Cement and Clinker: March 2022

PUMICE

Bimsstein

PUMICE STONE

PUMICE SAND

Pumice Pozzolan as a Green Product

The “green” tag is generally given to products and processes that are not energy intensive or do no harm to the environment. That is, of course, a very basic definition...the term “green” is now a widely applied marketing term for just about anything.

Pumice pozzolan is green by the simple fact that the most crucial step in the manufacturing process—the superheating that gives pumice is amazingly versatile properties—has already been taken care of by Mother Nature. Pumice is “naturally calcined,” which simply means that the pumice has already had it’s time in the furnace: a volcanic furnace. Unlike metalolin, silica fume, and fly ash, pumice does not need to be heated or calcined to change its chemical makeup to make it useful as a pozzolan.

Contrast, for example, Portland Cement—the key ingredient for concrete. Portland Cement is manufactured by mining limestone, crushing it, and then (critical!) heating it in a furnace to change its physical properites. The resulting “clinkers” are then ground down to about -325 mesh. The result is ever-so useful cement powder. So, in terms of a carbon footprint—the energy needed to produce the final useful product—Portland Cement, is a major concern of industry and governments alike. Cement production constitutes a major portion of all major green house gases production.

Fortunately, when it comes to concrete, pumice makes an incredibly useful pozzolan (the Roman word for pumice was “pozzolana”), and pozzolans do wonderful things to enhance and improve standard concretes. So, replacing part of the Portland Cement power with pumice powder (pozzolan), significantly moves the green needle on the concrete while imparting incredible high-performance characteristics as well. A bonus on top of a bonus.

The process: pumice is mined from an ancient volcanic deposit, crushed and transported to the refining plant, where it is again crushed and separated into the various particles sizes utilized by industry…from half-inch aggregate all the way down to an ultra-fine grind of 3-microns—the equivalent of smoke. The refining process needs little energy and uses no fresh water.