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Polymer modified jute fibre as reinforcing agent controlling the physical and mechanical characteristics of cement mortar

Construction and Building Materials 49 (2013) 214–222

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Construction and Building Materials
journal homepage: www.elsevier.com/locate/conbuildmat

Polymer modified jute fibre as reinforcing agent controlling the physical
and mechanical characteristics of cement mortar
Sumit Chakraborty, Sarada Prasad Kundu, Aparna Roy, Basudam Adhikari, S.B. Majumder ⇑
Materials Science Centre, Indian Institute of Technology, Kharagpur 721 302, India

h i g h l i g h t s
 Methodology to disperse polymer modified jute fibre homogeneously into the mortar.
 Significant improvement of CCS, MOR, and FT in jute fibre reinforced mortar.
 Substantial improvement in TI as well as the PCRE in modified mortar.
 Plausible mechanism to explain the improvement in mechanical properties.

a r t i c l e

i n f o


Article history:
Received 5 September 2012
Received in revised form 26 July 2013
Accepted 18 August 2013
Available online 10 September 2013
Keywords:
Cement
Polymer
Fibre reinforcement
Mechanical properties
Interfacial bonding

a b s t r a c t
Polymer modified alkali treated jute fibre as a reinforcing agent, substantially improves the physical and
mechanical properties of cement mortar with a mix design cement:sand:fibre:water::1:3:0.01:0.6. The
workability of the mortar is found to increase systematically from 155 ± 5 mm (control mortar) to
167 ± 8 mm (0.2050% polymer modified mortar). The density of the mortar is increased from 2092 kg/
m3 to 2136 kg/m3 with a concomitant reduction of both water absorption and apparent porosity. Optimal
polymer content in emulsion (0.0513%) is found to increase the compressive strength, modulus of rupture
and flexural toughness 25%, 28%, 387% respectively as compared to control mortar. Based on the X-ray
diffraction and infra-red spectroscopy analyses of the mortar samples a plausible mechanism of the effect
of modified jute fibre controlling the physical and mechanical properties of cement mortar has been
proposed.
Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction
Natural fibres as reinforcing agent in cement matrix are nowadays being considered as effective alternative to steel and other
inorganic synthetic fibres [1,2]. Natural fibres such as sisal, coconut, sugar-cane bagasse, hemp, jute are reported to yield improved
mechanical strength of the cement based composites [3–7]. Additionally they also enhance the post-cracking resistance, yield
high-energy absorption characteristics and improve the fatigue
resistance of cement based composites [8–10]. Reviewing the literature, it remains difficult to disperse the natural fibre into cement
matrix and also their long term durability in cement matrix is yet
to be investigated [11–14]. The potential application of natural fibre reinforced cement composites are limited to those area where
energy must be absorbed or the areas prone to impact damage.
Accordingly, natural fibre reinforced cement composites are most
suitable for shatter and earthquake resistant construction, foundation floor for machinery in factories, fabrication of light weight
⇑ Corresponding author. Tel.: +91 3222 283986; fax: +91 3222 282274.
E-mail address: subhasish@matsc.iitkgp.ernet.in (S.B. Majumder).
0950-0618/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.


http://dx.doi.org/10.1016/j.conbuildmat.2013.08.025

cement based roofing and ceiling boards, wall plaster, and construction materials for low cost housing [15].
Variety of factors influences the physical and mechanical properties of natural fibre reinforced cement composites. These factors
may be grouped according to (i) the type and characteristics of
reinforcing fibres, (ii) nature of the cement based matrix and mix
design, and (iii) way of mixing, casting and curing of the composites [15]. Among these parameters, the compatibility between the
fibre and cement based matrix leading to a homogeneous distribution of the reinforcing fibres remains one of the most dominating
factors that influences the mechanical properties of these composites [16]. The fibre–matrix compatibility is dominated by the
chemical composition of the reinforcing fibre together with their
surface properties. Due to the parametric dependence of so many
factors, the wide scattering in the mechanical properties of natural
fibre reinforced cement composites as tabulated in Table 1 seem to
be obvious.
In the present work, we aim to investigate the effect of jute fibre
as a reinforcing agent to cement mortar. For homogeneous distribution of jute fibre into the cement matrix we have modified both
the chemical composition as well as surface properties of jute fibre


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S. Chakraborty et al. / Construction and Building Materials 49 (2013) 214–222
Table 1
Comparative study of mechanical behavior of different fibre reinforced cement composites.
Fibre type

