Concrete is pretty impressive when it comes to thermal mass, unless what you really need is thermal resistance. The solution? Concretes using foamed-stone aggregates.
Concrete is pretty impressive when it comes to thermal mass, unless what you really need is thermal resistance. The solution? Concretes using foamed-stone aggregates. The appeal of lightweight insulative concrete is that in many applications, the need for thermal resistance can, perhaps, be met with a material that is much, much more than a one-trick functional add-on.
The Soft Underbelly of Common Insulation
Typical insulations—the fibery stuff and the foamy stuff—are structurally feeble and susceptible to damage and degradation. They have little resistance to compaction forces. They offer nothing to impede fire and in some cases, exacerbate it. Sunlight eats up foam. Fibers wick-up moisture. Tunneling insects and critters meet no resistance. Time itself weighs on blown-in loose fills, degrading effectiveness as they sag, settle, bridge and shift, relentlessly compressing under their own weight. None of that is an issue with insulative concrete.
Another mark against the soft stuff is the thermal bridging that happens across the structural members (like studs and joists) that provide the hollow spaces to hold the foam and fiber materials—each one a built-in gash in the insulative envelope. Not an issue with insulative concrete.
Finally, a significant ingredient in the effectiveness of a soft-blanket insulation recipe is the quality of the labor-intensive installation. Too-short and too-long batts, overstuffed crannies, torn vapor barriers, missed or ignored bays and hollows, thin spots, and a host of other who-cares installation shortcomings degrade rated r-value. Sure, poor craftsmanship can happen anywhere within the construction process. Insulated concretes need to be mixed and cured correctly, but overall, the possibilities for junk craftsmanship are significantly reduced.
Insulated Concrete Types
Insulative concrete comes in two types: Cellular concrete is made by a process that creates air voids in the cement paste, using preformed or formed-in-place foam. Aggregate concrete is made with lightweight, foamed-stone aggregates such as pumice, expanded perlite, expanded clays, shales, and slates.
In insulative aggregate concrete, the functional r-value and cured strength is directly related to the character of the foamed stone aggregates used. The information that follows is centered on two in particular: pumice and expanded perlite. Sponge-like and hard-skinned, these frothy bits of glassy volcanic stone are readily locked up by the cement binder. From the sand-sized particles to the chunky stones, the monolithic thermal resistance they provide becomes integral to the concrete itself.
Concrete strength is a combination of the binder’s lock-up force and the inherent strength of the aggregate within the matrix. The foamed-stone nature of a light, insulating aggregate means a corresponding decrease in fracture-resistant strength. In some applications, it matters little. In others, the loss of strength can be compensated for by savvy engineering moves. The type of insulative aggregate used will be a signficant factor in such calculations. Of course, there are structurally-critical applications were lightweight insulating concrete is not used.
Concrete thermal resistance values are determined by a combination of factors. These include overall concrete thickness, type of insulative-class aggregate used, size mix and quantity of that aggregate, cement to aggregate ratio, a quality cure, and in some cases, a moisture-proofing finish.
|LIGHTWEIGHT INSULATING AGGREGATES
|HESS GRADE 130E
|HESS GRADE 190E
|HESS GRADE 270E
|HESS GRADE 1 x 3/4 MN
|HESS GRADE 3/4 x 5/16 MN
|HESS GRADE 3/8 x #8 MN
|HESS GRADE 1/8 FINES MN
|Representative pumice grades. Other aggregate grades available.
|NOTE: Order a Grade Sample by clicking on the grade name. Download the Technical Data Sheet for the grade by clicking in the corresponding TDS link.
Insulative Concrete: R-Value Plus
Unlike structurally anemic fibers and foams, insulative concrete, by its very nature, combines r-value with other valuable characteristics. In some applications, the insulative value sings backup to a more prized characteristic.
ENDURING STRENGTH & MONOLITHIC MASS: If concrete is known for anything, it’s mass strength. Our civilization is built with the stuff—dams and interstates and skyscrapers and other massive constructs readily come to mind. Without concrete, we’re still cutting, hauling, and stacking stone; we’re mixing clay with straw and stomping it into brick forms. Even when bulked with lightweight aggregates, the concrete retains much of its characteristic strength. Pumice concretes can be formulated to reach 28-day strengths of 3000 psi or more. Perlite concretes up to 500 psi. As illustrated in the table below, insulating value and compressive strength are closely related: a higher aggregate-to-cement ratio improves r-value, but reduces strength. Combining denser aggregates (like pumice sand or silica sand) with perlite aggregate is another way to improve compressive strength.
