Investigating the role of chemically modified PET in enhancing the properties of green concrete with nano silica under freeze-thaw conditions

• 5% chemically modified PET + nano-silica maximizes compressive strength of green concrete • Optimal mix retains 74% strength after 300 severe freeze-thaw cycles • Synergistic PET–EC–NS reduces water permeability by up to 34% vs reference • 15% PET with EC and nano-silica yields lowest mass loss under freeze-thaw • Recycled PET and 8.5% nano-silica create durable, eco-friendly C25 concrete Green concrete, characterized by the utilization of environmentally compatible concrete waste, represents a transformative shift in the concrete industry. Ongoing research focuses on the incorporation of waste additives across various concrete and cement products to enhance their mechanical properties and durability. This study examines the influence of different percentages of shredded recycled plastic bottles, specifically Polyethylene Terephthalate (PET), combined with Ethyl Cellulose (EC) and Nano Silica (NS) on the compressive strength, water permeability, and freeze-thaw resistance of C25 concrete. Advanced characterization techniques, including X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM), were employed to investigate alterations in the microstructure and corrosion products of the concrete formulations. The optimal compressive strength and minimal water permeability—both prior to and following 300 freeze-thaw cycles—were observed in the mixture containing 5% PET, EC, and 8.5% NS at 90 days of curing. Conversely, the blend of 15% PET with EC and NS exhibited the lowest mass loss after 300 freeze-thaw cycles. These findings underscore the potential of pozzolanic effects to enhance the engineering and transport properties of ultra-high-strength concrete. Furthermore, SEM analysis confirmed that the incorporation of 5% PET, along with EC and NS, resulted in increased density and compaction within the concrete matrix. Overall, this research indicates that the integration of waste materials not only reduces cement consumption and mitigates environmental pollution, but also enhances concrete performance, yielding significant improvements in both engineering characteristics and transport properties.