COMPREHENSIVE ANALYSIS OF THE ELEMENTAL COMPOSITION AND THERMAL STABILITY OF REINFORCED CONCRETE BASED ON RECYCLED MATERIALS

This paper presents a comprehensive comparative study focused on the elemental composition, physicochemical properties, and thermal stability of traditional reinforced concrete (TRC) versus alternative reinforced concrete (ARC) developed using recycled raw materials. The research aligns with the fundamental principles of circular economy and green chemistry, aiming to address the urgent need for sustainable infrastructure reconstruction in Ukraine. The investigation primary focuses on the synergy between the chemical nature of binders and their macro-scale performance under extreme conditions. Elemental analysis, conducted via X-ray fluorescence (XRF) spectroscopy using the ElvaX Pro spectrometer, revealed a fundamental divergence in the chemical profiles of the studied systems. It was established that ARC, based on alkali-activated slag cements and recycled concrete aggregates, forms a high-calcium matrix (with calcium content reaching 91.494 %). This composition significantly differs from the multi-component silicate structure of traditional Portland cement-based systems. Experimental heating tests, simulating fire conditions with temperatures reaching up to 700 °C, allowed for the identification of a specific thermal damper effect in the alternative compositions. From a thermochemical perspective, the high concentration of calcium-bearing phases, such as calcium silicate hydrates (C-S-H) and carbonates, facilitates enhanced energy absorption through endothermic dehydration and decarbonisation processes. This mechanism results in a 15–20 % reduction in the rate of internal temperature rise compared to traditional concrete. To verify the structural integrity of the materials after thermal exposure, non-destructive ultrasonic testing was employed using an AU2000 flaw detector. The results demonstrated that despite surface-level degradation, the internal layers of the ARC maintain superior stability and acoustic consistency. The study concludes by justifying the environmental and technical feasibility of integrating recycled aggregates into construction practices as a tool for decarbonisation. Furthermore, the practical potential for implementing these findings into the educational process for chemical technology and civil engineering students is discussed, emphasizing the importance of quality control and innovative material certification in modern industry.