Hess Pumice markets two grades of natural pumice pozzolan: HessPozz and Hess UltraPozz.
Natural Pumice Pozzolan
Pumice pozzolan is the natural, sustainable pozzolan the Romans so successfully used in their millennia-defying concrete mixtures. Backed by confirming research done by top national scientists, quantifying university research, and the enduring evidence of Roman concrete, when it comes to selecting the ideal pozzolan, pumice pozzolan is the clear choice.
The construction industry widely “rediscovered” the benefits of pozzolan-boosted concrete when the coal-fired power generation industry was looking for a market to utilize the fly ash they were scrubbing from the furnace stacks. Sure, select types of fly ash function 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.
With finely ground and graded pumice being such an effective pozzolan in cementitious grout, it was a short step to applications in standard concrete and well cements. Those quantifiable benefits have been documented via extensive studies by the University of Utah, University of Texas-Austin, Washington University, and Clemson University.
Hess Pumice markets two grades of pumice pozzolan—standard HessPozz and Hess UltraPozz. Both are 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, no heavy metals. Pumice is a natural pozzolan, naturally calcined and born in the bowels of Nature’s most fearsome monuments: volcanoes.
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. [ ••• ]
BENEFITS OF PUMICE POZZOLAN
Specifically, research documents and quantifies how 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.
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. [ ••• ]
FLY ASH VS. PUMICE POZZOLAN
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 using 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 a performance-superior replacement pozzolan for fly ash.
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 PUMICE POZZOLAN GRADES
DS325 • 80%+ passing -325 mesh (APS 13–17µ)
NCS-3 (APS 3µ)
The graph below talks big. But it’s backed up with ASTM standards-research providing definitive data that Hess Standard Pozz (a natural, carefully refined pumice pozzolan) mitigates or eliminates the Alkali Silica Reaction (ASR) in curing concrete in the presence of even the most reactive aggregate.
MITIGATING THE ASR REACTION
University of Utah Study: Mortar mix designs tested according to a modified ASTM C1567 procedure using Type 1 cement and 25% replacement of fine aggregate with ground cullet glass. Hess Pozz (DS325) was used at 20% and 30% cement replacement. The percent length change for “acceptable expansion” is less than 0.1% at fourteen days with reactive aggregates.
ASR % LENGTH CHANGE
100Cement + 25%Glass
80Cement + 20%DS325 + 25%Glass
70Cement + 30%DS325 + 25%Glass
University of Texas-Austin Study: Resistance to ASR was measured according to the procedures of ASTM C1293, except for the concrete mixture design used, which is detailed in the MIXTURE DESIGN table below. The average expansion of each mixture was calculated from three or more bars, and the range was checked to see whether it was within the limits stated in ASTM C1293. RESULTS: The pumice SCM concrete mixture performed very well, and kept expansions below the 0.4% limit of ASTM C1293, validating the results found from the ASTM C1567 Accelerated Mortar Bar Test for ASR. The table below lists the average expansion of the concrete prisms at 24 months, along with the range of the data.
AVERAGE ASR EXPANSION % (24 MONTHS)
0.109 ± 0.020
15% Pumice (DS325)
0.022 ± 0.007
15% Fly Ash
0.016 ± 0.017
25% Pumice (DS325)
0.015 ± 0.001
25% Fly Ash
0.016 ± 0.005
ALKALI SILICA REACTION IN BRIEF
There is nothing simple about ASR. Despite the extensive damage it does to the civilization’s infrastructure and the years of studies and testing standards and mitigation recommendations, the mechanisms driving the expansive gels that do the damage continue to defy definitive understanding. [ ••• ]
HOW PUMICE POZZOLAN MITIGATES ASR
The science behind the amazing pozzolanic reaction ignited by pumice pozzolan is this: the aggregate-binding concrete glue—Calcium Silica Hydrate (CSH)—is the result of combining water and Portland cement. But that same hydration reaction also produces Calcium Hydroxide (CH) by-products (up to 25% of the hydrated Portland cement) that not only do nothing to contribute to concrete strength and density, but actively work against it, introducing grief like the integrity-destroying alkali silica reaction as well as a swarm of other future ills that result from CH-induced porosity. [ ••• ]
ISSUES MITIGATING WITH FLY ASH
Although fly ash can have a mitigating effect on the alkali silica reaction, it is critical that the right fly ash is used. Because fly ash is the byproduct of burning coal, the effective qualities of the ash vary widely. [ ••• ]
Pozzolanic Hydraulic Lime (PHL) Binders
Hess Pozz is used to formulate high-performance modern lime plasters and binder products. The Romans used a similar mix design to create their enduring renderings. Earthaus Plasters produces a line of these pozzolan+lime plasters that includes both thin-coat interior artisan plasters and construction-centric products, including a lime binder formulation used for mixing sand-bulked PHL plasters to skin and protect breathable wall systems like those made of strawbale or earth-based materials. PHL binders are also used to make hempcrete.
GET A PUMICE SAMPLE
If you’d like to sample a pumice grade (or several), we have a nice selection of stock pumice grades available to purchase in small quantities via our Pumice Products Store.
If you’d like to run tests and trials using our pumice in your commercial product formulation or industrial process, please contact us at firstname.lastname@example.org 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.
We know pumice. We’ll answer your questions, help determine the ideal grade for your needs, get you sample grades for testing, or help figure out the logistics for getting pumice to you—whatever’s needed.