Oxygen-functionalized calcined petroleum coke-induced C-S-H formation: Coupling silicate polymerization, pore structure, and mechanical response

Abstract

Calcined petroleum coke (CPC) is a carbonaceous solid residue produced through high-temperature treatment, characterized by poor dispersibility and weak solid-liquid interfacial interactions in cement systems. This study proposes an acid treatment to enhance the interfacial compatibility of CPC through surface oxygen functionalization. The structural, chemical, and surface properties of CPC were characterized, and its influence on C-S-H was systematically investigated using a CaO-nanosilica system with Ca/Si ratios of 0.8, 1.4, and 2.0. Functionalized CPC was incorporated at 0-5% of the total CaO and nanosilica mass. The CPC/C-S-H composites were analyzed in terms of phase evolution, interlayer structure, silicate polymerization, pore structure, and nanomechanical properties. Results showed that acid treatment introduced oxygen-containing groups on CPC, increasing the specific surface area and pore volume by 14% and 16%, respectively, and transforming the surface from hydrophobic to hydrophilic while preserving the conjugated carbon framework. Functionalized CPC effectively regulated early C-S-H formation, with an optimal dosage of 2%. CPC addition caused denser, stacked plate-like C-S-H assemblies while reducing total pore volume by 0.082, 0.036, and 0.144 cm³/g at Ca/Si = 0.8, 1.4, and 2.0, respectively. CPC addition also reduced tobermorite interlayer spacing, increasing the polymerization degree by up to 22% in silica-rich C-S-H. CPC still promoted early C-S-H development and a 3.4-5.7% increase in polymerization degree in jennite-like, shorter-chain C-S-H. CPC incorporation refined gel pores and increased the average C-S-H modulus by 1.8-11.7%. These findings reveal how surface-functionalized CPC promotes the early formation and subsequent structural evolution of C-S-H through interfacial physicochemical interactions.