Valorization of Waste Polyethylene Terephthalate as a Partial Fine Aggregate Replacement in Concrete: An Experimental Assessment of Fresh and Hardened Properties

Plastics have become integral to modern life, owing to their durability, affordability, versatility, light weight, and ease of manufacture. They find application across a wide range of sectors, including packaging, transportation, healthcare, construction, electronics, agriculture, water supply systems, and household goods. The steady rise in urbanization, industrial activity, and consumer demand has driven a corresponding surge in global plastic production and consumption. Yet the persistence of most plastics in the environment has created a pressing ecological problem, a challenge that is especially acute in developing countries where waste management infrastructure remains weak. Polyethylene terephthalate (PET), widely used for beverage and water bottles, makes up a substantial share of municipal solid waste and ranks among the most conspicuous forms of plastic pollution in both urban and rural settings (Qaidi et al., 2023; Mostafaei et al., 2026). Worldwide, plastic waste is generated at a scale of millions of tonnes annually, with PET accounting for a sizeable proportion owing to its dominance in the packaging sector. Poor disposal practices, ranging from open dumping and burning to indiscriminate littering, have given rise to a host of environmental problems, including drainage blockages, soil contamination, flooding, visual blight, and harm to aquatic life. In Nigeria and other developing countries, discarded PET bottles are a familiar sight along roadsides, in drains, around markets, on construction sites, and in public spaces. Given that PET can take centuries to break down, its continued accumulation represents a long-term environmental hazard (Uche et al., 2026; Oke et al., 2025). These concerns have prompted researchers and environmental agencies to step up efforts toward sustainable waste management strategies centred on recycling, reuse, and resource recovery. Among the most promising avenues is the incorporation of waste materials into construction products, particularly concrete. As the most extensively used construction material in the world, concrete owes its popularity to its versatility, strength, durability, and comparatively low cost. However, the ongoing extraction of natural aggregates such as sand and gravel for concrete production has taken a toll on the environment, depleting natural resources and disrupting ecosystems. This has fuelled growing interest in alternative, sustainable materials that can partially replace conventional concrete constituents without substantially compromising structural integrity (Qaidi et al., 2023; Reana et al., 2026). Against this backdrop, the use of waste PET as a partial fine aggregate replacement in concrete has emerged as an attractive solution that simultaneously addresses plastic pollution and resource conservation. A growing body of research has shown that incorporating PET particles into concrete mixes affects key engineering properties, including compressive strength, tensile strength, density, workability, thermal insulation, shrinkage, and durability. PET-modified concrete also tends to be lighter, making it a candidate for non-structural and lightweight construction uses. Beyond its technical merits, recycling PET into concrete reduces pressure on landfills and supports circular economy principles within the construction sector (Mostafaei et al., 2026; Uche et al., 2026). More recent studies have reinforced this picture, showing that controlled replacement levels of fine aggregate with PET can yield compressive strengths suitable for specific applications. The general trend reported is that lower PET replacement percentages tend to preserve mechanical performance better, whereas higher proportions can weaken the bond between cement paste and aggregate due to the hydrophobic nature of plastic. Even so, several researchers maintain that PET concrete holds considerable promise for sustainable construction provided the replacement ratio is carefully optimized (Qaidi et al., 2023; Xiao et al., 2026). This expanding interest has, in turn, spurred further investigation into how PET-based concrete performs under varying mix proportions and curing regimes. In the Nigerian context, where plastic waste management remains a persistent challenge, repurposing waste PET bottles into construction materials offers a potentially valuable dual benefit: environmental relief and economic gain. Such an approach could ease pollution, conserve natural fine aggregate resources, cut material costs, and support more sustainable infrastructure development. It is against this backdrop that evaluating the engineering performance of PET-incorporated concrete, with particular attention to compressive strength, becomes an important step toward establishing its practical suitability for construction. This study, accordingly, investigated the effects of waste PET on the compressive strength of lightweight concrete when used as a partial fine aggregate replacement. Specifically, the research compared the compressive strength behaviour of concrete produced with two different coarse aggregates, namely washed gravel and crushed granite, while varying the proportion of PET waste substituted for sand. The study further examined how different PET replacement levels influenced strength development at curing ages of 7, 14, 21, and 28 days, with a view to identifying the optimum replacement level capable of delivering satisfactory compressive strength. In addition, the suitability of the resulting PET-modified concrete for construction use was assessed by benchmarking the results against relevant British Standard specifications for concrete. The impetus for this research stems from the mounting accumulation of PET bottle waste in the environment and the corresponding need for sustainable approaches to its disposal. The non-biodegradable nature and long environmental lifespan of PET waste have made it a significant ecological concern, while the construction industry continues to face mounting demand for conventional materials such as sand and gravel. Integrating waste PET into concrete production therefore offers a means of tackling environmental pollution while conserving natural resources and lowering construction costs. In this way, the study contributes to ongoing efforts to develop construction materials that are both environmentally sustainable and economically viable through innovative recycling approaches. The scope of the study was confined to the use of PET waste as a partial fine aggregate replacement in concrete prepared at a 1:2:4 mix ratio, using two types of coarse aggregate, washed gravel and granite. The experimental work comprised slump testing, specific gravity determination, and compressive strength testing, with PET replacement levels varied up to a maximum of 8%. The results obtained were assessed in line with the relevant British Standard specifications.