The influence of opoka mineral additive on the physico-mechanical properties of gas-ceramics based on low-plasticity clay

The article presents the results of scientific and experimental research on the development of highly porous gas-ceramics based on low-plasticity clay from the Rubezhinsk deposit. As a mineral additive, highly dispersed microporous siliceous rock-opoka from the Taskala deposit was used. Opoka is a lightweight, hard, microporous rock characterized by high natural porosity (55-60%) and a density of 1.3-1.5 g/cm³. Hydrogen peroxide, chemically composed of H₂O₂ (perhydrol), was employed as the foaming agent. The raw clay material contains 68% SiO₂, 11.8% Al₂O₃, 3.6% Fe₂O₃, and 5.6% CaO, and is classified as low-plasticity with a plasticity index of 6.5%. X-ray diffraction analysis revealed that the clay is predominantly composed of quartz, feldspar, calcite, and hematite, while the opoka consists primarily of amorphous silica. Experimental studies demonstrated that introducing 10-30% finely ground opoka into the clay slip reduces sedimentation of molded samples during drying from 12% (without additive) to 4% (at 30% opoka), thereby decreasing shrinkage and accelerating structural strength development by 10-15%. The resulting gas-ceramic samples exhibited average densities ranging from 565 to 785 kg/m³, compressive strength between 2.5 and 3.8 MPa, total porosity from 68.4% to 75.2%, and thermal conductivity values of 0.18–0.24 W/m·°C. These results indicate that the use of siliceous opoka significantly improves the performance characteristics of porous ceramics. Thus, the developed gas-ceramic materials combine low density, enhanced strength, and low thermal conductivity, making them suitable for use as effective structural-thermal insulation components in building envelope systems, particularly for the northern regions of Kazakhstan.