Synthetic polymers and nanostructured materials additives for engineered cementitious materials: Plausible route for recycled polymer utilization

Portland cement is the most widely used construction material, but its primary component, clinker, is produced through an energy-intensive process that significantly contributes to global CO2 emissions. To reduce this environmental impact, recent efforts are focused on developing ultra-high-performance cementitious systems that minimize clinker content while enhancing strength and durability. In this context, synthetic polymers and nanostructured materials are emerging as key additives. Synthetic polymers serve as superplasticisers, air-entraining agents, adsorbents, and carriers for self-healing agents. At the nanoscale, they modify hydration kinetics, improve crack resistance, and enhance long-term durability. Nanomaterials such as nano-silica, graphene oxide, CNTs, nano-alumina, and nanoclays improve the microstructure and mechanical performance of concrete. When polymers are combined with nanomaterials, they form interfacial networks that promote uniform nucleation of calcium-silicate-hydrate, resulting in dense, defect-free matrices. Incorporating recycled polymeric waste, such as polyethylene terephthalate, polypropylene, polystyrene, and ground rubber, introduces a circular economy approach. After surface modifications, these waste materials can function as microfibres or fillers, improving freeze-thaw resistance, chloride impermeability, and structural longevity. Polymer-nanomaterial hybrids offer multiple advantages, such as lower embodied carbon, enhanced durability, smart functionality, lightweight strength, and plastic waste valorization. However, the major challenges in using these materials are high material costs, variability in recycled inputs, durability uncertainties, fire resistance issues, and regulatory gaps. Addressing these through multiscale modelling, life-cycle analysis, and large-scale field validation is essential. This review highlights the role of polymers and nanomaterials in enabling sustainable, high-performance concrete aligned with circular economy principles.