A Systematic Review of the Mechanical and Durability Performance of Eggshell Powder as a Partial Replacement in Cement in concrete production

Concrete is the invisible skeleton of the modern world, the material that holds up our bridges, skyscrapers, and homes. Yet, the primary ingredient that binds it together, Portland cement, comes with a heavy environmental price tag. Making cement requires heating limestone to extreme temperatures, a process that releases massive amounts of carbon dioxide into the atmosphere. As the world seeks to build a greener future, scientists have been hunting for ways to swap out some of this cement with other materials that are less harmful to the planet. One such candidate has been hiding in plain sight, accumulating in landfills and kitchens for decades: eggshells.

Eggshells are mostly made of calcium carbonate, the same mineral found in the limestone used to make cement. Because they are a waste product from the food industry, they are abundant and free. The idea is simple: if you grind eggshells into a fine powder and mix them into concrete, they might take the place of some of the cement, reducing the need for the polluting material while still keeping the concrete strong. However, simply throwing crushed shells into a mix is not enough. The powder needs to be processed correctly, and there is a limit to how much can be used before the concrete becomes weak. Researchers have been testing this idea for years, but the results have been scattered across hundreds of different studies, making it hard to know exactly how well it works or what the best recipe is.

To cut through the confusion, a team of researchers from Takoradi Technical University in Ghana conducted a massive review of the existing science. They did not mix concrete in a lab themselves; instead, they acted as detectives of the literature, gathering and analyzing ninety separate studies that had already been published. These studies covered everything from how the powder was prepared to how the final concrete held up under pressure and water. By looking at the big picture, they were able to identify clear patterns that individual experiments had missed, offering a definitive guide on whether eggshells can truly become a building material.

The researchers found that the answer is a cautious "yes," but with very specific conditions. When eggshell powder is used to replace a small portion of the cement—specifically between five and ten percent of the total weight—the concrete performs just as well as, or sometimes even better than, standard concrete. At these low levels, the tiny particles of eggshell act like a filler. Imagine a jar of large marbles; if you shake it, there are gaps between them. If you pour in fine sand, the sand fills those gaps, making the jar heavier and more compact. Similarly, the fine eggshell powder fills the tiny spaces between the cement grains, making the mixture denser and tighter. This densification helps the concrete resist water and prevents it from becoming porous, which is a key factor in how long a building lasts.

However, the benefits disappear quickly if you try to use too much. The review showed that once the replacement level goes above ten to fifteen percent, the concrete begins to lose its strength. This happens because eggshells are not a true substitute for cement in a chemical sense. Cement is a reactive material that hardens through a chemical reaction with water, creating a glue that holds the rock and sand together. Eggshells, even when ground up, do not react in the same way. If you put too much of them in the mix, you are essentially diluting the glue. There is not enough reactive cement left to bind everything together, leading to a weaker structure that is more likely to crack and crumble. The researchers noted that this drop in strength is especially noticeable in the ability of the concrete to resist pulling forces, which is critical for preventing cracks.

The way the eggshells are prepared also matters significantly. The studies reviewed showed that the powder must be clean and very fine. If the shells are not washed properly, leftover organic matter from the egg can interfere with the hardening process. Furthermore, the size of the powder particles is crucial. The best results came from shells that were ground into a powder so fine that it could pass through a very small sieve. Some researchers also heated the shells to high temperatures before grinding them, a process that changes the chemical structure slightly and makes the powder more reactive. While this heating step can improve performance, the review suggests that simply using finely ground, clean shells at low replacement levels is often sufficient and more practical.

Durability was another major focus of the review. Concrete that lasts a long time must be able to keep water out, as water is the main enemy that causes steel reinforcement to rust and concrete to crack. The analysis confirmed that concrete with five to ten percent eggshell powder absorbs less water than standard concrete. The fine particles block the tiny channels through which water would normally seep, creating a more solid barrier. This suggests that in warm, wet climates where moisture can accelerate the decay of buildings, this type of concrete could be particularly useful. However, the researchers warned that these durability gains vanish if the replacement level is too high, as the resulting porous structure allows water to penetrate easily.

The team also looked at the bigger picture of where this material fits in the construction industry. They concluded that eggshell powder is not a miracle cure that can replace cement entirely. Instead, it is a valuable supplement for specific types of construction, particularly for buildings that do not require the highest possible strength. In regions like Ghana, where poultry farming generates tons of eggshell waste and infrastructure development is booming, this approach offers a way to turn a waste problem into a construction solution. It aligns with the concept of a circular economy, where waste from one industry becomes a resource for another, reducing the need to mine new limestone and lowering the carbon footprint of building materials.

Despite these promising findings, the researchers emphasized that more work is needed before this method becomes a standard practice. Most of the studies they reviewed were short-term experiments conducted in laboratories, and there is very little data on how this concrete holds up over many years or in real-world construction sites. They called for standardized rules on how to process the eggshells to ensure consistency, as the quality of the powder can vary wildly depending on how it is cleaned and ground. They also suggested that future research should look at combining eggshells with other sustainable materials to see if they can work together to improve performance even further.

Ultimately, this review provides a clear roadmap for using eggshells in concrete. It confirms that the idea is scientifically sound, but only when applied with precision. By sticking to a low replacement rate of five to ten percent and ensuring the powder is finely ground and clean, builders can create a sustainable material that is strong, durable, and kinder to the environment. The eggshell, once destined for the trash, has the potential to become a quiet, unassuming component of the structures that will house the future, provided we respect the limits of its strength and the importance of getting the recipe right.