Original article

Relationships among the chemical,mechanical and geometrical propertiesof basalt fibers

Calvin Ralph , Patrick Lemoine, John Summerscales ,Edward Archer and Alistair McIlhagger

Abstract

We investigated the chemical, mechanical and geometrical properties of basalt fibers from three different commercial

manufacturers and compared the results with those from an industry standard glass fiber. The chemical composition of

the fibers was investigated by X-ray fluorescence spectrometry, which showed that basalt and glass fibers have a similar

elemental composition, with the main difference being variations in the concentrations of primary elements. A significant

correlation between the ceramic content of basalt and its tensile properties was demonstrated, with a primary depend-

ence on the Al2O3 content. Single fiber tensile tests at various lengths and two-way ANOVA revealed that the tensile

strength and modulus were highly dependent on fiber length, with a minor dependence on the manufacturer. The results

showed that basalt has a higher tensile strength, but a comparable modulus, to E-Glass. Considerable improvements

in the quality of manufacturing basalt fibers over a three-year period were demonstrated through geometrical analysis,

showing a reduction in the standard deviation of the fiber diameter from 1.33 to 0.61, comparable with that of glass

fibers at 0.67. Testing of single basalt fibers with diameters of 13 and 17 mm indicated that the tensile strength and

modulus were independent of diameter after an improvement in the consistency of fiber diameter, in line with that of

glass fibers.

Keywords

basalt fibers, chemical properties, mechanical properties, physical properties

Environmental issues, such as the waste disposal andrecyclability of composites, are becoming increasinglyimportant to both industry and governments andhave led to the promotion of natural fibers as reinforce-ments in polymer composites.1–3 Fibers typically usedas reinforcements in polymers are glass or carbon fibersdue to their good mechanical properties, especiallytheir strength; however, they are not environmentallyfriendly.4,5 Natural fibers, including plant fibers such askenaf and flax, have poor mechanical properties andare prone to thermal degradation,6,7 making themuncompetitive with glass and carbon fibers. This hasled to a focus on basalt fibers.

Continuous basalt fibers have a simple manufactur-ing process that does not require any additives.8

Basalt fibers are produced by melting basalt rock attemperatures between 1350 and 1700 �C and then pull-ing the molten material downwards through a

platinum–rhodium die (bushing) using the spinneretmethod.9 The melting of basalt rock is conducted intwo stages: it is first fused in the initial furnace andthen transferred to the primary furnace, which controlsthe temperature of the melt and feeds the bushings.10

The fibers for processing are primarily heated by over-head gas heaters. The dark color of basalt means thatmaterial close to the surface of the melt absorbs infra-red energy from the gas burners, making it difficult toobtain a homogeneous melt. There are two methods to

University of Ulster at Jordanstown, UK

Corresponding author:

Calvin Ralph, University of Ulster at Jordanstown, Shore Road,

Newtownabbey BT37 0QB, UK.

Email: ralph-c@ulster.ac.uk

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overcome this: holding the basalt melt in the heatingstage for longer or, more commonly, using immersedelectrodes to electrically heat the melt.10,11

The chemical composition of basalt varies dependingon the geographical location and conditions of forma-tion of the source rock. Basalt consists primarily ofsilicon, aluminum, calcium and iron oxides, similar toglass fibers.12–14 Fibers produced from basalt consistof the minerals olivine, plagioclase, pyroxene and clino-pyroxene.15 Basalt is classified according its SiO2 con-tent, where alkali basalts contain up to 42% SiO2,mildly acidic basalts contain 43–46% SiO2 and acidicbasalts contain >46% SiO2. To manufacture continu-ous basalt fibers, the basalt rock must fall within theacidic class (>46% SiO2).

16 Recent research17 hasshown that the melting properties of basalt used inmanufacturing fibers varies depending on the mineralclass of the basalt rock. The melting process is a crucialstage in the production of continuous basalt fibers andthe homogeneity of the melt can affect the quality, diam-eter and performance stability of the basalt fibers.The ability to produce basalt fibers with a consistentdiameter is important if these fibers are to competewith glass fibers. Significant variations in fiber diameterwill affect the fiber quality, the ability to model basaltcomposites, the fiber volume fraction and, potentially,the interfacial adhesion through increased or reducedsurface area.18,19

Basalt fibers have superior mechanical properties toplant fibers and comparable, or better, properties toglass fibers.3,18,20 The density of basalt is between 2.6and 2.7 g/cm3, whereas the density of E-Glass is 2.5–2.6 g/cm3.21 Basalt fibers have excellent sound insula-tion, a thermal resistance higher than that of glass,good chemical resistance to both acidic and alkalineconditions (higher than E-Glass) and are biologicallyinert.12,22,23 The cost of basalt fibers (about £6.00/kg)is currently higher than that of E-Glass (about£1.50/kg), although lower than that of S-Glass (about£16.00/kg). E-Glass fiber manufacturing costs haveeconomies of scale as an established reinforcementmaterial, whereas basalt fiber production costs are com-promised by early stage small-scale production. Asbasalt is the most common rock on Earth, there is anabundant supply available; however, because basaltfibers require a certain SiO2 content, there are currentlyonly about three dozen mines and quarries with certi-fied rock suitable for fiber manufacture, with the major-ity in Ukraine and Russia.24 The properties of basalt,together with its environmentally friendly nature,25

mean that it has potential as a competitor or replace-ment for glass fiber and as a new fiber in various appli-cations. Short and continuous basalt fibers havetherefore been the focus of recent research with theaim of identifying their potential applications.12,21,26–34

