Manufacturing process
The technology for producing basalt continuous fiber (BCF) is a one-stage process: melting, basalt homogenization, and fiber extraction. Basalt is heated only once. Further processing of BCF into materials is carried out using "cold technologies" with low energy costs.
Basalt fiber is made from a single material, crushed basalt, from a carefully chosen quarry source. Basalt of high acidity (over 46% silica content) and low iron content is considered desirable for fiber production. Unlike with other composites, such as glass fiber, essentially no materials are added during its production. The basalt is washed and then melted.
The manufacture of basalt fiber requires the melting of the crushed and washed basalt rock at about 1,500 °C (2,730 °F). The molten rock is then extruded through small nozzles to produce continuous basalt fiber filaments.
The basalt fibers typically have a filament diameter of between 10 and 20 μm, which is far enough above the respiratory limit of 5 μm to make basalt fiber a suitable replacement for asbestos. They also have a high elastic modulus, resulting in high specific strength—three times that of steel. Thin fiber is usually used for textile applications mainly for production of woven fabric. Thicker fibers are used in filament winding, for example, to produce compressed natural gas (CNG) cylinders or pipes. The thickest fibers are used for pultrusion, geogrid production, unidirectional and multiaxial fabric production, and as chopped strand for concrete reinforcement.
As of 2018, one potential application of continuous basalt fibers was to produce reinforcement bars that could replace traditional carbon-steel rebars, which are susceptible to corrosion in reinforced concrete after pH decreases due to concrete cover carbonation caused by atmospheric CO2. However, such a challenging application would necessarily require the use of low-alkali cement (LAC) when making concrete to prevent the harmful alkali–silica reaction from developing, which could otherwise dissolve at high pH the amorphous silica from basalt fibers, leading to the formation of damaging swelling silicagel that induces tensile stress in high-pH concrete.
