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Peformance-Boosting Pumice Pozzolan

emplacing nuclear waste at the WIPP site in NM

ABOVE: Failing overpass support made from standard concrete (without pozzolan density and strength improvments) suffering from sulfate, chloride, and freeze-thaw attacks. BELOW: Pumice pozzolan powder (HP Grade DS325).

pumice pozzolan powder Hess Pozz ships in palleted bags or pneumatic railcars or truck trailers

Hess ships bulk pozz to batch plants in pneumatic rail- or truck-borne containers.

IT’S EASY TO GET JADED by the constant stream of tech and product-tweak advances promising all kinds of amazing results. Sometimes, embracing the latest and greatest is more trouble than it appears to be worth.

01—For additional information, see Pumice and Roman Concrete.

Fly Ash as a Pozzolan

The construction industry widely “rediscovered” the benefits of pozzolan-enhanced concrete when the coal-fired power generation industry was looking for a way to utilize the fly ash waste they were scrubbing from the stacks. They found that fly ash had the pozzolanic characteristics and chemical makeup to improve Portland cement-based concrete, and one class, in particular (Class F), was an adequate mimic for natural pumice pozzolan.

coal fired power plant exhaust stacks and cooling towers

The Original Pozzolan

Sometimes, the original is still the best. Quantifying research on the pozzolanic character of pumice—Hess Pumice, in particular—and its effect on concrete was conducted by the University of Utah and the University of Texas-Austin (and others), provides the hard data concrete engineers need to formulate and specify mix designs that result in concrete that is up to challenge of its environment. In every key performance category, pumice-blended cement delivers[02]. Of particular interest in the two-year study done by the University of Texas-Austin—a study commissioned by the Texas DOT to evaluate alternative SCMs to fly ash—is the inclusion of Class F fly ash in the same concrete strength and durability tests, laying down a comparative baseline. The research quantified pumice as an ideal SCM replacement for fly ash across the board[03].

02—Download a summary of the pumice pozzolan research from the University of Texas-Austin and the University of Utah.

03—Download a summary of the University of Texas-Austin research quantifying fly ash vs. pumice performance data.

Why Pozzolan?

When Calcium Hydroxide (CH) is created, that leaves less cement powder for converting into Calcium Silicate Hydrate (C-S-H)—the all-important binding agent in concrete. The result is a cured concrete with less density and strength than it should—and could—have. To make matters worse, not only does by-product CH contribute nothing to concrete performance and durability, it instigates a handful of problems that actively work against and drastically affect the integrity of the concrete.

04—For additional information, see ASR Mitigation with Pumice-Blended Cement on this site.

Additional Benefits From Pozzolan

By incorporating a carefully refined pumice pozzolan into a concrete mix design, additional benefits are realized:

—The concrete reacts and cures predictably pour after pour…something that can not be said for industrial by-product pozzolans.

—Pure pumice pozzolan is the environmentally safe, health-friendly pozzolan choice—free of crystalline silica, arsenic, beryllium, cobalt, lead, mercury, selenium and other hazardous contaminants.

—Because pumice is naturally calcined by nature, pumice pozzolan has a negligible carbon footprint. When used as a supplementary cementitious material to replace up to 20 percent of the Portland cement, by weight, in a concrete mix, the immense carbon footprint of concrete is significantly decreased on a pound-for-pound basis.

As for the pumice from the Hess deposit, in particular, there are two additional benefits: our pozz has a whiteness that scores a GE brightness of 84, resulting in a beautiful, consistently light-colored concrete that is ideal for use in precast and GFRC applications where color matching is critical. Additionally, our pumice pozz has a specific gravity of 2.35. Most other pozz products are 2.6 or higher, meaning economically, you can use less Hess Pozz, by weight, to achieve the same or even greater benefit.

Hess Pozz; Hess UltraPozz

Hess Pumice Products produces two grades of pumice pozzolan: Hess Standard Pozz (HP Grade DS325) and Hess UltraPozz (HP Grade NCS-3).


—Download a summary of the Pumice Pozzolan Research (including the effectiveness of pumice pozzolan to flatline ASR) from the University of Texas-Austin and the University of Utah.

—Download a summary of the University of Texas-Austin Research quantifying fly ash vs. pumice performance data.

—Visit the Hess Pozz website.