With the increased demand for basalt fibers, therehas been an increase in the number of establishedmanufacturers. Glass fibers have a relatively standardperformance, whereas the performance and quality ofbasalt fibers from different sources or manufacturershas not yet been fully examined. It is therefore import-ant to understand the variations in basalt fibers fromdifferent manufacturers, such as the chemical compos-ition, consistency of diameter and mechanical proper-ties. The aim of this work was to analyze these factorsand to determine whether there are any variations orrelationships between them.

Materials and methods

Materials

Several types of commercial basalt fiber were character-ized and compared with commercially available glassfibers (Table 1). Each fiber was provided in the directroving form with a general purpose size primarily suit-able for use in epoxies. Companies A and C werechosen due to their long establishment and classifica-tion among the world leaders in basalt fiber manufac-ture, whereas Company B is a relatively new (5 years)and fast-emerging competitor within the market.E-Glass from Company D was selected because theyare a well-established glass fiber manufacturer.

Methods

X-ray fluorescence spectrometry. The chemical compos-ition of the fibers was determined by X-ray fluorescence(XRF) spectrometry. The fibers were initially placed ina muffle furnace at T¼ 650 �C for 30 minutes to removeany sizing present on the fibers. Pyrolysis is commonlyused to remove sizing and the temperatures and timeused in this work were higher than those reported to berequired to remove all organic sizing.35–37 After cool-ing, the desized fibers were milled for 2 minutes at

Table 1. Basic data for the investigated fibers

Designation

Fiber

type Manufacturer

Nominal

diameter

(mm)

Linear

density

(Tex)

BF1 Basalt Basaltex 13 150

BF2 Basalt Mafic 13 300

BF3 Basalt GBF 13 400

BF4 Basalt Basaltex 17 600

BF5 Basalt Mafic 17 500

Glass fibers Glass PPG 14 300

2 Textile Research Journal 0(00)

520 rpm in a Retsch PM100 planetary ball-mill toachieve a consistent powder. The powder fiber sampleswere mixed with CEREOX Licowax (Fluxana, BM-0002) at a ratio of 4:1 to bind the powder and thenpressed (Retsch PP25) to produce pellets for XRF ana-lysis. CEREOX was used as a binding agent because itis clean and stable under X-rays and is designed specif-ically for XRF because it does not influence the results.XRF spectrometry was performed using a ThermoScientific Niton FXL FM-XRF analyzer. Eachsample was tested in three spots with a testing time of150 s per spot.

Analysis of fiber diameters. Scanning electron microscopy(SEM) with a JEOL JSM-6010 microscope was used todetermine the actual fiber diameter of the basalt andglass samples. Fibers were coated with gold to improvethe image quality and accuracy. A set of 100 measure-ments was recorded from 15mm samples taken at 1mintervals along the roving length to give a total of 300measurements per fiber type. Fiber sizing was notremoved prior to the measurements because the calcu-lated sizing thickness was <16 nm and therefore negli-gible. SEM was used instead of standard opticalmicroscopy due to its increased image quality.

Mechanical testing. Single fiber tensile tests were per-formed according to ASTM D3379 using an Instron5564 instrument with a 200N load cell. As-receivedfibers were separated and bonded to cardboard tem-plates, clamped in the grips of the test machine andthe template was carefully cut before the start of thetest. A minimum of 10 tests was performed for eachsample at a constant crosshead rate of 1mm/min for25, 50 and 100mm gage lengths. As it was not possibleto use an extensometer or strain gage due to the smalldiameter of the fragile fibers, the recorded load versusdisplacement results were used in conjunction withthe compliance method stated in ASTM D3379.

The indicated compliance was calculated using equa-tion (1).

Ca ¼ I=Pð Þx H=Sð Þ ð1Þ

where I is the total extension for straight line section ofthe load–time curve extrapolated across the full chartscale, P is the full scale force, H is the crosshead speedand S is the chart speed. The true compliance is thencalculated as:

C ¼ Ca � Cs ð2Þ

where Cs is the system compliance. Young’s moduluswas calculated as a corrected value using the followingequation:

E ¼ L=CA ð3Þ

where L is the specimen gage length and A is the aver-age filament area.

