Concrete may be the backbone of modern construction, but its reliance on cement comes at a steep environmental cost. What if industrial waste, something as ordinary as residue from old aluminium engine parts could not only reduce this burden but also make concrete stronger and more efficient? Recent research has uncovered exactly that possibility, pointing to a new way forward in sustainable building materials.
Image Source: Scientific Reports
Scrap aluminium engine residue (SAER)
Researchers have found that substituting just 2.5 per cent of cement with scrap aluminium engine residue (SAER) in foamed concrete can significantly enhance both compressive strength and thermal insulation. This approach not only improves performance but also provides a sustainable way to reduce industrial waste.
A recent study published in Scientific Reports investigated the effects of different SAER proportions (1.5 per cent, 2.5 per cent, and 5 per cent by weight of cement) on the fresh, mechanical, thermal, and microstructural properties of foamed concrete (FC). The findings highlight that, at the right dosage, this industrial byproduct serves as a valuable additive for producing lightweight, high-performance concrete.
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Why for foamed concrete?
Foamed concrete (FC) is a lightweight material produced by incorporating stable, pre-formed foam into cement paste or mortar, resulting in a uniform mixture with low and controlled density. Its ease of handling, combined with excellent thermal properties, makes it a popular choice for non-structural and semi-structural applications such as wall panels, partitions, and slabs.
In recent years, researchers have increasingly focused on enhancing FC by incorporating waste materials as partial replacements for sand or cement, or as fillers. Among these, metals have been particularly effective in improving toughness, flexural strength, and impact resistance. Despite these advances, tensile cracking remains a persistent challenge for FC.
Past studies with waste tire steel fibres demonstrated notable gains in tensile strength. Building on this approach, the present research explores the potential of scrap aluminium engine residue (SAER), an industrial byproduct often discarded by engine repair shops, as an additive. The study examines whether SAER can strengthen the mechanical and thermal performance of FC while simultaneously contributing to sustainable waste management.
How was the study carried out?
The foamed concrete (FC) mixes were designed with two target densities: 900 kg/m³ (FC-900) and 1100 kg/m³ (FC-1100), each prepared at a constant water–cement ratio of 0.4. Scrap aluminium engine residue (SAER) was incorporated at 1.5 per cent, 2.5 per cent, and 5 per cent by weight of cement. The residue, collected from local lath shops, was carefully cleaned, dried, and sieved to remove moisture and achieve a uniform particle size.
A commercially available foaming agent was used to generate stable foam, ensuring consistency across all mixes. The fresh-state properties assessed included slump flow (to evaluate workability), density, and stability, defined as the mix’s ability to retain its form without collapse prior to setting.
For hardened properties, compressive strength was measured on standard 150 × 150 × 150 mm cubes, while flexural strength was evaluated on 40 × 40 × 160 mm prisms using a universal testing machine. Thermal conductivity was determined by placing the hardened specimens between a hot plate (55 ± 2 °C) and a cold plate (25 ± 2 °C) for two hours. Microstructural characteristics were analysed through X-ray diffraction (XRD) and scanning electron microscopy (SEM).
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Outcome of the result
At a dosage of 2.5 per cent SAER, both FC-900 and FC-1100 exhibited remarkable strength improvements. Compressive strength increased by 92.8 per cent in FC-900 and by an impressive 242.9 per cent in FC-1100, while flexural strength rose by 68.8 per cent and 67.8 per cent, respectively. These findings identify 2.5 per cent SAER as the optimum level for mechanical enhancement. Beyond this threshold, however, strength declined, most notably at 5 per cent SAER, likely due to particle agglomeration and weakened bonding.
In terms of fresh properties, the inclusion of SAER raised the density of the mixes but reduced their workability. Slump flow consistently decreased with higher SAER content, with the FC-1100 mix containing 5 per cent SAER recording the lowest spread. This indicates that while SAER contributes to improved density and stability in the early stages, excessive amounts may hinder handling and placement.
Thermal performance also peaked at the 2.5 per cent dosage. FC-900 demonstrated a 44 per cent reduction in thermal conductivity, highlighting its enhanced potential for insulation. This positions SAER-modified foamed concrete as a promising material for applications where energy efficiency is a priority.
Microstructural analyses provided further confirmation. XRD and SEM results revealed that at 2.5 per cent SAER, the concrete developed a dense and uniform structure with reduced porosity. By contrast, samples with 5 per cent SAER displayed poor crystallinity and particle clustering, explaining the observed decline in strength and workability.
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