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^{1}Faculty of Engineering, Sports and Science, University of Bolton, Bolton, UK

^{2}Department of Civil Engineering, University of Salford, UK

- *Corresponding Author:
- Elshafie S

Faculty of Engineering, Sports and Science

University of Bolton, Bolton, UK

**Tel:**441204900600

**E-mail:**[email protected]

**Received Date**: June 27, 2016; **Accepted Date:** July 14, 2016; **Published Date**: July 24, 2016

**Citation: **Elshafie S, Boulbibane M, Whittleston G (2016) Mechanical Performance
of Reinforced Concert with Different Proportions and lengths of Basalt Fibres. J Material Sci Eng 5:271. doi:10.4172/2169-0022.1000271

**Copyright:** © 2016 Elshafie S, et al. This is an open-access article distributed under
the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

**Visit for more related articles at** Journal of Material Sciences & Engineering

This paper discusses the effect of the fraction (0.2-0.3% by volume) and length (22 mm and 24 mm) of basalt fibre on the mechanical properties of concrete. The paper aims to evaluate the effect of different combinations of basalt fibres on the mechanical properties of concrete, as well as identify the best basalt fibre length and content that have the optimum influence on concrete. This paper is considered to be distinct from other research work as it fills the literature gap by presenting new unknown facts and also adds new knowledge. For example, it identifies the best basalt fibre length and content combination that demonstrates an improvement in the mechanical properties of concrete. It suggests the use of a blend of 12 mm short and 24 mm long fibres as they have a significant effect on the mechanical properties of concrete, it validates the results obtained from the laboratory by using a statistical analysis of variance ANOVA software, as well as determine the correlation between the mechanical properties of concrete. The results showed that the optimum basalt fibre length and content that enhanced the mechanical properties of concrete is 24 mm long fibre with content of 0.2% by the total volume of concrete. It also show that changing basalt fibre length and content enhance not only both tensile and flexural strengths of concrete, but also reduce its compressive strength, workability and air content of concrete, as well as maintain the unit weight and modulus of elasticity values. In this context, the incorporation of basalt fibres within the mixture becomes an important parameter for strengthening concrete in the construction industry.

Workability; Unit weight; Air entrainment; Compressive strength; Tensile strength; Flexural strength; Modulus of elasticity

During the process of selecting an appropriate material for construction industry, the mechanical properties of material are considered to play a major role in this selection, which depends strongly upon understanding the material microstructure and components. In this context, it’s important for engineers to possess a deep understanding of how the microstructure is formed, and how the addition of new materials can influence the engineering properties Adam Warren [1].

To achieve this, the mechanical properties of the concrete should be tested. The mechanical properties of the materials play a significant role in defining the characteristic of the concrete and are defined as the characteristics of materials that are revealed when that material is subjected to mechanical loading. One way of improving the mechanical properties of concrete is by adding fibres to the concrete mixture, and determining their influence on the mechanical properties of concrete, such as: compressive strength, tensile strength, flexural strength, elastic modulus and workability.

Previous investigations on reinforcing concrete containing basalt fibres with different proportions have confirmed the possibility of enhancing the mechanical properties of concrete significantly. Addition of basalt fibres will have significant effect on the mechanical properties of concrete, as they are capable of resisting the high alkalinity environment of concrete, can bond chemically with cement, are a noncorrosive material, have high thermal resistance to heat, and also have a high tensile strength. As a result, basalt fibres are considered to be a promising material to improve the concrete strength.