Results and discussion

The chemical composition of the studied fibers is givenin Table 2. The primary compound found within boththe basalt and E-Glass fibers is SiO2. The basalt fibershave a relatively consistent SiO2 content of 48.82–49.69mass per cent (mass%) across different manufacturers,consistent with the requirement to spin continuousbasalt fibers. The glass fibers had a higher SiO2 contentof> 53 mass%, in agreement with previous studies andspecifications.9,12,38,39 The basalt fibers contained fiveessential elemental components (SiO2, Al2O3, CaO,MgO and Fe2O3). Similarly, the glass fibers weremainly formed from five primary groups (SiO2,Al2O3, CaO, MgO and B2O3). Boron could not bedetermined with the equipment used in this work, butit is known that glass fibers contain 0.4–5 mass%

Table 2. Chemical composition of basalt and glass fibers

Element Oxide

BF1 BF2 BF3 Glass fibers

Element

(mass%)

Oxide

(mass%)

Element

(mass%)

Oxide

(mass%)

Element

(mass%)

Oxide

(mass%)

Element

(mass%)

Oxide

(mass%)

Si SiO2 22.52 48.82 23.22 49.69 23.26 49.58 24.78 53.02

Al Al2O3 6.79 12.83 7.12 13.45 6.11 11.54 5.91 11.16

Ca CaO 4.50 6.02 4.51 6.03 3.62 4.85 12.53 16.77

Fe Fe2O3 5.18 7.41 5.25 7.51 4.87 6.96 0.17 0.24

Mg MgO 2.45 4.06 2.03 3.36 3.08 5.10 1.82 3.02

Ti TiO2 0.56 1.18 0.58 1.21 0.43 0.90 0.05 0.10

K and Na K2O+Na2O 1.12 2.44 1.20 2.50 1.67 2.13 0.27 0.36

Ralph et al. 3

boron, with the exception of some new boron-free glassfibers, but boron is not present in basalt.9,38,40,41 Theglass fibers shared further oxides with basalt fibers,such as TiO2, K2O, Na2O and Fe2O3, but in muchlower quantities (<1 mass%). These results highlightthe chemical differences between glass and basaltfibers, with the higher content of Fe2O3 contributingto the increased temperature resistance and darkercolor of basalt fibers. With the exception of a smallvariation in the SiO2 and Al2O3 contents (about 1mass%), samples BF1 and BF2 had a similar chemicalcomposition. Sample BF3 had a similar SiO2 content toBF1 and BF2, but varied consistently by 1–2 mass%for all other elements. A higher CaO content reducesthe melting temperature of basalt and leads to easierhomogenization of the melt, which known to aid fiberproduction.42 Samples BF1 and BF2 had a similar CaOcontent, whereas the CaO in sample BF3 was about1.25 mass% lower, which could lead to an inhomogen-eous melt unless adjustments are made to the furnacetemperature.

Fibers from sample BF2 were chosen for furtherinvestigation to determine the consistency of fibermanufacture over time. Table 3 gives details of thefibers tested. The batches of fibers were manufacturedabout one year apart. The average measured diameterdid not vary significantly between years, but a clearchange in the standard deviation is evident, with animprovement from 1.33 to 0.61. This deviation clearlyshows considerable improvements in the consistency offiber manufacture. The fiber diameter is related to

parameters such as the velocity of the molten material,the haul-off rate and the internal diameter of the bush-ing.43 It is believed that improvements in the melthomogeneity result in better control of the diameterof basalt fibers, as seen with glass fibers.44

The improved results for sample BF2 were comparedwith the diameters of fibers from other manufacturers(Table 4). In addition to fibers tested in this work, theresults were compared with previous studies onTechnobasalt and D.S.E Group fibers (designated sam-ples BF6 and BF7, respectively).45 The nominal diam-eter stated by the manufacturers of basalt fibers was13 mm across all samples. Glass fibers were measuredas 13.87 mm compared with the stated diameter of14 mm, with a low standard deviation of 0.67. Thediameter of basalt fibers needs to be consistent if theyare to be competitive with glass fibers and to assist inthe prediction and modeling of basalt composites.Figure 1 shows the distribution of fiber diameterseach test fiber.

Fiber from one of the leading basalt manufacturers(sample BF1) was on average 1.16 mm larger than thespecified diameter and had a higher standard deviationof 1.2. Although samples BF3 was close to its stateddiameter, the standard deviation was more than doublethat of glass fibers. Sample BF6 fibers were> 1 mmlarger than specified, with a very high standard devi-ation of 2.9, suggesting poor consistency in fiber manu-facture. These results highlight the current gap betweenglass and basalt fibers in terms of fiber manufacture andquality. However, the improved fiber of sample BF2

Table 4. Results of measurements of fiber diameters

Sample

Stated

diameter (mm)

Average

diameter (mm)

Standard

deviation

Coefficient of

variation (%)

BF1 13 14.16 1.20 8.46

BF2 13 13.31 0.61 4.61

BF3 13 12.61 1.38 10.97

BF6 (Ref. 45) 13 14.1 2.9 4.76

BF7 (Ref. 45) 13 12.70 1.50 4.00

Glass fibers 14 13.87 0.67 4.84

Table 3. Results of measurements of fiber diameter for sample BF2

Manufacturer

Date of

manufacture

Stated

diameter (mm)

Measured

diameter (mm)

Standard

deviation

Mafic February 2014 13 13.39 1.33

April 2015 13 13.43 1.10

August 2016 13 13.31 0.61

4 Textile Research Journal 0(00)

showed significant improvements, with a diameter closeto the stated value and, more importantly, a standarddeviation of 0.61, lower than that of the glass samples.It is clear there have been some significant improve-ments in the manufacture and quality of basalt fibersin recent years. The larger diameter fibers of samplesBF4 and BF5 had a high consistency in diameter withstandard deviations of 0.83 and 0.69, respectively,although this is probably a result of the easier manu-facturer of larger fibers.

