Aggregate for Lightweight, Insulating Concrete

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Expanded perlite is the lightest of all mineral aggregates suitable for concrete. Insulative and lightweight, perlite-aggregate concrete is used for a variety of construction processes and industrial products—including roof decks, chimney linings, statuary, decorative stone, tile mortars, gas fireplace logs, floor systems and fills, fuel storage tanks, insulating tank and pool bases, and to boost sound and fire-resistance properties in walls, floors and structural steel.

Perlite Concrete: An Overview

When used as the primary aggregate in concrete, expanded perlite provides several key advantages to the construction and precast manufacturing applications. Though lightweight perlite concrete is not usually suited for structural or load bearing uses, in other applications it provides improvement in load stress, noise reduction, thermal transfer resistance, and fire rating.

Generally speaking, perlite concrete can be divided into two categories—Ultralight and Lightweight. Ultralight perlite concrete has a density less than 50 lbs/ft3 (800 kg/m3) and is used primarily for roof decks, raised planting beds, curtain walls, and permanent insulation applications like liquefied natural gas (LNG) storage tanks. Lightweight perlite concrete has densities from 50 to 110 lb/ft3 (800 - 1800 kg/m3), includes microsilica sand and offers high compressive and flexural strength, making it suitable floor finishes and fills. In both types, use of an air entraining agent improves workability, provides density regulation, and preserves insulation value.

Perlite Concrete (Ready Mix)

Both ultralight and lightweight perlite concretes can be mixed in the same batching plants and transported to the jobsite in the same transit mixers as standard concrete, but there are key considerations to take into account. The Perlite Institute publishes a specifications guide for ready/transit mix perlite concretes that provides detailed information on batch-ingredient order, mixing times, and transportation. This specifications guide also discusses field-control calculations for on-site checks and adjustments to insure proper wet densities, using the correct amount and proper concentration of the air entraining agent, and the use of a super plasticizer to reduce water-to-cement ratio and enhance strength of the mixes using sand. Pumping equipment recommendations and placement instructions are also covered. Two tables of mix design data—ultralight insulating and lightweight perlite concrete—are provided. Download below.

Perlite in Well Cements

Perlite’s ability to handle heat provides an effective lightweight cementing material that exhibits little material loss due to its ability to bridge voids and seal fractures. Other advantages include larger yield at a lighter density, insulating qualities, excellent fluid loss characteristics, and lower hydrostatic pressure on surrounding formations.

Perlite Insulating Concrete for Roof Decks

Typical rigid insulation systems are complex and difficult to install and can lose up to 30% of their published insulation values due to product shrinkage, thermal drift, and thermal bridging over steel deck through mechanical fasteners. There are no such issues with perlite concrete roof decks. Perlite concrete roof decks are seamless, providing a smooth, even monolithic base for direct-adhered roofing membranes. Perlite concrete may be placed over slotted galvanized steel decking, precast or poured-in-place concrete, or even over sound existing roofing materials.

Perlite concrete is an ideal base for built-up and single-ply roofing systems. It has superior wind and fire resistance, and, with the addition of polystyrene insulation sandwiched in the perlite concrete, high thermal resistance values are economically achieved. The result: an incredibly durable roof deck that will insulate and resist fire for the life of the building. Re-roofing is only a matter of replacing the membrane.

Perlite concrete mix formulations can be designed with densities from 20 to 50 lbs/ft3, meaning a perlite concrete roof deck system with a R-30 rating can come in at under 8 lbs. per square foot.

Other considerations in play: perlite concrete roof deck systems are readily sloped for drainage; fire ratings from 1 to 3 hours are possible; lightweight perlite concrete can be pumped, poured, or plastered into place; cured perlite concrete can be nailed, sawn, and worked with typical tools.

Testing and Approvals. Perlite concrete roof deck insulation systems have been tested and approved for wind and fire ratings by Underwriters Laboratories, Factory Mutual, and other code authorities. Perlite concrete roof decks with polystyrene insulation board meet the criteria for U.L. Class 90 and FM 1-90 wind resistance.

Manufactured Decorative Stone Products

The greatest advantage of using expanded perlite aggregate in cultured (manufactured) stone and brick veneer products is the weight savings—as much as a third the weight over typical mix designs. That weight savings has clear advantages: less rigorous support structure (like ledges and footings) for the veneer, and cost savings in handling and shipping.

Perlite concrete’s insulative and fire-resistant properties also add value to the cultured stone products, contributing directly to the heat-transfer equation of the building envelope.

Generally speaking, mix designs for perlite aggregate-based cultured stone products range from 1:4 (binder:perlite) to 1:20 by volume.

Insulating Storage Tank and Pool Bases

Perlite concrete’s superior insulative properties really come into play when used in to form the base for heat transfer-resistant storage tanks and in-ground vinyl swimming pools.

Trapezium-shaped, Perlite Concrete Blocks (PCBs) are useful for forming a base ring at the double-wall of insulated storage tanks. PCB grade specifications provide for varying needs in compressive strength, density, and thermal conductivity.

For in-ground swimming pools, heat loss into the ground is substantially reduced, thus providing a more consistent pool-water temperature and reducing the load on heating equipment. The smooth workability of a perlite concrete pool base provides a firm, seamless foundation for vinyl pool liners—and key to the longevity of the liners.

Typical mix design ratios range from 1:5 (binder:perlite) to 1:8, with the higher ratios of perlite providing more thermal conductivity resistance. A minimum base thickness of two inches (5cm) is necessary to achieve the strength and insulative benefits.

Insulating Underground Pipelines

Perlite concrete makes an excellent rigid insulative sheath for underground pipe and duct lines. Lightweight perlite concrete can be form-cast around pipe sections above ground and lowered into the trench or poured around the pipe or ducting already placed in the ground on precast perlite blocks, allowing the perlite concrete to completely surround the pipeline.

Sound Insulation

The fused-bubbles cellular structure of expanded perlite aggregate mitigates the propagation and transfer of sound waves, giving perlite concrete strong sound-blocking qualities when used in floor, ceiling and in-fill walls. By varying the amount of perlite used in the concrete mixture, a balance between weight and sound-blocking performance can be customized. For example, densities greater than 62 lb/ft3 (1,000 kg/m3) offer a high degree of sound-blocking.