**Materials**

**Basalt fibres: **The chemical composition of the basalt fibres is given
in **Table 1**. This was derived through Van de Velde K [2] analysis. To promote bonding between the fibres and the cement it was initially
intended to use a cross-linking agent and coat the fibres. A justification of
the chosen cross-linking agent will now be discussed. Calcium-Silicate-
Hydrate (C-S-H) reaction outputs have been notoriously difficult to
predict and model. However, recent advancements in this field [3,4] have
opened up the potential integration of chemically compatible additives
to hydrated cement gel structures. Shahsaveri [5] and Sakhavand
[6] provide a concise summary of current research on integrating
polymeric and organic additives into the nano-scale structure of C-S-H.
Their paper (in particular pages 85-88) briefly defines and discusses
the following as possible options in this regard; Poly(methacrylic acid)
(PMA); Poly(4-vinyl benzyl trimethylammonium chloride); Poly(vinyl alcohol) (PVA); Poly(ethylene-co-vinyl acetate) (EVA); Poly(acrylic
acid) (PAA); Polyethylene glycol (PEG);18hexadecyltrimethylam
monium (HDTMA); Dimethyl sulfoxide (DMSO); and Methylene
blue (MB). PVA in particular shows good bonding potential with the
silicates in the C-S-H structure [6]. The accepted bonding model and
associated observations describe hydrogen bonding with slip-stick
mechanisms under applied loads. This infers that there would be an
increase in flexural toughness of the macro-scale material–a beneficial
and complimentary property when considering the other constituent
materials used within the mix. Having established that PVA has
chemical bonding potential with the silicates of the cement hydration
products it should be noted from Table 1 that the greatest constituent
compound of the basalt fibres is silica (SiO_{2}).

Compound | w% in Basalt |
---|---|

Fibres | |

SiO_{2} |
51.6-57.5 |

Al_{2}O_{3} |
16.9-18.2 |

CaO | 5.2-7.8 |

MgO | 1.3-3.7 |

B_{2}O_{3} |
-- |

Na_{2}O |
2.5-6.4 |

K_{2}O |
0.8-4.5 |

Fe_{2}O_{3} |
4.0-9.5 |

**Table 1:** Chemical composition of basalt fibres [2].

**Aggregates:** Fine aggregates were well graded with a fifty-fifty mix
of coarser sand and finer sand. The coarser sand had 32% passing a 600
μm sieve whilst the finer sand had 97% passing a 600 μm sieve when
a grading classification test was performed in compliance with BS EN
1015-1:1999 (BSI, 1999).

A locally sourced coarse aggregate of limestone chippings was selected with a 10 mm nominal maximum size of aggregate. In justification of the selected aggregate size (which deviates from conventionally larger aggregate sizes used in construction practice) it was intended to choose aggregate which was smaller in size than the lengths of basalt fibres used. It was hoped that taking this approach would improve fibre bridging through the concrete composite and encourage fibre fracture failure modes as opposed to fibre pull-out failure modes, thus utilising the full load capacity potential of the fibrelarger aggregate pieces would create discontinuities within the concrete composite.

In essence, the relative sizing between the constituent materials used in the mix was intuitively derived through a ‘scaling of structural strength’ approach as discussed in depth by Bazaant [7].

**Cement: **There are many blends of cement currently available with
the most common ones listed in BS EN 206:2013 (BSI, 2013). Ordinary
Portland Cement (OPC) CEM I was used which avoided any bonding
complexities through additions such as Pulvarised Fuel Ash (PFA). The
use of OPC ensured sufficient C-S-H silicates would be produced to
create hydrogen bonds with the PVA coated basalt fibres.

Eleven concrete mixes were cast with different percentages of Basalt
fibres lengths and proportions, as shown in **Table 2**. In order to assess
the effect of changing basalt fibre content and lengths on concrete
mechanical properties, the research methodology presented in this
section comprises two main steps:

Specimen | Basalt | Basalt Fibre | Basalt Fibre |
---|---|---|---|

Mark | Fibre | 12mm | 24mm |

Content % | Length % | Length % | |

M1(Control Mix) | 0% | 50% | 50% |

M2 | 0.2% | 50% | 50% |

m^{3} |
0.22% | 50% | 50% |

M4 | 0.24% | 50% | 50% |

M5 | 0.26% | 50% | 50% |

M6 | 0.28% | 50% | 50% |

M7 | 0.3% | 50% | 50% |

M8 | 0.2% | 0% | 100% |

M9 | 0.2% | 25% | 75% |

M10 | 0.2% | 75% | 25% |

M11 | 0.2% | 100% | 0% |

**Table 2:** Details of the concrete mixes.

**Stage 1:-** Aims to determine the optimum volume fraction of basalt
fibre on the mechanical properties of concrete by changing the total
basalt fibre content, from mixes (M1-M7) with basalt fibre content
varying from 0.2% to 0.3%, and then determine its influence on the
mechanical properties of the concrete.

