Metakaolin is an off-white manufactured pozzolanic mineral admixture that considerably increases many functioning features of cement-based products. This product is a refined kaolin clay that is calcined under a precise temperature range between 600-800 Celsius over a 12-hour time period. This firing creates an amorphous alumina silicate, that when used as a supplementary cementitious material to cement and water will react with the available calcium hydroxide in the portlandite to produce additional binding materials calcium silicate hydrate in cement. The added binder will allow for shortened set times as well as higher compressive and flexural strengths in the final finished cement.
Metakaolin is smaller in particle size when compared to cement grains, giving it a higher surface area. This increase in surface area allows for an extremely reactive mixture, thus giving it the desired increases in strength and durability.
“Metakaolin is designed to be a white substitute for silica fume and provides higher early strengths, which allows for earlier form stripping, earlier processing and quicker turnaround” (Chavali & Karunakar, 2016).
Metakaolin should conform to ASTM C618 Specifications for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Concrete, meeting AASHTO M295-11 standards, and is classified as a Class N material. Making concrete with metakaolin is a more proficient process as it diminishes the consumption of portland cement as well as strengthening desired properties of the concrete.
Metakaolin’s Environmentally Positive Impacts on Concrete
The manufacturing process of portland cement often creates a large amount of carbon dioxide emissions, a known green house gas. By replacing some of the portland cement into the overall cement mixture with Metakaolin, there is a reduction in overall total CO2 emissions.
Applications for Metakaolin
Metakaolin is ideally suited for cementing applications due to it being a reactive amorphous pozzolanic material that contains latent hydraulic properties and with an overall finer particle size than cement. These properties provide good particle packing capabilities. Because these properties are particularly desired in the oil and gas industry, they use metakaolin in their cementing mixture to increase the hardening strength of the cement to withstand compressive forces and reduce the overall permeability. Metakaolin is often used in a variety of other different applications.
For instance, Metakaolin is often used in: