Mechanical properties of oil palm trunk fibre reinforced concrete
Z Ahmad*, University Technology MARA, Malaysia
H M Saman, University Technology MARA, Malaysia
F M Tahir, University Putra, Malaysia
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Mechanical properties of oil palm trunk fibre reinforced concrete
Z Ahmad*, University Technology MARA, Malaysia
H M Saman, University Technology MARA, Malaysia
F M Tahir, University Putra, Malaysia
Abstract
An experimental study was conducted to compare the effectiveness of oil palm trunk
fibers used at relatively low volume fractions, in enhancing the mechanical properties of
concrete material. Fiber content ranges from zero to 3 percent by volume, fiber length is
25 mm and the concrete matrix compressive strength is about 30 MPa. Flexural and
compression tests were conducted according to BS 1881. The influence of fiber content
on the compressive strength and modulus of rupture is presented.
Keywords: compressive strength, fiber reinforced concrete, modulus of rupture
1. Introduction
A variety of fibers type, including man-made fibers or synthetic fibers such as steel, glass,
polypropylene and natural cellulose fibers. Investigations have been carried out in many countries on
various mechanical properties, physical performance and durability of concrete materials reinforced with
natural fibers from coconut husk, palm, bamboo, sugarcane, wood and other vegetable fibers. Trends in
the fibrous concrete applications over the last two decades indicate that no one fiber material and fibrous
composite material system has emerged to dominate the marketplace [1].
The trunk of oil palm tree can also be processed to form a good source of fiber. The process of
attraction of fiber does not require a sophisticated engineering process like the synthetic fiber. With
regard to the previous research on oil palm fibers, higher lignin was found in trunk fibers. The higher
content of lignin in trunk fiber helps to reduce water absorption in MDF (medium density fiber) board [2].
MDF board from OPTF (oil palm trunk fiber) was stronger and had better fiber-to-fiber strength of with
24.13 MPa of MOE recorded then the frond and EFB MDF [3]. Hopefully similar advantageous will apply
to concrete.
Important properties of the hardened fiber reinforced concrete composite are strength deformation
under load, crack arrest, durability, permeability and shrinkage. In general, the strength is considered to
be the most important property and the quality of natural-fiber reinforced concrete is judged mainly by
their strength. The ultimate strength depends almost entirely upon the fiber types, length and volume
fraction of fibers and also on the properties and proportion of other constituent materials [4]. The critical
factors affecting the modulus of rupture for composites in which the fibers pull out, rather than break, are
the volume, shape and orientation of the fibers and the bond strength between fiber and matrix [5].
Among the
many factors,
the two
most important .factors,
which
influence the
139
maximum loads, are the volume percentage of fibers and aspect ratio [6]. As mention by previous
researchers [4,5,14,15], very small amounts of fibers have little advantageous effect although in some
cases they can modify noticeably the properties of the hardened composite. Higher proportions of fibers
have a tendency to prevent complete compaction of the fiber reinforced mixed. The sequence of this can
be a substantial loss of compressive strength and poor durability of the hardened product. Therefore
based on this report, the main objective of this study is to compare the effectiveness of OPTF in
enhancing the mechanical property namely flexural strength and compressive strength of concrete
material for different volume percentage of fibers.
2. Research background
Economics and other related factors in many developing countries where natural fibers of various
origin are abundantly available, demand the construction engineers and builders apply appropriate
technology to utilize these natural fibers as effectively and economically as possible to produce goodquality fiber reinforced composite materials for housing and other need. Considerable research has
already done in investigating the properties of natural-fiber reinforced cement or concrete products using
fibers such as coconut coir, sisal, sugarcane bagasse, bamboo, jute, wood and vegetables in more than
40 countries [7]. Of particular interest has been the use of oil palm trunk fibers in the concrete, being
waste material from the clearance of the oil palm plantation. Tremendous amount of trunks is generated
during the replanting and not being effectively used.
3. Objective
This study is a part of a broad research program on the compatibility study of oil palm trunk fiber as
concrete reinforcement. The main objective of this study was to investigate the mechanical properties of
OPTF reinforced concrete namely compressive strength and flexural strength. In addition to that is to
obtain preliminary information on the relative difference in compressive strength and flexural strength
amongst the different percentage of fibers used in the matrix.
