CC BY-NC-ND
0International Journal of Sustainable Built Environment (2014) xxx, xxx-xxx
Gulf Organisation for Research and Development International Journal of Sustainable Built Environment
ScienceDirect www.sciencedirect.com
Original Article/Research
Mechanical performance and durability of treated palm fiber
reinforced mortars
Nesibe Gozde Ozerkan a, Bappy Ahsan a, Said Mansour b, Srinath R. Iyengarc *
a Center for Advanced Materials, Qatar University, Qatar Qatar Energy & Environment Research Institute, Qatar c Department of Mechanical Engineering, Texas A&M University, Qatar
Received 10 November 2013; accepted 18 April 2014
11 Abstract
12 The performance of cement mortar reinforced with varying percentages of treated bundled date palm fibers is investigated to appraise
13 their feasibility for structural and non-structural applications. The study first entailed the evaluation of two different alkali pre-treat-
14 ments at varying concentrations by subjecting treated and untreated bundled fibers to tensile testing. The suitable pre-treatment was then
15 adopted while casting cement mortar mixes. The physical properties of fresh mortar was studied through setting times and, for mortar
16 mixes cured up to 28 days, through parameters such as drying shrinkage and water absorption. The unconfined compressive strengths,
17 split tensile strengths as well as the flexural strengths of the cured mortar mixes at two different ages were undertaken to assess their
18 mechanical properties; while the durability was gauged based on their sulfate resistance for up to a period of four months.
19 Observed stress-strain behavior under tension led to the choice of 0.173% Ca(OH)2 as the preferred pre-treatment for the bundled
20 fibers used in the mortar mixes. This was further supported by the microstructural examination on the hardened mortars which, revealed
21 that the integrity of treated fibers remained intact within the cement matrix without hindering the hydration processes. Results also indi-
22 cated that inclusion of fibers improves the flexural strengths as well as the sulfate resistance of the mortar mixes. However, the cylinder
23 and cube compressive strengths decreased with the increase in treated fiber inclusion.
24 Although, the work reported in this paper was carried out on cement mortars, conclusions are expected to be relevant to fiber
25 reinforced concrete employing treated natural fibers.
26 © 2014 The Gulf Organisation for Research and Development. Production and hosting by Elsevier B.V. All rights reserved.
27 Q4 Keywords: Fiber reinforced mortar; Durability; Flexural strength; Date palm fibers; Mortars (materials); Mechanical performance
1. Introduction
* Corresponding author. Tel.: +974 44230497; fax: +974 44230011. E-mail addresses: gozdeozerkan@qu.edu.qa (N.G. Ozerkan), ahsan@ qu.edu.qa (B. Ahsan), smansour@qf.org.qa (S. Mansour), srinath. iyengar@qatar.tamu.edu (S.R. Iyengar).
Peer review under responsibility of The Gulf Organization for Research and Development.
Concrete and mortars made with Portland cement are 30
known to be easy to form and relatively strong in compres- 31
sion but weak in tension, tend to be brittle and have poor 32
impact strength and toughness. The weakness in tension 33
could be overcome by the use of conventional rod 34
reinforcement and to some extent by the inclusion of a 35
sufficient volume of certain fibers (Mehta and Monterio, 36
1997; Neville and Brooks, 1990; Price, 1951). 37
2212-6090/$ - see front matter © 2014 The Gulf Organisation for Research and Development. Production and hosting by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ijsbe.2014.04.002
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38 In concrete, fibers can be introduced as primary or
39 secondary reinforcement. Fibers work as primary rein-
40 forcement in thin-sheet products in which conventional
41 reinforcing bars cannot be used and includes no coarse
42 aggregate and a matrix with markedly higher cement con-
43 tent than normal concrete. The fibers are used as primary
44 reinforcement to increase both the strength and toughness
45 of the composite. Fibers are also included in the matrix as
46 the secondary reinforcement to control cracking induced
47 by humidity or temperature variations or to provide
48 post-failure integrity in the event of accidental overload
49 or spalling (Filho et al., 1999; Bentur and Mindness, 2007).
50 Reinforcing cement matrices with various fibers have
51 been reported to resist rapid propagation of micro cracking
52 under applied stress as well as the ability to withstand loads
53 even after initial cracking, thereby improving toughness
54 (Yurtseven, 2004). Furthermore, increase in the flexural
55 strength of the fiber-cement composite up to 30% had been
56 observed; however, fiber inclusion reduces the workability
57 Q5 of the fresh concrete and mortars (ACI, 2010).
58 Several fiber types in a variety of sizes, both manmade
59 and natural, have been incorporated into cement based
60 matrices which composed of paste, mortar or concrete.
