SILICA FUME EFFECTS ON PHYSICAL AND MECHANICAL PROPERTIES OF ASH-SLAG WASTE CERAMIC BODIES

Abstract

Ash-slag waste from thermal power plants can be used as a technogenic aluminosilicate component of ceramic bodies; however, increasing its content requires an assessment of ma-terial properties under specified forming and firing conditions. This study aimed to evaluate the feasibility of incorporating 50 wt.% fresh ground ash–slag waste from Pavlodar TPP and to determine the effect of silica fume on the properties of fired specimens. The scientific novel-ty lies in experimentally establishing, for this raw-material system, the effect of adding 3.0 wt.% silica fume to a ceramic body with a high content of fresh ash-slag waste: strength in-creases without the formation of additional identifiable crystalline phases or significant changes in water absorption, bulk density, and shrinkage. A reference composition contain-ing equal mass fractions of clay and ground ash-slag waste and a modified composition con-taining 3.0 wt.% silica fume were investigated. Cylindrical specimens were formed, dried to constant mass, and fired at 950 °C. The particle-size distribution, chemical composition, and phase composition of the raw materials were determined. Linear shrinkage, compressive strength, water absorption, bulk density, and the elemental and phase compositions of the fired specimens were evaluated. Silica fume increased the compressive strength from 14.60 to 16.85 MPa, corresponding to an increase of 15.4%. No significant differences were ob-served in water absorption, bulk density, forming moisture content, or linear shrinkage. After firing, both compositions exhibited similar crystalline phase assemblages. The results confirm the feasibility of incorporating fresh ground ash-slag waste at a content of 50 wt.% as a par-tial replacement for natural clay and of increasing material strength through the addition of 3.0 wt.% silica fume without adversely affecting the investigated properties.