Cement and Concrete Composites 74 (2016) 182e190

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Cement and Concrete Composites

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Influence of basalt fibres on free and restrained plastic shrinkage

John Branston a, Sreekanta Das a, *, Sara Y. Kenno b, Craig Taylor b
a
University of Windsor, Windsor, Ontario, Canada
b
MEDA Limited, Windsor, Ontario, Canada

a r t i c l e i n f o a b s t r a c t

Article history: Early-age cracking due to plastic shrinkage is often attributed to reducing the durability of concrete
Received 1 October 2015 structures. The objective of this paper is to evaluate the potential use of chopped basalt fibres in pre-
Received in revised form venting these cracks. Testing was undertaken to measure the magnitude of shrinkage strain that de-
15 July 2016
velops in unrestrained specimens, and the severity of cracking that occurs when shrinkage is restrained.
Accepted 1 October 2016
Available online 4 October 2016
Results indicate basalt fibres are effective in preventing cracks by reducing the magnitude of free
shrinkage, and by restricting the growth of cracks if they do occur. The latter mechanism is more
prominent when the w/c ratio is decreased.
Keywords:
Basalt fibre
© 2016 Published by Elsevier Ltd.
Minibars
Basalt fibre reinforced concrete
Durability
Plastic shrinkage cracking

1. Introduction which it can be replaced by rising bleed water. When restrained,

shrinkage will induce tensile stresses. If those stresses exceed the
Chopped basalt fibre is a relatively new concrete reinforcing tensile strength of the concrete, it will crack. Restraint is generally
material, with excellent mechanical properties and an environ- present to at least some degree in practical applications by internal
mentally friendly manufacturing process. The majority of research factors, such as rebar and aggregate, or by external factors, such as
into basalt fibre reinforced concrete has focused on its mechanical connections to walls and columns. Although initially shallow,
properties [1e3]. In these studies, the results do not suggest the plastic shrinkage cracks can grow to full-depth over time [7]. The
fibres are particularly effective in enhancing the post-cracking cracks are not only unsightly, but they allow the penetration of
response of the concrete, which is one of the most significant deleterious substances and can lead to the rapid deterioration of
benefits of fibre reinforcement [4]. Previous research has also structures; most notably the penetration of water and chlorides
indicated basalt fibres without any protective coating suffer from a enabling the corrosion of embedded steel reinforcement. Shrinkage
lack of long-term durability in the alkaline environment of concrete cracking is generally most prominent in structures with a large
[5,6]. Until this problem is resolved, a useful application of the fibre surface area to volume ratio, including: slabs-on-grade, tunnel
in its current state of development could be in enhancing the linings, and repair overlays. One prominent example is the reduced
durability of concrete by preventing early-age cracking due to serviceability of bridge decks due to early-age cracking. A number
plastic shrinkage. It seems probable the fibres could be effective in of reports published from various state departments of trans-
this regard before any potential degradation negates their benefit. portation (DOTs) in the United States of America suggest that
Plastic shrinkage refers to the volumetric contraction of cement- shrinkage is a major contributing factor to early-age cracking
based materials that occurs during the first few hours after place- [8e11]. In these reports, shrinkage refers to the strain that develops
ment, while the material is in a plastic state. The contraction is at both an early-age (plastic shrinkage), and over a longer duration
driven by a combination of autogenous mechanisms and capillary after the concrete has hardened (drying shrinkage). However, ac-
pressure that develops in the pore structure near the surface when cording to the Transportation Research Board [12], the mechanisms
the rate of water evaporating from the concrete exceeds the rate at that lead to plastic shrinkage cracks do not explain full depth
cracks, and therefore, it is probable drying shrinkage can propagate
plastic shrinkage cracks. Since cracks in concrete can propagate at a
* Corresponding author.
stress lower than that required to initiate them [13], the control of
E-mail address: sdas@uwindsor.ca (S. Das). plastic shrinkage cracking should be a key design consideration in

