A subject of the invention is a mixture comprising in proportions by mass: from 0.4 to 4%, preferably from 0.8 to 1.7%, of materials in the ultrafine particle size range, constituted by particles with a D90 smaller than 1 .mu.m and/or with a specific BET surface area greater than 6 m.sup.2/g; from 1 to 6%, preferably from 2 to 5%, of Portland cement; from 8 to 25%, preferably from 12 to 21%, of materials in the fine particle size range, constituted by particles the D10 and the D90 of which are comprised between 1 .mu.m and 100 .mu.m and with a specific BET surface area of less than 5 m.sup.2/g, different from the cement; from 25 to 50%, preferably from 30 to 42%, of materials in the medium particle size range, constituted by particles the D10 and the D90 of which are comprised between 100 .mu.m and 5 mm; and from 25 to 55%, preferably from 35 to 47%, of materials in the larger particle size range, constituted by particles the D10 of which is greater than 5 mm. The invention also relates in particular to premixes, concrete compositions and associated objects made of hardened concrete, as well as their preparation methods.