According to
Anthony Reed, market development manager for Engelhiard Corp.'s
MetaMax high-reactivity metakaolin, "At an HRM replacement
level of 8 percent to 10 percent, concrete is generally more
cohesive and less likely to bleed. As a result, the effort
required for pumping and finishing processes is reduced. Compressive
strength and density of hardened concrete are also increased.
Optimum pozzolanic benefits of metakaolin can be obtained by
replacing 10 percent to 20 percent of the portland cement in
the mixture with HRM. These levels produce concrete with lower
porosity and improved durability and resistance to impact and
abrasion."
Reed also points out that metakaolin reduces concrete slump
and generally requires the addition of a high-range water
reducer (HRWR). "Metakaolin should generally be added
to batch after portland cement and before HRWR is added," he
says. "Air entraining admixtures may require somewhat
increased dosage when used with metakaolin."
When using integrally colored concrete, metaknolin brightens
the shade of colored concrete by creating a lighter cementitious
base color, according to Nick Paris, marketing manager for
Davis Colors.