Concrete chemistry is beautiful fusion, and mixes can be developed to meet the demands of a particular application at a just-right performance balance. If a combination of seamless mass, enduring strength, and thermal resistance is the ideal, then foamed-stone aggregates provide the means.
|STRENGTH AND R-VALUE RELATIONSHIPS
|CEMENT / AGGREGATE
|4 ft3 BAGS
THICKNESS: 4 in
|1 / 8
|1 / 6
|1 / 4
|CEMENT / AGGREGATE
THICKNESS: 4 in
|1 / 4
|1 / 3
|See in-depth publications (in linked resources) for complete mix design tables. Mix designs are for reference only.
LIGHTWEIGHTNESS: Another aspect of concrete that readily comes to mind: that gray mass of cast stone and sand is wicked heavy. The heaviness is directly attributable to the weight of the sand and aggregate that bulks it. Foamed stone aggregates, trading air-filled vesiciles (pumice) and microscale bubble-clusters (expanded perlite) for weighty density, lighten the load.
Lightweight concrete reduces the dead load on formwork and on structural supports, trusses, girders and footings, thus reducing structural costs. Lightweight concrete can be handled in larger volumes with standard equipment and is proportioned, mixed and placed using the same equipment and tools as standard sand-and-gravel concrete. As for precast concrete applications, foamed-stone aggregates form the foundation of the entire cast stone veneer industry. Precast statuary, planters, pavers, decorative architectural elements—all benefit from reduced shipping and handling weight costs.
SOUND INSULATION: Perlite concrete, when used in walls and floors, blocks both airborne and impact noise by virtue of its cast-mass cellular structure—presenting a series of successive air compartments that obstruct the propagation of sound waves. Increasingly, building codes require such sound mitigation in intertenancy walls and floors for high-density housing.
FIRE RESISTANCE: Using a combination of foamed-stone aggregates and mix design, fire ratings of 1 to 3 hours can be attained. Fire ratings are a critical consideration for use in intertenancy walls and floors, industrial facilities, and more. Resistance to spalling under direct flame is also a characteristic of insulative concretes.
Typical Uses for Insulative Concrete
Insulating concrete certainly is not a direct replacement for fiber and foam systems, but in specific applications to meet specific needs, it can provide the ideal combination of value and performance.
INTERTENANCY WALLS & FLOORS: Office buildings, combined office and industrial spaces, schools, and multifamily housing buildings all house differing-need occupants under one roof. Issues like sound transmission, fire-spread denial, unit-to-unit thermal transfer, and security all need addressed. Lightweight aggregate concrete addresses each and every one.
ROOF DECKS: The insulating performance (R and U values), reduced structural load, and fire-denial properties of a lightweight aggregate concrete combine in a strong, monolithic roof deck. Bundle that with the ability to slope to drains, use on shallow curved or pitched surfaces, combine with and protect other insulating materials (like EPS foam), apply in a single-phase operation, and finish with standard roof membranes.
See: PERLITE LIGHTWEIGHT INSULATING CONCRETE ROOFING (a Perlite Institute publication)
FLOOR SYSTEMS: Insulating concrete floors ward against the spread of fire, block sound, provide an extremely durable, stable surface, and insulate between stacked spaces.
See: PERLITE IN SOUND INSULATION APPLICATIONS (a Perlite Institute publication).
WELL CEMENTS: Filling the annular space between well bore and well casing with insulating concrete prevents contamination, supports the casing string and well bore, and protects against casing corrosion. These critical functions must be met even in extreme temperature and pressure environments, in the which foamed aggregate concretes are quite effective. Lightweight, insulating aggregates also reduce well cement density, which puts less pressure on surrounding geologic layers and eases the demands on equipment and labor. Perlite in particular is a natural choice when insulating performance and a low density slurry are needed. Perlite aggregate concrete also holds onto its excellent fluid loss characteristics for longer.
See: PERLITE FOR USE IN WELL CEMENTS (a Perlite Institute publication).
LARGE CONCRETE BLOCKS: Lightweight insulating concrete blocks can be solid cast and site-assembled as dual-purpose foundation and insulating base. One such use is to form a bottom ring beam at the double-wall of cryogenic storage tanks, providing excellent thermal insulation at negative temperatures and structural support against static and dynamic loads.
See: PERLITE CONCRETE BLOCKS (a Perlite Institute publication).
IN-GROUND VINYL POOL BASES: Once the pool walls are erected, the insulative concrete base can be screeded to the desired contours. This supporting foundation of smooth concrete not only fights heat loss but extends the functional life of the vinyl liner.