The tensile strength and tensile modulus of allthe 13 mm fibers are presented in Figure 2(a) andFigure 2(b), respectively. Initial observations of the ten-sile strength indicated that the fiber strength decreasedas the fiber length increased for all fibers. This behavioris widely associated with an increase in the flaw popu-lation due to the longer fiber length and has beenobserved in both carbon and glass fibers.46,47

There are two variables within these samples thatmay influence the mechanical properties: the fibertype/manufacturer and the fiber length. Two-wayANOVA was performed to determine the dependenceof the tensile strength and modulus of the filaments onthese two factors.48 The prerequisite of ANOVA todetermine the equality of variances was determined bythe Levene test.49 The test statisticW was calculated by:

W ¼N� kð Þ

ðk� 1Þ

Pki¼1 Nið �Zi �

��Z Þ2Pki¼1

PNi

j¼1 ðZij � �ZiÞ2

ð4Þ

where k is the number of different groups, N is the totalnumber of measurements, Zij ¼ jYij � �Yij where �Yi isthe mean of the ith group and Yij is the value of themeasured variable for the jth case of the ith group, ��Z isthe mean of all Zij and �Zi is the mean of the Zij for theith group. The resulting P values for the tensile strengthand tensile modulus were 0.23 and 0.49, which are sig-nificantly higher than the significance level (a¼ 0.05).

Therefore the null hypothesis theory of standard vari-ations can be accepted. ANOVA was then performedwith the fiber type being Factor A and fiber lengthbeing Factor B. The calculated P values fromANOVA were used as results considering a significancelevel of a¼ 0.05. The null hypothesis of equal means isaccepted when P>a and hence rejected when P<a.

Table 5 gives the results for the results of the two-way ANOVA for tensile strength and tensile modulus.The reported F value is the variation between thesample means/variation within the samples and isused for determining the P value. For tensile strength,the very low P value relating to the fiber length showsthat variations in gage length are relevant at the 5%significance level, indicating a strong dependence of thestrength on gage length. Low P values for Factor Aalso indicate a dependence of fiber strength on thefiber type/manufacturer. Previous studies have con-firmed the strong dependence of basalt fiber strengthon gage length,15 but indicated that there was nodependence on fiber type. When the lower values ofsample BF3 were removed from the ANOVA analysis,the corresponding P value for fiber type increased to0.5, which is in agreement with previous findings andhighlights the poor mechanical performance of sampleBF3 fibers. However, as sample BF3 is a commerciallyavailable fiber, it is important to include it in the

Figure 2. Tensile properties of 13 mm basalt and glass fibers.

Figure 1. Distribution of the diameters of basalt and glass fiber

samples.

Ralph et al. 5

analysis and hence it can be suggested that there is adependence of tensile strength on fiber type.

A similar trend for tensile modulus can be seen fromANOVA results. The low P values for both Factor Aand Factor B show that the elastic modulus depends onboth fiber type and fiber length. It has previously beensuggested15 that the modulus did not depend on fiberlength. This change may be explained by the gagelengths used during testing, which previously focusedon 10–40mm. When the values for the 100mm gagelength were removed from the ANOVA analysis, thecorresponding P value for fiber length increased to0.16, indicating that the tensile modulus across differentfiber lengths was not significantly different. However,comparable testing performed on E-Glass fibers43 withlengths of 5–80mm showed that tensile modulusincreased as the fiber length increased, in agreementwith the results found for longer basalt fibers. Thisincrease, despite the modulus correction, can be attrib-uted to the dependency of the test equipment on thesample gage length. This dependency is manifested as acontribution to elastic deformation from the testingequipment and is in agreement with the work ofPardini and Manhani,47 who reported an increase inmodulus with gage length for both glass and carbonfibers with the ASTM correction and rigidity methods.Comparisons between glass and basalt fibers show thatbasalt is characterized by a higher tensile strength and acomparable elastic modulus to that of glass. It is notedthat the mechanical properties are lower than the valuesstated in the technical data sheet.

The tensile data was further analyzed by applyingWeibull statistics. Data for each fiber and eachgage length were sorted in ascending order. Fromthis, the corresponding value of the cumulative failureprobability, PF, was determined using the median rankestimator.50

PF ¼i� 0:3

Nþ 0:4ð5Þ

where i is the ith term of total number of tests N.The Weibull parameters m (shape) and ro (scale) weredetermined for each fiber manufacturer and gage length

by fitting the data points with the two-parameterWeibull distribution in equation (6):

ln �ln 1� PFð Þ½ � ¼ m ln �ð Þ �mlnð�oÞ ð6Þ

Figure 3 shows the Weibull plots obtained fromequation (6) for sample BF2 fibers and Table 6 givesthe parameters m and ro for all fibers and lengths. Thelower values of m for sample BF3 suggest that the flawsare less evenly distributed throughout the fiber, result-ing in a greater scatter in strength.47,50,51 Samples BF1and BF2 have similar values, with the exception of100mm lengths, where the m value for BF1 is consid-erably lower than that for BF, indicating a less homo-geneous material over longer lengths.

