PSI - Issue 70

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

511

• Ultimately, this study aims to inform engineers, researchers, and policymakers about practical, eco-efficient solutions for next-generation concrete composites with balanced structural performance and environmental responsibility. 2. Methodology and materials This experimental study aims to evaluate the mechanical and flexural performance of M40 concrete incorporating hybrid fibers (steel, polypropylene, and coir yarn) and varying levels of Class F fly ash (10%, 20%, 30%) as partial cement replacement. A total of 13 concrete mixes were prepared, including a control mix without fly ash or fibers, and combinations with each fiber type at 1% volume fraction. The fibers were selected based on their relevance to real-world construction practices: • Steel fibers: Aspect ratio 60, tensile strength 1100 MPa.

• Polypropylene fibers: 12 mm monofilament, tensile strength 500 MPa. • Coir yarn fibers: 0.3 mm diameter, 220 MPa tensile strength, untreated. Concrete specimens were cast and tested for: • Compressive strength (150×150×150 mm cubes) – IS 516:2020 • Split tensile strength (150×300 mm cylinders) – IS 5816:1999 • Flexural strength (500×100×100 mm prisms) – IS 516:2020 • Load-deflection behaviour (700×150×150 mm beams under two-point bending)

All specimens were demoulded after 24 hours and cured in water at 27 ± 2°C for 28 days before testing. The outcomes were analyzed to identify the optimal fly ash – fiber combination for strength, ductility, and sustainability. .

a.

Steel Fibers

b.

Polypropylene Fibers

c.

Coir Yarn Fibers

Fig.1 Various Fibers used

2.1 Mix Proportions Following IS 10262:2019 and IS 456:2000 concrete mix, an M40 concrete mix was designed with a purpose to provide optimal strength and durability. The given control mix consisted of OPC 53 grade, river sand, 20 mm crushed granite and 0.40 water-cement ratio. In an attempt to improve sustainability through minimizing heat of hydration and refining microstructure, class F fly ash of 10%, 20% and 30% was added in the form of partial cement replacement. Fiber-reinforced concrete mixes were discovered with the use of 1% volume fraction of steel, polypropylene, and coir yarn fibers. Such fibers enhanced mechanical properties, crack, and ductility, which led to a structurally efficient and

sustainable high-performance concrete. Table 1. Material Proportions of Mix design.

Steel Fibers (%)

Fine Aggregate

Coarse Aggregate

Polypropylene Fibers (%)

Coir Yarn Fibers (%)

Mix ID Cement FlyAsh

Water

Admixture

M40 Control

400

0

750

1150

160

0

0

0

4

40 80

750 750 750 750

1150 1150 1150 1150

160 160 160 160

0 0 0 1

0 0 0 0

0 0 0 0

4 4 4 4

M40-FA10 360 M40-FA20 320 M40-FA30 280

120

360

40

M40-