PSI - Issue 70

Vudata Harsha sai et al. / Procedia Structural Integrity 70 (2025) 509–516

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FA10-SF M40 FA20-SF M40 FA30-SF M40 FA10-PPF M40 FA20-PPF M40 FA30-PPF M40 FA10-CYF M40 FA20-CYF M40 FA30-CYF

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3. Results and Discussions 3.1

Compressive Strength Concrete specimens of cubes (150 x 150 x 150 mm) were tested for compressive strength using 2000 kN Universal Testing Machine as per IS 516:2020. The load was uniformly applied till failure. The maximum load registered was used to determine the compressive strength at definite curing ages for consistency and accuracy in evaluation of performance. Compressive strength of fiber-reinforced concrete (FRC) was tremendously affected by the type of the utilized materials as well as percentage fly ash substitution. The control mix (M40-Control) attained twenty-eight-day strength of 45.2 MPa. The addition of 10% and 20% Class F fly ash (M40-FA10 and M40-FA20) led to strength increase to 46.8 MPa and 47.5 MPa respectively which were associated with increased particle packing, refined microstructure and pozzolanic reactions. However, the replacement of 30% (M40-FA30) caused the decrease to 43.1 MPa resulting from diminished early-age hydration. Strength was increased further by the addition of 1% steel fibers (M40-FA20-SF) up to 49.8 MPa due to the bridging effect on the microcracks. Polypropylene (M40-FA20-PPF) and coir yarn fibers (M40-FA20-CYF) achieved 48.1 MPa and 47.2 MPa, respectively, which helped to improve the ductility and post-crack strength.

Fig.2 Compressive strength Test setup

Fig.3 Compressive strength Results

The 28-day compressive strength results (Fig. 3) confirm that 20% fly ash replacement yields optimal densification of the cement matrix, increasing strength by 12% over the control. This agrees with Mohanraj and Vidhya’s findings on pozzolanic microstructure refinement in cactus-infused concrete (Mohanraj & Vidhya, 2023). At 30% fly ash, a slight strength reduction (−4.7%) occurs due to slower early hydration, consistent with Johnston (2001). Incorporation of 1% steel fibers in the 20% fly ash mix further boosts strength to 49.8 MPa, as steel fibers act as effective crack bridgers (Banthia & Trottier, 1995; Loganathan et al., 2022). Polypropylene and coir yarn fibers achieve 48.1 MPa and 47.2 MPa respectively, enhancing post-crack load capacity in line with Yin et al. (2015) and Ali et al. (2012).