Natural Pumice Pozzolan for High-Performance Concrete

The construction industry widely “rediscovered” the benefits of pozzolanic concrete when the coal-fired power generation industry was looking for a market to utilize the fly ash they were scrubbing from their stacks. Sure, fly ash functions as a replacement pozzolan, but natural pumice pozzolan has added benefits. That fact was proven by extensive studies done by top scientists using modern processes at the United States’ Sandia National Laboratories and Canada’s Atomic Energy Commission. They were tasked with developing a long-lived cementitious grout to seal the microfractures in the waste isolation storage chambers deep underground at the U.S. Department of Energy’s Waste Isolation Pilot Plant project in New Mexico. They formulated an effective and enduring cementitious grout mix design that included Hess UltraPozz as the vital pozzolanic component.

Pumice pozzolan is the natural, sustainable pozzolan the Romans so successfully used in their millennia-defying concrete mixtures. So, based on modern research done by top national scientists and on the evidence provided by millennia-defying Roman concrete, when it comes to selecting the ideal pozzolan, HessPozz is the clear choice.

HessPozz and Hess UltraPozz is made by precisely refining a clean, pure pumice—an amorphous white silica created by volcanic events millennia ago. Pumice is not a by-product of pollution control processes; it contains no hazardous materials. Pumice is a natural pozzolan, naturally calcined and born in the bowels of Nature’s most fearsome monuments: volcanoes.

failed concrete overpass structure

The Problem with Standard Concrete

Fact is, standard concrete just isn’t good enough. Almost as soon as standard concrete is placed, the process of degradation begins. Recent studies suggest that only about 75% of the cement powder is converted to Calcium Silicate Hydrate (CSH), the binder that glues concrete together. Most of the remaining 25% is converted to Calcium Hydroxide (CH), a by-product of the hydration reaction between water and cement—a by-product that has a tendency to create a host of problems that have a deleterious effect on the concrete’s long-term performance, and even its appearance. Adding a high-purity natural pumice pozzolan—HessPozz or Hess UltraPozz—to the concrete formulation mitigates or completely eliminates the CH problem. In fact, the pumice pozzolan turns the CH into additional CSH, densifying the concrete and making it nearly impermeable.

While chemical resistance is perhaps the biggest benefit to adding pumice pozzolan to concrete formulations, it is by no means the only gained advantage.

For example, in regions with reactive aggregate, alkali-silica reaction (ASR) is an ever-present problem. Quantifiable research has shown pumice-blended cement (using pumice from the Hess deposit) to be a highly effective mitigator of ASR.

The benefits (below) of pumice as an across-the-board effective pozzolan have been documented via extensive (and on-going) studies by the University of Utah, University of Texas-Austin, Washington University, Clemson University and others as well as the intitial research done by Sandia National Labratories and Atomic Energy of Canada Limited. [DOWNLOAD THE RESEARCH]

Benefits of HessPozz

Specifically, research document and quantifies that using Hess StandardPozz or UltraPozz in concrete formulations—
• Enhances Long-term Compressive Strength
• Fortifies Against Chloride Attack
• Provides High Resistance to Sulfate Attack (Class 3 Severe Sulfate Environment Exposure Qualification)
• Mitigates or Eliminates Destructive ASR
• Reduces Heat of Hydration
• Increases Abrasion Resistance
• Greatly Reduces Permeability
• Improves Durability

Safe, Attractive and Green

Recent studies corroborated previous test data indicating that Hess natural pumice pozzolans are free of Crystalline Silica and other hazardous materials. Our pumice is so safe it is also used as a mild abrasive to clean teeth and as an exfoliation agent in skin creams. While by-product pozzolans struggle with regulated contaminants, Hess’ natural pozzolan is an environmentally safe, health-friendly choice.

Naturally calcined, pumice pozz is effective, abundant and green! In some applications, Hess UltraPozz can replace up to 50% of the Portland cement typically needed, thus reducing, on a pound for pound basis, the colossal carbon footprint standard cement leaves behind.

If concrete color matters, as it often does in exposed finish or decorative precast concrete applications, the consistent brightness of Hess pozzolans can’t be beat. [SEE MORE ON DECORATIVE CONCRETE APPLICATIONS]

Fly Ash vs. Pumice Pozz

At the behest of the Texas Department of Transportation, the University of Texas at Austin ran a research study over a two-year period (2012-2014) to identify the ideal natural pozzolans to replace Class F fly ash in concrete applications. They also ran the same tests with fly ash to establish a baseline for comparing the performance results of the tested pozzolans with fly ash. The results clearly show that pumice pozzolan (from the Hess deposit in Southeast Idaho) to be the ideal replacement pozzolan for fly ash. [SEE AND DOWLOAD THE DATA AT FLYASHREPLACEMENT.COM]

Hess Pozzolan Grades

We offer two pozz grades: Hess Standard Pozz (DS325) and Hess UltraPozz (NCS-3).

Why choose one over the other? If you have a high-end (typically precast) application, the UltraPozz will provide the best result in every concrete-performance category. Standard pozz is the best fit for large-scale applications—infrastructure, roads, buildings.

Hess Standard Pozz DS-325 Hess UltraPozz NCS-3
Dx Micron Size Dx Micron Size
D50 14-16 D50 2-4
pumice pozzolan improves concrete performance and longivity ASR Miti•Gator flatlines the alkali-silica reaction in concrete


Our extensive logistical expertise allows us to ship pumice pozzolan anywhere on the planet—packaged in 44lb/20kg bags, 1-ton super sacks, or in bulk pneumatic rail cars and pneumatic trucks.


•If you’d like to run tests and trials using our pumice in your commercial product formulation or industrial process, please contact us at with your request. We look forward to answering your questions, helping you select the best grade for your process, or helping you explore the fit of pumice for your needs. PLEASE include your name, your company or organization, pertinent project details, ship-to address, and preferred contact information in the sample request email.

pumice store logo

•If you’d like a bit of pumice for personal use, we have a nice selection of pumice grades available to purchase via our Pumice Products Store.


We know pumice pozzolans. We’ll be glad to answer your questions, provide you with testing data, or provide a sample for your own testing—whatever you need.

•SALES: If you need to talk availability, pozz grades, logistics, Jason Kimberling, Sales Manager, at extension 142 or email

•RESEARCH: Perhaps you are exploring the possibilities—thinking pumice pozz may fit your particular need, thinking you’d like to see the existing research data, thinking you’d like to do some testing of your own—then we invite you to contact Brian Jeppsen, VP Research and Development, at (208) 766-4777 x111 or email:


Fact is, standard concrete just isn’t good enough. Replacing some of the Portland cement with pumice pozzolan amps concrete performance.

DiTrevi FountainDi Trevi Fountain, Rome


Waste Isolation Pilot Plant Extensive research done by Sandia National Labratories for the U.S. Dept. of Energy concluded that the centuries-long solution to sealing fractures in the salt-rock tunnels used to isolate energy-generation waste was a ultrafine cementitious grout that included Hess UltraPozz.

Roman Coliseum pumice concrete The Romans discovered the secret to enduring concrete: pumice pozzolan.

Concrete Products Magazine CONCRETE PRODUCTS magazine ran an article on our expanding pumice pozzolan processing capabilities and national distribution.

Hess Pozz Website
Extensive pozz information over on the website. 208.766-4777  •  Malad City, Idaho 83252