Issue 78

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

The control concrete exhibited portlandite accumulation from 7 to 28 days confirming continued hydration but incomplete pozzolanic consumption—this observation is consistent with EDAX high Ca/Si (2.14) and SEM abundant portlandite crystals—corresponding to the moderate compressive strength (28.0 MPa). GO 0.03% displayed highest crystallinity among all samples with sharpest, most intense peaks at 28 days indicating well organized hydration products, while simultaneously showing reduced portlandite peak heights relative to control despite superior strength (34.5 MPa, +23.2%)—evidence of enhanced pozzolanic consumption producing additional C-S-H rather than portlandite accumulation, crystallographically confirming the strength enhancement mechanisms, validating GO's dual role as nucleation accelerator (producing well-crystallized products) and pozzolanic reaction promoter. CNT 0.1% exhibited well-developed crystalline structure with organized peak patterns at 28 days supporting the SEM observations of a dense reinforced matrix and the EDAX results indicating relatively silica-rich C–S–H (Ca/Si 1.38). The XRD result are consistent with the enhanced tensile performance (3.23 MPa, +31.8%). Excessive dosages, GO 0.05% and CNT 0.2-0.3% showed broader peaks, lower intensities, and increased background signal indicating disordered hydration around agglomerate clusters—crystallographic evidence confirming microstructural defects (SEM) and the mechanical degradation observed. The hybrid formulation displayed combined GO-CNT features with organized crystalline structure, intermediate portlandite peaks, well-developed C-S-H hump, and good overall crystallinity, validating the balanced chemistry (EDAX Ca/Si 1.92) and integrated microstructure that produces balanced mechanical performance without phase interference. Addressing the literature gap on multi-age crystallographic characterization in hybrid SCM-nanomaterial systems [5,7,8,14], this comparative analysis across 16 the investigated samples at two ages establishes that optimal nano-modification (GO 0.03%, CNT 0.1%) enhances both crystalline organization and pozzolanic reactions, demonstrating nanomaterials extend benefits beyond physical reinforcement to chemical promotion of beneficial hydration in GGBS/Fly Ash composite cement systems. oncrete sustainability requires balancing mechanical performance with environmental footprint. This section quantifies environmental benefits of hybrid nano-modified composite cement concrete compared to conventional OPC-based formulations, demonstrating that substantial CO ₂ emission reductions can be achieved while enhancing rather than compromising structural performance. Hybrid nano-modified composite cement concrete achieves substantial environmental benefits while enhancing mechanical performance, demonstrating sustainability and performance are complementary rather than competing objectives. A CO ₂ emission reduction of 39.2% (246 vs 405 kg/m³ conventional concrete) was achieved through two principal mechanisms: (i) cement reduction enabled by nano-reinforcement maintaining strength with lower binder, and (ii) the utilization of Composite Cement containing 40-50% supplementary cementitious materials (GGBS 30-35%, Fly Ash 10-15%) with drastically lower carbon footprints (GGBS: 0.05 kg CO ₂ /kg vs OPC: 0.9 kg CO ₂ /kg). As shown in Tab. 11, the effective OPC content decreases by 45.3% from 450 to 246 kg/m³ equivalent—representing a substantial contribution toward decarbonizing construction responsible for 8-10% of global anthropogenic CO ₂ emissions [1,2]. Carbon intensity improves by 50.7% from 14.46 to 7.13 kg CO ₂ /MPa, reflecting both lower emissions and higher compressive strength (34.5 vs 28.0 MPa)—delivering required structural capacity with half the carbon footprint per unit strength. Incorporating GGBS and Fly Ash diverts industrial waste from landfills supporting circular economy principles while reducing primary resource extraction, aligning with Sustainable Development Goals (SDG 9, 11, 12, 13). Potential lifecycle benefits include enhanced durability (densified microstructure, refined ITZ) extending service life 25-40% amortizing embodied emissions over longer periods; reduced maintenance from superior crack resistance (108-111% flexural enhancement) and chemical resistance (purer C-S-H, lower porosity); potential for thinner structural elements via higher strength multiplying emission savings. Economic viability is supported by the very low nanomaterial dosage (0.164 kg/m³, <3% material cost increase), cement savings (40 kg/m³) offsetting nanomaterial expense, SCM substitution reducing cementitious cost 15-25%, accelerated construction (69-77% early-age strength) enabling faster formwork removal reducing financing costs, and extended lifecycle with reduced maintenance providing long-term value. Furthermore, the magnetic stirring dispersion utilizes conventional mixing equipment (pan mixer, drum mixer) compatible with existing ready-mix/precast operations avoiding expensive ultrasonication infrastructure, enabling field implementation without major capital investment. However, a detailed techno economic analysis is recommended in future work to quantify cost-benefit relationships under field conditions. C E NVIRONMENTAL IMPACT AND SUSTAINABILITY ASSESSMENT

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