Replacing natural sand in concrete with waste foundry sand (WFS), particularly when paired with supplementary cementitious materials (SCMs) like metakaolin or silica fume, can make concrete stronger, more durable, and cheaper to produce, according to new research published in Scientific Reports.
Study: Sustainable concrete production through the integration of waste foundry sand, fly ash, silica fume and metakaolin. Image Credit: RHJPhtotos/Shutterstock.com
The findings suggest an opportunity to repurpose industrial waste into a valuable construction resource, offering both performance gains and environmental benefits.
Why it Matters
Concrete is the backbone of modern infrastructure, but its production carries a significant environmental cost, largely due to cement manufacturing. SCMs such as metakaolin, fly ash, and silica fume are already helping to address this challenge by reducing cement use while improving concrete’s resistance to chemical attack, weathering, and abrasion. They also limit permeability, protecting structures from degradation caused by alkali-silica reaction and sulfate attack.
By introducing WFS into the mix, researchers aimed to build on these advantages, improving strength and durability while also tackling the problem of disposing of foundry waste. With its fine particles and silica content, WFS has the potential to enhance concrete’s microstructure and extend its service life.
Study Overview
The team began by selecting materials that met international standards for both physical and chemical properties. Concrete mixes were designed with close attention to workability, aggregate size, target strength, and water-to-cement ratios.
Trial batches were prepared to achieve the desired slump, then cast into test specimens and cured in water for 28 days. After curing, the specimens were tested for compressive and tensile strength, ultrasonic pulse velocity (UPV), and acid resistance.
Key Findings
After 28 days of curing, the test specimens revealed clear advantages to incorporating WFS into concrete mixes. Compared with the control samples, those containing WFS—either on its own or in combination with SCMs—displayed significant improvements in both mechanical strength and durability, along with measurable cost savings.
Replacing 20 % of natural sand with WFS increased compressive strength by 17.9 %, while combining this replacement with 10 % metakaolin pushed the improvement to 24.1 %. Tensile strength also rose steadily as the proportion of WFS increased.
The researchers explained that WFS’s fine granules act as micro-fillers, reducing internal voids and producing a denser concrete matrix. This effect, combined with the silica in WFS, encourages the formation of calcium-silicate-hydrate (CSH) gel—a compound that enhances bonding and contributes to long-term durability.
These benefits were also reflected in other performance metrics. Ultrasonic pulse velocity (UPV) and density values both improved with higher WFS content, and all mixes containing WFS showed greater resistance to acid attack than the standard concrete, indicating improved resilience under aggressive environmental conditions.
Economically, the gains were just as clear. Replacing 20 % of natural sand with WFS cut production costs by 3.27 % per cubic meter. The optimal blend with 5 % silica fume lowered costs by 2.01 %, while the 10 % metakaolin combination achieved the largest savings at 5.03 %.
Looking Ahead
The researchers conclude that WFS, regardless of whether it is used alone or in combination with SCMs, can deliver measurable performance and economic benefits while supporting sustainable waste management.
However, they did note that further testing is still needed. The study did not include long-term durability trials such as freeze-thaw cycles, sulfate exposure, or carbonation resistance, nor did it conduct a full life cycle assessment (LCA).
Future work will focus on extended durability testing under varied environmental conditions, alongside an LCA to balance CO2 savings against the energy and resources required for processing.
Journal Reference
Ali, T. et al. (2025). Sustainable concrete production through the integration of waste foundry sand, fly ash, silica fume and metakaolin. Scientific Reports, 15(1). DOI: 10.1038/s41598-025-13277-9. https://www.nature.com/articles/s41598-025-13277-
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