See: PERLITE INSULATING CONCRETE POOL BASE (a Perlite Institute publication).
UNDERGROUND PIPELINES: Piping and ducting can be insulated against temperature fluctuations in the soil in shallow-bury ditches (less than six feet) with insulative concrete. The poured-around or form-cast lightweight insulating concrete jacket also mitigates against loss when piping heated or chilled contents, provides impact, compression and settling protection, and strengthens joinings against seperation. All that in a seamless, shapeable, fire, rot, and vermin-proof material.
See: INSULATING UNDERGROUND PIPE AND DUCTING WITH PERLITE CONCRETE (a Perlite Institute publication).
ANIMAL HOUSING; STALLS & COOPS: Confined animal housing structures like barns, runs, stalls, and coops using insulative concrete floors combine improved facility temperature management with durability and cleanability. Concrete allows the floor to meet function-specific needs—slope to drains, inset channels and grating, surface textures, hard anchor points, platforming, and more.
DECORATIVE STONE & BRICK VENEERS: Beyond classic good looks, decorative veneers (especially when laid up with foamed-stone sand aggregate mortar) provide additional inches of r-value, sound mitigation, fire resistance, and rugged, maintenance-free durability—all that in a lightweight cladding.
PRECAST ARCHITECTURAL ELEMENTS: Decorative elements and accents, panels and GFRC veneers, statuary and planting containers: all can be cast from lightweight insulative concrete.
Primarily used to seriously improve the strength, density and longevity of standard concrete (as well as mitigate several other concrete ills), super-fine pumice pozzolan is also used in lightweight insulating concrete to improve compressive strength and flatline the alkaline silica reaction. Pumice pozzolan works by dramatically improving the chemical reaction process within the hydrated concrete paste that forms Calcium Silicate Hydrate (CSH)—the binding agent that makes concrete what it is.
More information and quantifying data on pumice pozzolans: HESS POZZ SITE.
Perlite or Pumice?
Perlite and pumice are closely related, both birthed by volcanic action, but arrive at their useful, foamed-stone natures differently.
PERLITE: Expanded perlite consists of up to 95% trapped air by volume—each particle a clustered fusion of tiny, rigid-skinned bubbles. That form factor is obtained by flash heating crushed perlite ore, transforming the moisture trapped within the hard, dense ore to steam and popping it—expanding it to its bright white frothy state. Once expanded, it becomes widely useful to industry, including as a lightweight insulating concrete aggregate.
Expanded perlite’s exceptional flyweight lightness and insulative performance comes with a corresponding fragility which must be taken into account when determining concrete application, mix design, production, and placement.
PUMICE: Pumice was calcined (expanded) naturally during violent volcanic action: water, trapped in the molten rock by immense pressure, is blasted into the atmosphere; that water erupts into steam, which froths and foams the rapidly cooling rhyolitic magma as it falls back to earth. The result is pumice. Under magnification, the vesicles (chambers) that trap the air are of myriad size and shape, from microns to millimeters. And the foamed-stone character goes clear through: even when crushed to sands and powders, pumice retains its airy form factor.
The porosity of pumice—even within the same deposit—can vary widely: 50 to 90% is typical. Pumice chamber walls, while much thinner than those of common scoria (basaltic magma), are thicker and stiffer than those enclosing the fused bubbles in expanded perlite. The tradeoff for more inherent strength and rigidity is less volume for trapped air and so increased weight and loss of insulative value. Pumice from the Hess deposit is a tough, slightly denser pumice, ideally suited for use as a concrete aggregate where strength is a primary consideration.
PUMICE PERLITE BLENDS: Pumice and expanded perlite can be used together in insulative concrete mix designs as needed to meet a variety of needs, leveraging the performance values of each.
COST DIFFERENCES: As for cost, the price differences are found in the beneficiation processes.
Expanded perlite (and other expanded stone products) are mined, crushed, screened to size, and furnace expanded to attain useful form. The now-expanded perlite can be packaged in super sacks or bulk loaded into covered trucks or rail cars.
Pumice aggregate and sand grades are simply mined, crushed, screened to grade, and sold by the ton as low-cost, minimally processed mine grades.
Talk to An Expert
Here at Hess, we’ve been mining and refining pumice and perlite for decades, meeting the specs for a wide assortment of industrial applications. Including concrete—our office building is made of pumice concrete. We’re happy to lend those years of savvy to you for your next project or explore ideas and possibilities with you.