Type of modification

Mechanical properties
a

Eucalyptus
Hemp
Jute
Kraft banana
E grandis
Kenaf (1.2, %)
Kraft
Coconut husk
Bagasse fibre
Jute
a
b
c
d
e
f






APTS
CaCl2
SBR, Vinyl ester
Carboxylated SBR

Reference
b

d

2

e

f

CCS (MPa)

MOR (MPa)

MOE (GPa)

FT (kJ/m )

TI

31.1
32.65
27.97


3.87
4.62
4.44
21.7
22.2
4.7
12.1
2.2
14.5
9.1




6.7
8

16.3
1.1
6.8
0.5

0.53
0.73
0.62
0.59
1.5
1.3
0.82



1.86
















0.63

1.69

0.102

33.4

4.1
35.4

PCRE (J)
[2]
[6]
[7]
[10]
[17]
[18]
[12]
[13]
[14]
Present research

Compressive strength.
Modulus of rupture.
Flexural modulus.
Fracture toughness.
Toughness index.
Post cracking resistance energy.

by a combined dilute alkali and polymer emulsion treatment. The
effect of fibre modification on the physical and mechanical properties of cement mortar has been investigated. Moreover, the effect
of chemical treatment of the reinforcing fibres on their durability
in highly alkaline cement environment has also been investigated.
Finally, the plausible mechanism of such fibre treatment controlling the physical and mechanical properties of cement mortar is
elucidated.
2. Experimental
2.1. Preparation of alkali and polymer modified jute fibre reinforced cement mortar
Portland pozzolana cement confirming with IS 1489-1991 (reaffirmed 2005)
(Ambuja cement) [19] was used as the binder material for the preparation of cement mortar. The oxide composition of this cement is shown in Table 2. The local
river sand was used for the preparation of cement mortar. This sand did not contain
any organic substances which might affect cement hydration reaction. To evaluate
grading zone and average particle size of sand, sieve analysis was performed. From
the sieve analysis (Fig. 1), it was confirmed that the used sand is in grading zone II
with average particle size 0.3 mm. TD-4 grade jute fibres were used as reinforcing
agent. As received jute fibres, being long enough, could not be used as reinforcing

Table 2
The oxide composition of Portland pozzolanic (Ambuja) cement.

a

c

Composition

SiO2

CaO

MgO

Fe2O3

Al2O3

C

L.I.a

Weight (%)

27.28

50

1.96

6.18

9.20

0.76

2.66

Loss of ignition.

agent in cement. Therefore to use the jute fibre as reinforcement in cement composite, the long jute fibres were chopped into 5 mm length. The average diameter of
used jute fibre was 0.062 ± 0.014 mm.
The treatment composition of jute with alkali and polymer latex is shown in Table 3. First the requisite amount of jute as mentioned in Table 3 was soaked with
the 0.5% alkali solution following which the spent alkali solution was decanted
out after 24 h of soaking. Next the respective amounts of Sika latex containing
41% solid (carboxylated styrene butadiene (SBR)) was diluted with 1000 ml of water
and added to the alkali soaked wet jute.
The cement mortar was prepared following the composition shown in Table 4.
In the mix design the weight fraction of cement:sand:fibre:water was kept
1:3:0.01:0.6. The total alkali and polymer treated jute (as shown in Table 3) were
mixed with half part of the cement required to make the mortar. A mechanical mixer was used to make uniform slurry after 10–15 min mixing. The required amount
of sand, rest of the cement and additional amount of water was mixed thoroughly
with the slurry for another 10–20 min. The fresh mortar thus prepared was cast
immediately in 110 mm (length (l)) Â 20 mm (breadth (b)) Â 20 mm (depth (d))
mould for flexural specimen and 70.6 mm cubic mould for compressive specimen.
The mortar samples were allowed to set in the moulds for 24 h at ambient temperature (30 ± 2 °C). The samples after setting were removed from the mould and
water cured for 7, 28, 42, and 90 days. After curing, the mortar specimens were
dried under ambient condition. For the characterization of polymer modified jute
fibre reinforced mortar, minimum six samples of each batch were tested.
As shown in Table 4, nine different formulations (viz., 1–9) were used for the
preparation of the mortar samples. In these mortar samples, the ratio of cement:sand:fibre were kept constant, however, the solid polymer: water (weight to volume) ratio were varied. The solid polymer content in emulsion (defined as
weight of solid polymer in 100 ml water) was varied in between 0.0257% and
0.205% (w/v). In this experiment, for each formulation 6 samples were fabricated
for each test.
To evaluate the durability of the alkali polymer modified jute fibres in alkaline
cementitious medium, the combined alkali polymer modified jute reinforced cement paste was prepared with the mix design cement:alkali treated jute:water
1:0.01:0.6. In this test 100 mm long jute fibres were used. Initially the jute fibres
were treated with 0.5% NaOH solution for 24 h followed by mixing with polymer

Fig. 1. (a) A comparative study of cumulative mass (%) passing of fine aggregate (sand) through the equivalent spherical diameter sized sieve with the standard value of
grading zone II, (b) retention of fine aggregate on different equivalent spherical diameter sized sieve.