As the Weibull parameters were obtained at differentgage lengths, it is possible to predict the tensile strengthat lengths outside the experimental range.52 This can beachieved using equation (7), in particular at a cumula-tive probability failure PF¼ 0.5.

� ¼ �o1

AoLfln2

� �1=mð7Þ

where Ao is the cross-sectional area and Lf is the gagelength of the fibers. The resulting plot obtained usingthe parameters from Table 6 are shown in Figure 4. Thepredictions from the Weibull statistics for samples BF1

Table 5. Two-way ANOVA results for tensile properties of basalt fibers

Tensile strength Tensile modulus

Sample

Degrees

of freedom F P F P

Factor A (fiber type) 2 8.48 0.0364 9.46 0.0305

Factor B (fiber length) 2 28.28 0.0044 16.38 0.0118

Interaction 4 18.38 0.0077 12.92 0.0147

Figure 3. Weibull plot for sample BF2 fibers.

6 Textile Research Journal 0(00)

and BF2 are very similar, with the exception of sampleBF3, in agreement with the ANOVA results in Table 5,highlighting that there may be a difference between thestrength of fibers from different manufacturers.

The mechanical properties of 17mm fibers fromCompany B (BF5) and A (BF4) are shown in Figure 5.The 17mm fibers show the same trend as the 13mm fibersin that the tensile strength increases as the fiber lengthdecreases and the tensile modulus increases as the lengthis increased.

The Weibull statistics were performed again for the17 mm fibers. The m and ro Weibull parameters areshown in Table 7, whereas the prediction of strengthat different lengths from equation (7) is presented inFigure 6.

Unlike the 13 mm fibers, there was a notable differ-ence in strength between the 17 mm fibers in samplesBF4 and BF5. Sample BF4 had a consistently lowerm value at 25 and 50mm gage lengths and was compar-able at 100mm, indicating that sample BF5 had betterhomogeneity.50 The m value decreased at 100mmlength for both fibers, confirming that critical fiberflaws are more likely to be encountered at longer gagelengths. The difference in performance between samplesBF4 and BF5 is shown in Figure 6.

It has widely been thought that the tensile strengthand modulus of natural fiber increases as the fiberdiameter decreases.53–56 This was shown by fibers

Figure 5. Tensile properties of 17 mm basalt and glass fibers.

Figure 6. Tensile strength of 17 mm basalt fibers as a function of

gage length.

Figure 4. Tensile strength of 13 mm basalt fibers as a function of

gage length.

Table 7. Weibull parameters for strength of 17mm basalt fibers

Fiber

25 mm 50 mm 100 mm

ro (MPa) m ro (MPa) m ro (MPa) m

BF4 1962 13.32 1797 28.6 1476 20.2

BF5 2210 20.2 2001 47.64 1634 15.66

Table 6. Weibull parameters for strength of 13mm basalt fibers

Fiber

25 mm 50 mm 100 mm

ro (MPa) m ro (MPa) m ro (MPa) m

BF1 2065 38.19 1942 31.63 1730 12.71

BF2 2066 42.52 1971 26.38 1765 25.69

BF3 1972 18.56 1775 32.18 1477 15.67

Ralph et al. 7

from Company A, where there was a clear decrease intensile strength and tensile modulus as the fiber diameterincreased [Figure 7(a) and 8(a)]. By contrast, the tensileproperties of glass do not depend on the fiber diameteras a result of improvements in the consistency of manu-facture of glass fibers.57 Comparisons of tensile strengthand tensile modulus between the 13 and 17mm basaltfibers from Company B (samples BF2 and BF5) canbe seen in Figures 7(b) and 8(b).

The tensile strength is nearly constant for the twofiber diameters of samples BF2 and BF5, with theexception of the longer 100mm lengths, where a slightreduction in strength is seen at larger diameters. Thecause of this difference is unknown, although thereare more likely to be critical fiber flaws in longer fiberlengths, which may be more prominent at larger diam-eters. The tensile modulus for sample BF5 showed littledeviation, suggesting that tensile strength is independ-ent of fiber diameter.

The independence of fiber strength and diameter forsamples from Company B is in agreement with previouswork.45 Otto57 showed that, when fibers of differentdiameters are formed under controlled, near-identicalconditions, their break strengths are identical and hence

are reliant on the process of formation rather than thediameter. This applies to diameters >9 mm. With thedemonstrated increase in the quality of basalt fibersfrom Company B, basalt fibers are shown to behavein a similar manner. These findings apply only tofibers on their own and not fibers embedded in a poly-mer matrix. Fibers tows consisting of fibers with asmaller diameter, but constant weight, have anincreased surface area, which, in turn, generates moreinteraction and adhesion to the matrix and results in ahigher mechanical performance.19 However, as thefibers begin with the same mechanical properties, it isthought that the effect of surface area may not be aslarge as for fibers that have a different performance atvarying diameters.

