PURPOSE: To reduce temperature-based crazing with the jointing method in placing mass concrete, and shorten the construction term.

CONSTITUTION: Mass concrete is constructed being split plumb in two blocks 10a, 10b. A certain gap 12 is generated between these blocks 10a, 10b, and concrete of retard hardening type is poured into this gap 12 before the placed concrete for the blocks 10a, 10b hardens, or concretely expressed, in the period from attainment of such a state, that the form used in placing concrete for the blocks can be separated, to 10 days after concrete placing. This concrete of retard hardening type is prepared by adding to concrete for example a substance of cellulose ether type, oxicarbonic acid, organic highpolymer of polyole series, or organic highpolymer of oxicarbonic acid compound polyole series.