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S. Chakraborty et al. / Construction and Building Materials 49 (2013) 214–222

Table 3
Treatment composition of jute with alkali and polymer latex.
Ingredients

For modification with alkali and polymer latex

Jute fibre (2–5 mm long) (g)
Aqueous sodium hydroxide (0.5%) (ml)a
Water based Sika latex (41% solid content) (ml)

30
900
0.625
0.257b
1000

Water (ml)
a
b

30
900
1.250
0.513b
1000

30
900
2.500
1.025b
1000

30
900
5.000
2.050b
1000

After 24 h of soaking in alkali spent alkali solution was decanted.
Weight of polymer of Sika latex in respective formulations on dry basis.

Table 4
Composition of jute reinforced cement mortar.
Components

Cement (kg)
Sand (kg)
Raw/0.5% alkali treated jute
Weight of polymer (dry basis)
Water (ml) (for polymer emulsion)
Additional water (ml) (for mortar mixing)
a
b
c
d

Formulation No
1

2

3

4

5

6

7

8

9

3
9



1800

3
9
30a


1800

3
9
30b
0.257c
1000d
800

3
9
30b
0.513c
1000d
800

3
9
30b
1.025c
1000d
800

3
9
30b
2.050c
1000d
800

3
9
30b
0.513c
1000d
740

3
9
30b
1.025c
1000d
680

3
9
30b
2.050c
1000d
620

Weight of water soaked raw jute (g).
Weight of alkali treated jute (g).
Weight of polymer of Sika latex in respective formulations on dry basis.
Added water for making polymer emulsion (ml).

emulsion (0.0513% polymer content in emulsion) for 10 min. The combined alkali
polymer modified jute fibres were then dispersed in cement slurry to prepare jute
cement paste. After waiting for 24 h, the semi-hardened and hydrated jute cement
paste was water cured up to 360 days. During curing, at least twenty-five single
strand jute fibres were isolated in regular intervals (cured for 7, 28, 42, 90, 180
and 360 days), washed sequentially in water and acetone, and oven dried at
105 °C for 24 h. Finally, the tensile strength of these fibres was measured using a
universal testing machine.

2.2. Physical properties and microstructure of jute fibre and fibre reinforced mortar
Flow behaviour of the freshly prepared cement mortar (which indicates its
workability) is estimated by a flow table test in accordance with IS 1727 standard
[20]. The bulk density (both wet and dry), water absorption, and apparent porosity
of the water cured mortar samples were estimated according to ASTM C 948 [21]
standard.
Fourier transformed infra-red spectroscopy (FTIR) measurements were performed on jute fibre as well as mortar samples using a spectrometer (Nexus 870,
Thermo Nicolet Corp. USA). Oven dried (at 85 °C for 1 h) jute fibre as well as powdered mortar samples were mixed with KBR to make pellets for FTIR measurements. The FTIR spectra were recorded in the wave number range between
4000–400 cmÀ1 after averaging 32 scans.
The structural characteristics of raw as well as alkali modified jute fibres and
the water cured mortar samples were investigated using an X-ray diffractometer
(Ultima III, Rigaku Inc. Japan). Cu Ka radiation (40 kV, 30 mA) was used to record
the X-ray diffractograms of these samples in the rage of 2h between 10° and 60°
maintaining at a scanning rate of 1ominÀ1.

Fig. 2. Load deflection curve of Polymer modified jute reinforced mortar.

The micrographs of the jute fibre and fractured surface of the mortar specimens
were recorded using a scanning electron microscope (Vega-LSV, TESCAN, Czech
Republic). A thin gold coating was applied on the surface of the samples to avoid
charging.
2.3. Mechanical properties of jute fibre and jute fibre reinforced mortar
The compressive strength measurements were carried out using a 1000 kN
hydraulic universal testing machine (AIM: 31402, S. No. 091020). Mortar cubes
(volume = 3.52 Â 105 mm3) samples were tested (without any preload) using a
loading rate 13 kN minÀ1 in compliance with the IS 516 standard [22]. The compressive strength or cold crushing strength (CCS in MPa) was calculated measuring
the fracture load (F in N) and area of the face of the cube (A in mm2) using the following relation.

