Highly Reactive Metakaolin Concrete – Properties and Applications

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The reactivity of metakaolin is based on chemical composition and reactive surface. Highly reactive metakaolin has become available as a considerably reactive pozzolanic material in concrete. This type of material is not like other admixtures for example fly ash, blast furnace slag, and silica fumes in terms of production because it is produced from high purity kaolin clay by calcinations at temperatures ranging from 700 to 800 ^o C. The average size of highly reactive metakaolin particle, which is smaller than cement particles, is ranging from 1 to 2 and it is white in color which in return influences the color of the final product. Specific gravity of highly reactive metakaolin is 2.5. In this article, highly reactive metakaolin properties, influence of metakaolin on fresh and hardened concrete properties, durability, and application of concrete containing highly reactive metakaolin will be explained briefly.

Fig.1: Highly Reactive Metakaolin

Fig.2: Micro Texture of Metakaolin

Properties of Fresh Concrete Containing Highly Reactive Metakaolin

It is claimed that, initial and final setting time of concrete incorporating about ten percent highly reactive metakaolin is like controlled concrete. Bleeding of concrete containing metakaolin can be neglected due to its considerably high specific surface which is around 20m²/g. It is reported by Zhang and Malhotra that autogenous temperature rise of concrete incorporating metakaolin is more than that of concrete with zero metakaolin content. Figure-3 shows different heat generation of concrete made with metakaolin and zero metakaolin content concrete. Introducing metakaolin into concrete lead to increase water demand which means the mixture may need superplasticizer to achieve necessary workability.

Fig.3: Generation of Heat in Controlled Concrete and Concrete Incorporating Metakaolin

Mechanical Properties of Hardened Concrete Incorporating Highly Reactive Metakaolin

The properties of concrete hardened concrete containing metakaolin are:

1. Strength development of concrete made with highly reactive metakaolin
2. Drying shrinkage of metakaolin concrete

Strength development of concrete made with highly reactive metakaolin:

As it can be seen from Table-1 which is taken from Zhang and Malhotra investigation, concrete containing metakaolin achieved greater strength compare to controlled concrete at any given time. The table provides flexural strength, tensile strength, and modulus of elasticity of both controlled and metakaolin concrete. The data show that, concrete incorporating metakaolin gives better outcomes for all aforementioned properties compare with those of controlled concrete.

Table-1: Mechanical properties of both concrete incorporating metakaolin and controlled concrete

Drying Shrinkage of Concrete Incorporating Highly Reactive Metakaolin

It is demonstrated that, after seven days of curing, drying shrinkage strain of concrete contained metakaolin is lower than controlled concrete drying shrinkage. After 112 days of curing in 50% relative humidity, the drying shrinkage of controlled concrete was higher than metakaolin concrete by approximately 20%. Figure-4 show the drying shrinkage of both controlled and metakaolin concrete at different ages up to 112 days.

Fig.4: Drying Shrinkage of Controlled Concrete and Metakaolin Concrete

Durability of Hardened Concrete Incorporating Highly Reactive Metakaolin

Air entrained concrete containing about ten percent of metakaolin by mass supremely withstand ingression of chloride ions and has outstanding durability to repeated cycles of freezing and thawing. Metakaolin in concrete tend to reduce the size of pores which consequently lead to obtain more strength, higher density, and more resistance to acid. Furthermore, metakaolin improves concrete resistance to alkali silicate reactions and sulfate attack.

Application of Concrete Containing Metakaolin

• Improving strength of lightweight concrete, decrease permeability, and releasing post tensioning earlier. Such advantages could be seen in Benicia Martinez Bridge located in California / United States, Figure-5.
• Develop flexural strength early, increase both reflectability and durability factor in I5 California Truck Tunnel which repaired after fire immediately, Figure-6.
• Increase strength and tackle alkali silicate reactions, Pinalito Hydro Project, Figure-7.
• Enhance chloride resistance, increase permeability, durability, and strength, Brayton Point Cooling Towers, Figure-8.

Fig.5: Benicia Martinez Bridge

Fig.6: I5 California Truck Tunnel

Fig.7: Pinalito Hydro Project

Fig.8: Brayton Point Cooling Towers