Researchers have discovered that replacing just 2.5 % of cement with scrap aluminum engine residue (SAER) in foamed concrete significantly increases both compressive strength and thermal insulation, offering a practical way to boost performance while reducing industrial waste.
Study: Microstructural and mechanical characterization of foamed concrete reinforced with scrap aluminum engine residue. Image Credit: Flegere/Shutterstock.com
A recent study published in Scientific Reports evaluated how different proportions of SAER (1.5 %, 2.5 %, and 5 % by weight of cement) influence the fresh, mechanical, thermal, and microstructural properties of foamed concrete (FC). The results suggest that at the right dosage, this industrial byproduct can be a valuable additive for lightweight, high-performance concrete applications.
Why Use SAER in Foamed Concrete?
Foamed concrete is a lightweight material created by mixing a stable, pre-formed foam into cement paste or mortar, producing a uniform mixture with a low and controlled density. It’s widely used for non-structural and semi-structural applications such as wall panels, partitions, and slabs due to its ease of handling and thermal properties.
In recent years, researchers have explored ways to enhance FC using various waste materials such as sand or cement replacements or fillers. Metals, in particular, have been added to improve toughness, flexural strength, and impact resistance. However, tensile cracking remains a common issue in FC.
Previous studies using waste tire steel fibers have shown improvements in tensile strength. This research takes a similar approach, investigating whether SAER, an aluminum byproduct commonly discarded by engine repair shops, can be used to improve FC’s mechanical and thermal properties while addressing waste management challenges.
How the Study Was Conducted
The foamed concrete mixes were prepared using two target densities: 900 kg/m3 (FC-900) and 1100 kg/m3 (FC-1100), both with a fixed water–cement ratio of 0.4. SAER was added at 1.5 %, 2.5 %, and 5 % by weight of cement. The scrap material was sourced from local lath shops, then thoroughly cleaned, dried, and sieved to eliminate excess moisture and ensure uniform particle size.
A commercially available foaming agent was used to produce consistent foam across all mixes. The fresh properties evaluated included slump flow (to assess workability), density, and stability—defined as the mix’s ability to hold its shape without collapsing before setting.
For hardened properties, compressive strength was tested using standard 150×150×150 mm cubes, while flexural strength was measured using 40×40×160 mm prisms on a universal testing machine. Thermal conductivity was assessed by placing the hardened samples between a hot plate (55?±?2?°C) and cold plate (25?±?2?°C) for two hours. Microstructural features were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM).
What the Results Showed
At 2.5 % SAER, both FC-900 and FC-1100 mixes showed a dramatic increase in strength. Compressive strength rose by 92.8 % for FC-900 and by 242.9 % for FC-1100. Flexural strength also improved significantly—by 68.8 % and 67.8 %, respectively. These results highlight 2.5 % SAER as the most effective dosage for mechanical enhancement. However, strength values declined when SAER was increased to 5 %, likely due to particle agglomeration and poor bonding.
Adding SAER increased the fresh density of the mix but reduced workability. Spread flow decreased with higher SAER content, and the 5 % SAER mix for FC-1100 recorded the lowest slump. This suggests that while SAER improves density and stability in early stages, it may compromise ease of handling at higher concentrations.
Thermal performance also improved significantly at the 2.5 % dosage. FC-900 showed a 44 % reduction in thermal conductivity, indicating enhanced insulation potential. This makes SAER-modified FC particularly useful for applications where thermal efficiency is critical.
XRD and SEM results supported the mechanical and thermal findings. At 2.5 % SAER, the FC displayed a dense, uniform microstructure with minimal porosity. In contrast, mixes with 5 % SAER showed poor crystallinity and clumping of particles, which contributed to the reduction in strength and workability.
Conclusion and Future Directions
This study demonstrates that scrap aluminum engine residue, when added at 2.5 % of the cement weight, can significantly enhance the structural and thermal performance of foamed concrete. Beyond improving performance, this approach offers a sustainable pathway to repurposing industrial waste in construction materials.
However, more research is needed to validate the long-term durability of SAER-modified FC under varying environmental conditions, including freeze–thaw cycles, wet–dry exposure, and chemical attack. Future studies should also assess the economic and environmental impacts of large-scale implementation, including cost-benefit and life-cycle analyses.
Journal Reference
Alzlfawi, A. (2025). Microstructural and mechanical characterization of foamed concrete reinforced with scrap aluminum engine residue. Scientific Reports, 15(1). DOI: 10.1038/s41598-025-16494-4. https://www.nature.com/articles/s41598-025-16494-4
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