CCS ¼ F=A

ð1Þ

The flexural tests were performed using a universal testing machine (Hounsfield H10KS). A three point bending configuration was used to determine the modulus of rupture (MOR). Rectangular water cured mortar specimen (110 mm
(l) Â 20 mm (b) Â 20 mm (d)) was used as sample. During the flexural tests, the
span length (L) = 60 mm and constant loading rate 1.2 mm minÀ1 were maintained
as per IS 4332 [23] specification. The MOR is determined using the following
relation
2

MOR ¼ 3P Á L=ð2 Á b Á d Þ

ð2Þ

Fig. 3. Variation of the density (wet and dry), water absorption and apparent
porosity of jute modified mortar samples with the polymer content in emulsion (%).


S. Chakraborty et al. / Construction and Building Materials 49 (2013) 214–222
Table 5
The flow table value of the control and polymer modified jute cement mortar.
Formulation
No.

Solid polymer content in
emulsion (%)

Water
cement ratio

Flow table
value (mm)

1
2
3
4
5
6
7
8
9



0.0257
0.0513
0.1025
0.2050
0.0513
0.1020
0.2050

0.60
0.60
0.60
0.60
0.60
0.60
0.58
0.56
0.54

155 ± 5
156 ± 6
157 ± 8
161 ± 6
164 ± 5
167 ± 8
156 ± 8
156 ± 8
151 ± 7

217

FT ¼ ðAbsorbed energy during flexural testÞ=ðArea of the broken sectionÞ

ð3Þ

where the numerator is the area under the load deflection curve (shaded region
in Fig. 2). Flexural modulous (F.M) is estimated using the following relation
3

F Á M ¼ m Á L3 =ð4b Á d Þ

ð4Þ

where ‘m’ is the slope of the load–deflection curve during elastic deformation
(usually in the deflection regime between 0.05 and 2.0 mm) and L is support span
length. Toughness indices (TI) are defined as ratio of the whole area under the flexural load–deflection curve and the area under the deflection of maximum load. This
is also termed as peak load toughness indices [6]. Finally, the difference between
the total absorbed energy during flexural test and absorbed energy up to peak load
is known as post cracking resistance energy. This is estimated as the difference between the whole area under the flexural load–deflection curve and area under the
deflection of maximum load.
The tensile strength of the jute fibres, isolated from jute reinforced cement
paste after curing for specified period in the range of 7–360 days, were measured
using a 10 kN universal tensile testing machine (H10KS, Hounsfield, Salfords, UK).
A gauge length of 25 mm was employed with a crosshead speed of 2 mm/min in
accordance with ASTM D3822-01 (ASTM, 2001) [24]. For this test each single fibre
was mounted within a cardboard frame (with a rectangular opening of 15 mm in
width and 30 mm in height) using adhesive. The frame was placed within the jaws
of universal testing machine (UTM) equipped with a 100 N load cell. At least
twenty-five single fibres each randomly drawn from cement paste were tested.

3. Result
3.1. Physical, mechanical and microstructure analysis of combined
alkali and polymer modified jute fibre reinforced mortar

Fig. 4. Variation of flexural modulus (FM), compressive and flexural strength of the
control and fibre-reinforced mortar samples (cured for 28 days) with the polymer
content in emulsion (%).

Fig. 5. SEM micrographs of the fractured surface of the (a) control, (b) 0.0257%, (c)
0.0513%, and (d) 0.02050% polymer modified jute reinforced mortar specimens.

where P is the fracture load, ‘L’ is the support span length, ‘b’ is the breadth and
‘d’ is the depth of the mortar samples. From the recorded load–deflection curve
(Fig. 2); flexural modulus (FM), flexural toughness (FT), toughness index (TI), and
post cracking resistance energy (PCRE) are estimated as described below:
Toughness is the energy absorption capacity of the composite which defines its
ability to resist fracture under static, dynamic or impact load. The flexural toughness (FT) is determined using the following relation

