Construction castable material with controllable flow or slump comprising (a) a binder comprising fly ashes comprising from 1.5% to 35% by weight of CaO and a Lost on Ignition (LOI) value from 0.5% to 5.5% by weight, representing from 10% to 60% of the binder weight and ground granulated blast furnace slag comprising from 40% to 70% by weight of CaO and from 30 to 60% by weight of SiO2, representing from 40% to 90% of the binder weight, (b) an activator comprising alkaline reagents selected from the group composed by water glass, preferably in solution with 30 to 50% by weight solid content, sodium metasilicates and sodium hydroxide, (c) sand, fine and coarse aggregates and (d) organic acids or conjugated salts of organic acids in a dosage from 0.001% to 3% by weight with respect to the binder.