**Stage 2:-** Using the optimum volume fraction of basalt fibre
obtained from stage 1, the research is then carried out by changing the
percentage content of basalt fibre lengths (12 mm and 24 mm) using
mixes (M8-M11) by varying the percentage content of basalt fibre
lengths of 12 mm and 24 mm between 0% and 100%. The objective is
to identify the optimum basalt fibre length and content that have an
influence on the mechanical properties of concrete.

In this research, concrete mixing was carried out in a laboratory
at a temperature of 20°C. Both coarse and fine aggregates were stored
in dry conditions, and normal tap water was weighed and added
to the mixture. All materials were mixed in a concrete mixer with a
maximum capacity of 0.06 m^{3}. In order to obtain a good concrete mix,
the following procedure was adopted.

A mixture of fine aggregates consisting of 50% coarse grey sand and 50% fine red sand was added, with a quarter of the water content. After 60 seconds of mixing, the 10 mm limestone coarse aggregate was added to the mixture with another quarter of the water content for another 60 seconds. Afterwards, the cement, including the basalt fibres at 12 mm and 24 mm, was added. The high range water reducer was then added to maintain the content of the water and to ensure the full distribution of particles. Finally, the mixing continued for another 180 seconds.

Mixing is continued until a uniform and well compacted concrete mixture is obtained. After mixing, casting was performed into two layers for each mix and the mixes were vibrated to remove the air content from the concrete. For each of the eleven concrete mixes, the concrete was cast three times in cubes, steel prisms and steel cylindrical moulds.

After casting, the concrete was left to dry for 24 hours at a laboratory room temperature of 20°C before moulding. The cubes, prisms and cylindrical samples were then kept constantly in water at 20°C and tested after 28 days to determine their mechanical properties.

In practice different standards can be followed for testing the properties of hardened concrete, in this study BS EN 12390-3:2009 was used to determine the compressive strength, BS 12390-6:2009 to determine the tensile strength, BS 12390-5:2009 to determine the flexural strength, and BS 1881-121:1983 to determine the elastic modulus of the concrete. For testing the fresh properties of the concrete, the BS EN 12350-2:2009 slump test was used to determine the workability of fresh concrete, BS EN 12350-6:2000 was used to determine the unit weight of fresh concrete, and BS EN 12350-7:2009 was used to determine the air entrainment of fresh concrete. Each test was performed and repeated three times. For this research, a statistical analysis (ANOVA) was used to investigate the variance of the data at each mix assuming a null hypothesis equals 0.05 (i.e., the confidence interval is 95%). This gives a measure of how the data distributes about the mean, and the difference between mixes. In particular, one-way analysis of variance (ANOVA) is used to determine whether there are any significant differences between the means of independent variables. The individual data and ANOVA results are summarised in Table 3. The null hypothesis assumes that there is no difference between the test data (not significant), whereas the alternative hypothesis assumes that there is a difference between them.

A = Accept the null hypothesis

R = Reject the null hypothesis

**Influence of the basalt fibre on the hardened properties of
concrete**

Compressive strength: Many parameters are known to affect the
compressive strength of concrete, most of them being interdependent.
Some of the important parameters that may affect the compressive
strength of concrete are W/C ratio, properties of the aggregates,
air-entrainment, curing conditions, testing parameters, specimen
parameters, loading conditions, and test age. **Figures 1 **and** 2** represent the obtained compressive strength at 28 days for the different concretes
mixes M1 to M11. The compressive strength test is carried out according
to BS EN 12390-3:2009 and is calculated from an average of three
specimens. As can be seen from **Table 3**, the statistical analysis for the
compressive strength shows that changing basalt fibre proportions and
lengths variations leads to reject the null hypothesis, and this statically
means that there is a difference between the means of the values. Hence
changing fibres proportions and lengths has direct and significant effect
on the compressive strength of the concrete.

