Introduction
Basalt fiber (BF), known as “the green industrial material of the XXI-century”, combines ecological safety, natural longevity and many other properties. It is not a new material, but its applications are surely innovative in many industrial and economic fields, from building and construction to energy efficiency, from automotive to aeronautic, thanks to its good mechanical and chemical performances. Hence basalt fiber has gained increasing attention as a reinforcing material especially compared to traditional glass and carbon fibers. In this context, several studies on glass and carbon fiber reinforced composites address the significance of basalt fiber as a new reinforcing material.
Basalt fiber
As it is well known, basalt is the name given to a variety of volcanic rocks, known principally for its resistance to high temperatures, strength and durability, widely diffused all around the world, in which SiO2 accounts for the main part, followed by Al2O3, then Fe2O3, FeO, CaO and MgO. For this reason, basalt rocks are classified according to the SiO2 content as alkaline (up to 42% SiO2), mildly acidic (43 to 46% SiO2) and acidic basalts (over 46% SiO2). Only acidic type basalts satisfy the conditions for fiber preparation.
Basalt applications are well known from the Roman ages were the material was used in its natural form as a paving and building stone: actually basalt can also be formed into a continuous fiber having unique chemical and mechanical properties, so that it is ideally suited for demanding applications requiring resistance against high temperatures, insulation properties, acid and solvent resistance, durability, mechanical strength, low water absorption, etc.
Among others, two more characteristics must be highlighted:
- Suitable for fire protective applications- basalt fiber can replace almost all applications of asbestos without any impact on human health, thanks to the fiber’s size that make it non-breathable. In this regard, in 1998 an official list containing the names of the materials that can replace asbestos – Decreto Ministero dell’Industria del Commercio e dell’Artigianato 26.03.1998 –Elenco contenente i nomi delle imprese e dei materiali sostitutivi dell’amianto che hanno ottenuto l’omologazione – was published in Italy and among those materials there is also the basalt fiber;
- Eco-compatibility material- basalt fiber is has easier recyclability if compared, for example, to glass fiber. In fact the principal problem in glass fiber recycling is that it melts during incineration, sticking to the inside of the incineration chamber. The result is a costly clean-up effort and significant downtime. Basalt, instead, has a melting point of about 1400 °C; this means that after some composite material containing basalt fibers is incinerated, the only product left is an unmolten, fully usable basalt that can be swept from the incineration. And this is naturally a considerable added value.