Iron-containing binder

A binder composition for mortar or concrete, comprising:

• a) an iron-containing silicate precursor, wherein said silicate precursor comprises at least 20 wt % Fe, calculated as if present in the form Fe2O3, and at most 80 wt % Fe, calculated as if present in the form Fe2O3, with reference to the dry composition, and wherein said silicate precursor comprises at most 30 wt % Al2O3, with reference to the dry composition;
• b) an alkali-containing activator;
• and
• c) an iron-complexing agent;
• wherein said iron-containing silicate precursor a) is a non-ferrous metallurgical slag, such as a zinc metallurgical slag, a nickel metallurgical slag, a lead metallurgical slag, a tin metallurgical slag, or a copper metallurgical slag;
• wherein at least 30 wt % of said iron-containing silicate precursor a) is amorphous;
• wherein said alkali-containing activator b) comprises at least one oxide, hydroxide, silicate, carbonate, aluminate, aluminosulphate, sulphate, fluoride, fluorosilicate, fluoroaluminate (or aluminium hexafluoride) of an alkali metal or earth alkali-metal, or mixtures thereof;
• and
• wherein the iron-complexing agent c) comprises at least one salt having a functional group selected from phosphate and phosphonate.