Description | ANOVA Result |
---|---|

Compressive Strength (28 days) | |

Variation in Fibre Content / 50% 12mm-50% 24mm | R |

Variation in Fibre Lengths / 0.2% fibre content | R |

Tensile Strength (28 days) | |

Variation in Fibre Content / 50% 12mm-50% 24mm | A |

Variation in Fibre Lengths / 0.2% fibre content | R |

Flexural Strength (28 days) | |

Variation in Fibre Content / 50% 12mm-50% 24mm | R |

Variation in Fibre Lengths / 0.2% fibre content | R |

Modulus of Elasticity (28 days) | |

Variation in Fibre Content / 50% 12mm-50% 24mm | A |

Variation in Fibre Lengths / 0.2% fibre content | A |

**Table 3:** ANOVA results.

**Figure 1** shows the effect of changing basalt fibre content on the
compressive strength of the concrete. Using basalt fibres leads to
slight reduction in the compressive strength of concrete for all mixes.
The compressive strength of the concrete reduces with the increase
of the fibre content until 0.26%, after which this value decreased
dramatically by 36% when 0.30% fibre content is used. This result
is in good agreement with other researchers Paverz Ansari [8]
who obtained the same trend, when basalt fibre content increased
from 1% to 1.5%. Mustapha Abdulhadi [9] results also showed
that the compressive strength of the cubic concrete reduces when
increasing the basalt fibre content from 0.9% to 1.2% at 28 days. This
considerable concrete compressive strength reduction is attributed to
the following factors: Firstly, adding fibres to the concrete mix will
reduce the cement paste cohesiveness, which plays a significant role
in changing the compressive strength of the concrete. In particular,
the compressive strength of concrete depends mainly on the cement
matrix, and the effect of enhancing concrete compressive strength
is not prominent by adding basalt fibre Jianxun Ma [10]. Secondly,
as the fibre content increases, the coarse aggregate is decreased to
maintain a constant mixture volume. Decreasing the coarse aggregate
content has a direct impact on compressive strength Khaled Soudki
[11]. Thirdly, as the volume content of the basalt fibres is added, the presence of voids caused by the use of higher fibre volume of basalt
fibres increases, causing reduction in the compressive strength of the
concrete Tehmina Ayub [12].

In addition, as seen in Figure 1, the average compressive strength
development of concrete mixes M1 – m^{3} shows these mix proportions
meet the strength requirement for high concrete strength, achieving,
on average, 41 MPa, although the highest compressive strength value
was achieved when concrete contained no fibres in M1, achieving an
average strength of 48 MPa. **Figure 2** shows the effect of changing basalt
fibre lengths on the compressive strength of the concrete for different
mixes, M8-M11. The highest compressive strength achieved by all
mixes in this series was for mixture M8, containing pure 100% 24 mm
basalt fibre, while the remaining mixes, containing a mixture of 24 mm
and 12 mm basalt fibres, achieved various strengths ranging from 28-40
MPa. This noticeable improvement in concrete compressive strength
when using longer fibres 24 mm is in also in a good agreement with
other researchers observation Jerin Johnson, 2016, Palchik P.P [13,14].
Their results show using longer basalt fibres of 24 mm leads to improve
the concrete compressive strength significantly. In contrast, it is noticed
that using 100% pure basalt fibre of 24 mm and 12 mm, such as in
mix M8 and M11, has a greater effect on the compressive strength of
the concrete than using a mixture of 24 mm and 12 mm with various
percentages, as in M9 and M10, on the concrete compressive strength.
This may be attributed to the effect of longer basalt fibres of 24 mm on
concrete to create a longer anchorage to hold concrete particles firmly,
which will also have a significant effect on the tensile and flexural
strength of the concrete.

**Figure 3** shows the main effect of the optimum basalt fibre content
and length on the compressive strength of the concrete. Mixing basalt
fibres with concrete has not enhanced the concrete compressive strength,
as concrete is naturally very strong in compression. When concrete is
compressed, the interface only serves to transfer compressive stresses
from one aggregate to the next; however, under tension, the aggregates
try to pull apart. Hence, concrete fails under small stress in tension, but
remains strong in compression Rakshita Nagayach [15].