61 The choice of the most commercially significant types of
62 fibers varies from synthetic organic materials such as poly-
63 propylene or carbon, synthetic inorganics such as steel or
64 glass, natural organics such as cellulose or sisal to natural
65 inorganic asbestos. Although, most of the developments
66 involve the use of ordinary Portland cement; the use of
67 high alumina cement, cement with additives such as fly
68 ash, slag, silica fume, etc. to improve the durability of the
69 composite or to minimize chemical interactions between
70 the fibers and matrix have also been reported (Bentur
71 and Mindness, 2007).
72 Natural fibers; either unprocessed or processed, have
73 been used to reinforce cement based products in various
74 applications around the world. These include materials
75 Q6 obtained from different parts of plants. For example, fibers
76 of jute, ramie, flax, kenaf and hemp are obtained from the
77 stem whereas sisal, banana and pineapple are obtained
78 from the leaf and cotton and kapok from the seed. Natural
79 fibers are composites with a cellular structure including dif-
80 ferent proportions of cellulose, hemicellulose and lignin
81 which constitute different layers (Filho et al., 1999; John
82 et al., 2005).
83 Natural fibers have a high tensile strength and a low
84 modulus of elasticity; however, they have a high variation
85 on their properties which could lead to unpredictable
86 fiber-cement composite properties (Swamy, 1990; Li et al.,
87 2006). There are several studies on the evaluation of the
88 use of different types of natural fibers in concrete and mortar
89 applications. Aggarwal (1995) suggested that in countries
90 where bagasse is substantially available, it can be used for
91 the production of cement-bonded building materials, since
92 the results obtained from the study showed that the devel-
93 oped composites meet most of the requirements of various
94 standards on cement-bonded particle boards and have high
levels of performance even in moist conditions. Coconut 95
fibers can also be used as reinforcement and to substitute 96
sand in the development of composite reinforced coconut 97
fiber. Moreover, increasing the content of coconut fiber 98
increased the modulus of rupture and compressive strength 99
of the composites up to a certain optimum composition. The 100
composites manufactured with short coconut fibers and 101
ordinary Portland cement matrix presented a significant 102
reduction in toughness (Abdullah et al., 2011; Filho et al., 103
2000). On the other hand, bamboo fiber is a satisfactory 104
fiber for incorporation into the cement matrix, and does 105
not vary greatly in flexural strength and fracture toughness 106
values (Coutts, 1995). It is also proved that the composites 107
reinforced with sisal fibers are reliable materials to be used 108
in practice for the production of structural elements to be 109
used in rural and civil construction, and improvement in 110
flexural strength and splitting tensile strength was reported 111
(Filho et al., 1999; Al Rawi and Al Khafagy, 2009). Several 112
other studies have been carried out on evaluating the 113
behavior of cement composites with natural fibers from 114
bamboo (Ghawami, 2005), sisal (Filho et al., 2009), coir 115
(Aggarwal, 1992), vegetable origin (Agopyan et al., 2005; 116
Toledo Filho et al., 2005), etc. 117
Although natural fibers have some advantages like low 118
density, less abrasiveness, and lower cost when compared 119
to inorganic reinforcing fibers, they also have some disad- 120
vantages such as mechanical and thermal degradation dur- 121
ing processing, poor wettability and high moisture 122
absorption. Moreover, it is known that the natural fibers 123
include high content of hydroxyl groups (OH) which causes 124
the hydrophilic behavior. The hydrophilic behavior of fiber 125
produces poor adhesion between fiber and matrix when the 126
natural fiber is faced to develop composite material. This 127
problem is mainly improved by several chemical treatment 128 methods suggested by researchers. These treatment meth- Q7 129
ods range from being saline treatment, alkali treatment 130
and graft copolymerization of monomer. In order to mod- 131
ify and clean the surface of natural fiber, alkali treatment is 132
one of the most common methods employed. Alkali treat- 133
ment has been reported to decrease the surface tension and 134
to improve the interfacial adhesion between the fiber and 135
matrix. Furthermore, in the literature, several possible 136
explanations can be found discussing the positive effects 137
of alkali treatment on the properties and structure of nat- 138
ural fibers (Tan, 1997; Bledzki and Gassan, 1999; Rong 139
et al., 2001; Aziz and Ansell, 2004; Weyenberg et al., 140
2006; Bachtiar et al., 2008; Kriker et al., 2008; Bachtiar 141
et al., 2012; Nordin et al., 2013). 142
Date palm trees are native to the middle-east region; 143
their fibers can be easily and abundantly found in countries 144
like the State of Qatar. The idea of reinforcing concrete 145
with date palm fibers was studied by Kriker et al. (2005). 146
They had looked into the durability and mechanical prop- 147
erties of date palm surface fibers in hot-dry climate. They 148
concluded that Male date palm surface fibers (MDPSFs) 149
had the most tensile strength compared to other types of 150
date palm fibers. As the volume of fiber is increased in 151
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the concrete, more post-crack flexural strength and toughness coefficient were observed but at the same time a reduction in first crack and compressive strength was noted. Another research was launched by the same group to study the durability of male date palm surface fibers immersed in alkaline solutions which resulted in concluding that the durability of MDPSF reinforced concrete is poor (Rao and Rao, 2007). Also it was reported that the male date palm surface fiber had an average tensile strength and weak elastic modulus and the increase in percentage and length of the fiber in concrete has a beneficial effect on the ductile behavior (Kriker et al., 2005).