4.0 Experimental program
4.1 Materials
The oil palm trunk fibers were taken directly from the plantation when the trees newly fell using
special excavator machine. After that the fibers were undergone cleaning process to remove the
parenchyma. This parenchyma needs to be removed since it contains sugar, which can retard the
concrete hardening process. Then the fibers were cut according to specified length (25 mm). According to
ACI 544.1 R-60 [6], the length of fibers may vary from 25 to 500mm. For this study the fiber length is fixed
at 25mm. OPT fiber is light yellowish when in fresh state as shown in Fig. 1.0. However, the color
changes as the fiber tend to become dry, from light yellowish to dark brown. Even though the color
changes but the fiber still carries strength. The basic requirements of natural fibers when used as
reinforcement in concrete matrices are high tensile strength and elastic modulus. The tensile strength of
the fiber was found to be 300 - 600 N/mm 2 . Bulk density of fibers is 1200 kg/m 3 • The diameter of clean
fiber is between 0.3 - 0.6 mm. When compared with other natural fibers that have been used, OPTF
tensile strength is comparable and in certain fiber types, OPTF is better as shown in Table 1.0.
Fig. 1.0 Oil palm trunk fiber
140
Table 1.0 Properties of natural fibers
Bulk Density
(kglm 3)
1200
145-280
700-800
NA
NA
NA
NA
Fiber types
Oil palm trunk
Coconut
Sisal
Sugarcane
Bamboo
Jute
Flax
(Source: Aziz M.A .et al) [8]
Tensile Strength
(N/mm2)
300-600
120-200
280-568
170-290
442
250-350
1000
NA- Not available
4.2 Mixes
The concrete constituents used were ordinary Portland cement, fine aggregate, coarse aggregate
and OPTF. Ordinary Portland cement confirmed the requirements of BS 12:1958. Fine and coarse
aggregate confirmed the grading BS 882:1992. Coarse aggregate has maximum size of 20 mm. To
compare the properties of fibrous concrete with plain concrete, water-cement ratio was kept constant at
0.5. The proportions of aggregates were kept unchanged for the same reason. Table 1.0 shows the
details of concrete mix proportions in kg/m 3 used for this investigation.
Table 2.0 : Mix Design [ in kglm1
Mix
Fiber By Volume
Cement
Water
1
0%
360
180
Coarse
Aggregate
1075
2
1%
358
179
1061
522
3
2%
355
176
1046
515
4
3%
350
175
1037
511
Fine Aggregate
530
NOTE: Batch quantities: kg/m 3
Assume R.D(relative density) for aggregate =2650 kg/m 3
Cement: Sand: Coarse aggregate (1 :1.5:3)
Maximum size: 20mm
Water cement ratio: 0.5 (constant)
4.3 Test specimen and test method
The test specimen used for flexural strength was 150 x 150 x 750 mm rectangular beam. In total 72
such beams have been cast. The mixing of fiber in concrete was performed according to the ACI 544-1 R57 recommendations.
The plain and fiber reinforced concrete mixtures were manufactures in a rotary drum mixer. The
mixing procedure is described in the following:
1.
Charge the mixer with all the sand and gravel.
2.
Start the mixer and add one-third of the water.
3.
Add all the cementitious materials together with another one-third of the water over a 4 min. period.
4.
Add the fibers to the mix in a gradual manner such that bunching up of fibers on the mix is
prevented; the addition of fibers usually takes about 3 mins.
5
Add remaining cementitious materials followed by the remainder water to the mixture over a
3-min period.
Fresh plain and fibrous mixes were tested for workability by slump (BS 1881: Part 102: 1983) and
VeBe (British Standard 1881: Part 104: 1983) test methods. Specimens for hardened material tests were
then manufactured by casting fresh concrete inside molds with compaction achieved through external
141
vibration. All the hardened specimens were cured according to BS 1881: Part 111: 1983 by water
immersion.
The following tests were performed on hardened concrete specimens;
1. Flexural strength tests were performed for each mix composition on 150 x 150 x 750 mm
prismatic specimens in accordance to BS 1881: Part 118: 1983 using third point bending. The
tests were carried out for three different days of curing; 3,7 and 28 days.
2. Compressive strength tests were performed for each mix composition according to BS 1881: part
119: 1983 (Method for Determination of compressive strength using portions of beams broken in
flexure) also for different curing days; 3,7 and 28 days.
5.0 Experimental result
All test results are summarized in Table 3.0, while graphical presentations of the results are displayed
in Fig. 2.0, Fig. 3.0 and Fig. 4.0. Each strength value presented in Table 3.0 is the average of 6
specimens. A total of 72 beams for flexural and 72 broken beams for compressions were tested in this
investigation. The results of this investigation are applicable to the material and type of fiber used.