Fig. 3 shows the variation of the density (wet and dry), water
absorption and apparent porosity of jute modified mortar samples
as a function of the polymer content in emulsion (%) used for cement hydration. As shown in the figure, the densities are increased,
whereas the water absorption as well as apparent porosity is reduced with the polymer content. Usually in most of the studies
on polymer modified cement composites, the weight ratio of polymer: cement is kept more than 5% [25–28]. It is reported that higher polymer: cement affects the cement hydration, however,
coherent polymer film retards the propagation of tiny cracks in cement mortar forming an interpenetrating structure with the modified cement mortar with lower rigidity. Therefore optimum
polymer: cement ratio improves the mechanical properties of cement mortar. Unlike all these reports, in the present work, very
small amount of SBR based latex is used to make the cement mortar. As shown in Table 5, the flow table value of the jute-modified
cement mortar is systematically increased with the polymer content in emulsion used for cement hydration. The role of the polymer modification in controlling the physical and mechanical
properties of jute fibre reinforced concretes are discussed later.
Fig. 4 shows the variation of flexural modulus (FM), compressive strength (CCS) and modulus of rupture (MOR) of the control
and fibre-reinforced mortar samples (cured for 28 days) with the
polymer content in emulsion (%). Interestingly, both compressive
strength and MOR are improved up to the 0.0513% polymer content. Thus with polymer modification, the CCS and MOR of the control mortar has increased from 28 MPa and 7.0 MPa to 35 and
9.0 MPa respectively. With further increase of polymer content
up to 0.2050%, the CCS and MOR of the jute reinforced polymer
modified mortars are decreased however, still remains comparable
to/better than the control sample. In contrast to this, the flexural
modulus values are decreased with the increase of the polymer
content (%). As expected, the CCS and MOR values increase with
curing days, however, the trend of their variation with the polymer
content in emulsion remains similar to that presented in Fig. 4 for
mortar samples cured for 28 days. Thus for 90 days cured mortar
samples the CCS and MOR values are measured to be 37.9 MPa
and 12.8 MPa respectively. As presented in Table 5, the flow table
values were systematically increased with the increase of the polymer content in emulsion (%). For the polymer content 0.0513%, the


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S. Chakraborty et al. / Construction and Building Materials 49 (2013) 214–222

Fig. 6. The force-extension curves of control, raw jute reinforced and polymer
modified jute reinforced mortar specimens with polymer contents varying from
0.0257% to 0.2050% (six samples of formulation Nos. 1–6 as indicated in Table 4).

water content required for cement hydration was reduced from
60% to 58% to yield the flow table value (156 ± 8 mm) similar to
that of control mortar (155 ± 5 mm). As a result, the CCS and
MOR values of the mortar samples were found to increase further
up to 36 MPa and 9.3 MPa respectively after 28 days curing. Interestingly, when the curing time is increased for 90 days, the CCS and
MOR values of these samples are increased to 38.4 MPa and
14 MPa respectively. The above results illustrate that by tuning
the processing methodologies, the mechanical properties of polymer modified jute reinforced cement mortars may be fine tuned
depending on the application needs.
Fig. 5 shows the SEM micrographs of the fractured surface of the
(a) control, (b) 0.0257%, (c) 0.0513%, and (d) 0.2050% polymer modified jute reinforced mortar specimens. As observed clearly in
Fig. 5(c) and (d), with the increase of the polymer contents the
porosity of the mortar matrix is markedly reduced. The rubber like
SBR contains both rigid styrene and flexible butadiene chains [29]
which help to form coherent polymer film and probably an interpenetrating structure with the mortar matrix. Unlike the other literature reports, in this work we have found that a comparatively
diluted polymer emulsion is sufficient to yield a coherent polymer
film. As presented earlier in Fig. 4, since the flexural modulus is reduced with the increase in the polymer content, therefore it advantageous to keep the polymer content low enough to form a
coherent film and interpenetrating structure with the mortar
matrix.
Fig. 6 shows the force-extension curves of control, raw jute
reinforced and polymer modified jute reinforced mortar specimens
with polymer contents varying from 0.0257% to 0.2050% (6 samples of formulation Nos. 1–6 as indicated in Table 4). It is observed

Fig. 8. Variation of the flexural toughness (FT) and toughness index (TI) with the
polymer content in emulsion (%).

Fig. 9. Variation of the post cracking resistance energy (PCRE) with the polymer
content in emulsion (%).

from the figure that maximum load is carried by 0.0513% polymer
modified jute fibre reinforced cement mortar sample. Very small
extension is observed for control sample as compared to that of
the mortar sample prepared by polymer modified jute fibre reinforcement. This is due to the occurrence of sudden failure for control sample (Fig. 7(a)), however higher extension for polymer
modified jute reinforced cement mortar is due to the gradual failure as envisaged from the Fig. 7(b). The mortar specimens were
also characterized in terms of their flexural toughness and toughness index characteristics. As explained previously (Fig. 2) the fracture toughness and toughness index were calculated from this load
extension curve. As envisaged from Fig. 6, initially, the load

Fig. 7. Failure mode in bending test of the control and polymer modified jute reinforced cement mortar samples.


