Utilization of silica-enriched filter cake industry by-products as partial ordinary portland cement replacement

Abstract In recent years, industrial byproducts have been converted into useful and valuable commercial items. Reusing these byproducts plays a crucial role to ensure the circular economy and thereby safeguard the environmental impacts. In Ethiopia, the Aluminate Sulphate chemical factory disposes of filter-cake waste materials in landfills that have high silica content. The factory is using pure kaolin and other raw materials for the production of Aluminum Sulphate and Sulphuric Acid by burning at high temperatures. By-products materials were collected from the factory and then calcined (post-treated) at 600 °C for 2h in a muffle furnace. From Atomic Absorption Spectrometry measurement result, it is confirmed that the post-treated (at 600 °C/2h) silica-enriched filter-cake waste materials have a similar composition to Metakaolin (MK). Post-treated filter cake (named MK) became more amorphous having high reactive silica with very low impurities as it was calcined and quenched rapidly. In this study, the properties of blended Ordinary Portland Cement (OPC)-mortar samples were investigated with the addition of heat-treated filter cake waste materials (0%–20%) as a partial OPC replacement. X-ray diffraction, Fourier Transform-Infrared Spectroscopy, Differential Thermal Analysis, Scanning Electron Microscope, and Atomic Absorption Spectrometry were used to investigate the properties of mortar samples that contain post-treated filter-cake (MK) materials and OPC-cement. The flexural and compressive strengths of 10% MK + 90% OPC-mortar samples were enhanced at early curing ages, 7 & 28 days. Moreover, the flexural and compressive strengths of OPC mortars with 15% MK have been improved at 28 days of curing age. However, 20% MK + 80% OPC blended mortars have not shown any improvement in mechanical properties. Setting time, soundness, water absorption, and apparent porosity of cement pastes with the addition of post-treated filter cake (MK) are also analyzed.