**Tensile strength:** The tensile strength test results for the different
concretes mixes, M1 to M7 and mixes M8 to 11, at 28 days, are
summarised in both **Figures 4** and **5**. The statistical analysis for the
tensile strength results using **Table 3** show that changing basalt fibre
proportions leads to accept the hypothesis, while changing its length
0 variations leads to reject the null hypothesis, which means there is a statistical difference between the means of the values when changing
the basalt length; however, changing the content has no significance on
the tensile strength.

The tensile strengths for different basalt fibre mixtures with
different proportions, M1 to M7, and lengths, M8–M11, at 28 days, are
shown in Figures 4 and 5. As presented in **Figure 4**, Mixture 1 with 0%
fibre content had an average tensile strength of 2.3 MPa, while all other
mixes, apart from M5, achieved a higher tensile strength than the
control mixture M1, reaching a tensile strength of 2.8 MPa on average.
The optimum tensile strength was achieved when mixing fibre content
of M2 0.2% of the total volume of the concrete mix. The test was then
carried out by using the optimum basalt fibre content of M2 0.2 % and
changing the basalt fibre lengths percentages of 12 mm and 24 mm
to precisely determine the effect of changing the length of fibres on
tensile strength of concrete. **Figure 5** shows that Mixture 8, with 100%
24mm basalt fibre length, achieved the highest tensile strength with an
average of 3.2 MPa. The tensile strength of the concrete increased by
17% and 28% versus the control mixture of 0% fibres when using basalt
fibre content of 0.2% with 24 mm long fibres, respectively. Tensile
strength results obtained by Yihe Zhang [16], Elba Helen George [17]
show the same trend, as both authors used basalt fibres with different
dosages, and that resulted in improving the tensile strength of concrete.
Jianxun Ma [10] experimental work results showed that changing the
basalt fibre lengths enhanced the tensile strength of the concrete. This increase in is due to the fact that basalt fibres reduced crack growth
and consequently led to higher failure loads. The fibres created a bridge
through the split portions of the cylinder and prevented the two parts
from splitting Khaled Soudki [11]. It is also noticed that longer fibres
(24 mm) improved the tensile strength of the concrete much more than
12 mm fibres. This is due to the high tensile strength of these fibres and
their ability to form longer bridges to hold concrete particles. On the
other hand, **Figure 6** shows the effect of fibres in concrete. The tensile
strength of concrete is obviously improved by adding basalt fibre,
when compared with normal concrete 0% fibres. The splitting tensile
strength of concrete increased with increase in the content and length
of basalt fibre.

**Flexural strength: **The flexural strength test results for the different
concretes mixes, M1 to M7 and mixes M8 to M11, at 28 days, are
summarised in both **Figures 7 **and** 8**. The statistical analysis for the
flexural strength results using **Table 3** show that changing basalt fibre
proportions and length variations leads to reject the null hypothesis,
which means there is a statistical difference between the means of the
values; hence, changing fibre proportions and lengths has a significant
effect on the flexural strength of the concrete. The test for the flexural
strength development of concrete was also carried out at different ages
of seven days, 28 days, 84 days, and 168 days using the optimum basalt
fibre that has influence on the flexural strength of the concrete. A three
point bending test was used using a 150 × 150 × 750 mm prism. The
flexural strength of the concrete under the three point bending test was
calculated using the following formula:

(1)

Where:

F is the load (force) at the fracture point (N)

L is the length of the support span

b is width

d is thickness

σ is the flexural strength in (MPa)