http://dx.doi.org/10.1016/j.cemconcomp.2016.10.004
0958-9465/© 2016 Published by Elsevier Ltd.
 J. Branston et al. / Cement and Concrete Composites 74 (2016) 182e190 183

regards to mitigating cracking at later ages, and in-turn, minimizing measurement of strain when the specimens are unrestrained (free
long-term maintenance costs. shrinkage), and the measurement of crack severity in specimens
It has been well established that the addition of short, randomly that are restrained from shrinking with a rectangular restraint
distributed fibres to concrete is an effective method in mitigating element. The primary importance of this study lies in the fact there
plastic shrinkage cracking. The fibres are effective in this regard for is minimal literature addressing the usefulness of basalt fibres for
two reasons: first, they reduce the overall shrinkage strains and early-age crack control in concrete. Secondly, the work provides
lower the possibility of tensile stresses exceeding tensile strength, some insight on test methods for measuring free and restrained
and second, the fibres are able to restrict their development if they plastic shrinkage, for which there seems to be a lack of any one
do occur [14]. According to Naaman et al. [15], the addition of any generally accepted test method.
fibre with a diameter smaller than 40 mm, an aspect ratio above
200, in volume fractions of 0.2%e0.4%, should effectively eliminate 2. Experimental procedure
plastic shrinkage cracking in concrete. Hence, it is unsurprising
such a wide variety of fibres have been shown to be beneficial in 2.1. Environmental chamber
this regard, including: steel, glass, various synthetic fibres (poly-
propylene, polyethylene, polyvinyl, and carbon), and various nat- All testing was completed in an environmental chamber that
ural fibres (sisal, coconut, flax, and cellulose) [15e20]. However, the operated at a temperature of 48  C (±2  C) and relative humidity of
mechanisms by which different fibres reduce plastic shrinkage 15% (±3%). This was achieved by connecting a heater fan to a
strain, and the resultant cracking, is not as thoroughly studied. This temperature and humidity controller capable of reading tempera-
is an important consideration in order to understand the circum- ture accurate to ±1.5  C and relative humidity to ±2%. These con-
stances in which the use of a particular type of fibre is most ditions resulted in an evaporation rate of approximately 0.75 kg/
effective. m2/h. The environmental chamber is depicted in Fig. 1.
Only one study, completed by the Florida Department of
Transportation (FDOT), could be found in regards to the usefulness 2.2. Free shrinkage testing
of basalt fibres on early-age cracking due to shrinkage. The study
concluded that stiff fibres, including basalt, steel, and glass, should The test setup for the free (unrestrained) shrinkage testing was
not be used for early-age crack control due to drying shrinkage, developed based on similar methods used by other researchers
since it was evident their stiffness initiated cracking sooner, and the [23,24]. Concrete specimens were 500 mm in length and 80 mm by
cracks were wider [21]. The conclusions were based on the results 80 mm in cross-section. The interior of the forms were lined with a
of the ASTM C1581 [22] test method, in which a steel ring is used as thick polypropylene sheet (vapour barrier) that was lightly coated
a restraint element. In that case, the poor performance of the stiff with Teflon spray. A Teflon plate was placed at one end of the form
fibres may be due to the relatively lower ability of the fibres to bend with a 9.5 mm diameter bolt threaded into it that extended 30 mm
and align with the circumference of the cracks that develop due to into the form. The Teflon plate was loose fitting so that it could
the circumferential shrinkage stress induced by the ring, in com- move with minimal resistance. As shrinkage occurred, the plate
parison with the other more flexible fibres used (e.g. poly- was moved by the bond between the bolt and the concrete. The
propylene). The results in that study may not be a good displacement of the plate was measured with a 5 mm linear vari-
representation of the effectiveness of basalt fibres in structures able differential transformer (LVDT) that was accurate to 5 mm. A
with more typical rectangular geometry, where there is greater 25 mm thick piece of foam was placed behind the Teflon plate so
probability of the fibres bridging cracks in a more favorable that movement due to thermal expansion was also possible. The
orientation. The test method has previously been criticized for forms were placed in the environmental chamber and data was
producing an unrealistic stress field in regards to repair overlays collected for 4 h. Free shrinkage test results reported in this study
[14]. are the mean values calculated based on three specimens per fibre
The purpose of the experimental work reported in this paper is dosage. The setup is illustrated in Fig. 2.
to evaluate the influence of three different types of basalt fibre on
the plastic shrinkage of concrete. The basalt fibres used in this study 2.3. Restrained shrinkage testing
are: bundle dispersion fibres (BD), filament dispersion fibres (FD)
and minibars (MB). The influence of the fibres is quantified by the The test setup for restrained shrinkage testing closely followed