Hence, there is a need for further investigating properties of date palm fibers and understanding their contribution to the performance of cement-fiber composites.
2. Materials and methodology
The objective of this paper is to evaluate the performance of cement mortar reinforced with varying percentages of treated bundled date palm fibers so as to appraise their feasibility for structural and non-structural applications.
2.1. Materials
2.1.1. Fiber sampling and extraction
Date palms are classified as male and female tree. While the female trees produce flowers, the male trees produce pollen. In this study, the female date palm leaves were used according to the previous researches (AlMaadeed et al., 2013), it is discovered that female leaves have better tensile properties. The date palm leaves were obtained from the female trees which are planted at the women campus of the Qatar University. The female trees bear the date fruits. The bundled fibers (thickness 0.7-4 mm) were peeled out by means of scissors from date palm leaves and cutting them in lengths of 10 cm.
2.1.2. Fiber pretreatment
The treatment of date palm fibers was performed by NaOH and Ca(OH)2 solution immersion. The NaOH pellets used to prepare the solution were manufactured by the BDH Laboratory Supplies, U.K. and were of general purpose reagent category. Extra pure Ca(OH)2 was used to prepare the second solution and was supplied by Riedel-de Haen, Germany.
2.1.3. Mortar preparation
Sand (or fine aggregate) procured from the Qatar Sand Treatment Plant, having 2.73 specific gravity, unit weight (i.e. the weight per unit volume of a material) of 1.65 kg/l and water absorption of 2.15% and ordinary Portland Cement Type I supplied by Al Khalij Cement Company which conforms to BS EN 197-1 (BSI, 2000), were used in this study.
The mortar mixes used in this study have been detailed in Table 1.The volume fraction is defined as the volume of fibers divided by the volume of the composite (fibers and concrete), and typically ranges from 0.1 to 3%. In this study, the aim was to vary the volume fractions of the bundled fibers in the mix beyond 2.0%. However, while attempting to do so, during sample preparation, excessive separation of the mortar components was observed which pose difficulty in mix workability as well as in preparing and obtaining monolithic compacted samples. Hence, it was decided to limit the maximum fiber inclusion to 2.0%.
2.2. Experimental methods
2.2.1. Fiber pretreatment
The bundled fibers were treated by immersing individually either in 2.0% of NaOH solution (based on recommendations from study performed by AlMaadeed et al., 2013) or 0.173% Ca(OH)2 (as per room temperature solubility range). Additionally, for direct comparison, 0.173% of NaOH solution was also considered. The fibers were immersed in the solution for an hour and then placed in an oven at 60 °C for 3 h to dry. 10 cm length of treated fibers was then cut to prepare them for the tensile test.
2.2.2. Fiber properties
Tensile test was performed using a Lloyd 1KN tensile tester to examine the elongation and maximum tensile load that can be applied to bundle palm leaf fibers (treated and untreated) of 10 cm length whose thickness ranged between 0.7 mm and 4 mm. The procedure specified in ASTM-D3822 (ASTM, 2007) was followed. A minimum of at least 10 replicates of treated and untreated fibers were tested. The tensile tester was equipped with a linear variable differential transformer (LVDT) to measure the corresponding deformation/strains and Young's stiffness modulus (E).
