Issue 78

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

regions concentrating silica while excluding calcium—elemental evidence supporting the mechanical degradation and SEM observed defects. The hybrid formulation exhibited an intermediate Ca/Si ratio of 1.92, balanced between GO 0.03% and CNT 0.1% effects, with (Al+Fe)/Ca ratio of 0.14 matching optimal values indicating well-developed C-S-H without antagonistic interactions, chemically validating the balanced mechanical performance across properties. Unlike previous studies examining GO or CNT individually [5-8], the present systematic compositional analysis across 16 samples suggests that nano-modification influences pozzolanic reactions in GGBS/Fly Ash composite cement systems: optimal dosages produce purer C-S-H (reduced (Al+Fe)/Ca, S/Ca ratios) with favorable silicon-rich compositions, extending benefits beyond physical reinforcement to chemical promotion of beneficial hydration reactions. X-Ray Diffraction analysis (XRD) XRD analysis identified crystalline phases and their evolution across curing ages, providing complementary information of hydration mechanisms observed through SEM and EDAX. Fig. 14 present representative XRD diffractograms of the optimized graphene oxide (GO) and carbon nanotube (CNT) mixes at 28 days. For completeness, the XRD results of all eight mixes at 7 and 28 days along with the phases present in the concrete mixes were identified and the results are summarized in Tab. 10.

Sample Designation

Phase Identification & Crystalline Maturity

Control (0% Nano) - 7 Days Control (0% Nano) - 28 Days

Distinct Quartz peaks; broad humps indicating semi-crystalline C-S-H. Increased peak intensities for Portlandite (CH), reflecting mature hydration. Similar to control but with slightly more defined early hydration peaks. Crystalline phases consistent with standard hydrated cement-based concrete. Shorter, better-defined peaks for CH, indicating accelerated early growth. Sharpest and most intense peaks for C-S-H and CH; indicates highest crystallinity. Peaks for Albite and Quartz identified; slightly lower intensity than 0.03% GO. Reduction in peak intensities compared to optimal dosage due to agglomeration.

GO 0.01% - 7 Days GO 0.01% - 28 Days GO 0.03% - 7 Days GO 0.03% - 28 Days GO 0.05% - 7 Days GO 0.05% - 28 Days CNT 0.1% - 7 Days CNT 0.1% - 28 Days CNT 0.2% - 7 Days CNT 0.2% - 28 Days CNT 0.3% - 7 Days

High intensities of Anorthite and Portlandite detected.

Well-developed crystalline structure; reinforces the dense binder matrix.

Peak intensities stable; lower than 0.1% CNT dosage.

High degree of hydration; peaks similar to 0.1% dosage but less organized.

Quartz and Anorthite peaks present; peak counts stable at ~1500.

Very high peak counts (>3000) for crystalline products; indicative of high CNT loading. Shorter, better-defined peaks for CH, indicating accelerated early growth.

CNT 0.3% - 28 Days

(GO 0.03% + CNT 0.1%) – 7 Days (GO 0.03% + CNT 0.1%) – 28 Days

Sharpest peaks for C-S-H and CH; indicates highest crystallinity. Table 10: XRD result analysis.

XRD patterns revealed characteristic peaks enabling phase identification: Quartz (SiO ₂ ) from unreacted aggregates at 2 θ = 20.9°, 26.6°, and 50.1° (sharp, high-intensity peaks persisting across all samples); Portlandite (Ca(OH) ₂ ) at 2 θ = 18.0°, 34.1°, and 47.1° (indicating cement hydration product and pozzolanic reaction substrate); Broad C-S-H hump at 2 θ = 29-32° (semi-crystalline/amorphous calcium-silicate-hydrate gel, dominant binding phase); Ettringite (calcium sulfoaluminate) at 2 θ = 9.1° and 15.8° (early hydration product); Calcite (CaCO ₃ ) at 2 θ = 29.4° (from limestone filler or carbonation of portlandite). Peak intensity, sharpness, and background-to-peak ratio provide quantitative indicators of crystallinity and phase abundance.

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