Enhancing Mechanical Performance of Geopolymer Concrete with Manufactured Sand: An Experimental Study

Abstract

Concrete remains one of the most widely used and dependable construction materials globally. However, the rising demand for Ordinary Portland Cement (OPC) and natural river sand in the construction sector has led to significant environmental concerns. The production of OPC contributes heavily to CO? emissions—approximately one ton of CO? is released for every ton of OPC produced—due to limestone calcination and fossil fuel combustion. Additionally, the overexploitation of river sand has caused environmental degradation and supply shortages. This study explores a sustainable alternative by investigating the mechanical performance of geopolymer concrete (GPC) incorporating manufactured sand (M-sand) as a substitute for natural river sand. Geopolymer concrete, composed of Class F fly ash, ground granulated blast furnace slag (GGBS), and activated with alkaline solutions such as sodium silicate (Na?SiO?) and sodium hydroxide (NaOH), offers a viable replacement for OPC-based concrete. The mixes were prepared with NaOH molarities of 12M and 16M for G30 grade concrete. A sodium silicate to sodium hydroxide ratio of 2.5 and a SiO? to Na?O ratio of 2 were maintained. Oven curing was conducted at 60°C. Manufactured sand was used as a partial and full replacement for natural sand at 0%, 50%, and 100%. The primary objective of this experimental investigation was to assess and compare the compressive strength, split tensile strength, and flexural strength of geopolymer concrete (G30) with conventional M30 grade concrete. The results revealed: 1) Compressive strength of G30 increased by 2.47% compared to M30 concrete. 2) Split tensile strength of G30 improved by 2.45% over M30. 3) Flexural strength of G30 showed a 2.5% increase relative to M30. These findings underscore the potential of geopolymer concrete with manufactured sand as a sustainable and high-performance construction material, reducing environmental impact while maintaining structural integrity.

Introduction

Concrete is essential for modern infrastructure and is the second most consumed material globally after water, with about three tons used per person annually. The construction boom, especially in countries like India, China, and the US, drives high demand for Ordinary Portland Cement (OPC) and natural river sand. OPC production, exceeding 4.1 billion tons annually, is environmentally problematic due to heavy CO? emissions (about 1 ton CO? per ton of OPC) and the depletion of limestone reserves, which may be exhausted in 40 years. River sand is also becoming scarce due to unsustainable mining.

To address these environmental challenges, alternatives like manufactured sand (M-sand) and industrial by-products such as fly ash (FA), ground granulated blast furnace slag (GGBS), red mud, and rice husk ash (RHA) are being used in concrete production. These materials promote sustainability by reducing waste and CO? emissions.

Geopolymer concrete, first conceptualized in 1972 by Joseph Davidovits, is a promising eco-friendly alternative that uses aluminosilicate-rich industrial by-products activated by alkaline solutions instead of OPC. It offers benefits like higher strength, better durability, acid and heat resistance, lower shrinkage, and a significantly smaller carbon footprint. Geopolymer concrete combined with M-sand can effectively reduce the environmental impact of construction.

The research aims to explore geopolymer concrete as a sustainable substitute for OPC concrete, evaluate its mechanical properties using fly ash and GGBS, study the effects of replacing river sand with M-sand, and assess durability improvements.

The study covers detailed material properties, mix design methods, and emphasizes the environmental and performance advantages of geopolymer concrete, highlighting its growing adoption in India and worldwide.

Conclusion

Based on the experimental investigations carried out, the following conclusions have been drawn: 1) Geopolymer concrete (G30) exhibited a maximum compressive strength of 42.37 N/mm² at 28 days when cured with 12M NaOH solution, surpassing the performance of conventional M30 concrete. 2) The compressive strength of conventional M30 concrete was recorded at 41.37 N/mm² after 28 days of curing. 3) The improved strength in geopolymer concrete is primarily attributed to the rapid polymerization reaction facilitated by oven curing and the aging of alkaline activators. 4) An oven curing temperature of 60°C for 24 hours was found to be optimal for achieving enhanced mechanical properties. 5) The compressive strength of G30 showed a 2.47% improvement compared to M30 conventional concrete. 6) The split tensile strength of geopolymer concrete increased by 2.45% compared to its conventional counterpart. 7) A 2.5% enhancement in flexural strength was also observed in G30 compared to M30 concrete. 8) Geopolymer concrete achieved higher early-age strength under oven curing conditions compared to conventional water-cured concrete. 9) The compressive strength of geopolymer concrete increased with NaOH molarity up to 16M, indicating the importance of activator concentration in strength development. 10) Economically, G30 geopolymer concrete was found to be 7.52% more cost-effective than traditional M30 concrete, making it a viable alternative for sustainable construction.

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Copyright

Copyright © 2025 Akash Bharatkumar Patel. 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.