PUMICE APPLICATIONS

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.

Pozzolan Rediscovered

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. [ ••• ]

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, which mitigates a list of other common problems—chemical attacks and freeze-thaw damage, to name two.

While infiltration resistance and enduring strength are perhaps the biggest benefits to adding pumice pozzolan to concrete formulations, they are 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.

BENEFITS OF PUMICE POZZOLAN

Specifically, research documents and quantifies how using Hess StandardPozz or UltraPozz in concrete formulations—

bullet Enhances long-term compressive strength.

bullet Fortifies against chloride attack.

bullet Provides high resistance to sulfate attack (Class 3 Severe Sulfate Environment Exposure qualification).

bullet Mitigates or eliminates destructive ASR.

bullet Reduces heat of hydration.

bullet Increases abrasion resistance.

bullet Greatly reduces permeability.

bullet Heals autogenously.

bullet 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. [ ••• ]

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
BRAND NAME	HP GRADE

Hess Pozz	DS325 • 80%+ passing -325 mesh (APS 13–17µ)
Hess UltraPozz	NCS-3 (APS 3µ)

Flatlining ASR

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.
MIXTURE	ASR % LENGTH CHANGE	RATING
100Cement + 25%Glass	0.699	Deleterious Expansion
80Cement + 20%DS325 + 25%Glass	0.029	Acceptable Expansion
70Cement + 30%DS325 + 25%Glass	0.011	Acceptable Expansion


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.
MIXTURE	AVERAGE ASR EXPANSION % (24 MONTHS)
Control	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. [ ••• ]

Basically, ASR damage results from the meet-up of three essential components: reactive silica (present in the aggregate), alkalies (mostly from the Portland cement), and moisture. When these three components are present in sufficient quantities, they form moisture-holding gels that relentlessly expand within and around the aggregates, shattering the concrete from within. Long before the symptomatic cracking is visually evident in the concrete structure, the integrity of the concrete microstructure has already been wrecked.

ASR can be prevented by eliminated one of the three, and the go-to move is to avoid using reactive aggregate. But that's not as simple as it would seem. While aggregates can be classified generally as reactive and non-reactive, not all siliceous aggregates are prone to ASR and not all so-called and classified non-reactives are completely immune to ASR. Too many factors are in play—aggregate mineralogy, degree of crystallinity, solubility.

Instead of running that gauntlet of maybe-maybe-not, a project engineer can turn to a supplementary cementing material (SCM), like Hess' pumice pozzolan. Fly ash is cheaper, sure, but its effectiveness is a crap-shoot (see Pumice Pozz Instead of Fly Ash, below). Laboratory tests done using highly-reactive cullet glass proves that choosing HessPozz as the mitigating SCM shuts down the alkali silica reaction, even when dosed at as little as a 20% Portland cement replacement.

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. [ ••• ]

Replacing some of the Portland cement with natural pumice pozzolan sets off a reaction within the hydrated concrete paste that consumes trouble-making CH and converts it into additional CSH. The pozz also reduces the alkali content of the concrete mix as well as the pH of the concrete pore solution.

Think of it as molecular reclamation: concrete is densified and strengthened while trouble-making CH is consumed and repurposed. ASR is flat-lined.

Also, a major reduction in concrete permeability (porosity) means sulfate and chloride attacks are mitigated. Reinforcing steel is protected without the need to thicken the cover concrete. The water-infiltration freeze-thaw cycle is impeded. Efflorescence is practically eliminated. Compressive strength gets a significant boost.

Benefit after benefit. Structure after structure. Mile after mile.

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. [ ••• ]

Quoting for a U. S. Federal Highway Administration report (FHWA-RD-03-047): “Perhaps the most important parameter affecting the ability of fly ash to control ASR expansion is the CaO content of the ash. Specifically, fly ash lower in CaO produces a calcium silicate hydrate (C-S-H) structure with a lower calcium to silicon ratio, which imparts a negative surface charge, leading to the absorption of cations, especially alkalies. In addition, low-calcium ashes are more effective in controlling ASR because the alkalies contained in the ash generally are not available to the pore solution, whereas high-calcium ashes tend to make their alkalies more readily available. Although higher-lime ashes can still be used to combat ASR, significantly higher dosages may be needed, especially when using highly reactive aggregates.”

Hess Pozz/ASR Miti•Gator™ has no such performance variance. It works consistently and predictably. No need to test to find out what you're going to get and how much you’re going to have to dose.

Concerns with ongoing availability and performance quality of Class F fly ash spurred the Texas Department of Transportation to commission a two-year study (2012-2014) by the University of Texas-Austin to evaluate commercially available pozzolans to take the place of fly ash in improving concrete performance. Hess Standard Pozz was used in the study and performed exceptionally well in every test category—making it the ideal pozzolan.

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 salesteam@hesspumice.com 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.

R&D: (208) 766-4777 x111
rd@hesspumice.com

Sales: (208) 766-4777
salesteam@hesspumice.com

DOWNLOADS

HESS CORPORATE BROCHURE
INFORMATIONAL PUBLICATIONS
WHITEPAPER: PUMICE AND LEED CERTIFICATION
WHITEPAPER: ULTRAFINE PUMICE POZZOLAN FOR GLASS FIBER REINFORCED CONCRETE (GFRC)
WHITEPAPER: PUMICE POZZOLAN FLATLINES ASR PROBLEMS
BRIEF: HESS POZZ VS. FLY ASH
BRIEF: MYTH—MORE STRENGTH REQUIRES MORE CEMENT
ARTICLE: CONCRETE PRODUCTS MAGAZINE
DIRECTORY: ALL INFO PUBLICATIONS
RESEARCH SUMMARIES
RESEARCH: KEY EXCERPTS, ATOMIC ENERGY CANADA—HESS ULTRAPOZZ
RESEARCH: UNIVERSITY OF TEXAS-AUSTIN—HESS POZZ
RESEARCH: UNIVERSITY OF UTAH—HESS POZZ
RESEARCH: UNIVERSITY OF UTAH—ASR RESISTANT CONCRETE
RESEARCH: COMBO SUMMARY—U of TEXAS-AUSTIN and U of UTAH REPORTS
RESEARCH: NATURAL POZZ AND GFRC DURABILITY—WASHINGTON UNIVERSITY ST. LOUIS
DECLARATIONS & CERTIFICATIONS
DECLARATION: NON-CRYSTALLINE SILICA
DIRECTORY: ALL DECLARATIONS AND CERTIFICATIONS
DATA SHEETS
SDS: PUMICE POZZOLAN
TDS: HESS POZZ
TDS: HESS ULTRAPOZZ