Laboratory production of calcium sulfoaluminate cements with high industrial waste content

A drawback of conventional calcium sulfoaluminate (CS̄A) cement production is the use of the costly raw material bauxite as a source of alumina to form the main clinker phase ye'elimite. Replacement of bauxite with industrial wastes can benefit CS̄A cements economically and environmentally. This study demonstrates the use of high amounts of red mud, a sulfate-rich/high-lime fly ash, and desulfogypsum as raw materials in producing CS̄A clinkers and cements with better mechanical performances than an all-natural raw material CS̄A reference cement. Mineralogical compositions of the clinkers and hydrated cement pastes were investigated using x-ray diffraction, isothermal calorimetry, thermogravimetric analysis and scanning electron microscopy. Compressive strength development of mortars, made with citric acid, were studied up to 28 d. It was found that increasing fly ash increases the belitic nature, and increasing red mud increases the ferritic nature of the clinkers. Mortars with 28-d strengths exceeding 40 MPa could be made with cements containing ~38% waste and only half the bauxite in the reference. Medium early and ultimate strength mortars could be made with a ~55% waste cement when bauxite was reduced to a quarter of the reference, with small additions of Ca(NO3)2·4H2O or Li2CO3. Desulfogypsum, as a source of sulfates, was more beneficial to strength development than natural gypsum. Ye'elimite reactivity was enhanced in red-mud containing cements. Cements with both fly ash and red mud experienced lower carbonation than those made with only one of the two wastes.