Analysis of the Influence of PET and Glass Packaging Waste Materials on the Physical and Mechanical Properties of Cementitious Composites  
[PERSON]  
1 Faculty of Civil Engineering and Architecture, Kielce University of Technology, Al. Tysialecia Paristwa Polskiego 7, 25-314 Kielce, Poland; [EMAIL_ADDRESS] (G.  
PP, LDPE, LLDPE, HDPE, MDPE, PS, PET, and other thermoplastic polymers [1]. In 2021, PET production constituted about 6.2% of global and 5.3% of European plastic production, equating to approximately 24 million tonnes and 9.3 million tonnes, respectively [1]. The immense production volumes pose substantial management challenges, given that plastics are predominantly categorised as non-biodegradable, persisting in the environment for centuries. Accumulated unrecycled polymer waste threatens ecosystems and human health [3]. An eco-conscious approach focuses on mitigating environmental pollution through effective waste management strategies. Eurostat data indicates a 117% in-crease in plastic recycling and a 77% increase in incineration energy recovery between 2006 and 2020, with landfilling reduced by approximately 47%. Nonetheless, about 23% of post-consumer plastic waste still ends up in landfills. Plastic packaging recycling in the EU was at 37.6% in 2020, marking an 11.2% increase since 2006 but showing a 4.8% de-crease compared to 2016, raising significant concerns [4]. Polymer recyclates have potential applications across various sectors including the construction industry, enhancing the rate of material recycling. Polymer wastes such as PET, PP, LDPE, EVA, PVC, ABS, SBS, and others are utilised, inter alia, to modify mineral and asphalt mixes to bolster their mechanical and operational parameters, like rutting resistance, strength, and viscoelastic and fatigue properties [5; 6; 7]. Thermoplastic elastomers enhance the binder's elastic properties and fatigue resistance, while plastomers enhance the stiffness and deformation resistance under load, prolonging the service life of asphalt pavements, especially those burdened with heavy traffic or situated in hot climates [8]. The granulation and type of polymer determine the efficiency of asphalt modification and dictate its functionality [9]. The literature posits the feasibility of employing polymer waste as a partial substitute for fine and coarse aggregate or as fibres for concrete reinforcement [10; 11; 12; 13]. Waste PE, PP, and PET in forms like pellets or flakes can compromise the compressive strength of mortars, while enhancing the insulation and impact resistance and reducing the water vapour permeability [14]. The alteration in mechanical properties of concretes, using PET as a substitute for part of the fine aggregate, is contingent upon the dimensions, shape, and percentage of waste. Generally, an increase in PET percentage induces a decline in flexural and compressive strength, concrete density, and consistency [15]. The usage of PET, measuring between 5 and 15 mm and 2.6 and 11.4 mm, as a substitute for 25-75% and 10-20% of fine aggregate, respectively, led to a decline in the aforementioned properties [16; 17]. Conversely, there are instances which report the enhanced strength of concrete with a 10% composition of PET, having a grain size of 2-4.9 mm and 0.05-2 mm [18]. Other authors have indicated that the optimum content of PET used as a fine and coarse aggregate is only 1% by volume or less [19; 20]. PET coarse aggregate proves beneficial for structural concrete, enhancing the workability of concrete mixes with lower water to cement ratios, without a substantial compromise to mechanical properties [11]. Polymers like PP and PET, when used as reinforcing fibres, mitigate the occurrence of cracks during plastic shrinkage [21; 22] and augment the flexural strength of cementitious composites. Studies by [PERSON] and [PERSON] reveal that finer and elongated PP fibres outperform the coarser and shorter ones in regulating the plastic shrinkage of concrete.