Performance Investigation on Strength Properties of Metakaolin Based Geopolymer Concrete

Abstract

Among the most commonly used construction materials worldwide is concrete. Cement is the main component used in the manufacturing of concrete. However, because cement manufacture uses natural resources, there are environmental issues due to the significant energy consumption and carbon dioxide (CO2) emissions. This has increased the demand for using additional materials to make concrete instead of Portland cement. Therefore, this study aimed to investigate the strength properties of metakaolin based geopolymer concrete (MKGPC). Grade 25 MKGPC was given a mix design. Alkaline solutions containing 12 and 16 molars were used to cast the MKGPC specimens. They were then cured at ambient temperature as well as in a hot oven set at 100°C for 24 hours. The compressive strength and split tensile strength were investigated at 3, 7 and 28 days curing periods. The results from the investigation reveal that 16 molars and at ambient temperature had better results in terms of compressive strength and split tensile strength at all the curing periods. Therefore, this study concludes that the optimal molarity and cure regime for producing MKGPC are determined to be 16 molars and ambient temperature. As a result, the study suggests producing MKGPC using 16 molars and cured at an ambient temperature.

Introduction

1. Background and Motivation

• Ordinary Portland Cement (OPC) is widely used in construction due to its availability, strength, and workability.

• However, OPC production causes significant environmental harm, including:

  • High CO? emissions (0.9 tonnes per tonne of cement).

  • Natural resource depletion (e.g., limestone extraction).

  • Energy-intensive manufacturing process.

• There's a global push toward sustainable alternatives, leading to interest in geopolymers—cementitious materials formed from aluminosilicate sources and strong alkalis.

2. Geopolymer Concrete (GPC)

• Geopolymers, first developed by Davidovits, are eco-friendly binders formed via alkali activation of materials like metakaolin (calcined kaolin).

• They exhibit:

  • High strength, durability, and resistance to heat and chemicals.

  • Applications across civil, automotive, and aerospace industries.

• Geopolymerization is a polycondensation reaction involving alkali silicates and aluminosilicate precursors.

3. Research Gap

• Although many studies have explored geopolymer concrete, limited research exists on:

  • Effects of different molarities of alkaline solutions.

  • Curing conditions (ambient vs. high temperature).

  • Specifically for metakaolin-based geopolymer concrete (MKGPC).

4. Objectives of the Study

• To evaluate compressive and split tensile strength of MKGPC:

  • Using 8 M and 16 M NaOH solutions.

  • Under ambient and 100°C oven curing.

  • At curing ages of 3, 7, and 28 days.

5. Materials and Methods

• Metakaolin: Produced from local kaolin in Nigeria, calcined at 650°C.

• Alkaline Activator:

  • NaOH: 8 M (320g/L) and 16 M (640g/L).

  • Na?SiO? solution: SiO?:Na?O = 2:1 by mass.

• Aggregates: Locally sourced river sand and granite.

• Testing Methods:

  • Compressive Strength: Using standard crushing test (BS EN 12390-3).

  • Split Tensile Strength: Calculated using Garba's formula.

6. Key Results

A. Compressive Strength at Ambient Temperature

• 16 M MKGPC showed ~23.9% higher strength than 8 M at all curing ages.

• Higher NaOH molarity improved bonding and reaction rate, increasing strength.

B. Compressive Strength at 100°C

• Contrary trend: Strength decreased with higher molarity and heat.

  • 12 M and 16 M samples lost ~22.5% and 44.3% strength, respectively, by 28 days.

• Excessive heat led to moisture loss, cracking, and strength reduction.

Conclusion

This study aimed to evaluate the strength properties of metakaolin based geopolymer concrete. The following can be inferred as conclusions from this study: 1) The hardening of geopolymer pastes was impacted by the curing temperature. Cracks appeared on metakaolin based geopolymer concrete (MKGPC) specimens as the curing temperature to 100°C. 2) The best curing regime for the production metakaolin based geopolymer concrete (MKGPC) is ambient temperature. This curing regime gives best results in terms of compressive strength and split tensile strength than 100oC temperature. 3) The alkaline solution concentration has a major impact on MKGPC\'s strength characteristics. The compressive strength rose as the molarity concentration of 12 molars. However, at 16 molars, the specimens lost strength. As a result, the optimal molarity content for MKGPC is 12 molars.

References

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Copyright

Copyright © 2025 Lawal Muhammad Aliyu, Musa Aminu Alhaji, Ephraim Kaase Tersoo, Tukur Almustapha. 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.