Andrew Goss crafts jewelry, such as this bracelet, with metakaolin-enriched concrete. Photo courtesy of Anderw Goss

Concrete Admixtures, Metakaolin, Pozzolans

You may never have heard of metakaolin, but chances are it’s coming your way. This admixture — now being used in everything from fashionable floors to custom countertops — makes concrete stronger, brighter and more workable while decreasing the amount of portland cement needed in the mix.

Metakaolin (pronounced meta-ká-lin) is a type of pozzolan, materials that enhance the strength, density and durability of concrete. While decorative concrete contractors are at the vanguard of many concrete innovations, some have been slow to discover these materials. This is changing, however, since high reactivity metakaolin, a relatively new type of pozzolan, offers features unavailable from other highly reactive pozzolans — improved concrete appearance and workability.

Over half of the portland cement concrete used in the United States now contains pozzolans, according to the National Ready Mix Concrete Association. Fly ash and silica fume, the most common pozzolans, are problematic in decorative concrete: They are typically dark in color and, because they are industrial byproducts, are not uniform in color. Silica fume is a highly reactive pozzolan capable of producing very strong and durable concrete, but results in “sticky” mixtures that are difficult to place and finish and require special curing techniques.