2.2.3. Mortar and sample preparation
Sand, cement, water and treated palm fiber bundles were mixed to prepare the fresh mortar in a concrete mixer for four mixes with varying percentages (i.e. 0.0%, 0.5%, 1.0% and 2.0 wt.%) of treated date palm fiber bundles. The mortar was placed in molds to prepare four kinds of samples namely cylindrical, cubical, prism and shrinkage/ sulfate whose dimensions are provided in Table 2. After 24 h, the samples were demolded, marked, dimensions taken and immersed in large drums filled with tap water at room temperature to cure.
2.2.4. Physical properties of the fresh and hardened mortars
The setting time of the fresh mortar was recorded using
a Vicat's apparatus in accordance to ASTM C807 (2008). The ASTM C1403 (ASTM, 2012b) method was followed to measure the water absorption of the hardened mortar after 7 and 28 day curing time. The sorptivity test method was based on the ASTM C1585 and was used to determine
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Table 1
Details of the mortar mix designs.
Mix No. w/ca Fiber inclusion Sand Cement
(wt.%) content (kg/m3) content (kg/m3)
1 (control) 0.485 0.0 1197 400
2 0.515 0.5 1173 400
3 0.540 1.0 1157 400
4 0.550 2.0 1127 400
w/c denotes water-to-cement-ratio.
Table 2
Dimensions of mortar samples.
Sample type Dimensions (mm)
Cube 50 x 50 x 50
Cylinder 100 x 200 (diameter x length)
Shrinkage/Sulfate Bars 280 x 25 x 25
Prism 160 x 40 x 40
the rate of absorption of water by hydraulic cement concrete by measuring the mass increase of a disk specimen at 1, 5, 10, 20, 30, 60, 180, 240, 300 and 360 min time intervals when one surface of the specimen was submerged in 3-5 mm of water. The water absorption and the sorptivity tests were performed in triplicates. The change in length of the mortar bar samples was measured to identify the drying shrinkage according to ASTM C 596 (ASTM, 2009). Length comparator readings of the mortar samples were recorded on the 4, 11, 18, and 25 days of sample curing. Shrinkage results were based on observations made on six replicate specimens per mix.
2.2.5. Mechanical testing
Mechanical testing of hardened mortar samples after 7 and 28 days of curing tests was performed in triplicate. Cylindrical and cubical samples were subjected to compressive loading based on ASTM C 39 and C 109 (ASTM, 2012, 2012a), respectively; wherein the maximum load and stress at failure were recorded. The flexural strength of the prism samples was determined according to ASTM C293 (ASTM, 2010) by the three point bending test. The load at failure was noted and accordingly, the flexure strength of the sample was then calculated. The tensile splitting test of the cylindrical samples was performed as per ASTM C496/C496M (ASTM, 2011) by applying compressive force along the length of the specimen until failure.
2.2.6. Durability studies
The sulfate resistance of the mortar bars was determined according to ASTM C 1012 (ASTM, 2013a,b). The mortar bars were cured in lime water as per Section 9.2 of the aforesaid standard and then immersed in sodium sulfate solution. The length changes were measured using length comparators in the durations as provided in Section 9.4 of the standard. Six replicate specimens per mix were subjected to durability testing for a period of up to 4 months.