S. Chakraborty et al. / Construction and Building Materials 49 (2013) 214–222
Table 6
Tensile strength retention (%) of raw and alkali polymer (0.0513%) modified jute fibres
exposed in alkaline cementitious environment for 7–360 days.
Exposure time (days)

0
7
28
42
90
180
360

Tensile strength retention (%) of raw and combined
alkali polymer modified jute in cement environment
Raw jute

Modified jute

100.0
98.5
92.8
91.9
82.1
77.6
73.7

100.0
99.8
99.1
98.7
96.7
94.3
93.2

219

of the polymer content. Comparing the results presented in Table 1,
it is encouraging to note that as compared to other jute fibre reinforcement report, substantial improvement is achieved in CCS,
MOR and FT values reported in the present work.
Fig. 9 presents the variation of the post cracking resistance energy (PCRE) with the polymer content in emulsion. The PCRE is
substantially improved up to 0.0513% polymer content. With further increase of the polymer content, the PCRE is reduced, however, up to 0.2050% polymer content the estimated PCRE is found
to be far improved as compared to the control mortar sample.
The results presented above are summarized as follows: Addition of diluted SBR based latex in alkali modified jute-fibre reinforced mortar is found to systematically increase the flow-table
value and density, while reducing the water absorption and apparent porosity of the mortar. Using optimal polymer content in emulsion (0.0513%) substantial improvement in CCS and MOR values
has readily been achieved. The flexural toughness is also markedly
increased when 0.0513% polymer modifier is used. Irrespective of
the polymer contents the flexural modulus is decreased with the
increase in the polymer content in emulsion (%). We have observed
that the toughness index as well as the post cracking resistance
energies is substantially improved in polymer modified jute reinforced mortars.
3.2. Durability study of jute fibre in cement medium

Fig. 10. The X-ray diffraction patterns of (i) control mortar and (ii) 0.0513% polymer
modified jute reinforced mortar samples cured for 28 days. The letters referring to
the XRD peaks are (a) Alite, (b) Belite, (c) Calcite, (g) Genite, (p) Portlandite, and (q)
Quartz.

The durability of raw as well as combined alkali polymer
(0.0513%) modified jute fibre (in alkaline cement paste) was also
investigated by estimating the value of tensile strength retention
of respective fibres. Table 6 shows the tensile strength retention
(%) of raw and combined alkali polymer (0.0513%) modified jute fibres as a function of time for alkaline cementitious environment.
As shown in Table 6, in cement environment, combined alkali polymer (0.0513%) modified jute fibres have better tensile strength
retention (%) as compared to their raw jute counterpart. After
360 days exposure in cement paste, almost 93% of tensile strength
was retained in combined alkali polymer modified jute fibre as
compared to 74% retention for raw jute fibre. The main reason of
natural fibre degradation in alkaline matrix is attributed to be
due to Ca2+ fixation (known as mineralization) on fibre surface
[30]. When the fibre surface is coated with polymer latex, the
Ca2+ fixation seems to be minimized to retard the degradation.
4. Discussion

Fig. 11. Experimental, fitted and the deconvoluted XRD peaks in the 2h range
between 15° and 40° of control mortar sample.

carrying capacity increases up to 0.0513% polymer modified jute fibre reinforced cement sample (formulation code of the sample is
4). With further increase of polymer content load carrying capacity
decreases gradually. Therefore, optimal polymer content (0.0513%)
shows maximum load carrying capacity.
Fig. 8 shows the variation of the flexural toughness (FT) and
toughness index (TI) with the polymer content in emulsion (%).
As compared to the control specimen, the flexural toughness is
substantially increased up to 0.0513% polymer content. With further increase of the polymer content the FT values are decreased,
however, the values still remain better than the control sample.
On the other hand, the toughness index increases with the increase

In the preceding section we have reported an overall improvement of the physical characteristics and mechanical properties of
polymer modified alkali treated jute fibre reinforced cement mortar samples. The durability of raw as well as combined alkali polymer (0.0513%) modified jute fibre (in alkaline cement paste) has
also been reported.
In order to find a plausible mechanism controlling these
improvements we have performed X-ray diffraction and FTIR analyses of the modified jute fibres and cement mortar samples. Fig. 10
shows the X-ray diffraction patterns of (i) control mortar and (ii)
0.0513% polymer modified jute reinforced mortar samples cured
for 28 days. It is known that the major constituents of Portland
pozzolana cement are alite (a) [tricalcium silicate C3S (Ca3SiO5)],
belite (b) [dicalcium silicate C2S (Ca2SiO4)], tricalcium aluminate
[C3A (Ca3Al2O6)], and tetracalcium alumino ferrite [C4AF (Ca4AlnFe2ÀnO7,)]. As compared to ordinary Portland cement (OPC), the
Portland pozzolana cement contains substantial amount of quartz
(q) and minute quantity of gypsum (g) as well. The hydration of
alite and belite phases produces Ca(OH)2 (p) (portlandite) and
amorphous calcium–silica–hydrate (C–S–H) [31]. All the


