Mathematical approach to application of industrial wastes in clay brick production—Part II: Optimization

The effects of organic and inorganic waste sludges, coal dust, fly and landfill ashes, soybean crust, sawdust, sunflower flakes and their ash addition to representative heavy clay were investigated. Changes introduced to shaping moist (SM), shrinkage (ΔSk) and weight loss (ΔGk) in Bigot’s curve critical point, and plasticity coefficient (PC) by Pfefferkorn were studied. The highest sensitivity to drying showed samples with coal dust addition, while the greatest plasticity and shaping moist was detected in samples with 50 wt% of fly and landfill ashes.The influence of waste material used, its’ content and also firing temperature were independent parameters that influenced compressive strength, water absorption, firing shrinkage, weight loss during firing and volume mass as dependent parameters. Second order polynomial mathematical models predicted fired products characteristics, and were later used to determine the optimum conditions by Response Surface Method (RSM), coupled with Fuzzy Synthetic Evaluation algorithm (FSE), using trapezoidal function. The choice of the parameters optimal interval that characterized fired products (water absorption, compressive strength, weight loss during firing, firing shrinkage and volume mass), depended on a final usage of the raw material in heavy clay brick industry. The optimization results showed that sunflower hulls, wood sawdust, soybean husks and saturation sludge are best to be used in solid bricks production. Coal dust, landfill ashes and neutralization (inorganic) sludges are best to be used in hollow bricks production. Sunflower hulls ash can be added in higher quantity to heavy clay to produce blocks or in lower quantity in roof tiles. Fly ashes addition of 50 wt% allows roof tiles production. The optimal temperature for solid bricks and hollow blocks production is found to be 900–950 °C.