The flexural strength development of concrete mixed with different
proportions of basalt fibre is illustrated in **Figure 7**. It is evident that
increasing basalt fibre content increases the flexural strength of the
concrete when compared to the control mixture, M1, 0% fibre content.
The optimum basalt fibre content was achieved when using basalt
content of M2, 0.2%, while mixture M1 0% basalt fibre achieved the
lowest value. The flexural strength ranged from 1.3 MPa to 2 MPa when
changing the basalt content, while this value increased when changing
the length of the fibres, ranging from 1.5 MPa to 2.5 MPa as can be seen
from **Figure 8**. The **Figure 8** also shows that the flexural strength of the
concrete increased sharply when using basalt fibre content mixtures of
M2, m^{3} and M4, 0.2%, 0.22%, 0.24%, respectively, at 28 days and then
gently decreases afterwards to give a lower strength values when using
contents of M5, M6, and M7, 0.26%, 0.28%, and 30% respectively. The
increased number of fibres that cross the crack surface is one of the
main reasons to increase the flexural strength of the concrete, as they
reduce the crack opening. Kayali [18], Zollo [19] also reported that
the presence of basalt fibre with different contents has a contribution to the flexural strength of concrete. The test was then carried out by
using the optimum basalt fibre content of M2, 0.2 %, with changing
the basalt fibre lengths percentages of 12mm and 24mm, to precisely
determine the effect of changing the length of fibres on flexural strength
of concrete. According to **Figure 8**, Mixture 8, with 100% 24mm basalt
fibre length, consistently displayed the highest flexural strength with
an average of 2.3 MPa. The differences in the flexural strength due to
the change of the length of the fibres were considerable and average
values of 2.3 MPa, 2.1 MPa and 1.7 MPa were recorded when using
different lengths of fibres. In contrast, using longer fibres, such as 24
mm, resulted in increasing the flexural strength of fibres, as can be seen
from **Figures 7 **and** 8**, but, when using a blend of 12 mm and 24 mm
fibres, the flexural strength remained the same, achieving an average
value of 2 MPa. This is perhaps because of the ability of the longer
fibres that cross the crack region to reduce the concrete cracks more
significantly than the short fibres, as they are able to transfer load more
efficiently, and also redistribute stress. The longer fibres take to transfer
stress, the longer time it takes for the crack to develop; hence, the higher
the tensile and flexural strength that can be reached. The same result
was achieved by Jianxun Ma [10], who concluded that increasing the
fibre length and content will increase the flexural strength of concrete.

In general, the flexural and tensile strength of the concrete
reinforced basalt fibre are increased with the increase dosage and length
of the basalt fibre. When the fibre content is 0.2% by total volume, which
is equal to 0.27 kg/m^{3} and the basalt fibre length is 24 mm, It appears
that for mixes with 0.2% of fibre content and length of 24 mm achieved
an overall higher flexural and tensile strength in comparison to other
mixes investigated in this analysis. As a result, the use of basalt fibres is
regarded as a strengthening material for the concrete, and can have a
significant effect on the concrete structures. On the other hand, **Figure 9** show the main effect of fibres in the flexural strength of concrete. From
the graph, it is clear that the flexural strength of concrete is increased
by adding basalt fibre, when compared with normal concrete 0% fibres.
The flexural strength of concrete increased with increasing the content
and length of basalt fibre. In Particular, mixing concrete with 24 mm
basalt fibre length will have a larger effect on the flexural strength of the
concrete when compared with using different fibre lengths.

The flexural strength development of concrete at different ages of
seven days, 28 days, 84 days and 168 days using the optimum basalt
fibre mixture (M8) that has influence on the flexural strength of the
concrete is illustrated in **Figure 10**. The **Figure 10** shows that the flexural
strength of the concrete increases sharply when increasing the age of the
test, reaching its minimum value at seven days, and maximum value at
168 days. This is due to the hydration of cement, as well as the chemical reaction on the concrete, as they require time to formulate, which helps
concrete gain more strength. The presence of basalt fibres also plays
a major role, as they enhance the flexural strength of the concrete.
Using the same figure, it can be seen that there is a big difference in
concrete strength at the different testing ages of seven days, 28 days, 84
days and 168 days. The lowest values were registered at seven days, with
similar average values of 2.2 MPa recorded after 28 and 84 days, while
the largest strength average values of 2.4 MPa were recorded after 128
days. The rate of the flexural strength increase with days is considerably
fast, ranging, on average, from 1.3 MPa to 2.4 MPa. In other words,
the flexural strength development between seven and 168 days was not
only influenced by the presence of basalt fibres, but also by the curing
time of the concrete.

