roman pantheon dome used pumice concrete

Advantage Pumice


HessPozz is not a by-product. It was not scrubbed from the waste stream of some industrial process. Sourced from the purest commercial deposit of white pumice on the planet, HessPozz is consistent in chemical make-up, grade, color, and the pozzolanic reaction it ignites within curing concrete. Bag after bag, yard after placed yard, concrete that is performance-blended with HessPozz is comfortably predictable.


Formulating a denser concrete will make a lot of the problems that plague ordinary Portland cement concrete simply go away. A densified impermeable concrete matrix means little to no moisture infiltrates the concrete, and that means freeze-thaw damage is mitigated or eliminated. And if the water can't get in, those nasty concrete-wrecking chlorides and sulfates that ride the moisture in are also kept out, protecting both the concrete itself and the reinforcing steel within from chemical attack. Another problem that gets squelched—efflorescence. Denser concrete means calcium hydroxide (what little is left that is not consumed by the pozz) can't reach the surface and react with atmospheric carbon dioxide and effloresce. Denser concrete also means more strength (compressive and flexural) and better abrasion and wear resistance.


Stronger concrete is a matter of getting more Calcium Silicate Hydrate (C-S-H)—the chemical glue that makes concrete what it is—into the reaction. Conventional approach is to add more Portland cement, but that just exacerbates the problems inherent in ordinary cement. Pumice pozzolan is not cementitious by nature, but when used as a replacement for a percentage of the Portland cement (up to 40%), it fuels a powerful pozzolanic reaction that works at the molecular level within the concrete paste to create additional C-S-H from Calcium Hydroxide (CH).*

*CH is a deleterious by-product of the hydration reaction between water and cement. Studies show that only about 75% of the cement powder is converted to C-S-H. The remaining 25% is converted to CH. Not only does CH contribute nothing to concrete strength and durability, it instigates a handful of problems that actively work against and drastically affect the integrity of the concrete.


‘Reactive’ aggregates within the concrete can combine with deleterious CH, destroying the bond between the aggregate and the C-S-H, creating an expansive gel that touches off a slow-motion explosion, shattering the concrete from within, destroying its integrity and requiring replacement well short of its engineered lifespan. Research from two universities quantifies the performance of HessPozz in mitigating the alkali-silica-reaction even in the presence of the most reactive aggregates. And it does so for pennies a yard.


For those manufacturing precast concrete products—statuary, fencing, tilt-up panels, GFRC panels, architectural accents, and decorative stone veneer products—color can matter as much as performance. HessPozz is consistently white, scoring an 84 on the GE Brightness scale, allowing for rich, vibrant concrete coloring.


HessPozz is a finely graded pumice. Pumice does not need to be super-heated to acquire its useful properties, Mother Nature took care of the calcination. HessPozz is used as a percentage of cement replacement, (cement itself is a product of an energy-intensive super-heating process), so the carbon footprint score for the placed concrete goes down. The cement-replacement benefit of HessPozz also positively impacts the consumptive demand vs. cement production balance.


Hess refines two grades of pumice pozz: Hess StandardPozz (14-16µ) and Hess UltraPozz (2-4µ). The grade choice is a final strength and accelerated performance choice, with mix designers selecting UltraPozz when performance demands call for enhanced nucleation and growth of hydration products and/or the ultimate in cured strength.