Issue 78

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

M ATERIALS AND METHODS

T

his study employed a systematic experimental program to evaluate hybrid nano-modified composite cement concrete incorporating GGBS, Fly Ash, Graphene Oxide (GO), and Carbon Nanotubes (CNTs). The overall workflow of the experimental program, including material preparation, dispersion, mixing, casting, curing, mechanical testing, and microstructural characterization is illustrated in Fig. 1, which provides a schematic representation of the methodology and testing protocol. All constituent materials used in the investigation are summarized in Tab. 2, including commercially procured (JSW manufacturers) composite cement conforming to IS 16415:2015 [25], Zone II river sand, crushed granite coarse aggregate, high-purity GO and CNTs, and a polycarboxylate ether (PCE) superplasticizer.

Figure 1: Schematic representation of experimental methodology.

Mix design followed IS 10262:2019 [26] guidelines for M30 grade concrete (characteristic compressive strength of 30 MPa). The target mean strength was calculated as f cm = f ck + 1.65 σ = 30 + 1.65(5) = 38.25 MPa assuming good quality control (standard deviation of 5 MPa). The control mix (Mix 1) consisted of: cement 450 kg/m³, water 216.0 kg/m³, fine aggregate 559.04 kg/m³, coarse aggregate 960.80 kg/m³, water-cement ratio of 0.48, a polycarboxylate superplasticizer was added at 1.80 kg/m³ (0.4% by cement weight) and a target slump of 100±10 mm. For the nano-modified mixtures (Mixes 2–8), the mix proportions were adjusted to maintain the target M30 concrete grade, a water-to-binder ratio of 0.48, and the desired workability. The influence of GO and CNT incorporation on the fresh and hardened properties of the SCM-based concrete was subsequently evaluated through experimental testing. For the nano modified mixtures (mixes 2-8), the cement content was reduced to 410 kg/m³ (for the same M30 grade concrete), water content to 196.8 kg/m³ (w/c ratio of 0.48), fine aggregate content was increased to 605.7 kg/m³, and coarse aggregate content to 1028.7 kg/m³. A polycarboxylate superplasticizer was added at 1.64 kg/m³ (0.4% by cement weight). Eight mix designs were evaluated: (1) Control (0% nanomaterial); (2) GO 0.01%; (3) GO 0.03%; (4) GO 0.05%; (5) CNT 0.1%; (6) CNT 0.2%; (7) CNT 0.3%; (8) Hybrid (GO 0.03% + CNT 0.1%) as shown in Tab. 3. All percentages of nanocomponents are expressed by weight of cement. The objective of the study was not solely to investigate the isolated effect of GO and CNT additions, but rather to develop and evaluate practical nano-modified SCM-based concrete mixtures that satisfy the target strength and workability requirements. The control mixture was designed as a conventional SCM-based M30 concrete with a binder content of 450

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