Utilisation of Bagasse Ash and Slag Sand as Cement and Fine Aggregate Replacements in Self-Compacting Concrete

Abstract

This experimental study focuses on the performance of M50 grade Self-Compacting Concrete (SCC) incorporating Sugarcane Bagasse Ash (SCBA) as a supplementary cementitious material and slag sand as a substitute for natural fine aggregate. SCC mixes were first developed with 5%, 10%, and 15% replacement of cement by SCBA to determine the optimum percentage. Based on fresh and strength performance, 10% SCBA was identified as the optimum replacement level. Keeping SCBA constant at 10%, slag sand was then introduced at 10%, 20%, 30%, and 40% as a replacement for fine aggregate. The fresh characteristics were evaluated using slump flow, V-funnel, and L-box tests, while mechanical properties were studied through compressive, split tensile, and flexural strength tests. The results revealed that slag sand replacement up to 20% improved both workability and strength of SCC. Higher replacement levels showed a marginal decrease in performance. The optimum combination was obtained at 10% SCBA and 20% slag sand. The study demonstrates that agricultural and industrial by-products can be effectively utilized to produce sustainable high-strength SCC.

Introduction

The increasing demand for concrete has amplified the environmental impact of Ordinary Portland Cement (OPC) production, which is energy-intensive and emits significant CO?. Sustainable alternatives, such as agricultural and industrial by-products, can reduce this impact. Sugarcane Bagasse Ash (SCBA), a waste from sugar industries, is rich in silica and exhibits pozzolanic activity, making it a viable partial cement replacement. When finely processed, SCBA reacts with calcium hydroxide during cement hydration to form additional cementitious compounds, enhancing strength, durability, and reducing permeability. Slag sand, a by-product of the steel industry, can replace natural river sand, improving particle packing, reducing permeability, and enhancing long-term concrete performance.

Self-Compacting Concrete (SCC), which flows under its own weight without vibration, benefits from these materials by improving both fresh and hardened properties while promoting sustainability. The study investigates M50 grade SCC with SCBA as cement replacement and slag sand as fine aggregate replacement for eco-friendly, high-strength concrete.

Literature Review Highlights:

• SCBA improves compressive, flexural, and tensile strength, reduces permeability, and enhances chemical resistance in concrete. Optimal replacement levels vary, often 10–15%, with finer ash yielding better results.

• SCBA stabilizes fresh concrete rheology, enhancing flowability, viscosity, and workability in SCC.

• Slag sand enhances mechanical strength, durability, and density, while supporting sustainable construction by conserving natural sand.

• Combinations of SCBA with other additives (GGBS, fibers, recycled materials) further improve strength, durability, and sustainability.

Materials Used:

• Cement: JSW OPC 53 grade (specific gravity 3.15).

• GGBS: Pozzolanic by-product from steel production (specific gravity 2.85, fineness 3%).

• Fine Aggregate: Natural river sand (Zone II).

• Coarse Aggregate: 10 mm crushed angular aggregate (specific gravity 2.6–2.7).

• SCBA: Processed sugarcane waste, rich in reactive silica.

• Slag Sand: Processed steel slag with angular particles, improving bond and reducing permeability.

• Superplasticizer: CERA Hyper Plast XRW-40 (1.2% dosage) to enhance flowability and stability.

Mix Proportions:

• Control SCC mix (M0): 70% OPC + 30% GGBS.

• SCBA introduced at 5%, 10%, 15% of cement.

• Based on optimal SCBA (10%), slag sand replaced fine aggregate at 10–40%.

Fresh and Hardened Properties:

• Fresh SCC properties evaluated using slump flow, T50 time, L-box, and V-funnel tests.

• All mixes exhibited adequate self-compacting characteristics per EFNARC standards.

• Mineral admixtures and superplasticizer improved workability, stability, and flowability without segregation or bleeding.

Conclusion

1) All mixtures met the fresh property requirements specified by EFNARC guidelines. Although higher replacement levels slightly reduced flowability (slump flow decreased from 715 mm to 655 mm) and passing ability (L-box ratio from 0.97 to 0.82) while increasing viscosity (V-funnel time from 7.5 s to 11.4 s), the mixes retained satisfactory self-compacting behavior throughout the replacement range studied. 2) Replacing cement with SCBA alone showed beneficial effects up to 10%. The mixture containing 10% SCBA (M2) recorded the highest strength among SCBA-only mixes, with 28-day compressive strength reaching 62.8 MPa (5.72% higher than the control), along with noticeable improvements in split tensile and flexural strengths. 3) SCBA replacement beyond 10% proved detrimental. At 15% SCBA (M3), compressive strength fell to 57.4 MPa, confirming 10% as the upper safe limit for SCBA when used as the sole cement replacement. 4) Combining 10% SCBA with copper slag sand produced a clear synergistic improvement. The optimum performance was achieved with 10% SCBA + 20% copper slag sand (M5), which exhibited the highest values across all mechanical properties: 64.5 MPa compressive strength (+8.59%), 4.54 MPa split tensile strength (+3.42%), and 5.66 MPa flexural strength (+5.20%) at 28 days. 5) Increasing slag sand content beyond 20% (while keeping SCBA at 10%) led to a gradual strength reduction. At 40% slag sand (M7), compressive and split tensile strengths dropped below the control values, primarily due to the higher angularity and water demand of the slag particles at elevated dosages. 6) The results demonstrate that controlled incorporation of SCBA and copper slag sand not only maintains the self-compacting characteristics but also enhances the mechanical performance of SCC, simultaneously promoting the valorization of agro-industrial and metallurgical by-products.

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Copyright

Copyright © 2025 N. S. Ganesh, V. K. Visweswar Rao. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.