Modulus of elasticity: The statistical analysis for the modulus
of elasticity results using **Table 3 **show that changing basalt fibre
proportions and length variations leads to accept the null hypothesis,
which means there is no statistical difference between the means of the
values; hence, changing fibre proportions and lengths has no significant
effect on the modulus of elasticity of the concrete. The elastic modulus
is calculated within elastic range in its ascent in stress-strain curve and
is expressed in function of compressive strength of concrete. **Figure 11**,
shows the elastic modulus for all mixes. Based on the graph in **Figure 11**,
the modulus of elasticity for all mixes ranged from 12000 MPa to 21000
MPa. Mixture M8 (100% 24 mm basalt fibre with 0.2% content) had the
highest modulus of elasticity, while Mixture M1 (the control mixture) had the lowest modulus of elasticity. Basalt fibres slightly increased
the modulus of elasticity of the concrete. This may be attributed to the
effect of fibres to enhance the concrete density, as a result improving
the concrete toughness and resistance to deformation. The modulus of
elasticity achieved by M2, m3 and M4 was 29%, 1.15%, and 33% above
of the control mixture, no fibres, respectively. The greatest increase in
the modulus of elasticity occurred between m3 and M4, followed by a
gradual decrease from M4 to M6. The general value of the modulus of
elasticity mixed with different fibres increased and decreased slightly
compared to the control mixture. This indicates that basalt fibre had
not contributed majorly to the modulus of elasticity of the concrete.
This result is possibly due to the strong ability of concrete to resist the
compressive strength load when it is applied, also due to the inability of
fibres to resist the vertical load when applied. Ramakrishnan [20] also
reported that basalt fibre has no effect on the modulus of elasticity of
concrete.

**Correlation between the compressive strength and tensile
strength:** The relationship between the compressive and tensile
strengths is presented in **Figure 12**. No correlation can be seen between
those two concrete properties, as found R2 values were 0.03 and 0.15
for mixing concrete with the optimum content and optimum length,
respectively. This may be attributed to the use of different basalt
mixtures between M2 and M8. For M2 mixture, a blend of 50% of 12 mm and 50% of 24 mm basalt fibre lengths was used, while, for M8,
only 100% 24 mm basalt fibre length was used. As a result, this affected
the relationship between the two concrete properties.

**Correlation between the compressive strength and flexural
strength:** **Figure 13** shows the correlation between the influence of
basalt fibres at optimum length and content on concrete compressive
and flexural strengths. There seems to be a strong correlation between
using optimum concrete length and content, M2 and M8, as found from
the R2 coefficient values being 0.6 and 0.5, respectively. In addition,
all data points in the graph seem to fit approximately in a straight
line, which shows a linear and strong relationship between these two
concrete properties.

**Correlation between the tensile strength and flexural strength: **The relationship between the concrete tensile and flexural strength
is presented in **Figure 14**. No correlation can be seen between those
two concrete properties, as found R2 values were 0.0853 and 0.5
for optimum basalt length M8 and optimum basalt content M2,
respectively. However, by using the graph, the data points seem to fall
in the same range between tensile strength values of 2.3 MPa–3.6 MPa
and flexural strength values ranging from 1.8 MPa–2.3 MPa. It is also
noticed that higher values were recorded when using optimum basalt
fibre M8, as 100% longer fibre 24mm was used, which increased the
values of the tensile and flexural strengths, respectively.

**Correlation between the compressive strength and modulus
of elasticity:** In **Figure 15**, the relationship between the compressive
strength and modulus of elasticity for optimum basalt fibre length (M8)
and content (M2), as well as the corresponding best fit linear line, are
shown. As in the case of the correlation between the compressive and
modulus of elasticity, it is noticed that there is a positive relationship
between the two variables, as their corresponding R2 values are 0.9
and 0.4, respectively; however, the distribution of the data points
is relatively high. There seem to be no consistency in increasing and
decreasing values between the two parameters by using Mixtures
M8 and M2, which indicates that there is no correlation between the
compressive and modulus of elasticity of concrete when mixed with
different mixtures.

**Workability:** From the results presented at **Figure 16**, the target
slump values for all basalt fibre mixtures ranged from 85 mm to 70 mm.
It is also noted that the slump value reduced with increasing the basalt
fibre content. These results were also obtained by Ali Elheber [21], N.
Shafiq [22] and can be seen plotted in Figure 16. This is mainly because
basalt fibre has the ability to absorb certain moisture when added to
the concrete, causing a reduction in the slump of the concrete, which
also improves the concrete permeability, as it reduces the pore gaps
in the concrete microstructure Jianxun Ma [10]. On the other hand,increasing the content of the fibres in concrete enhances the mass
added to the mixture, which leads to a decrease in the flow ability of
the concrete Tumandir [23]. From the test result observed, there was
no aggregate segregation and full homogeneous mix was observed
from the test. Also, the result showed that adding different basalt fibre
content between 0% to 0.30%, had a major effect on the concrete slump.
In general, the concrete remained in good condition and remained
workable after the addition of basalt fibres.

