PSI - Issue 70

Nithin A V et al. / Procedia Structural Integrity 70 (2025) 215–222

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3. Results and Discussions 3.1 Mechanical Properties of Ternary Blended Geopolymer Concrete

The compressive strength values of the TBGC specimens with varying binder proportions are shown in Table 2. In the mix IDs F60G40, F30H30G40, and F30G40H30-40CS, fly ash (FA) was partially replaced with hydrous clay (HC) at 30%, while M-sand was substituted with CS at 40%. A 22.33% increase in compressive strength, a 32% increase in splitting tensile strength and a 27% increase in flexural strength was observed in the mix F30G40H30-C40 compared to the control mix (F60G40). This improvement is attributed to the partial dissolution of silicate and aluminate phases from HC in the alkaline medium, which, along with GGBFS and FA, contributed to the formation of a quasi-geopolymer network. The oxide composition of HC revealed 44.90% SiO 2 and 37.47% Al 2 O 3 , while X-ray diffraction (XRD) patterns confirmed the occurrence of both semi-amorphous and crystal phases(Nithin et al., 2024). The reactive components of incorporated copper slag contribute to the geopolymerisation process while simultaneously serving as a micro-filler, thereby enhancing the mechanical properties of the geopolymer binder matrix and interfacial transition zone(Rathanasalam et al., 2020; Sreenivasulu et al., 2020).

Table 2. Mechanical Properties of TBGC mixes Mix ID

Compressive strength (MPa)

Splitting tensile strength (MPa) Flexural Strength (MPa)

7 days 31.33 25.51 37.78

28 days

7 days

28 days

7 days

28 days

F60G40

41.78 31.11 51.11

2.61 2.21 4.62

3.96 2.97 5.23

2.16 1.57 2.78

2.46 1.92 3.12

F30H30G40

F30H30G40-40CS

3.2 Ternary Blended Geopolymer Concrete Slabs (TBGCS) Initial cracking consistently appeared at the mid-span along the shorter edge, orientated parallel to the longer side of the TBGCS. As the load increased, these cracks began to deviate from their original paths, extending toward the slab's corners. All slab specimens were simply supported and structurally detailed to ensure flexural failure as the governing mode. Table 3 presents the summary of flexural studies on the tested TBGC slab specimens. Notably, the slab made with mix F60H30G40-40CS exhibited delayed crack initiation, indicating approximately a 26.25% increase in first-crack load compared to the control. The load-deflection response remained almost linear until cracking began and transitioned into a nonlinear trend in the post-cracking phase (Fig.3). Among all mixes, the F60H30G40-40CS slab showed a marked improvement in load-carrying and deflection capacity. The control slab (F60G40) reached failure at an ultimate load of 54.38 kN, corresponding to a maximum mid-span deflection of 42.05 mm. In contrast, the TBGC slab incorporating 30% FA, 30% HC, 40% GGBFS, and 40% CS (F30H30G40-40CS) exhibited significantly enhanced performance, failing at a higher ultimate load of 78.70 kN with a maximum midspan deflection of 28.35 mm. The enhanced flexural characteristics of GPCs incorporating GGBFS, FA and HC had a positive impact on the delayed crack initiation and load carrying capacity of TBGCS (Altay Eren, 2022; Sammak & Mousavinejad, 2023). The corresponding load-deflection curves for the TBGC slabs are illustrated in Fig. 3. It was also observed that using a binder blend of FA: HC: GGBS at 30%, 30%, and 40%, respectively, along with 40% copper slag (CS) as fine aggregate, significantly enhanced the slab’s ultimate load -bearing capacity. The slab F30H30G40-0CS reached failure at an ultimate load of 48.575 kN, corresponding to a maximum mid-span deflection of 44.75 mm. The replacement of M-sand with 40% CS has reduced the voids in fine aggregates compared to conventional type, improving the intergranular bonding in the GPC(Manibalan et al., 2024). This also contributed in the enhancement of flexural behavior and crack resistance of TBGCS. Both CS and HC are by-products, having negligible carbon footprint compared to conventional materials like cement and M-sand. Collectively, these findings promote an economic, low carbon construction practice aligned with circular economy principles, emphasizing the practical viability of the proposed TBGC system for sustainable infrastructure.