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S. Chakraborty et al. / Construction and Building Materials 49 (2013) 214–222

Fig. 12. (a) The FTIR spectra of (i) alkali treated jute fibre and (ii) polymer (0.0513%) modified jute fibre, (b) the FTIR spectra of (i) mortar (control) and (ii) 0.0513% polymer
modified jute reinforced mortar specimen cured for 28 days, (c) the experimental, fitted and deconvoluted modes for the mortar (control) specimen.

Table 7
Assignment of the FTIR modes of hydrated cement mortar.
Peak position
(cmÀ1)

Assignment

3638
3400–3100

OAH stretching of Ca(OH)2
Symmetric and asymmetric stretching (m1 and m3) of the
OAH vibrator of the water molecules
The asymmetric stretching of HAC bond present in the
organic compound
m2 Deformation mode of the molecular water HAOAH
absorbed

2928
1644
1477 and 1420
970

m3 of COÀ2
3
The m3 stretching of SiAO bond of calcium silicate hydrate
(CASAH). This mode accounts for the polymerization of the
SiO4À
4 units present in C3S and C2S during hydration

diffraction peaks corresponding to these phases in the cured mortar specimens are indexed in Fig. 10. As noted in Fig. 10, the characteristic peak that corresponds to portlandite phase (p) appears at
2h = 18°. The diffraction peak of the major reactant alite (a) is identified at 2h = 29.4°. Estimation of the ratio of the integrated area of
the portlandite (p) and allite (a) peak ratio could therefore be treated as the index of the degree of hydration. The XRD pattern of the
cured mortar specimen was fitted using a commercial software
(Peakfit 4.1, Jandel Scientific) and Fig. 11 shows the fitted as well
as deconvoluted XRD peaks in the 2h range 15–40°. Similar fitting
was also performed of the XRD pattern of 0.0513% polymer modified jute reinforced cement mortar sample (not shown). We have
found that the integrated peak area ratio of the peaks corresponding to the portlandite (p) and alite (a) phase (Ap/Aa) of the control

sample (0.169) is reduced to 0.140 in polymer modified jute reinforced mortar sample. This is indicative to two possibilities: first,
as compared to the control sample, either the formation of portlandite is less in the polymer modified mortar specimen or the hydrated product (portlandite) (in the polymer modified jute
reinforced mortar specimen) is consumed elsewhere. To better
understand this phenomenon we have performed FTIR analyses
of the alkali modified jute fibre and the polymer modified jute fibres. Fig. 12 (a) compares the FTIR spectra of alkali treated jute fibre with the one after polymer modification. As shown in the
figure, the absorption band 3559 cmÀ1 is assigned to be due to
OAH stretching. The mode at 2921 cmÀ1 is assigned to be due to
CAH stretching vibration. The absorption band at 1739 cmÀ1 is absent in alkali modified fibre and appears only in polymer modified
fibre (encircled with dotted mark). The mode is assigned to be due
to the C@O stretching of ester linkage [32]. The appearance of this
band is indicative to some kind of interaction between the polymer
additive and alkali modified jute fibres. In Fig. 12(b) we have compared the FTIR spectra of (i) control mortar and (ii) 0.0513% polymer modified jute reinforced mortar specimen cured for 28 days.
All the absorption bands are indexed and the assigned modes along
with their wave numbers are tabulated in Table 7 [33]. As indicated
in Table 7, the absorption mode at 3638 cmÀ1 is indexed to be due
to OAH stretching of the portandite (Ca(OH)2) phase. The mode
2928 cmÀ1 is due to asymmetric stretching of HAC bond from
the organic moieties present in the mortar sample. Considering
the mode 2928 cmÀ1 as an internal standard [34], the change in
the intensity of the OAH stretching mode of portandite phase (both
in control and polymer modified mortar specimens) is estimated
by fitting these modes using commercial software. The typical fitting and the deconvoluted modes for the control specimen is
shown in Fig. 12(c). The ratio of the integrated area of OAH


S. Chakraborty et al. / Construction and Building Materials 49 (2013) 214–222

221

Fig. 13. Schematic of the plausible mechanism for the interfacial bonding between the alkali modified jute fibre and cement matrix (see text for details).