Fig. 1. Environmental chamber.

184 J. Branston et al. / Cement and Concrete Composites 74 (2016) 182e190

Fig. 2. Free plastic shrinkage test setup.

the method proposed by Banthia and Gupta [14], with two excep- reported in this study are the mean values calculated based on
tions: the length of the restraint element (Fig. 3a) was increased three specimens per fibre dosage.
from 300 mm to 500 mm to match that of the free shrinkage
testing, and the thickness of the mortar overlay was reduced from 2.4. Materials and specimen preparation
60 mm to 35 mm to represent a typical concrete cover for the
application of the results directly to a rehabilitation project in the All mixes were made with general use limestone (GUL) Portland
field. The restraint elements had an average 28 day compressive cement conforming to CSA A3001 [25], and regular drinking water.
strength of approximately 60 MPa. The mortar overlay was placed Fine aggregate was local river sand with a fineness modulus of 2.7,
over the restraint element and then the form was placed in the and the coarse aggregate was well-graded with a maximum size of
environmental chamber. The form was carefully removed after 1.5 h 19 mm. The cement had a Blaine fineness of 488 m2/kg, and con-
in order to increase the exposed surface area of the concrete, and sisted of 9.5% limestone (94% CaCO3 in limestone). The chemical
in-turn, the severity of the cracking. Fig. 3b depicts the develop- composition of the cement can be found in Table 1.
ment of cracks after removing the specimen from the environ- The cement fineness and chemical composition have a direct
mental chamber after a total of 4 h. The cracks were measured influence on shrinkage, and are further discussed in section 3.2.
using a 240 magnification digital microscope. The total area of all Mortar was generally used in this study to increase the magnitude
cracks on the surface for each specimen was measured, and the of shrinkage strain and in-turn, cracking severity, so that the in-
largest crack width was recorded. Restrained shrinkage test results fluence of the fibre could be more readily measured. Table 2 shows

Fig. 3. Restrained shrinkage testing.

Table 1
Portland cement type GUL chemical composition (%).

Loss on ignition SiO2 Fe2O3 Al2O3 CaO Free CaO MgO SO3 K2O Na2O TiO2

4.8 18.2 2.76 4.5 62.3 1.5 3.1 3.47 0.45 0.22 0.21

Note: Chemical composition as provided by manufacturer.

 J. Branston et al. / Cement and Concrete Composites 74 (2016) 182e190 185

Table 2
Mass proportions of concrete mixes used.

Designation Cement Water Fine Aggregate Coarse Aggregate Super-plasticizer Description

M1 1 0.5 2 0 0 Control mix

M2 1 0.35 2 0 varied Low w/c ratio
M3 1 0.5 2 2 0 Add coarse aggregate
M4 1 0.5 1 0 0 Increased cracking
M5 1 0.35 1 0 varied Low w/c ratio

the proportions (by mass) of each type of mix used in this work, Table 3
along with a description indicating the purpose of the mix. Fibre dosages and test matrix.