Table 3.0 Summary statistics for the volume study
0
133
106
2
3
98
65
mean
mean
3
11.99
16.2
7
16.43
20.70
28
27.24
31.00
3
19.33
22.7
7
28.1
29.8
28
32.24
35.1
3
14.2
14.9
7
15.63
18.1
28
22.26
25.1
3
11.13
11.2
7
14.38
17.4
28
23.83
20.1
An analysis of variance was performed to determine if there were differences in mean flexural
strength (modulus of rupture), and compression strength, among the difference volume of fiber tested. As
indicated through ANOVA, there is convincing evidence that fiber volume affects or influence the flexural
strength [p-value=0.02] and also affects the compressive strength [p-value = 0.01] at 5% significance
level. The result presented in Fig.4.0 indicate that the flexural strength obtained with 1.0 percent volume
fraction of OPTF can be reached at 18.35 percent greater or 2.2 times the corresponding properties of
plain concrete. Presence of 1.0 percent fiber also increases the compressive strength by 13.22 percent or
1.1 times than the plain concrete as shown in Fig. 4.0. Compressive strength is more dominants
compared to flexural strength with the inclusion of OPTF.
To determine how the volume of fibers affects the compressive strength, a linear regression was
performed. The regression analysis yielded strong evidence that volume percentage affects the
compressive strength [p-value =0.005]. However, the relationship between compressive strength and
volume of fiber was not very strong [R2 = 0.562] at 28 days. The variation in the compressive strength is
142
explained by 56.2 percent variation in the volume of fiber used. The other 43.8 percent variation can be
explained by other factor such as length of fibers, moisture content, absorption capacity of the fiber,
mixing method and etc. Previous researches [1] indicate that volume of fiber affect or increase the
compressive strength at the 1.0% volume fraction. The addition of 1.0% (volume) of jute fiber gives
13.49% increases in the compressive strength [6]. The same analysis was performed to determine how
fiber volume affected the flexural strength. Test results and regression lines (with 95% confidence
intervals) representing the effects of OPTF reinforcement on flexural strength and compressive strength
of concrete are presented in Fig. 5.0(a), and (b). The flexural and compression strengths are observed to
increase with OPTF reinforcement at the lower dosage and tend to decrease as the amount of fiber
increases.
Fig. 6.0 (a), shows the diameter size of the fiber and the bonding between fiber and the matrix. The
loose interface in the bonding may contribute to the strength reduction when further increase in fiber
volume. At 1.0 percent, the effect of fiber in transferring (distributing) the stress is dominant. However for
more than 1.0 percent, the second effect (loose interface) is dominant. The reduction in strength as the
volume of fiber increases may also due to the increase in void content, since the water/cement is
maintained. This can reduce the workability as the amount of fiber increases that can be seen from the
value of slump as shown in Table.3.0. The use of fibers as reinforcement of concrete and cement
therefore requires frequent adjustment of the mix proportions in the process of maximizing the positive
contributions of the fibers to chosen properties of hardened concrete [13]. Therefore in this study, the
addition of 1.0 percent fiber volume cannot be concluded as the optimum contribution. In this
investigation, the mix proportions is fixed, therefore it can only conclude that the addition of OPTF does
improve the compressive and flexural strength of the concrete. Further investigation need to be done in
order to conclude the optimum amount of OPTF in maximizing the properties of concrete.
6.0 Conclusion
The effectiveness of OPTF in enhancing the mechanical properties of concrete materials was
compared with plain concrete. All the plain and fibrous concrete mixtures were designed with a fixed
proportion. The only variable parameter is the percentage of volume fiber; 0,1,2, and 3. The hardened
material mechanical properties were assessed through flexural and compression tests. The following
conclusions were derived.
1. Oil palm trunk fibers increased the flexural strengths of concrete material with 1.0 percent volume
fraction of OPTF. The average flexural strengths were 18.35 percent higher or 2.2 times the
corresponding properties of plain concrete.
2. Oil palm trunk fibers increased the compression strengths of concrete material with 1.0 percent
volume fraction of OPTF. The average compression strengths were 13.22 percent higher or 1.1
times, the corresponding properties of plain concrete.
3. OPTF fibers, when used at 1.0 percent volume fraction, produced compressive strength and
flexural strength comparable to those obtained with other fibers such as jute.
4. 1.0 percent volume fraction is not the optimum amount of fiber needed to increase the strength.
There are other factors need to be studied.