**Unit weight: Figure 17** shows the mean density recorded by each
concrete mixture, from M1 to M7. The density of the specimens ranged
from 2400 to 2415 kg/m^{3}. This lies within the range of 2200 to 2600 kg/
m^{3}, specified as the density of normal weight concrete Neville [24]. The
graph shows that, as the content of the basalt fibre increases, there is
a slight increase in the unit weight of the concrete due to the fact that
basalt fibres are the lightest component in the concrete mixture and
their effect on the concrete unit weight can hardly be noticed. This is
similar to the results obtained by Thumandhir [23], who indicated that
basalt fibres have little effect on the concrete unit weight, as can be seen
from **Figure 17**.

**Air entrainment: **The air content of the basalt fibre-reinforced
concrete ranged from 3.7% to 4.8%, as shown in **Figure 18**. The control
mix (M1) achieved the highest rate of air content, as expected, while
M7 with basalt fibre content of 0.30% recorded the lowest air content
in concrete. The air content results indicate that, as the basalt fibre
content increases (M1-M7), the air content decreases. This is due to the
ability of fibres to fill voids in concrete when higher content of fibres is added to the concrete mixture. This result was also achieved by O.
Gencel [25], who found that the void content of the concrete reduces
with increasing the fibre content. It is also evident that the concrete
mixture with longer fibre length (100% 24 mm), Mixture 8, had
slightly lower air content values than the concrete with shorter fibres
(M9–M11). Air entraining provides an additional benefit to concrete
mixes. This is mainly because it has a major influence on enhancing the
workability of the concrete as it acts as air bubbles, which reduce the
friction between the cement and the surrounding aggregate. Therefore,
this reduces the interlocking and cohesion between the particles and
also reduces the content of the water in concrete; hence, improving the
concrete’s workability. To understand this phenomenon, **Figure 19** is
given to illustrate the correlation between the workability and the air
content in concrete. By using Figure 19, the graph shows that, as the
air content in the concrete increases, the slump of the concrete also
increases. And, when the air content value is between 4-5% of the total
concrete volume, the corresponding slump is approximately 75 mm.
This result was achieved by both Lerch [26] and myself, as can be seen
from the graph below. As mentioned earlier, it is noted that, when more
basalt fibre content is added to the concrete mixture, the values of the
slump and air content decrease. In contrast, the relationship between
the slump and air content is completely different, as there is a linear
relationship between the two features, as can be seen from **Figure 19**.
By using the same **Figure 19**, there was a slight difference between the
author’s and Lerch’s values; this is due to the difference between the
aggregate sizes that were used by the authors. In general it can be said
that the properties of fresh concrete can be significantly improve by the
addition of fibre, especially when controlling air content, unit weight
and workability.

In this paper, the fresh and the hardened mechanical properties of concrete were investigated using different lengths of basalt fibres of 24 mm and 12 mm. This comprehensive investigation used analytical software, ANOVA, to analyse the results, and validated these values against the results obtained from the laboratory samples. The presented data indicate that the optimum basalt fibre content to have the most influence on concrete is 0.2% by the total volume of concrete, using basalt fibre length of 24 mm. It also show that changing basalt fibre length and content enhanced not only both tensile and flexural strengths of concrete, but also reduced its compressive strength, workability and air content of concrete, as well as maintain the unit weight and modulus of elasticity values. These results were also confirmed by using ANOVA software, as the analysis software indicated that change of the proportional and length of basalt fibre has significant effect on the tensile and flexural strengths, but has no major effect on the modulus of elasticity and compressive strength. A reasonable correlation between compressive strength and flexural strength was noticed, as well as between compressive strength and the modulus of elasticity for optimum basalt fibre length and content.

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