Coloring and Strength Effects of Calcined Manganese Ore in Ceramic Brick Containing Ash-Slag Waste

The replacement of clay by coal ash in fired brick is limited by the resulting strength loss. This study examines whether a calcined manganese ore can color a brick body containing ash-slag waste (ASW) without reducing its strength. Four mixes of a medium-plasticity clay with 0 or 20 wt.% ASW (Pavlodar thermal power plant TPP-1) and 0 or 7 wt.% Bogach manganese ore calcined at 1200 °C were fired at 950 °C and characterized by X-ray fluorescence, X-ray diffraction with Rietveld refinement, image-based CIELAB colorimetry and physico-mechanical tests. In the ASW-containing body, the ore raised the mean compressive strength from 9.89 ± 1.33 to 12.41 ± 3.46 MPa (three specimens per mix, p = 0.34) without significant changes in water absorption and density; by mean strength, this body corresponds to grade M100 (GOST 530-2012), class fb ≥ 10 MPa (EN 771-1) and grade NW (ASTM C62-17). Hausmannite (Mn3O4) introduced with the ore persisted as a crystalline phase after firing in both ore-containing mixes (about 2% of the crystalline fraction); the mechanism of the strength change was not established. The ore lowered the lightness L* of the ASW-containing body from 67.3 to 43.3 (ΔE00 = 22.9) at an essentially constant hue angle (57–60°); the fired body is dark brown.