143
Fig.6.0(a): The diameter size of
the fiber
Fig.6.0(b): The bonding between fiber
and matrix
~r------------------------,
~
/ \
\
I
I
J
I
I
I
I
f
/ \
'-
\
\
'-
\
\
a DAYS28
\
VOL
a OAY28
'
VOlUME
1I:~'~-'~' __ '_""i:l
VOl.
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DAY7
.. DAVS3
VOLUME
VOL
a OAY3
VOlUME
Percentage 01 Fibers
Volume Percentage of Fibers
Fig.2.0: Flexural strength (Nlmm2) vs Percentage
of fibre (volume) for variation days of curing 3,7
and 28.
Strength (Nlmm2) versus Volume
Percentage of Fiber
J.!. COMF
VOL
A R.EXI
VOL
Volume percentage of fiber
Fig. 4.0 : Flexural Strength and compression
strength (Nlmm 2) vs Percentage of fiber (Volume) for
28 davs
144
Fig.3.0: Compressive strength (N/mm2) vs
Percentage of fibre (volume) for variation days
of curing 3,7 and 28.
50 ~-------------------------------------------------------,
~
~
40
.<::
'g>
~
.,
30
.~
(J)
[l!
~
o
20
U
10 +------,------~------r_----_r----~r-----_r----~,_----~
-.5
0.0
.5
1.0
1.5
2.0
2.5
3.0
3.5
Percentage of Fibers
Fig.5.0 (a); Relationship between Compressive
Strength and Volume of Fibers at 28 days.
32
30
@'
E
E
%
-='"c:
~
e
::>
x
u..
28
26
24
.9!
22
20
-.5
0.0
.5
1.0
1.5
2.5
Volume percentage of fiber (%)
Fig.5.0 (a): Relationship between Flexural Strength
and Volume of Fibers at 28 days
145
3.0
3.5
8.0 Acknowledgments
The authors are thankful to the University Technology Mara, Malaysia (Biro Research Center) for
providing this project with financial support. Bio-Alam Sdn. Bhd provided the materials used in this
investigation. These contributions are gratefully acknowledged.
The authors would also like to thank Mr. Saiful and Mr. Mohd Nazir for providing this project with their
help in the experimental work.
References:
[1] Sorovshian, P., and Khan, Hsu, J.w., " Mechanical Properties of Concrete Materials Reinforced with
Polypropylene or Polythylene Fibers," ACI Material Journal, V.89, No.6, Nov - dec 1992, pp 535 - 540.
[2] Myers, G., and J.D. McNatt (1993) "Selected Properties of Commercial High-Density Hardboards."
Forest Products Journal Vol. 43(4) : 59-63
[3] Liew, Lionel (1996) " Properties of Medium Density Fiberboard Made from Oil Palm (Elaeis
guineensis) Fibers." Master Forestry (Wood Industry) Project Report. Faculty of Forestry, University
Putra Malaysia, Serdang
[4] Aziz M.a, Paramasivam P., Lee S.l., " Concrete Reinforced with natural fibers", Proceeding Concrete
Technology & Design, Vol. 2, 1984, pp. 106-115
[5] Keer, J.G., "Natural Fiber Reinforced Concrete and Cemenf', Proceedings Concrete Technology &
Design, Vol. 1, 1984, pp.65 - 67
[6] ACI Committee 544-1 R " Natural Fiber Reinforced Concrete," ACI Journal Proceedings, V.79, SeptOct 1982, pp.57 - 64
[7] Fordos, Z., " Fiber Reinforced Concrete" ,Proceedings Concrete Technology & Design, Vol. 5, 1984,
pp.32- 41
[8] Aziz M.a, Paramasivam P., Lee S.l., " Concrete Reinforced with natural fibers", Proceeding Concrete
Technology & Design, Vol. 2,1984, pp.119-120
[9] BS 1881: Part 102 : 1983: Slump Test
[10] BS 1881: Part 104: 1983: VeBe Test
[11] BS 1881: Part 111 : 1983: Curing Method By Water Immersion
[12] BS 1881: Part 118 : 1983: Method for Determination of Flexural Strength
[13] BS 1881: Part 119 : 1983: Method for Determination of Compression Strength using Portion of
Broken Beams in Flexure (equivalent cube method)
[14] P. Bortos, Fresh Concere: Properties and Test, Elsevier Science Publishers B.V., 1992 , pp. 235 236
[15] Faisal F.w., and seminar A.A., "Mechanical properties of High Strength Fiber Reinforced Concrete."
ACI Materials Journal, V.89, No.5, Sept-OCT.1992,pp.449-452
146