The mechanical properties of basalt and glass fibershave been related to their chemical composition.Attempts have therefore been made to improve themechanical properties of basalt fibers through the add-ition of extra elements during manufacturing, resultingin positive improvements.58 A relationship between theceramic-like content (SiO2+Al2O3), which is the pri-mary composition of basalt, and the mechanical prop-erties has been demonstrated; however, a correlation

Figure 7. Diameter–tensile strength relationship for samples (a) BF4 and (b) BF5.

Figure 8. Diameter–tensile modulus relationship for samples (a) BF4 and (b) BF5.

8 Textile Research Journal 0(00)

with the Al2O3 was not seen.42 Figure 9 shows the rela-

tionship between the tensile strength and the ceramic-like and Al2O3 contents.

Although glass fibers are shown on the same graphin Figure 9, they were not included in the correlationdue to their different chemical composition. There is aclear correlation between tensile strength and the cera-mic-like content (Figure 9(a)), but also a significantrelationship with the Al2O3 content (Figure 9(b)).Two-way ANOVA was performed for tensile strengthwith the ceramic content as Factor A and the Al2O3

content as Factor B. The ceramic content generated aP value of 0.001, below the level of significance(a¼ 0.05). The resulting P value for Al2O3 was consid-erably lower at 1.3523� 10�7, suggesting that the ten-sile strength is more dependent on the Al2O3 content.Comparisons with the tensile modulus (Figure 10) indi-cate that there is no significant correlation between themodulus and the ceramic-like or Al2O3 content. Similarcomparisons of mechanical properties with other elem-ents found within basalt fibers yielded no evident rela-tionship, suggesting they have a low importance indirectly determining the mechanical properties of fibers.

Conclusions

The chemical composition, fiber diameter and mechan-ical properties of different basalt fibers were investigatedusing XRF spectrometry, SEM and tensile testing. Themain components of the basalt fibers were SiO2, Al2O3,CaO, MgO and Fe2O3, with small amounts of TiO2,K2O and Na2O. The glass fibers had similar chemicalcomponents/constituents to basalt, with the main differ-ence in composition being higher levels of Fe2O3 inbasalt. The chemical composition of basalt remainedlargely consistent between manufacturers, with onlysample BF3 showing a variation in Al2O3, CaO andMgO content. The diameter of the basalt fibers variedbetween manufacturers, with most showing a higherstandard deviation than glass. Significant improvementsin the distribution of fiber diameters was demonstratedfor the first time, with sample BF2 being comparablewith the glass fiber standard, suggesting advancementsin the manufacturing quality of basalt fibers.

The mechanical properties of basalt fibers varybetween manufacturers, although the properties offibers from Company A and Company B were

Figure 10. Chemical composition–tensile modulus relationships.

Figure 9. Chemical composition—tensile strength relationships.

Ralph et al. 9

comparable. The basalt fibers were characterized by ahigher tensile strength than the E-Glass fibers and a simi-lar tensile modulus. ANOVA was used to show thedependence of fiber strength on gage length, with shorterfiber lengths yielding a higher tensile strength and fiberlengths >50mm yielding a higher tensile modulus.

For most of the commercial basalt fibers tested,the properties of the basalt fibers was dependent onthe fiber diameter. Contrary to common belief, thestrength and modulus of basalt fibers was independentof the fiber diameter for fibers from Company B, withfibers ranging from 13 to 17 mm diameter displayingcomparable properties. A clear correlation betweenthe mechanical properties and the chemical compos-ition of basalt fibers was evident, with fibers showinga strong dependence on the ceramic-like content(SiO2+Al2O3), but primarily the Al2O3 content, con-firmed by ANOVA. Basalt fiber technology has reacheda point where adoption should no longer constrainedby product variability. The cost and performance offibers currently lies between those for E-Glass and S2-Glass. The wider adoption of basalt fibers as reinforce-ment in composites will require mass production tomeet the demand for fibers and should lead to theircosts becoming competitive with the established E-Glass reinforcement.

Acknowledgements

The authors thank Ulster University, Northern IrelandAdvanced Composites and Engineering Centre and Axis

Composites for support and provision of testing equipmentand Mafic Basalt for the provision of materials.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with

respect to the research, authorship, and/or publication of thisarticle.

Funding

The authors disclosed receipt of the following financial sup-

port for the research, authorship, and/or publication of thisarticle: This work was supported and funded by aDepartment for Employment and Learning CAST award

Grant number B00527885.

ORCID iD

Calvin Ralph http://orcid.org/0000-0001-9307-820XJohn Summerscales http://orcid.org/0000-0002-3557-0404

References

1. Lopresto V, Leone C and De Iorio I. Mechanical charac-terisation of basalt fibre reinforced plastic. Compos B Eng

2011; 42: 717–723.2. Al-Oqla FM and Sapuan SM. Natural fiber reinforced

polymer composites in industrial applications: Feasibility

of date palm fibers for sustainable automotive industry.

J Clean Prod 2014; 66: 347–354.

