Use of flue dust as additive for concrete

The use of flue dust which occurs in the dry cleaning of the flue gases of large furnaces and which, when it is obtained, contains free calcium oxide and is moistened with 5 to 15% by weight, preferably 8 to 12% by weight, of water with the addition of 2 to 10% by weight, preferably 4 to 8% by weight, of ligninsulphonate, melamine resin or mixtures thereof (based on the amount of water) and is then dumped as an additive for concrete. The dumping is carried out only as temporary storage, however at least long enough for the free calcium oxide to be decomposed to less than 1.5% by weight, based on the dry flue dust, to form predominantly Ca(OH)2 while to the greatest possible extent excluding the formation of CaCO3. Then the temporarily stored flue dust is dried and recomminuted.