PSI - Issue 70

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

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alternate to M-sand was also explored on the hardened properties of TBGC. The flexural property on slab specimens of control mix and optimum mix with and without CS was experimentally investigated. 2. Experimental Study 2.1 Materials and Mix Design Fly ash (FA) of Class F, ground granulated blast furnace slag (GGBS), and hydrous clay waste (HC) were considered as the binder materials for this study. The fine aggregates consisted of copper slag (CS) and manufactured sand (M-sand), both with a size less than 4.75 mm. For proper gradation, a combination of 6mm and 12.5mm aggregates was used as coarse aggregates. The flakes of sodium hydroxide were premixed with water to the required 12 molar concentration. A naphthalene-based admixture, added at 1.5% of the total binder weight, was used to enhance the workability of the mix. The mix ratio was obtained after trials by varying the proportions of binder materials, fine aggregates, coarse aggregates, and superplasticizer to develop a 40 MPa grade TBGC mix. The optimum proportions of FA, GGBS, and HC are obtained at 30%, 40%, and 30% for binder materials and at CS and M-sand at 40% and 60% for fine aggregates, respectively. A fine aggregate to coarse aggregate ratio of 0.41:0.59 was used in the TBGC mix design. The ratio of sodium silicate to sodium hydroxide, solution to precursor ratio, and NaOH molarity were taken at 2.5, 0.4, and 12 respectively, for all mixes. For preliminary studies, standard cube, cylindrical, and beam specimens of sizes 150 × 150 × 150 mm, 150 × 300 mm , and 500 x 100 x 100 mm, respectively, were cast and tested in accordance with IS 516 (Part 1/Sec 1): 2021. The mix proportions of TBGCs are presented in Table 1. F60G40 represents TBGC of 60% FA and 40% GGBS as binder materials and AL represents alkaline solution.

Table 1. Mix Proportions of TBGC mixes in kg/m 3 Mix ID

FA HC GGBS AL M-sand CS 6 mm 12 .5 mm SP

F60G40

300

0

200

200 200 200

742 742

0 0

325 325

729 729 729

7.5 7.5 7.5

F30H30G40

150 150 200

F30H30G40-40CS 150 150 200

374.5 367.5 325

2.2 Details and preparation of specimens The TBGC mix was tested for slump prior to placement, and a value range of 70-75 mm was observed. In this study, three sets of two-way ternary blended geopolymer concrete slabs (TBGCS) with dimensions of 1550 × 1050 × 60 mm were cast. The span-to-depth ratio of the slabs was taken as 25. The slabs were reinforced with 6 mm diameter main bars spaced at 135 mm center-to-center (c/c) in the transverse direction and 6 mm bars at 200 mm c/c in the longitudinal direction. The reinforcement bars used in this study had a yield strength (f y ) of 443 MPa and an ultimate tensile strength (f u ) of 583 MPa. The strain gauges of 10 mm grid length were affixed to the underside of the reinforcement bars at the mid-span region, where flexural load was expected to be highest. Prior to installation, the bar surfaces were ground smooth and thoroughly cleaned with acetone to ensure proper adhesion and accurate strain measurements. First the cover concrete of 15 mm thickness was added, following by placing the reinforcement layer, and the remaining concrete was poured and compacted. The slab specimens were removed from the moulds after 24 hours and placed in the laboratory for 7 days and is shown in Fig. 1 (a). The slab geometry and 16-point loading are schematically illustrated in Fig 1 (b) and 2. Prior to mounting the slab specimens on the loading frame, all surfaces were whitewashed to aid in the clear identification and tracking of crack development.

2.3 Loading Setup and Instrumentation

The slabs were tested using a loading frame with a capacity of 1500 kN. The frame comprised main support beams and cross beams on which the slabs were placed. Load transfer to the main frame was facilitated by vertical square tubes positioned at all four corners, forming an integrated and effective setup. Each slab was simply supported along all four edges, with effective spans of 1.5 m and 1.0 m in orthogonal directions. A 16 -point static loading test was