3. Ku H, Wang H, Pattarachaiyakoop N, et al. A review on

the tensile properties of natural fiber reinforced polymer

composites. Compos B Eng 2011; 42: 856–873.4. Das S. Life cycle assessment of carbon fiber-reinforced

polymer composites. Int J Life Cycle Assess 2011; 16:

268–282.5. PwC. Sustainable Performance and Strategy. Life cycle

assessment of CFGF -Continuous Filament Glass Fibre

Products. London: PriceWaterhouseCoopers, 2016.

6. Arbelaiz A, Fernandez B, Ramos JA, et al. Mechanical

properties of short flax fibre bundle/polypropylene com-

posites: Influence of matrix/fibre modification, fibre con-

tent, water uptake and recycling. Compos Sci Technol

2005; 65: 1582–1592.7. Gassan J and Bledzki A. Thermal degradation of flax and

jute fibers. J Appl Polym Sci 2001; 82: 1417–1422.8. Bashtannik PI, Kabak AI and Yakovchuk YY. The effect

of adhesion interaction on the mechanical properties of

thermoplastic basalt plastics. Mech Compose Mater 2003;

39: 85–88.9. Militky J, Kovacic V and Rubnerova J. Influence of ther-

mal treatment on tensile failure of basalt fibers. Eng Fract

Mech 2002; 69: 1025–1033.10. Gur’ev V, Neproshin EI and Mostovoi GE. The effect of

basalt fiber production technology on mechanical proper-

ties of fiber. Glass Ceram 2001; 58: 62–65.

11. Fourne F. Synthetic fibers. Munich: Carl Hanser, 1999.12. Liu Q, Shaw MT and Parnas RS. Investigation of

basalt fiber composite mechanical properties for appli-

cations in transportation. Polym Compos 2006; 27(1):

41–48.13. Czigany T. Discontinuous basalt fiber-reinforced hybrid

polymer composites. In: Friedrich K (ed.) Polymer com-

posites: From nano to macro-scale. Munich: Springer,

2005, pp.309–328.

14. Czigany T. Trends in fiber reinforcements – the future

belongs to basalt fiber. Express Polym Lett. 2007; 1: 59.

15. Greco A, Maffezzoli A, Casciaro G, et al. Mechanical

properties of basalt fibers and their adhesion to polypro-

pylene matrices. Compos B Eng 2014; 67: 233–238.

16. Militky J and Kovacic V. Ultimate mechanical properties

of basalt filaments. Textile Res J 1996; 66: 225–229.

17. Chen X, Zhang Y, Hui D, et al. Study of melting proper-

ties of basalt based on their mineral components. Compos

B Eng 2017; 116: 53–60.18. Fiore V, Scalici T, Di Bella G, et al. A review on basalt

fibre and its composites. Compos B Eng 2015; 74: 74–94.19. Dhand V, Mittal G, Rhee KY, et al. A short review on

basalt fiber reinforced polymer composites. Compos B

Eng 2015; 73: 166–180.20. Djafari Petroudy SR. 3 – Physical and mechanical prop-

erties of natural fibers. In: Fan M and Fu F (eds)

Advanced high strength natural fibre composites in con-

struction. Cambridge: Woodhead Publishing, 2017,

pp.59–83.21. Czigany T. Special manufacturing and characteristics

of basalt fiber reinforced hybrid polypropylene

10 Textile Research Journal 0(00)

composites: Mechanical properties and acoustic emissionstudy. Compo Sci Technol 2006; 66: 3210–3220.

22. Landucci G, Rossi F, Nicolella C, et al. Design and test-

ing of innovative materials for passive fire protection.Fire Saf J 2009; 44: 1103–1109.

23. Wei B, Cao H and Song S. Environmental resistance andmechanical performance of basalt and glass fibers. Mater

Sci Eng A 2010; 527: 4708–4715.24. Ross A. Basalt fibers: Alternative to glass? https://

www.compositesworld.com/articles/basalt-fibers-alterna-

tive-to-glass (2006, accessed 21 April 2018).25. Jamshaid H and Mishra R. A green material from rock:

Basalt fibre – a review. J Textile Inst 2016; 107: 932–937.

26. Botev M, Betchev H, Bikiaris D, et al. Mechanical prop-erties and viscoelastic behavior of basalt fiber-reinforcedpolypropylene. J Appl Polym Sci 1999; 74: 523–531.

27. Bhat T, Chevali V, Liu X, et al. Fire structural resistanceof basalt fibre composite. Compos A Appl Sci Manuf2015; 71: 107–115.

28. Ding L, Liu X, Wang X, et al. Mechanical properties of

pultruded basalt fiber-reinforced polymer tube underaxial tension and compression. Construct Build Mater2018; 176: 629–637.

29. Pawlowski D and Szumigala M. Flexural behaviour offull-scale basalt frp rc beams – experimental and numer-ical studies. Procedia Eng 2015; 108: 518–525.

30. Scalici T, Fiore V and Valenza A. Experimental assess-ment of the shield-to-salt-fog properties of basalt andglass fiber reinforced composites in cork core sandwichpanels applications. Compos B Eng 2018; 144: 29–36.

