Waste eggshell valorization in the production of bricks: impact of its addition in different grain-sizes on their mineralogy, physical properties and durability

World egg production currently exceeds 97 million tonnes, and if not correctly disposed of, waste eggshell can pose a potential public health risk. Although eggshell has applications in the cosmetic and pharmaceutical industry, less is known about its reuse in the construction sector, with most research focusing on the production of cementitious materials due to its high calcium content. Very little work has been done on its possible use in brick manufacture. In this study, solid brick samples were produced, either without additives or with the addition of 20% by weight of eggshell with two different grain sizes, fine and coarse. Samples were fired at 800, 950 and 1100 °C. The addition of eggshell results in the formation of gehlenite at 1100 °C in the bricks with coarse residue, and anorthite and wollastonite in those with fine residue. The samples made with coarse residue showed levels of portlandite due to the hydration of CaO. The water absorption capacity was higher in the bricks that contained eggshell, especially coarse-grained, and decreased as the firing temperature increased due to the vitrification of the clay matrix. Vitrification also caused an increase in pore size. The samples without additives and those with fine eggshell were the most compact. The bricks containing coarse eggshell had larger pores, which together with the formation of portlandite reduced their compactness. Finally, the resistance of the bricks to salt crystallisation improved as the firing temperature increased, especially at 1100 °C. At this temperature, the most durable bricks were those without residues, although those fired with fine eggshells showed very similar values. At lower firing temperatures, there was greater variability in the results although, in general, the bricks with eggshell seem to resist better than those without it. This work has shown that eggshell, especially fine-grain, could be a valuable resource for the production of efficient and durable bricks. • Handmade bricks made with the raw material from Teruel have lower porosity than other handmade bricks fired at the same temperatures. • Bricks made with coarse eggshell develop a different mineralogy compared to those made with fine eggshell. • All bricks become more compact the higher the firing temperature. • Bricks with fine eggshell are as durable as the same bricks made without additives.