Use of an industrial solid waste as a pigment in clay bricks and its effects on the mechanical properties

The addition of mill scale, an important steel making byproduct, as pigment to fired clay bricks was investigated, as well as its effects on the physical, mechanical and microstructural properties. For this purpose, bricks were manufactured using clay from the Cundiboyacense highlands-a geographic region of Colombia-with the addition of mill scale at 0, 5, 10 and 15%. Once the bricks had been sintered, their density, porosity, water absorption, compressive and flexural resistance were measured. In addition, microstructural analysis using X-ray diffraction, as well as thermogravimetric analysis and differential scanning calorimetry analyses, were carried out on the four types of bricks, to facilitate comparison between them. Variations in hue between the four types of bricks, from dull orange to grayish red, an average decrease in flexural strength of 33% and an increase in average porosity of 4% compared to traditional bricks were observed. Furthermore, it was found that the added mill scale does not react chemically with the clay, being a stable addition. Additionally, mill scale oxidizes to hematite during the firing of the bricks, ultimately becoming a good pigment that changes its hue depending on the added quantity. Therefore, it was concluded that the addition of mill scale to bricks enables the reuse of this industrial by-product and reduces the consumption of clay (which is a non-renewable resource), while complying with minimum standards of compressive strength, flexural strength and porosity.