Issue 78

C. S. Karadumpa et alii, Fracture and Structural Integrity, 78 (2026) 146-167; DOI: 10.3221/IGF-ESIS.78.09

K EYWORDS . SCM-based concrete, Nanomaterials, Hybrid nano-modified concrete, Microstructure, Sustainability.

I NTRODUCTION oncrete remains indispensable in modern infrastructure; however, its environmental footprint is largely attributable to Ordinary Portland Cement (OPC) production, which contributes approximately 8–10% of global CO ₂ emissions and necessitates the development of sustainable alternatives [1,2]. Supplementary Cementitious Materials (SCMs) such as Ground Granulated Blast-furnace Slag (GGBS) and Class F Fly Ash have been extensively adopted to reduce cement consumption, lower embodied carbon emissions, and improve long-term durability through pozzolanic reactions that refine pore structure and reduce permeability [3,4]. Simultaneously, carbon-based nanomaterials such as Graphene Oxide (GO) and Carbon Nanotubes (CNTs) have attracted considerable attention because of their ability to accelerate hydration, refine microstructure, and enhance mechanical performance through nanoscale reinforcement mechanisms [5–9]. The combination of SCMs and nanomaterials therefore represents a promising strategy for developing sustainable, high performance concrete. Despite these advantages, several scientific and practical challenges continue to limit widespread implementation. SCM-rich concretes often exhibit slower early-age strength development, restricting their use in applications requiring rapid strength gain and early load transfer [3,4]. In addition, the effectiveness of GO and CNTs is highly dependent on achieving uniform dispersion within the cementitious matrix, since agglomeration and restacking may reduce reinforcing efficiency and adversely affect workability [5–7]. Furthermore, cost considerations, scalable dispersion techniques, and the absence of standardized implementation procedures remain important barriers to field adoption. GO, CNTs, and SCMs have each been widely investigated for enhancing the mechanical, durability, and microstructural performance of cement-based materials. GO primarily acts as a nano-nucleation agent that accelerates hydration and promotes matrix densification, whereas CNTs contribute through crack-bridging and stiffness enhancement due to their exceptionally high aspect ratio and tensile strength. SCMs improve long-term durability and reduce the carbon footprint of concrete, although their slower early-age reactivity remains a persistent limitation. Consequently, combining SCMs with nanomaterials has emerged as a promising approach for compensating early-age strength loss while maintaining long-term sustainability benefits. A critical review of the literature reveals that most published studies focus on GO-only systems, CNT-only systems, or SCM-based concretes investigated independently. GO-modified concretes have generally demonstrated improvements in compressive, tensile, and flexural strength at optimum dosages (typically 0.02–0.05%) together with reduced porosity and refined microstructures [10–13]. Similarly, CNT-based systems have shown enhanced tensile behavior, toughness, and crack resistance, although dispersion challenges remain a major concern [7,8,14,15]. Research on SCM-based binders confirms significant durability and environmental benefits but consistently reports reduced early-age strength development [16,17]. More recently, researchers have explored combinations of nanomaterials and SCMs, including GO–slag systems and CNT modified slag or fly ash binders [18,19,20,21]. These studies generally reported improvements in hydration kinetics, pore refinement, and mechanical properties. Hybrid nano-systems have also been investigated, including GO–CNT combinations and CNT–fibre composites [22,23,24], demonstrating the potential for synergistic behavior. However, most of these studies are limited to paste- or mortar-scale investigations and do not simultaneously incorporate SCM-rich binders, GO, and CNTs within a concrete system. In addition, comprehensive evaluations linking fresh-state properties, multi-age mechanical behavior, microstructural evolution, and environmental performance remain limited. To facilitate a systematic comparison, Tab. 1 summarizes relevant studies based on materials used, key findings, and remaining research gaps. The review indicates that, while substantial progress has been made in individual areas, limited investigations have evaluated hybrid GO–CNT reinforcement in SCM-based concrete while simultaneously assessing mechanical, microstructural, and sustainability-related performance indicators. This knowledge gap provides the motivation for the present research. Accordingly, this study investigates hybrid nano-modified composite cement concrete incorporating commercially available composite cement containing GGBS and Fly Ash together with GO (0.01–0.05%) and CNTs (0.1–0.3%). The specific objectives are: (a) to evaluate the combined effects of GO and CNTs on the fresh and hardened properties of SCM-based concrete; (b) to identify optimum nanomaterial dosages that maximize performance while maintaining acceptable workability; (c) to assess the effectiveness of nano-modification in mitigating the reduced early-age strength development associated with SCM-rich binders; and (d) to correlate mechanical performance with microstructural characteristics obtained from SEM, XRD, and EDAX analyses. C

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