Metakaolin is an affordable alternative
to using white portland cement to lighten the color of concrete,
Ralston says. 'The colors you can produce with metakaolin
are in a range you don't ordinarily see; we use it if customers
want concrete that is just a little more pastel." He
suggests that the higher early strength due to metakaolin
could reduce the waiting period before concrete is hard enough
to polish, and that the denser concrete may make countertops
more stain resistant.
Metakaolin is also finding its way into the fine arts. For
example, Andrew Goss, the author of Concrete Handbook for
Artists, uses metakaolin in concrete sculpture and jewelry.
He says, "Metakaolin can double the compressive strength
of the concrete, lowers permeability and increases density
but also has advantages over silica fume. Metakaolin makes
the mix creamier, less sticky, and is plain white in color."
Guidelines for use
Concrete with metakaolin can be placed,
finished and cured in pretty much the same manner as concrete
without HRM. It
complies with ASTM C 618—Specification for Coal
Fly Ash and Raw or Calcined Natural Pozzolan for Use as a
Mineral
Admixture in Concrete, Class N and is accepted under ACI
318—Building Code Requirements for Structural Concrete
and Commentary.