Cement to sand proportions of 1:2 (M1 and M2) and 1:1 (M4 Designation Fibre type Length (mm) Dosage
and M5) were selected in an attempt to produce results comparable Volume (%) kg/m3
to other researchers using different fibres [17,20,24,26]. A w/c ratio
PM No fibre 0 0
of 0.5 was selected as a control to produce a mix with a high flow.
BD-25-0.05 Bundle dispersion 25 0.05 1.3
For that reason, the mix would generally not be used in practical BD-25-0.1 0.1 2.6
applications. However, it is useful for laboratory testing since it BD-25-0.3 0.3 7.8
results in high shrinkage strain and promotes cracking, which FD-25-0.05 Filament dispersion 25 0.05 1.3
makes the effect of the fibres easier to measure. The purpose of FD-25-0.1 0.1 2.6
FD-25-0.3 0.3 7.8
reducing the w/c ratio was for insight on the benefit of the fibres in FD-12-0.05 Filament dispersion 12 0.05 1.3
a more realistic setting, where it is almost certain their effect on FD-12-0.1 0.1 2.6
workability will need to be accounted for with the use of super- FD-12-0.3 0.3 7.8
plasticizer. Consequently, the effect of superplasticizer in this MB-43-0.3 Minibar 43 0.5 6.2
MB-43-1.0 1.0 20
context should also be studied. Superplasticizer dosages in Table 2
listed as ‘varied’ refers to the increasing dosages required to pro-
duce an equivalent flow for increasing fibre dosages. It is well un-
derstood that fibres have an adverse effect on the flow (or mix time reached 3 min. Water (and plasticizer mixed in with the
workability) of concrete, and thus, greater quantities of super- water as necessary) was then added and the mix continued for
plasticizer were required as fibre dosages increased (further another 2 min. In all cases, the fibres dispersed without any
explained in section 3.1). Likewise, the effect of the fibres in a noticeable balling or clumping. The flow of the mortar mixes was
concrete mix with coarse aggregate (M3) is also considered as measured as per ASTM C1437 [27].
additional way of producing data more representative of actual
application. 3. Results and discussion
Three types of basalt fibre were evaluated: filament dispersion
(FD), bundle dispersion (BD) and minibars (MB). Filament disper- 3.1. Mortar flow
sion fibres disperse into individual filaments during mixing,
whereas bundle dispersion fibres have a coating (sizing) that keeps The effect of the 25 mm filament dispersion fibres on the flow of
the filaments together as a bundle. Minibars are an epoxy based the control mix M1, and the reduced w/c ratio max M2, is shown in
polymer reinforced with basalt filaments; essentially a scaled down Table 4, since they had the greatest effect of all fibres tested. In this
version of basalt fibre reinforced polymer rebar. These differences table, Di is the initial diameter of the mortar, and Df is the diameter
are depicted in Fig. 4. of the mortar after dropping the plate 25 times within 15 s.
The filament and bundle dispersion fibres consist of filaments Results for other types of fibre followed the same trend, and
16 mm in diameter, and the minibars are constructed with filaments thus, are not shown in this table. However, it should be noted that
17 mm in diameter. A summary of the fibre dosages used in this the order from greatest to least in terms of their effect on the flow
study is shown in Table 3. Designations are labelled according to was: FD-25, FD-12, BD-25, and MB-43. In cases where the mortar
fibre type, fibre length, and dosage. For example, the designation spilled off the plate before being dropped 25 times, the flow could
BD-25-0.1 indicates basalt bundle dispersion fibres of 25 mm not be accurately calculated. The effect of the fibres is evident by
length at a dosage of 0.1% by volume. the decreasing value of Di with increasing fibre dosages in M1. The
Cement and aggregate was mixed dry for 1 min. Next, fibres number of drops required to cause the mortar to spill increased
were slowly added by hand, and the dry mix continued until total from 17 without fibre, to 22 when a fibre dosage of 0.05% was used.

Fig. 4. Difference in dispersion of fibres used in this study.

186 J. Branston et al. / Cement and Concrete Composites 74 (2016) 182e190

Table 4 calculation, based on the chemical composition provided in Table 1.

