Mechanical Performance and High-Energy Photon Attenuation of a Slag-Based Geopolymer Concrete Incorporating Calcined Brezina Dam Sediments

Construction materials carry a heavy environmental cost, not just in the energy required to make them, but in the waste they generate. To address this, scientists have turned to geopolymer concrete, a type of building material that swaps the traditional cement binder for industrial by-products and local minerals. Instead of baking limestone to create cement, which releases vast amounts of carbon dioxide, geopolymer mixes use materials like ground granulated blast-furnace slag—a residue from steel production—and activate them with a chemical solution to bind everything together. This approach offers a way to build strong structures while reusing waste. Beyond just holding up buildings, there is a growing need for materials that can safely block high-energy radiation in medical and technical facilities. Finding a material that is both strong and effective at stopping radiation, while also being made from local waste, is a significant goal for sustainable engineering.

Researchers in Algeria set out to test whether a specific local waste product could serve this dual purpose. They focused on sediments that have settled at the bottom of the Brezina Dam. Over time, dams accumulate layers of silt and sand, which can become a management problem. The team collected this sediment, dried it, ground it into a fine powder, and heated it to a high temperature to change its chemical properties. They then mixed this calcined sediment with ground granulated blast-furnace slag, silica powder, sand, and gravel, using a liquid mixture of sodium silicate and sodium hydroxide to trigger the hardening process. The goal was to see how much of this dam sediment could replace other ingredients without making the concrete weak, and whether the resulting material could effectively block high-energy photons, the particles that make up radiation beams used in cancer treatment.

The team created four different versions of the concrete mix. One version contained no dam sediment at all, serving as a baseline. The other three versions replaced varying amounts of the silica powder with the calcined sediment, specifically using 10%, 20%, or 30% sediment in the binder portion. To ensure the material hardened correctly, the researchers placed the fresh concrete into an oven and heated it at different temperatures and for different lengths of time. They tested the strength of the hardened blocks by squeezing them until they broke and measuring how much force they could withstand. They also looked at how dense the material was, as density often plays a role in how well a material blocks radiation.

The results showed that the amount of sediment and the heating schedule mattered greatly. The mixtures containing 10% and 20% sediment generally performed better than the ones with no sediment or the highest amount of 30%. The best performance came from the mixture with 10% sediment, which was heated at 80 degrees Celsius for 10 hours. This specific sample reached a compressive strength of 58.41 megapascals, a measure of how much pressure it could take before failing. The mixture with 20% sediment also performed well, reaching 55.50 megapascals under the same conditions. In contrast, the mix with 30% sediment was the weakest and least dense, suggesting that adding too much of the dam material disrupted the structure of the concrete. The researchers found that longer heating times generally led to stronger concrete, but only up to a point, and the specific temperature had to be carefully controlled.

To understand how well this new concrete could stop radiation, the researchers did not use a real radiation source, which would be dangerous and difficult to measure precisely in a lab setting. Instead, they used a powerful computer simulation to model how a beam of high-energy photons would travel through the material. They simulated a beam similar to those used in modern medical linear accelerators. The computer calculated how deep the radiation would penetrate before its intensity dropped to half its original value, a measurement known as the half-value layer, and how deep it would go before dropping to one-tenth. For the geopolymer mix with 10% sediment, the simulation showed a half-value layer of 9.94 centimeters and a tenth-value layer of 27.19 centimeters.

These simulated numbers were very close to those of standard concrete, which showed a half-value layer of 10.11 centimeters. This suggests that the new geopolymer concrete, made with local dam sediment, would block radiation almost as effectively as the conventional concrete currently used in hospitals and technical facilities. However, the simulation also showed that a specialized concrete containing barium, a heavy element often added to shielding materials, performed better, with a much shorter distance required to reduce the radiation. The study makes it clear that while the geopolymer mix is promising, the radiation results are based entirely on computer models. The researchers emphasize that these findings are preliminary and that real-world experiments are needed to confirm that the material works as well in practice as it does in the simulation.

The work highlights a potential path forward for sustainable construction in Algeria and beyond. By turning a local environmental challenge—the accumulation of sediment in dams—into a useful building component, the researchers demonstrated that waste can be transformed into a high-performance material. The concrete proved strong enough for structural use and showed simulated radiation-blocking capabilities comparable to standard building materials. Yet, the path from the lab to the construction site requires further steps. The team noted that the radiation data needs experimental validation and that more detailed information on the material's long-term durability and environmental impact is needed. For now, the study stands as a solid proof of concept, showing that a blend of industrial slag and calcined dam sediment can create a concrete that is both mechanically sound and potentially capable of shielding against high-energy radiation.