Combined effects of bayer process bauxite waste (red mud) and agricultural waste on technological properties of fired clay bricks

Abstract

The sustainability of raw materials used in great amounts in the production of building materials used in the construction industry is of great importance. This research investigates the utilization of bayer process bauxite waste and agricultural residues as alternative additive materials for clay replacement to produce eco-friendly porous ceramic bricks. The use of organic and inorganic additives in brick production reduces the consumption of natural clay reserves and the weight of the brick. In addition, these additives have been used as pore formers in brick production to increase thermal performance and waste remediation in ceramic structures for environmental beneficial. Considering these issues, two different types of waste and their combinations were evaluated in brick production in the study. Hazelnut shells (HS) (from 2.5 wt% to 10 wt%), which is an agricultural waste, were used as pore former during firing of brick. On the other hand, this study is related to the evaluation of red mud waste (RM) (from 5 wt% to 30 wt%), which is released in large quantities at the result of Bayer process in the aluminum metallurgy and threatens environmental health, as an alternative raw material in the production of clay bricks. The compacted samples were fired at 900 °C and 1000 °C for 2 h to investigate the effects of firing temperature. Bulk density, water absorption, apparent porosity were determined by Archimedes method. Thermal conductivity and compressive strength of the samples were measured by a thermal conductivity analyzer with a modified transient plane source, and the mechanical test method, respectively. Also, the microstructural and leaching analysis of produced samples was performed. This research have confirmed that the potential use of these wastes decreases the bulk density and mechanical strength and increases the porosity, which leads to higher thermal insulation . The results indicated that samples produced with addition of 10% HS-30% RM exhibited the lowest thermal conductivity values (0.45 W/mK) and the acceptable compressive strength (9 MPa). Also, the effective thermal conductivity coefficient of the perforated brick model designed from this sample is found as 0.112 W/mK in ANSYS Fluent 19.1 Software. Furthermore, the brick samples with a high amount of waste materials show values of leaching toxicity much lower than the specified limits of the Environmental Protection Agency (EPA). The microstructures are also supporting the porosity ratios of brick samples. Based on the results, the combination of waste materials considered for making brick samples in this study can be used as additives in lightweight eco-friendly brick production to reduce waste landfill and recycle waste. • An agricultural residue is evaluated as a pore maker in brick production. • Red mud exhibits partially a flux effect with increasing firing temperature. • Addition of wastes increases porosity and lightweight bricks are produced. • Thermal conductivity of a perforated brick model designed from obtained results is simulated. • Leaching analysis is revealed that the fired bricks are eco-friendly.