A low heat buildup cement composition with a ratio of the compressive strength to the heat of hydration of at least 7.0 at an age of 13 weeks, developed particularly for use in massive concrete work. One invention of the composition comprises a powder which is produced by mixing the raw materials of CaO, SiO₂ and Al₂O₃ together followed by melting, quenching and pulverizing, is mainly amorphous and has a CaO to SiO₂ ratio of 0.8 to 1.5 by mole and an Al₂O₃ content of 10 wt % or less. Another invention thereof comprises a powdery mixture composed of at least 70 wt % of a powder which is the same as the one used in the above invention in respect of the CaO to SiO₂ ratio and the amorphousness but is different therefrom in that the Al₂O₃ content is 12 wt % or less and at most 30 wt % of a stimulative such as portland cement.

A cement admixture of a low environmental load type, capable of reducing hexavalent chromium, having a small slump loss or heat of hydration, hardly neutralized and capable of suppressing autogenous shrinkage to a low level; a cement composition; and cement concrete employing it, are presented.

The cement admixture comprises a slowly cooled slag powder which contains melilite as the main component and which has a carbon dioxide absorption of at least 2%, has a CO₂ absorption of at least 2%, has a loss on ignition of at most 5%, contains at least 0.5% of sulfur present as non-sulfuric acid form sulfur and/or has a concentration of non-sulfuric acid form sulfur to elute, of at least 100 mg/l, and further, preferably, has a degree of vitrification of at most 30%, a melilite lattice constant a of from 7.73 to 7.82 and/or a Blaine specific surface area of at least 4,000 cm²/g.