Properties and Applications of Highly Reactive Metakaolin Concrete

Highly reactive metakaolin is a pozzolanic material used in concrete due to its chemical composition and reactive surface. Unlike other admixtures such as fly ash, blast furnace slag, and silica fumes, highly reactive metakaolin is produced from high purity kaolin clay through calcination at temperatures ranging from 700 to 800 °C.

The particles of highly reactive metakaolin are smaller than cement particles, with an average size of 1 to 2, and they are white in color, which affects the final product’s color. The specific gravity of highly reactive metakaolin is 2.5. This article will provide a brief overview of the properties of highly reactive metakaolin, its influence on the properties of fresh and hardened concrete, its durability, and its applications in concrete.

Properties of Fresh Concrete Containing Highly Reactive Metakaolin

Concrete incorporating approximately ten percent highly reactive metakaolin is said to exhibit controlled initial and final setting times, similar to controlled concrete. The presence of metakaolin, which possesses a significantly high specific surface area of around 20m2/g, renders the bleeding of the concrete negligible.

According to Zhang and Malhotra’s report, concrete incorporating metakaolin experiences a higher autogenous temperature rise compared to concrete without metakaolin. Figure-3 illustrates the variation in heat generation between concrete samples containing metakaolin and those with no metakaolin content.

The addition of metakaolin to concrete leads to an increase in water demand, thereby necessitating the use of superplasticizers to attain the required workability of the mixture.

Mechanical Properties of Hardened Concrete Incorporating Highly Reactive Metakaolin

Concrete hardened with metakaolin exhibits several notable properties. Firstly, it displays enhanced strength development compared to conventional concrete. This is attributed to the highly reactive nature of metakaolin, which facilitates better pozzolanic reactions and improves the overall strength of the concrete matrix.

Additionally, metakaolin concrete demonstrates favorable characteristics in terms of drying shrinkage. Drying shrinkage refers to the reduction in volume that occurs as concrete loses moisture over time. In the case of metakaolin concrete, the presence of metakaolin helps to mitigate drying shrinkage, resulting in reduced overall shrinkage and improved durability of the hardened concrete.

Overall, the inclusion of metakaolin in concrete offers significant benefits, including improved strength development and reduced drying shrinkage. These properties contribute to the enhanced performance and longevity of concrete structures, making metakaolin a valuable additive in the construction industry.

Strength development of concrete made with highly reactive metakaolin:

Table-1, sourced from the study conducted by Zhang and Malhotra, clearly demonstrates that concrete incorporating metakaolin consistently outperforms controlled concrete in terms of strength at any given time. The table presents data on flexural strength, tensile strength, and modulus of elasticity for both types of concrete. Notably, metakaolin concrete exhibits superior results across all these properties, indicating its enhanced performance compared to the controlled concrete.

Drying Shrinkage of Concrete Incorporating Highly Reactive Metakaolin

After seven days of curing, the drying shrinkage strain of concrete containing metakaolin is found to be lower compared to the controlled concrete drying shrinkage. Furthermore, after a curing period of 112 days in an environment with 50% relative humidity, it was observed that the drying shrinkage of the controlled concrete was approximately 20% higher than that of the metakaolin concrete. Figure-4 illustrates the drying shrinkage of both the controlled and metakaolin concrete at various ages up to 112 days.

Durability of Hardened Concrete Incorporating Highly Reactive Metakaolin

Air entrained concrete with approximately ten percent metakaolin by mass exhibits exceptional resistance to chloride ion penetration and remarkable durability when subjected to repeated freezing and thawing cycles. The inclusion of metakaolin in the concrete mixture contributes to the reduction in pore size, resulting in increased strength, higher density, and enhanced resistance to acid. Additionally, metakaolin improves the concrete’s ability to withstand alkali silicate reactions and sulfate attack, further enhancing its overall durability.

Concrete Containing Metakaolin Applications

The Benicia Martinez Bridge in California, United States (Figure-5), demonstrates improved strength of lightweight concrete, reduced permeability, and the ability to release post-tensioning earlier. These enhancements contribute to the bridge’s overall structural integrity and performance.

Figure-6 showcases the I5 California Truck Tunnel, which underwent immediate repairs after a fire. The repairs focused on developing early flexural strength, while also increasing both reflectability and durability factors. These improvements enhance the tunnel’s safety and longevity.

In the Pinalito Hydro Project (Figure-7), efforts were made to increase the strength of the structures and address alkali silicate reactions. By implementing suitable measures, the project aims to ensure the longevity and reliability of the hydroelectric facilities.

Figure-8 illustrates the Brayton Point Cooling Towers, where the emphasis was placed on enhancing chloride resistance, reducing permeability, and improving durability and strength. These improvements contribute to the overall performance and lifespan of the cooling towers.

FAQs about Reactive Metakaolin Concrete

1. Concrete and Mortar: Metakaolin is used as a supplementary cementitious material in concrete and mortar formulations. It improves strength, durability, and workability of the mixture.
2. Ceramic and Refractory Products: Metakaolin is utilized in the production of ceramics and refractory materials. It enhances the mechanical properties, thermal stability, and resistance to chemical attacks.
3. Paints and Coatings: Metakaolin is added to paints and coatings to improve their performance and durability. It enhances the adhesion, abrasion resistance, and overall quality of the coatings.
4. Geopolymers: Metakaolin is a key ingredient in geopolymer technology, where it acts as a binder in place of traditional cement. Geopolymers offer excellent strength, chemical resistance, and fire resistance.
5. Fillers in Plastics and Rubber: Metakaolin is used as a filler in plastic and rubber products to improve their mechanical properties, dimensional stability, and resistance to wear.

These are just a few examples of the diverse applications of metakaolin. Its unique properties make it a valuable additive in various industries, contributing to the performance and sustainability of different products.

Related Articles:

1. Hardened Concrete Properties with Blast Furnace Slag (GGBFS)
2. Durability of Ground Granulated Blast Furnace Slag GGBFS Concrete
3. Highly Reactive Metakaolin Concrete – Properties and Applications
4. Characteristics of Rice Husk Ash Concrete – Workability, Strength and Admixtures
5. Factors Affecting Rheological Properties of Fresh Concrete
6. How to Reduce Environmental Impact of Concrete?
7. Factors Affecting Durability of Fiber Reinforced Concrete (FRC)
8. Long Term Properties of Geopolymer Concrete with Low Calcium Fly Ash
9. Heat Resistant Concrete or Refractory Concrete -Installation and Applications
10. Effect of Water Impurities on Concrete Strength, Durability and Other Properties