Flow of mortar. Such an analysis may be of interest if studying the effect of fibres in
Mix FD-25 dosage Super-plasticizer Di Df Flow low w/c ratio mixes where autogenous shrinkage mechanisms are
designation (%) (mL) (mm) (mm) (%) more prominent. Moreover, the relatively high fineness of the
M1 0 0 100 230* 130 cement used in this study will increase the rate of chemical
0.05 0 90 230* 156 shrinkage, but not the magnitude [28,29]. It could be of interest to
0.1 0 85 230 171 examine the effect of cement fineness on water demand, with the
0.3 0 70 195 179
intent of optimizing workability (e.g. minimizing superplasticizer).
M2 0 40 75 200 167
0.05 45 75 200 167 Notwithstanding the mechanisms causing shrinkage, further dis-
0.1 60 70 200 186 cussion will focus on the relative influence of the basalt fibres. The
0.3 110 70 195 179 mean shrinkage strains after 4 h are depicted in Fig. 6 for all fibre
Note: * indicates mortar spilled off the plate before 25 drops. dosages used in the control mix M1. The error bars represent one
standard deviation on either side of the mean.
Based on their work with steel fibres, Mangat and Azari [26]
At fibre dosages of 0.1% and 0.3% it did not spill. In the case of M2, suggested that the reduction in shrinkage strain is the result of a
superplasticizer was added to each mix in an attempt to produce an frictional force between the fibre-cement interface that restrains
equivalent flow for all fibre dosages. To achieve this, greater dos- the movement of the cement as it slides past the fibres. Experi-
ages of superplasticizer were required as fibre dosage increased. mental results shown in Fig. 6 would strongly agree with this
The underlying idea being that the most efficient use of materials explanation. The increase in contact surface area between fibres
would be using the smallest amount of superplasticizer to achieve a and cement when using filament dispersion fibres, as opposed to
minimum flow, or workability. In this case, that was a flow of bundle dispersion fibres or minibars, should theoretically increase
approximately 170%. frictional resistance, and thus, provides a probable explanation for
the results in Fig. 6. Building on this logic, it is not clear as to why
3.2. Free plastic shrinkage the 12 mm filament dispersion fibres had less effect than the
25 mm filament dispersion fibres; though the differences may
Preliminary testing showed that rapid increases in free simply be the result of variation in the data. Reduction in free
shrinkage strain occurred after approximately 120 min, and then shrinkage also correlates with the effect on the flow. That is, the
stopped after approximately 180 min. Shrinkage strains measured effect of each type of fibre ordered from greatest to least is the same
after 24 h in several specimens were deemed insignificant in for reductions to both flow and free shrinkage.
comparison with those occurring in the first few hours, regardless It was found that the 25 mm filament dispersion fibres produced
of fibre dosage. Significance in this case is based on the fact that the greatest reduction on free shrinkage (Fig. 6). Hence, these fibres
continuing the test for 24 h would not offer further meaningful were used in a low w/c ratio mortar mix (M2), and a concrete mix
insight into the discussion or conclusions resulting from this (M3), to determine if they were still effective in reducing free
testing. Thus, free shrinkage testing was stopped after 240 min (4 h) shrinkage in a more realistic mix. A plot comparing the develop-
for all specimens. Fig. 5 shows the mean values of strain measured ment of shrinkage strains in M2 and M3, as well as the influence of
over time for M1 specimens reinforced with BD-12, FD-25, and FD- FD-25-0.3 in both mixes, is shown in Fig. 7. Additionally, the mean
12 fibre at a dosage of 0.1% by volume. shrinkage strains after 4 h are depicted in Fig. 8. The error bars
In general, the behaviour depicted in Fig. 5 shows good agree- represent one standard deviation on either side of the mean.
ment with the behaviour found by other researchers using similar In the absence of any fibre, it can be seen from Figs. 7 and 8 that
test methods [17,20,23,24,26]. It should be noted that the strain is nearly equivalent reductions to the free shrinkage strain from M1
not only the result of water loss, but also autogenous mechanisms. (approximately 2400 micro-strain e Fig. 6) could be achieved by
During the first few hours of curing, autogenous shrinkage is fully either reducing the water content (M2), or by adding coarse
attributed to chemical shrinkage [28]. Chemical shrinkage is based aggregate (M3). In the case of M2, a fibre dosage of 0.3% did not
on the difference in volume of cement minerals before and after significantly reduce the free shrinkage strain (Figs. 7 and 8a). On the
hydration. The mineral with the greatest reduction in volume, and other hand, when that same fibre dosage was used in M3, a sig-
therefore effect on chemical shrinkage, is C3A, followed by C4AF, nificant decrease was found (Figs. 7 and 8b). This difference is most
C3S, and C2S [28,29]. The quantity of these minerals in the cement likely due to the addition of superplasticizer to the M2 mixes,
used in this study could be approximated with the use of the Bogue which was not present in M3 mixes. It would stand to reason that

