A Sustainable Alternative: Geopolymer Concrete Synthesized from Fly Ash, GGBS, and CDW

Abstract

The present study explores the potential of developing an eco-friendly geopolymer concrete (GPC) by utilizing industrial by-products—Ground Granulated Blast Furnace Slag (GGBS) and Fly Ash—as binders and replacing natural coarse aggregates partially with Construction and Demolition Waste (CDW). Manufactured sand (M-sand) was used in place of conventional river sand to enhance sustainability. The experimental investigation includes the preparation of geopolymer concrete with varying proportions of CDW and detailed evaluation of its mechanical properties such as compressive strength, split tensile strength, and flexural strength. Durability aspects like water absorption, acid resistance, and sulphate attack resistance were also studied. The results indicate that a mix with 30% CDW substitution and a 70:30 blend of Fly Ash to GGBS delivered optimum performance in both strength and durability parameters, making it a viable sustainable alternative to traditional concrete.

Introduction

Background & Motivation:
Rapid urbanization and infrastructure demand have led to excessive natural resource consumption and increased CO? emissions, particularly from cement production, which contributes 5–8% of global CO? emissions. This necessitates sustainable alternatives to conventional concrete.

Solution: Geopolymer Concrete (GPC):
Geopolymer concrete is a sustainable material that replaces Portland cement with industrial by-products like Fly Ash (FA) and Ground Granulated Blast Furnace Slag (GGBS). It is activated using alkaline solutions (NaOH + Na?SiO?), which initiates polymerization. GPC offers high strength, durability, and environmental benefits.

Innovations in this Study:

• CDW (Construction and Demolition Waste) was used as a partial replacement for coarse aggregates.

• Manufactured Sand (M-sand) replaced natural river sand as a fine aggregate.

• Aim: To develop eco-efficient GPC and evaluate its mechanical and durability performance.

Objectives

1. Develop GPC using FA and GGBS as binders.

2. Use CDW to replace natural coarse aggregates.

3. Replace river sand with M-sand.

4. Evaluate compressive, tensile, flexural strength, and durability (water absorption, acid & sulfate resistance).

Materials & Methods

• Five concrete mixes (M0–M4) with 0–40% CDW replacement.

• Constant binder ratio: 60% FA and 40% GGBS.

• 100% M-sand used.

• Alkaline activator: 12M NaOH + Na?SiO? in 1:2.5 ratio.

• Curing at ambient temperature, tested at 7 and 28 days.

Results & Discussion

Mechanical Properties:

• Compressive Strength: Increased with CDW up to 30% (M3 = highest at 46.8 MPa at 28 days).

• Split Tensile Strength: Best in M3 (4.2 MPa), improved in all modified mixes.

• Flexural Strength: Highest in M3 (4.9 MPa), all modified mixes outperformed control.

Durability:

• Water Absorption: Reduced in all modified mixes; lowest in M3 (3.5%).

• Acid Resistance: M3 showed least strength (4.5%) and mass loss (4.9%).

• Sulfate Resistance: M3 again had the best results, with only 3.2% strength loss.

Conclusion

The study on the development of eco-friendly geopolymer concrete with GGBS, Fly Ash as binders, and CDW as a partial replacement for coarse aggregates has yielded the following conclusions: 1) The geopolymer concrete mix with 30% replacement of CDW (Mix M3) exhibited the highest compressive strength of 44.0 MPa at 28 days, demonstrating that up to 30% CDW can be effectively utilized without compromising the structural strength of the concrete. 2) Similarly, the split tensile strength showed a consistent increase, reaching its peak at 30% CDW replacement (3.9 MPa), highlighting the improved bonding and cohesion between the geopolymer matrix and aggregates. 3) The flexural strength also exhibited an upward trend, with Mix M3 achieving a value of 4.8 MPa, which is indicative of the enhanced ductility and toughness of the concrete at this level of CDW incorporation. 4) Durability tests showed that the geopolymer concrete with up to 30% CDW replacement demonstrated superior resistance to water absorption, acid, and sulfate an attack, which suggests improved chemical stability and durability due to the alkali-activated binders (GGBS and Fly Ash). The mix also showed the lowest mass and strength losses in acid and sulfate resistance tests at 30% CDW. 5) Beyond 30% CDW replacement (i.e., Mix M4 with 40% CDW), a slight decline in all mechanical and durability parameters was observed. This suggests that higher CDW content adversely affects the interfacial bond and matrix cohesion, leading to a decrease in performance. 6) The use of Manufactured Sand (M-sand) in place of river sand did not negatively impact the performance of the geopolymer concrete and further enhanced its sustainability without compromising the mechanical or durability characteristics. 7) The use of industrial by-products (GGBS and Fly Ash) and construction waste (CDW) as a partial replacement for conventional materials demonstrates the potential for reducing the environmental footprint of concrete production and promoting sustainable construction practices. 8) Based on the results, geopolymer concrete with up to 30% CDW replacement is a promising alternative to conventional concrete for construction applications, offering both technical and environmental benefits.

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Copyright

Copyright © 2025 Kiran Kumar M S, Madhura R. 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.