Abstract: A concrete composition contains, per 1 m.sup.3 of the concrete composition, powders of normal portland cement, high-early strength Portland cement, and an inorganic material, in a total weight of from 400 to 600 kg; a formalin condensation product of melamine sulfonate in an amount of from 0.1 to 2.5 wt % based on the total weight of the powders; a hardening accelerator in an amount of from 0.01 to 1.50 wt % based on the total weight of the powders; and water, fine aggregate and coarse aggregate. The mixing ratio of the powers is so specified that the powder of high-early strength portland cement is in a range of from 20 to 500 parts by weight and the powder of an inorganic material is in a range of from 20 to 500 parts by weight on the basis of the powder of normal portland cement of 100 parts by weight. The water, fine aggregate and coarse aggregate are mixed in such a mixing ratio as to give a slump flow value ranging from 50 to 70 cm to the concrete composition.