31. Shi J, Wang X, Wu Z, et al. Fatigue behavior of basaltfiber-reinforced polymer tendons under a marine envir-onment. Construct Build Mater 2017; 137: 46–54.

32. Mousa S, Mohamed HM, Benmokrane B, et al. Flexuralbehavior of full-scale circular concrete members rein-forced with basalt FRP bars and spirals: Tests and the-

oretical studies. Compos Struct 2018; 203: 217–232.33. Zhang X, Gu X and Lv J. Effect of basalt fiber distribu-

tion on the flexural–tensile rheological performance of

asphalt mortar. Construct Build Mater 2018; 179: 307–314.34. Zhang X, Gu X, Lv J, et al. Mechanism and behaviour of

fiber-reinforced asphalt mastic at high temperature. Int JPavement Eng 2018; 19: 407–415.

35. Alves SMC, Da Silva FS, Donadon MV, et al. Processand characterization of reclaimed carbon fiber compo-sites by pyrolysis and oxidation, assisted by thermal

plasma to avoid pollutants emissions. J Comp Mater2018; 52: 1379–1398.

36. Burn DT, Johnson M, Warrior NA, et al. The usability of

recycled carbon fibres in short fibre thermoplastics: inter-facial properties. J Mater Sci 2016; 51: 7699–7715.

37. Liu Y, Farnsworth M and Tiwari A. A review of optimi-sation techniques used in the composite recycling area:

State-of-the-art and steps towards a research agenda. JCleaner Production 2017; 140: 1775–1781.

38. Miracle DB and Donaldson SL (eds) Glass fibers. ASM

Handbook, Vol. 21: Composites. Materials Park, OH:ASM International, 2001, pp.27–34.

39. Kolesov Yl, Kudryavtsev MY and Mikhailenko NY.

Types and compositions of glass for production of

continuous glass fiber (review). Glass Ceram 2001; 58:

197–202.

40. Vas LM, Poloskei K, Felhs D, et al. Theoretical and

experimental study of the effect of fiber heads on the

mechanical properties of non-continuous basalt fiber

reinforced composites. Express Polym Lett 2007; 1:

109–121.

41. Czigany T, Vad J and Poloskei K. Basalt fiber as a

reinforcement of polymer composites. Periodica

Polytech Ser Mech Eng 2005; 49: 3–14.42. Chen K, Zhou N, Liu B, et al. Improved mechanical

properties and structure of polypropylene pipe prepared

under vibration force field. J Appl Polym Sci 2009; 114:

3612–3620.43. Yang L and Thomason JL. Effect of silane coupling

agent on mechanical performance of glass fibre.

J Mater Sci 2013; 48: 1947–1954.

44. Thomason JL. The influence of fibre properties of the

performance of glass-fibre-reinforced polyamide 6,6.

Compos Sci Technol 1999; 59: 2315–2328.45. Deak T and Czigany T. Chemical composition and mech-

anical properties of basalt and glass fibers: A comparison.

Textile Res J 2009; 79: 645–651.46. Hitchon JW and Phillips DC. The dependence of the

strength of carbon fibres on length. Fibre Sci Technol

1979; 12: 217–233.

47. Pardini LC and Manhani LGB. Influence of the testing

gage length on the strength, Young’s modulus and

Weibull modulus of carbon fibres and glass fibre. Mater

Res 2002; 5: 411–420.48. MacFarland TW. Two-way analysis of variance.

New York: Springer, 2011.49. Lim T and Loh W. A comparison of tests of equality of

variances. Comput Stat Data Anal 1996; 22: 287–301.50. Nakamura AM, Michel P and Setoh M. Weibull param-

eters of Yakuno basalt targets used in documented high-

velocity impact experiments. J Geophys Res 2007; 112.

DOI: 10.1029/2006JE002757.51. Weibull W. A statistical distribution function of wide

applicability. J Appl Mech 1951; 18: 293–297.

52. Thomason JL. On the application of Weibull analysis to

experimentally determined single fibre strength distribu-

tions. Compos Sci Technol 2013; 77: 74–80.53. da Costa LL, Loiola RL and Monteiro SN. Diameter

dependence of tensile strength by Weibull analysis: Part

I. Bamboo fiber. Materia (Rio J) 2010; 15: 110–116.54. Bevitori AB, Da Silva ILA, Lopes FPD, et al. Diameter

dependence of tensile strength by Weibull analysis: Part

II. Jute fiber. Materia (Rio J) 2010; 15: 117–123.

55. Summerscales J, Hall W and Virk AS. A fibre diameter

distribution factor (FDDF) for natural fibre composites.

J Mater Sci 2011; 46: 5876–5880.56. Lee SM (ed.) Handbook of composite reinforcements.

New York: Wiley, 1992.57. Otto WH. Relationship of tensile strength of glass fiber to

diameter. J Am Ceram Soc 2006; 38: 122–125.58. Jung T and Subramanian RV. Strengthening of basalt

fiber by alumina addition. Scripta Metallurgica

Materialia 1993; 28: 527–532.

Ralph et al. 11