Atomic-Scale Interfacial Characterization and Circular Economy Assessment of Sustainable Concrete Incorporating DCFRP, GBFS, and Oyster Shell Waste

Abstract

Mitigating the carbon footprint of cementitious composites while sustaining mechanical performance remains a critical challenge in modern construction. This study investigates the atomic-scale origins of strength in a sustainable ternary waste valorization system incorporating Discarded Carbon Fibre Reinforced Polymer (DCFRP) fibres, S105 Granulated Blast Furnace Slag (GBFS), and Oyster Shell Powder (OSP). While previous research established the macroscopic viability of this composite, demonstrating a 22.4% increase in compressive strength the physicochemical mechanisms governing its performance remained unexplored. Employing X-ray Photoelectron Spectroscopy (XPS), this research reveals that the optimal mix (10% GBFS and 5% OSP) achieves a surface Calcium-to-Silicon (Ca/Si) atomic ratio of 0.47. Although lower than typical bulk C-S-H values reported in the literature (Ca/Si ≈ 0.8–1.7), this reduced ratio reflects a silica-enriched surface environment in the slag-blended system, consistent with enhanced silicate polymerization and surface-modified C-(A)-S-H chemistry. High-resolution Si2p spectra at 102.6 eV confirm enhanced silicate polymerization driven by the latent hydraulic activity of GBFS. XPS analysis indicates the presence of carbonate–aluminate interactions consistent with potential heterogeneous nucleation mechanisms at the OSP surface. While XPS does not provide spatial resolution of the ITZ, the observed chemical signatures support a chemically favourable environment for interfacial densification. Conversely, a chemical "dilution threshold" is identified at 15% OSP replacement, where unreacted calcite phases act as stress concentrators. These findings bridge the gap between phenomenological testing and molecular chemistry, establishing a scientific framework for a Circular Economy model that enables a 10% reduction in clinker consumption and the effective valorization of industrial and marine waste streams