Fig. 5. Mean curves for development of strain over time.

 J. Branston et al. / Cement and Concrete Composites 74 (2016) 182e190 187

Fig. 6. Mean strain values measured after 4 h in control mix (M1).

Fig. 7. Comparison between reduced w/c ratio mix (M2) and concrete mix (M3).

Fig. 8. Mean strain values measured after 4 h.

both the flow and shrinkage of the mortar are strongly influenced benefit of reducing shrinkage strain. Superplasticizer is a key
by the frictional effects of the fibres. Consequently, adding super- component in concrete mixes with a low w/c ratio (e.g. high-
plasticizer to the mix so that it is workable seems to negate the strength concrete). Thus, the addition of fibres in these types of
188 J. Branston et al. / Cement and Concrete Composites 74 (2016) 182e190

mixes will only be useful if they are effective in bridging shrinkage aggregate was reduced for mix M4, which in-turn increased the
cracks to restrict their growth. unit volume of cement and water. Since plastic shrinkage is largely
The FDOT [21] found that the addition of fibres (including influenced by the pore pressure of evaporating water, this resulted
basalt) at low dosages (<0.5%) generally did not have a significant in greater shrinkage strain and more cracking. In-turn, the effect of
effect on the workability of concrete; though it should be noted that the different fibres could be more easily distinguished. Fig. 9 shows
marginal decreases in the workability were found with stiffer fi- the typical appearance of fibre reinforced specimens with varying
bres. Boghossian and Wegner [17] studied the effect of flax, poly- fibre dosages versus an unreinforced specimen after 4 h. Addi-
propylene, and glass fibres on free shrinkage and found that glass tionally, the influence of the fibres on the total crack area and
fibres, having a higher elastic modulus than the other fibres, were largest crack width are shown in Figs. 10 and 11, respectively.
the only type of fibres to consistently reduce the free shrinkage Again, the 25 mm filament dispersion fibres had the greatest
strain. This may suggest that the use of relatively high-modulus effect. In this case, they produced the greatest reduction of the
fibres like basalt comes with a trade-off: they are more effective crack area and the crack width. The results from the free shrinkage
in decreasing the free shrinkage strain, but probably have a more testing correlated well with both measured parameters: total crack
adverse effect on workability than low-modulus fibres (e.g. poly- area and largest crack width. In other words, the magnitude of
propylene). Wongtanakitcharoen and Naaman [24] expressed the shrinkage strain was very indicative of the crack severity. However,
idea that assuming everything else being the same, fibres with a it is clear that the benefit of the fibres is not just because of their
higher elastic modulus should produce greater frictional resistance, ability to reduce free shrinkage strain. The fibres are effective, at
and therefore, lead to a greater reduction in free shrinkage strain. least partly, due to their ability to bridge cracks and restrict growth,
However, in their study with carbon, polypropylene, and PVA fi- as shown in Fig. 12.
bres, the results did not support that idea. That is likely due to the Further evidence of their ability to restrict crack growth is
fact that the condition of ‘everything else being the same’ was not provided in Fig. 13, in which it can be found that the 25 mm fila-
met, since the range of elastic modulus considered was the result of ment dispersion fibres are also effective in reducing the crack area
using different materials. Results presented in this paper would in the low w/c ratio mix M5. Free shrinkage testing revealed that
suggest it could be possible to predict the reduction fibres have on the fibres did not have a significant effect on the reduction in strain
free shrinkage strain by measuring their effect on the flow, for when superplasticizer was used to produce an equivalent flow to
which related literature suggests the fibre elastic modulus is likely that of the unreinforced control specimen. Therefore, their effec-
to be a major influencing factor. Although this could perhaps be of tiveness in this case must be attributed to their ability to restrict the
interest for future research, the ability of the fibres to prevent growth of cracks.
shrinkage cracking is most important. The performance of 12 mm filament dispersion fibres was very
similar to that of the 25 mm filament dispersion fibres. It is likely
3.3. Restrained shrinkage testing the greater bond strength, due to their increased length, makes
them more effective in restricting crack growth. Banthia and Gupta
Preliminary testing showed that at the lowest dosage (0.05% by [16] reported similar findings in their study on polypropylene fi-
volume), 25 mm filament dispersion fibres completely eliminated bres. In the case of bundle dispersion fibres and minibars, the fibres
shrinkage cracking in the control mix M1. Thus, the amount of fine were not observed bridging the cracks. This makes sense, since

