PURPOSE: To control the occurrence of bursting of a demolishing agent out of a hole for safety in demolishing operation, by incorporating at least a specified amount of a porous substance having pores of a specified diameter in at least a specified volume ratio into a static expansive demolishing agent composed mainly of CaO.

CONSTITUTION: At least 5wt.% porous substance having at least 10vol.% pores of a diameter of 0.05W1mm is incorporated into a static expansive demolishing agent composed mainly of CaO and, if required, containing calcium borate, SiO2, etc. Examples of the porous substance include a glass filter, a porous brick, an aerated concrete, a plastic foam, zeolite, charcoal, and lava. When the demolishing agent thus obtained is introduced into a bored hole of, e.g., rock, CaO will react with water to expand in volume so that an expansion force will cause cracking. Although the internal pressure will rise then due to heat generation, the incorporation of a porous substance can prevent bursting of solid material, such as CaO, out of the hole.