By Nidhi DhullReviewed by Susha Cheriyedath, M.Sc.Nov 18 2024A recent article published in Scientific Reports examined the mechanical and durability properties of concrete incorporated with waste plastic fibers and treated construction and demolition waste (CDW). The hand-shredded plastic fibers as concrete reinforcements were sourced from polyethylene (PE) bags and polyethylene terephthalate (PET) bottles.
Study: Impact of plastic waste fiber and treated construction demolition waste on the durability and sustainability of concrete. Image Credit: LadyRhino/Shutterstock.com
Background
Concrete, the most prevalent construction material, is ideal for various building projects with different load-bearing and environmental conditions due to its strength, long-lasting nature, and adaptability. However, concrete production consumes extensive natural resources, while demolishing concrete structures adds to the growing construction waste management crisis.
Incorporating CDW in concrete can conserve natural resources and reduce landfill waste, promoting a more sustainable construction industry. However, adhered mortar in recycled concrete aggregates increases water absorption, reduces density, and weakens bond strength, negatively impacting concrete’s overall strength and durability.
Various materials and methods have been explored to improve the properties of adhered mortar in recycled concrete aggregates. Notably, plastic waste can enhance the strength and durability of concrete. Therefore, this study investigated the characteristics of concrete comprising treated CDW instead of coarse aggregates and plastic waste fibers from PE bags and PET bottles.
Methods
Recycled CDW was sourced from a solid waste recycling plant and treated with polyethylenimine (PEI) to enhance surface texture and pore structure. This treated CDW was then incorporated into concrete at varying proportions.
Plastic fibers were prepared from discarded single-use PET bottles and PE bags. The fibers were manually shredded to 1´10 mm2 size and added to concrete in weight ratios of 0% to 1% to obtain plastic-fiber reinforced concrete (PFRC).
Different concrete mixes were evaluated for their compressive, split tensile, and flexural strengths after curing for 28 days following international standards. Additionally, the durability of the prepared specimens was assessed in 10% concentrated sulfuric acid for three months.
High-temperature exposure tests were performed on cubic specimens of various concrete mixes in an oven for six hours at 350 °C. The properties of the plastic fibers before and after high-temperature exposure were observed via a scanning electron microscope (SEM). Additionally, their elemental composition was examined through energy dispersive spectroscopy (EDS).
Finally, the carbon content in concrete blocks comprising recycled plastic waste was evaluated. Accordingly, the energy used throughout different production stages was assessed to determine the carbon “embodied” or “trapped” in the final product.
Results and Discussion
The M7 concrete mix, comprising 0.25% and 0.5% plastic fibers and 100% treated CDW, exhibited compressive strength comparable to the control concrete. Notably, all mixes with 0.25% PET exhibited compressive strength comparable to the control sample. The maximum strength reduction (23%) was observed for the specimen comprising 0.25% PET and 1% PE.
At an optimal fiber content, the concrete’s compressive strength increased by 11% relative to the mix with 100% CDW. This enhancement was accredited to the pretreatment and preconditioning of CDW with PEI, which minimized the pore structure of the CDW. The reduced porosity strengthened the CDW, improving the overall compressive strength.
The M7 mix demonstrated the highest split tensile and flexural strengths, 11.7% and 18.2% higher than the control mix, respectively. This was accredited to the ductile properties of the plastic fibers, which improved the concrete’s ductility and reduced stress concentrations in cracking zones.
The control mix and PFRC specimens demonstrated slight pale discoloration with no evident damage when constantly exposed to a temperature of 350 °C, revealing good thermal stability. The slight thermal deformation was accredited to expansion and contraction within the matrix during heat exposure.
The control and M7 specimens underwent significant erosion in sulfuric acid. Notably, the extent of erosion increased with the duration of acid exposure. However, the M7 specimens suffered less damage than the control specimens, owing to the plastic fibers’ robustness against sulfuric acid.
Considering economic aspects, treated CDW presented a cost-effective and eco-friendly alternative to coarse aggregates in concrete owing to the substantial savings in raw material, transportation, and lifecycle costs while fostering long-term sustainability in construction. Moreover, the M7 mix exhibited 1.3 times less energy demand and 1.2 times less embedded carbon than the control mix.
Conclusion
Overall, the researchers successfully demonstrated the advantages of incorporating plastic waste and CDW in concrete, providing an effective solution for waste disposal while enhancing the concrete’s mechanical properties.
The waste-incorporating concrete mixes exhibited comparable compressive strength to conventional concrete, with considerable improvements in flexural strength (11.41%) and tensile strength (17.72%) at optimal fiber dosages and 100% replacement of natural aggregate with treated CDW. The SEM and EDS analyses confirmed the minimal damage to the fibers from acid exposure and high-temperature exposure.
Moreover, the environmental and economic advantages of incorporating plastic waste fibers and treated CDW in concrete were considerable. Thus, such sustainable construction practices can lower resource consumption and mitigate the environmental impact of concrete structures.
Journal Reference
Duraiswamy, S., Neelamegam, P., VishnuPriyan, M., & Alaneme, G. U. (2024). Impact of plastic waste fiber and treated construction demolition waste on the durability and sustainability of concrete. Scientific Reports, 14(1). DOI: 10.1038/s41598-024-78107-w, https://www.nature.com/articles/s41598-024-78107-w
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