Microstructural and Impact Resistance Optimization of Concrete Composites with Waste-Based Aggregate Substitutions

In the context of growing challenges related to the safety and durability of civil infrastructure, the demand for concrete composites capable of withstanding dynamic and impact loading is steadily increasing. Conventional concrete, owing to its brittle nature and limited energy absorption capacity, does not always meet the performance requirements imposed on protective structures. The construction sector's substantial contribution to CO₂ emissions further underscores the need for environmentally responsible solutions. This study therefore explores the effects of partially replacing natural aggregate with waste-derived constituents such as SBR rubber granulate, copper slag, polypropylene and glass granulate on the mechanical properties and impact resistance of concrete. Scanning electron microscopy (SEM) and stereoscopic microscopy were used to characterize the additives' geometry and interfacial bond quality, providing deeper insight into cement paste-aggregate interactions. Compressive testing confirmed that introducing the recycled components does not preclude meeting essential strength criteria, whereas impact experiments revealed pronounced differences in failure mode, crack propagation, and the specimen's ability to dissipate kinetic energy. The experimental program was complemented by a life cycle assessment (LCA) that quantitatively estimated the CO₂ emissions associated with producing each mixture. The findings demonstrate that judiciously selected waste materials can reduce the consumption of virgin resources, enhance concrete functionality, and improve their protective performance, thereby advancing the principles of a circular economy.