Mathematical approach to application of industrial wastes in clay brick production – Part I: Testing and analysis

The objective of this study was to investigate utilization potential of organic and inorganic industrial wastes in clay bricks. Mineral composition of starting heavy clay sample is tested using an X-ray diffractometer. Chemical content and loss on ignition were determined in sludges, coal dust, fly and landfill ashes, soybean crust, sawdust, sunflower hulls and their ash. Different ratios of wastes were added to heavy clay, while the applied firing temperatures were in the range 850–1000 °C. The laboratory samples (tiles, solid bricks and hollow blocks) were tested by using the standard test methods. Changes in product׳s quality were studied in terms of relative differences to ceramic-technological parameters compared to samples without waste materials addition. It is noticed that all of the additives increased weight loss, firing shrinkage and water absorption, while decreasing compressive strength and volume mass. The greatest changes in performances were observed with addition of organic materials, whereas, among them, sunflower hulls initiated the lowest compressive strength. Inorganic additives introduced fewer changes to fired products, while fly ash caused the lowest decrease in compressive strength.Response Surface Methodology (RSM) was applied and Second Order Polynomial models (SOP) were used to show the effects of firing temperature, waste materials addition and their quantity on characteristics of fired products. High prediction accuracy was obtained, with coefficient of determination in the range of 0.896–0.999. It was concluded that all of the analyzed materials can generally be used in building bricks by taking advantage of low cost and environmental protection, whereby thermal conductivity decreases.