High-strength building ceramics based on fly ash – red mud mixtures

The work is devoted to the actual problem of creating high-strength ceramic materials based on technogenic waste. This problem is solved by using low-calcium (2.26 % ) aluminosilicate fly ash from the combustion of solid fuel (coal) as the main raw material component with the additions of high-iron (22–25 %  in the calcined state) bauxite sludge. The chemical and mineralogical features of the initial fly ash and bauxite sludge, as well as their structural and phase changes during heating were studied. The predictive analysis of the behavior of ash and bauxite sludge mixtures in the , and  systems made it possible to identify the fluxing effect of bauxite sludge additions to fly ash. The main criteria for designing compositions (  and  modules) of ceramic masses based on ash and sludge for the production of high-strength ceramics are proposed. The iron-alumina module is responsible for the formation of the melt; the calcium silicate module is responsible for the formation of the crystalline phase (anorthite) during firing. The established sintering-hardening effect of bauxite sludge additives in an amount of 10–25 % in compositions with fly ash provides a 1.7–2-fold increase in the compressive strength of samples of semi-dry pressing (from 95 to 206 MPa) at firing temperatures of 1200 °C. The recommended compositions are promising for obtaining densely sintered calcium aluminosilicate building ceramics (paving stones, porcelain stoneware, clinker bricks) with a predominantly anorthite crystalline phase with a water absorption of 0.5–2 % and a compressive strength of up to 175–200 MPa.