stretching mode and asymmetric HAC mode (AOAH/AHAC) are estimated from these fit. The ratio is estimated to be 0.39 for control
and 0.37 for 0.0513% polymer modified jute reinforced mortar
samples. In line to the XRD analyses presented above, the FTIR
analyses also indicate that the formation of portandite is retarded
in polymer modified specimens. Through these analyses it is
clearly demonstrated that the polymer coating are chemically
interacted with alkali modified jute fibre and retards the formation
of the major cement hydration product.
Viewing in light of the above analyses we are making an attempt to understand the improvement of both physical and
mechanical properties in polymer modified alkali treated jute reinforced mortar samples. Alkali treatment modifies the fibre composition by removing the amorphous constituents of jute fibres (viz.
hemicelluloses, wax etc.) and thereby increasing its crystallinity
[35]. The polymer latex modifies the surface of the fibre as well
as the mortar matrix to impart homogeneous distribution of the fibre as well as strong interfacial bonding to the mortar matrix. The
coherent polymer film and its interpenetrating structure with the
mortar matrix improve the density reducing the apparent porosity
of the modified mortar. The strong interfacial bonding between the
uniformly dispersed jute fibre and mortar matrix retard the crack
propagation during fracture. The main constituent of jute fibre is
cellulose which contains large number of inter and intra molecular
hydroxyl groups. During the alkali (NaOH) treatment, some of
these hydroxyl groups in the jute fibre react with Na+ ion to form
base exchanged cellulose fibres with OÀNa+ groups (see Fig. 13)
[36]. The carboxylated styrene butadiene rubber (SBR) based polymer latex contains carboxylic acid groups [27]. The base exchanged
cellulose fibre reacts with the ÀCOOH group of the carboxylated
SBR to form an ester linkage forming NaOH as by-product. The formation of such ester linkage has clearly been identified in FTIR
analyses (Fig. 12(a)) To form interfacial bonding to the mortar matrix, some of these ÀCOOH groups of the carboxylated SBR also reacts with the hydrated cement (Ca(OH)2) forming H2O as a byproduct. These reactions are also shown schematically in Fig. 13.
As some part of the hydration product (viz. portlandite) is consumed in such reaction, as indicated both in XRD and FTIR analyses
(see Fig. 10 and Fig. 12b) the amount of the hydration product is
found to be less in the polymer modified mortar samples. Since a
much diluted polymer emulsion is used in the present study, it

seems to be unlikely that the polymer modification itself would retard the cement hydration.
5. Conclusions
Jute as a natural fibre is used as a reinforcing agent to improve
the physical and mechanical properties of cement mortar. The mix
design of the mortar was kept, cement:sand:Fibre:water::1:3:0.01:0.6. The chopped jute-fibre (2–5 mm in length)
was pre-treated by immersing in 0.5% dilute sodium hydroxide
solution overnight prior to disperse in mortar matrix.
In this investigation the solid polymer content in emulsion (defined as weight of solid polymer in 100 ml water) was varied in between 0.0257% and 0.205% (w/v). A novel processing methodology
was developed to homogeneously disperse alkali and polymer
modified jute fibre into the mortar matrix. The combined alkali
and polymer treatment yield mortar where the workability is
found to increase systematically from 155 ± 5 mm (control mortar)
to 167 ± 8 mm (0.2050% polymer modified mortar). The density of
the mortar is increased from 2092 kg/m3 to 2136 kg/m3 with a
concomitant reduction of both water absorption and apparent
porosity.
Optimal polymer content in emulsion (0.0513%) is found to increase the compressive strength (CCS), modulus of rupture and
flexural toughness 25%, 28%, 387% respectively as compared to
control mortar without any jute reinforcement.
Though the toughness index as well as the post cracking resistance energies are substantially improved with the increase in
polymer strength, the flexural modulus is found to decrease as
compared to control mortar specimen. Based on XRD and FTIR
analyses we have identified that the alkali treatment and polymer
modification help the reinforcing jute fibre to form strong interfacial bond with mortar matrix. A plausible mechanism for such
bond formation has been proposed to explain the observed
improvements in physical characteristics and the mechanical properties of the mortar.
Acknowledgement
Part of this research work was supported by a research grant
from the National Jute Board, Govt. of India. One of the authors


222

S. Chakraborty et al. / Construction and Building Materials 49 (2013) 214–222

Mr. S.P. Kundu gratefully acknowledges CSIR for providing financial
support in the form of an individual junior research fellowship.

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