Issue 78

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

The hybrid formulation achieved 14.92 MPa (+98.9%), showing the closest approach to synergistic behavior among the investigated mechanical properties, suggesting flexural loading particularly benefits from combined GO matrix strengthening and CNT crack bridging under complex stress states (compression, tension, shear). At 56 days, optimal formulations maintained approximately 16.2 MPa (+35% vs control value of 12.0 MPa), providing persistent advantages enabling thinner slabs, longer spans, or reduced reinforcement requirements. Excessive dosages degraded performance: GO 0.05% yielded only 8.1 MPa (+8.0%) suggesting the adverse effects of particle agglomeration at higher dosages; while CNT 0.2-0.3% showed intermediate performance (13.2-14.35 MPa), inferior to CNT 0.1%, reinforcing optimal dosage identification as shown in the Figs. 8 and 9. The limitation of flexural test is that the load-deflection measurements were not recorded during the experimental program. The flexural tests were performed primarily to determine ultimate flexural strength, and instrumentation for continuous deflection monitoring was not available at the time of testing. Consequently, representative load-deflection curves cannot be provided. It is recommended that future studies incorporate detailed failure-mode characterization, digital image documentation, and instrumented flexural testing to evaluate crack propagation, toughness, ductility, and post-cracking behavior of nano-modified SCM-based concretes.

Figure 7: Flexural strength test specimen.

Figure 8: Flexural strength comparison with dosage of GO.

Figure 9: Flexural strength comparison with dosage of CNT.

M ICROSTRUCTURAL ANALYSIS

he mechanical property enhancements documented above require fundamental microstructural validation to establish casual link beyond empirical correlation. While existing literature demonstrates GO and CNT effects individually in OPC systems [5-8] or combined with single SCMs [18,19], very limited studies [12] has systematically characterized the integrated microstructure-property relationships in hybrid nano-modified composite cement concrete containing both GGBS and Fly Ash across multiple curing ages. This critical gap—identified in Section 2—is addressed through comprehensive SEM, EDAX, and XRD analysis correlating nanomaterial dispersion quality, C-S-H morphology, T

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