Condensed info from Composites Technology/Composites World, August 2006
Original article written/compiled by Anne Ross.

As it's possible that many readers have heard little of BASALT fibers, I thought it worth editing down this article to underline its highlites

...mike waters 2012, updated 2017

Basalt Fibers: a new alternative to Glass?

As a high-temperature performer with superior strength properties, this late-comer may be a better choice in some composite applications.

Basalt is a dense rock produced under intense volcanic heat, and it can be found in most countries across the globe. For many years, basalt has been used in casting processes to make tiles and slabs for architectural applications. Cast basalt liners for steel tubing already exhibit very high abrasion resistance in industrial applications. In crushed form, basalt also finds use as aggregate in concrete.

But more recently, continuous fibers extruded from naturally fire-resistant basalt have been investigated as a replacement for asbestos fibers in almost all of its applications. Since about 2000, basalt has also emerged as a contender in the fiber reinforcement of composites. Proponents of this late-comer claim their products offer performance similar to S-2 glass fibers at a price between S-2 glass and E-glass, and in some applications, offer manufacturers a less-expensive alternative to carbon fiber for products in which the latter might be 'over-engineered'.

EARLY BASALT FIBERS

Paul Dhé from Paris, France, was the first with the idea to extrude fibers from basalt. He was granted a U.S. patent in 1923. Around 1960, both the U.S. and the former Soviet Union (USSR) also began to investigate basalt fiber applications, particularly for military hardware, such as missiles.

Extrudability of basalt was later investigated in the northwestern U.S., where large basalt formations are concentrated. Owens Corning and several other glass companies conducted independent research programs which resulted in several U.S. patents. But around 1970, the U.S. glass companies abandoned basalt fiber research for strategies that favored their core product. The result was a better glass fiber, including successful development of S-2 glass fiber by Owens Corning.

During the same period, research in Eastern Europe was nationalized by the USSR's Defense Ministry and concentrated in Kyiv, Ukraine, where technology was subsequently developed in some secret. After the breakup of the Soviet Union in 1991, the results of Soviet research were declassified and finally made available for civilian applications.

Today, basalt fiber research, production and most marketing efforts are based in countries once aligned with the Soviet bloc. Companies currently involved in production and marketing include:

GLASS vs. BASALT

Basalt fiber is produced in a continuous process similar in many respects to that used to make glass fibers. In one way, the process is simpler because the basalt fiber has a less complex composition. Glass is typically 50 percent silica sand in combination with oxides of boron, aluminum and/or several other minerals—materials that must be fed independently into a metering system before entering the furnace. Unlike glass, basalt fibers feature no secondary materials so the process requires only a single feed line to carry crushed basalt rock into the melt furnace.

But negatively, basalt fiber manufacturers have less direct control over the purity and consistency of the raw basalt rock. While basalt and glass are both silicates, molten glass when cooled forms a noncrystalline solid. However, Basalt has a crystalline structure that varies based on the specific conditions during the lava flow at each geographical location. Moreover, the rate of cooling at the earth's surface, also influenced the crystal structure.

So although potentially available from mines and open-air quarries around the world, only a few dozen locations contain basalt that has been analyzed and qualified as suitable for manufacture of continuous thin filaments. It's largely recognized that basalt formations in the Ukraine are particularly well suited to fiber processing, with a nearby backup supply from Russia. But manufacturers prefer to use material from a single source to avoid most of the uncontrollable variables.

ROCK TO FIBER

The crushed basalt is furnace liquefied at a temperature of 1500°C/2732°F (glass melt point varies between 1400°C and 1600°C). But with basalt absorbing rather than transmitting infrared energy, it is more difficult to uniformly heat the entire basalt mix so basalt producers have employed several strategies to promote uniform heating.

Like glass filaments, basalt filaments are formed by platinum-rhodium bushings. As they cool, a sizing agent is applied and the filaments are moved to speed-controlled fiber stretching equipment and then on to winding equipment, where the fiber is spooled.

Because the basalt filament is more abrasive than glass, special bushings had to be developed to avoid frequent refurbishing.

GLASS FIBER vs. BASALT FIBER

On balance, the above differences lead to operating costs that exceed those for processing E-glass fiber, but it's claimed that the product clearly outperforms E-glass in most composites. In chopped mat, roving and unidirectional fabric forms, basalt fibers exhibit a higher breaking load and higher Young's modulus (a measure of the stiffness of a given material) than E-glass. In a study of basalt fibers and E-glass fibers conducted at the Composites Dept. of the University of Leuven in Belgium, unidirectional (prepreg) samples were produced, and the study reports that although each sample had a similar fiber volume fraction of 40 percent, the basalt/epoxy sample's strength tested 13.7 percent higher than that of the E-glass and exhibited 17.5 percent greater stiffness, although the basalt sample was 3.6 percent heavier. [Ed: Other tests have shown basalt fibers to be about 2-3% heavier than E-glass and 5-6% heavier than S-glass so this needs to be factored in.]

