Evaluation of aluminum dross for cement replacement in concrete mixture

The increasing global aluminum market presents both opportunities and challenges, particularly with the production of aluminum dross, which poses significant environmental concerns. In 2023, the global aluminum market size was 70, 593 million tonnes, which indirectly generating approximately 1, 411 million tonnes of aluminum dross, a hazardous by-product. Aluminum dross is considered as a toxic waste in which each tonne of dross is expected to produce 12 tonnes of gaseous pollutants, some of which are explosive, poisonous, and smelly. Presently, particularly in Malaysia, the industry faces challenges in managing aluminum dross as the treatment process involves an intensive cost of up to RM 2000 per tonne. Hence, there is a need for its utilization as an engineering material by using it as a filler material in concrete production. The cement industry is facing several difficulties, particularly due to raw materials shortages and environmental concerns relating to carbon dioxide, CO2 emissions into the atmosphere. In this context, the current research work intends to use aluminum dross as a cement replacement material to develop an eco-friendly concrete of M40 grade concrete. This research practice corresponds with the sustainability goals and promotes the circular economy by recycling aluminum dross. In the first stage of study, all six aluminum dross samples provided by Cenviro Sdn. Bhd. were undergone a treatment process prior to use in the concrete mixture to remove foreign matter, salts, and oxides. The first objective of the study characterized all the six treated aluminum dross samples by using X-Ray Fluorescence (XRF) analysis and ammonia test. Based on the outcome, aluminum dross sample 3 (S3) was selected to be substituted into the concrete mixture as it has the highest aluminum content of 53.1% and the lowest ammonia concentration of 75 ppm. The second objective compared the workability of the concrete-aluminum dross mixture based on the slump test and compressive strength. The results of control concrete, COM1 were compared to those of concrete samples containing aluminum dross by 5% (COM2), 10% (COM3), and 15% (COM4) weight of cement. Among aluminum dross concrete mixture, COM3-S3 (10% aluminum dross sample 3) recorded the highest slump flow at 113 mm, 7 mm lower than the control concrete. COM3-S3 also has the highest compressive strength than control concrete, COM1 at 41.3 MPa. The third objective of the study evaluated the mechanical, durability, chemical, and toxicity properties of the best treated aluminum dross replacement concrete mixture. It was discovered that the best percentage of aluminum dross S3 was 10% yielding better outcomes that standard concrete. It recorded the highest compressive strength of 41.3 MPa. Thermogravimetric analysis found that, concrete mix, COM3-S3 was more stable as it had 7.9% lesser percentage of calcium hydroxide compared to control concrete mix, COM1 due to pozzolanic reaction. Scanning electron microscopy analysis showed that the density of concrete increased owing to the formation of ettringite needles and calcium silicate hydrate in voids. Moreover, the toxicity analysis revealed that the ammonia content and the leaching of heavy and trace elements from the concrete were low and within acceptable limits. In a nutshell, aluminum dross discloses positive results to be as an additional cementitious material in concrete making to overcome environmental problems related to dross management and reduction in cement utilization producing an eco-friendly concrete.

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