What Is A Metakaolin in Concrete? Advantages & Uses Of Metakaolin
What Is A Metakaolin in Concrete?
Metakaolin, which is the anhydrous, calcined version of the clay mineral kaolinite, is a pozzolanic material that is commonly used in the production of concrete. It is created by heating china clay, or kaolin, to a temperature between 600 and 800ºC.
Because it is manufactured specifically for use, rather than being a by-product, metakaolin is a more consistent and controlled material than other pozzolanic materials.
When used to replace cement at a ratio of 5-10% by weight, metakaolin improves the cohesiveness of concrete and reduces the likelihood of bleeding during the finishing and pumping processes. Additionally, this replacement level also increases the compressive strength of the hardened concrete.
Higher replacement ratios (up to 20%) lead to a cement matrix with reduced porosity and permeability, which in turn improves the resistance of hardened concrete to attack from sulfates, chloride ions, acids, and other aggressive substances.
Furthermore, it also shows better performance in terms of freeze-thaw and abrasion resistance when concrete is finished and cured correctly. The first application of metakaolin was in the construction of large dams in Brazil during 1960s, primarily to suppress damage caused by alkali-silica reactions.
Effect Of Metakaolin On The Properties Of Concrete
The incorporation of Metakaolin into concrete leads to a number of changes in the properties of the concrete. For example:
The workability or slump of the concrete may decrease with increasing amounts of Metakaolin at the same water-cement ratio due to its fineness, but this can be counteracted by using water-reducing admixtures or in combination with fly ash.
Use of Metakaolin in concrete leads to improved early-age strength development, due to its filler and pozzolanic effects.
The microstructure of the concrete becomes denser when Metakaolin is used, resulting in improved impermeability due to pozzolanic and hydraulic reactions.
The resistance to expansion from alkali-silica reactions is increased when Metakaolin is partially substituted.
Incorporating Metakaolin into concrete reduces chloride permeability and improves resistance to attack from sulfurates and other aggressive substances such as mineral and organic acids.
High-Reactivity Metakaolin
High-reactivity metakaolin (HRM) is a highly processed form of aluminosilicate pozzolan that when mixed with slaked lime and moisture, creates a strong, slow-hardening cement. It is created by heating purified kaolinite in a rotary kiln at temperatures between 650–700 °C.
HRM is known to accelerate the hydration process of ordinary Portland cement within 24 hours and can also prevent deterioration of concrete caused by the Alkali Silica Reaction (ASR), making it particularly useful when using recycled crushed glass or glass fines as aggregate.
The amount of slaked lime that can be bound by metakaolin is measured by the modified Chapelle test.
Uses Of Metakaolin
Metakaolin is a pozzolanic material composed primarily of the mineral kaolinite. Metakaolin is a versatile material that can be used in many different ways.
It has high strength, performance, and lightweight properties which make it ideal for use in precast or poured-mold concrete, fibercement and ferrocement products, glass fiber reinforced concrete, countertops, art sculptures (such as those crafted by Albert Vrana), mortar and stucco.
Metakaolin has been widely used due to its superior properties and its ability to provide superior strength when compared to traditional concrete materials.
Its lightweight nature also makes it an ideal choice for applications such as countertops and art sculptures where weight is of primary concern.
Advantages Of Metakaolin
The benefits of using Metakaolin in concrete include improved compressive and flexural strength, reduced water and chloride permeability, reduced efflorescence, increased resistance to chemical damage, increased durability, decreased effects of alkali-silica reactivity, improved workability and finishing, decreased shrinkage, and improved color by making the concrete lighter in color and easier to tint.
Limitations Of Metakaolin
Metakaolin has many benefits, but there are some limitations to consider. Metakaolin has a number of limitations, the most important being that it requires careful quality control to maintain its desired properties.
High-quality controls must be consistent for it to be effective, and selection of material is also key as higher quality may cost more than lower materials.
Without proper adherence to these prerequisites, there can be adverse effects on its intended use such as reduced strength or poor durability.