Additionally though, basalt fibers are naturally resistant to ultraviolet (UV) and high-energy electromagnetic radiation, they maintain their properties in cold temperatures, and provides better acid resistance. Reportedly, since basalt is the product of volcanic activity, the fiberization process is more environmentally safe than that of glass fiber. (The "greenhouse" gases that might otherwise be released during fiber processing, were vented millions of years ago during the magma eruption). Further, basalt is 100 percent inert, so it has no toxic reaction with air or water, and is noncombustible and explosion proof.

FIBER TO FABRIC

Once producers mastered fiber manufacture, they faced additional challenges as the product was converted to useful reinforcement forms. Early on, it was found that woven basalt fabrics straight from a weaver's loom were fragile and easily damaged when sharply folded or bent, and were irritating to the skin. To make the product more stable, a combination of sizing and refined production techniques minimizes damage and enables basalt fiber manufacturers to produce strong fibers that can be braided and woven without inhibiting performance.

While basalt fiber is still not widely used, it is slowly making its way into the hand of consumers. At price points that vary between S-glass ($5/lb to $7/lb) and E-glass ($0.75/lb to $1.25/lb), basalt fibers have properties more akin to S-glass. A common use is in the fire protection sector because of its high melt-point. Fire-blocking tests show results more similar to a metal fabric … merely turning red to a hot torch that would pierce glass in a matter of seconds.

This burn resistance has earned basalt fiber a role as an asbestos replacement in friction applications such as composite brake pads, because it does not soften at elevated temperatures nor deposit on the brake disc or drum.

Continuous basalt fibers are now in use as reinforcement in more conventional composite structures. Basalt fibers reportedly wet out easily and therefore enable fast resin impregnation, making them suitable for resin transfer molding, infusion molding and pultrusion. So the overall claim is that "All products made with glass fiber can be made using basalt."

PROTOTYPE TO PRODUCTION

Here are some of the activities and use of basalt as per 2006.

Ahlstrom (Finland), has supplied biaxial basalt fabrics for testing in wind turbine blade laminates as basalt fiber laminates have a 15 percent higher modulus and 25 percent higher tensile strength over E-glass.
Original equipment manufacturers (OEMs) are beginning to investigate basalt fiber products for consumer goods as well. Gitzo SA (France), sells professional carbon fiber tripods and heads, but now has basalt tripods and monopods. Basalt tripod legs are roughly 20 percent lighter than aluminum legs and better at damping vibration.

Mervin Manu (Seattle. WA) currently makes two different snowboard models that incorporate a basalt fabric instead of the traditional fiberglass commonly used. The boards contain a proprietary wooden core with a basalt fiber lining on each side that results in lighter, stiffer snowboards. Such a board was first on exhibit at the 2005 JEC Composites Show.

In the automotive industry, Azdel Inc., GE Advanced Materials and glass-fiber producer PPG Industries, developed VolcaLite, a thermoformable composite that combines polypropylene (PP) and long chopped basalt fiber. The company claims that the basalt/PP system offers acoustic absorption properties, low coefficient of thermal expansion (CTE), and a high strength-to-weight ratio, providing good ductility. Although initially targeted for auto headliners, (made 50 percent thinner than conventional systems), there are clearly many other applications for this.

Technical Fibre Products Ltd. has taken chopped basalt fibers and made fine gauze nonwoven veils. as well as laminated and thermoformed automotive components. Johns Manville Europe has also produced wet-layed basalt veils.

Basalt fiber is becoming a contender in infrastructure applications as well. Sudaglass (Texas) produces several products from basalt fiber, including concrete reinforcement rods. Pultruded from unidirectional basalt fiber, the rods are reportedly 89 percent lighter than steel reinforcement rods, have the same coefficient of thermal expansion as concrete and are less susceptible to degradation in an alkaline environment. The company claims that 1 ton of basalt rods can provide reinforcement equal to 4 tons of steel rods.

As commercialization continues, consistent fiber supply looks more promising. For example, Kamenny Vek in Russia, was looking to turn out 30,000 metric tonnes (66 million lb) per annum by 2009.

 

2017 UPDATE

A 2016 Conference was held in Portugal on Material Fractures, and included some interesting papers on the Mechanical Properties and Behavior of Basalt which is still very much of interest for future composite construction, as when combined with new 'green' resins, can open up a future using composite materials that can be less contaminating.     Here is the link:    https://www.sciencedirect.com/science/article

 

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