Eggshell waste improves insulation in clay bricks, study finds

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A pile of discarded eggshells could have a surprising second life: inside building bricks. In 2025, researchers in Egypt tested fired clay bricks made with eggshell waste. As part of the study, researchers then found that the right amount of eggshell powder can significantly reduce heat transfer through the material. The study found that bricks containing 10% eggshell waste and fired at 1,100°C recorded a 50% reduction in thermal conductivity compared with ordinary clay bricks. Researchers also found that the thermal diffusivity and thermal effusivity also fell by about 30%.

How eggshell waste was added to clay bricks

The researchers collected eggshells, cleaned and dried them, then ground them into powder. The powder was mixed with clay from Egypt's Kharga Oasis. Researchers used different proportions of eggshells ranging from 1% to 10%. The study found that eggshells changed the internal structure of the bricks. During high-temperature firing, calcium carbonate in the eggshells breaks down and releases carbon dioxide. This process helps create pores inside the material.

10% eggshell bricks showed the biggest drop in heat transfer

The strongest thermal result came from the brick containing 10% eggshell waste. Compared to the untreated clay brick, the researchers recorded a 50% drop in thermal conductivity, meaning less heat could pass through the material. Thermal diffusivity and thermal effusivity each fell by about 30%, the research found. The results, researchers believe, can have significance for buildings in hot climates, where walls absorb and transfer heat from the outside into indoor spaces. Bricks with more air spaces can slow heat movement because air is a poor conductor of heat. The researchers found that adding eggshell waste changed the brick's internal structure and density, creating conditions that improved its insulation performance.

The waste problem is part of the attraction

The study also points to another potential benefit: recycling eggshells instead of sending them to landfills. The researchers noted that more than 110 billion eggshells are estimated to end up in landfills worldwide. Turning some of this waste into construction material could give it a useful purpose while reducing the need for some raw materials.