Fig. 9. Crack reduction with increasing fibre dosage in M4.

Fig. 10. Effect of fibres on total crack area on specimen surface in M4.
 J. Branston et al. / Cement and Concrete Composites 74 (2016) 182e190 189

Fig. 11. Effect of fibres on crack width on specimen surface in M4.

Fig. 12. Crack development without fibre (a) and with fibre (b).

Fig. 13. Effect of FD-25 on crack area in low w/c ratio mix M5.

cracks are more likely to develop where fibres are not present. The agreement of results would only be possible in the unlikely case
filament dispersion fibres cover a much greater area, and therefore, that cracks in fibre reinforced specimens in this work began
there is a higher probability they will bridge a developing crack. growing at a faster rate than the unreinforced specimens in the
Restrained shrinkage testing was not undertaken with the three weeks following testing.
concrete mix M3, since the size of the aggregate used relative to the
thickness of the overlay was prohibitive. However, it would be 4. Conclusions
reasonable to assume that basalt fibres would have a similar benefit
in concrete mixes and this could be of interest to future research. The results presented in this paper suggest basalt fibres are
The results of the restrained shrinkage testing in this paper would effective in mitigating the detrimental effects of plastic shrinkage
seem to disagree entirely with those of the FDOT [21], which not by reducing the magnitude of the shrinkage strain, and by
only found basalt fibres were ineffective, but detrimental. In that restricting the growth of cracks if they do occur. As the w/c ratio
case, crack measurements were taken after 12 and 28 days of decreases, it is the latter mechanism that becomes more promi-
curing, and so the results are not directly comparable. However, nent. However, related literature suggests that high-modulus fibres
190 J. Branston et al. / Cement and Concrete Composites 74 (2016) 182e190

like basalt have a more severe impact to workability than low- structures, Constr. Build. Mater. 96 (2015) 37e46.
[2] P. Iyer, S. Kenno, S. Das, Mechanical properties of fiber-reinforced concrete
modulus fibres. Therefore, the application of basalt fibres for
made with basalt filament fibers, J. Mater. Civ. Eng. (2015) 04015015.
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where the w/c ratio is often high enough that the fibres will not properties and microstructure of chopped basalt fibre reinforced concrete,
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[4] ACI Committee 544, 544.1R-96: Report on Fiber Reinforced Concrete (Reap-
Moreover, they will be more efficient in this scenario due to the proved 2009), Technical Documents, 1996.
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Models, and Determination of Material Properties (Reapproved 1999), Tech-
completely eliminated at a dosage of 0.1% by volume in all cases in nical Documents, 1991.
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could likely be eliminated at even lower fibre dosages, since the in fiber-reinforced cementitious materials, Exp. Tech. 31 (6) (2007) 44e48.
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