and free magnesia in the ratio in weight of from 60:40 to 98.3:1.7 and not more than 6% by weight of an inevitable impurity free from (CaO).sub.3 Al.sub.2 O.sub.3 determined in accordance with Japanese Industrial Standard (JIS) R 5202, said clinker being produced at a sintering temperature of from 1200.degree. to 1800.degree. C., and (2) the balance consisting of a reaction moderator consisting of at least one member selected from the group consisting of (a) at least one gypsum compound in an amount of 40% or less in terms of gypsum anhydride, (b) at least one polyhydroxyl substance in an amount of 5% or less, and (c) at least one member selected from borates and mixtures of at least one borate with at least one member selected from the group consisting of organic acids and organic acid salts, in an amount of 20% or less, each amount being based on the total weight of said demolition-facilitating clinker composition; and the clinker composition in the aqueous slurry is left to generate an expansion force due to a hydration reaction thereof and to demolish the durable structure.