2.2.7. Microstructure analyses 288
The microstructure and crystallinity (viz. scanning elec- 289
tron microscopy and X-ray diffraction) of the various types 290
of cured mortars reinforced with treated date palm fibber 291
bundles were studied. FEI Quanta 400 Scanning electron 292
microscope was used to study the microstructure of fibers 293
and that of the hardened fiber reinforced mortars. SEM 294
of samples was employed by firstly being dried and then 295
mounted on an aluminum stub using a strong conductive 296
double-sided adhesive tape. 297
X-ray diffraction was used to identify the crystalline 298
phases and the corresponding orientation of various 299
compounds in the 28 day cured fiber reinforced mortars. 300
Rigaku Ultima IV 2-Theta-2-Theta type X-ray Diffractom- 301
eter fitted with a copper anode diffraction X-ray tube oper- 302
ating at 40 kV and 40 mA was used in this study. The Peak 303
Search and Qualitative Analysis software provided by 304
Rigaku using JCPDS-ICDD library (PDF-2 Release 305
2007) was employed to identify the peaks of the raw 306
XRD data. 307
3. Results and discussions 308
3.1. Fiber properties and choice of pretreatment 309
Tensile strength (TS) was chosen as one of the parame- 310
ters to assess the performance of the treated and untreated 311
fibers taking into account the maximum stress observed 312 along with Young's modulus (E); which is a measure of 313
the tensile stiffness of the fibers under service loads and is 314
experimentally determined from the slope of a stress-strain 315
curve. 316
In order to obtain meaningful comparison of the various 317
fibers, both the strength and stiffness parameters were con- 318
sidered together. Therefore, a straightforward scatter plot 319
in Fig. 1 indicates the relation between the TS and E. Results 320
fell between the curves: 40.00*TS < E (MPa) < 78.13*TS. 321 Moreover, it is seen from the figure that the majority of 322
the points fall close to a single center line, represented by 323 E«56*TS. Also, it can be observed that the data for Q8 324
0.173% Ca(OH)2 treated fibers display closer correlation 325
with less variation compared to the aforesaid trend. 326
It can be inferred that the tensile strengths and stiffness 327
properties of the fibers are generally better for those treated 328
with Ca(OH)2 than those treated with NaOH. Further- 329 more, Fig. 2 presents the stress-strain profiles for untreated Q9 330
and treated using 0.173% Ca(OH)2, 0.173% NaOH and 331
2.0% NaOH bundled fibers. It is evident that treated fibers 332
experienced an overall loss in stress resistance when com- 333
pared to the untreated fibers. 334
It is also observed that the stress-strain curves for 335
0.173% Ca(OH)2 treated fibers displayed lesser variation 336
and more consistency in comparison with the untreated 337
fibers and NaOH samples treated at different concentra- 338 tions. Furthermore, changing NaOH concentration from 339
2.0% to 0.173%; do make slight favorable difference in 340
the tensile behavior of the bundled fibers. 341
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4,000 -
2,000 -
1,000 -
A Untreated Fibers ^ A O J /
□ Treated with 2.0% NaOH o Treated with 0.173% NaOH A ^ /
0— * O A a ^ oaao ^ o n __<
O Treated with 0.173% Ca(OH)2
□ □ / — A o <x> □ 0 A O
/ / / /
/ / / /
30.0 45.0 60.0
Tensile Strength - TS (MPa)
Fig. 1. Tensile Strength (TS) versus Young's Modulus (E) relation for fibers with and without various treatments.
342 Hence, it was decided to pursue only 0.173% Ca(OH)2 Also, since cement hydration releases calcium hydroxide it 345
343 treatment for further investigations with mortar mixes, is unlikely that fibers already treated specimens will 346
344 because the fibers displayed more or less uniform behavior. undergo further structural degradation.
N.G. Ozerkan et al. /International Journal of Sustainable Built Environment xxx (2014) xxx-xxx
Table 3
Setting time test results of mortar samples.
Mix No. Fiber Inclusion (wt.%) Average setting times (h) Initial Final
1(Control) 0.0 3:00 4:00
2 0.5 3:15 3:55
3 1.0 4:25 5:00
4 2.0 2:20 2:45
348 3.2. Physical properties of the fresh and hardened mortars
349 The physical properties of fresh and hardened mortars
350 were evaluated by performing the setting time, drying
351 shrinkage, water absorption and sorptivity tests.
352 Table 3 shows the average setting times of the various
353 mortar mixes tested. The overall trend seems to suggest
354 that the setting times are prolonged with the increase in
355 the fiber content. Although, with 2.0% of fiber inclusion,
356 the setting time decreased; which could be due to water
357 being absorbed by the excess fibers per se thereby making
358 the mix set quickly.
359 Fig. 3 represents the results of drying shrinkage test for
360 each mortar mix prepared in the study. It can be seen that
361 all mixes including different palm fiber ratios show different
362 shrinkage behavior. The rate of increase in shrinkage for all
363 mortar, except the mixture including 2.0% palm fiber, was
364 high up to 18 days which is a result of curing process, and
365 after 18 days it can be noticed that palm fibers have effect in
366 reducing shrinkage. Moreover, it can be observed from the
367 figure that the mortars reinforced with 2.0% palm fiber,
368 which is the maximum ratio tested in this study, has the
369 least shrinkage. This finding is in agreement with findings
370 of Singh et al. (2010) which showed that a higher volume
371 fraction, 4% of oil palm trunk fiber reduces shrinkage for
372 different core diameters.
373 Water absorption and sorptivity test results for mortar
374 mixes are presented in Figs. 4 and 5, respectively. The level 375Q10 of accuracy is shown in the figures by the error bars and
376 was generally similar for all mixes with average and maxi-
377 mum values of 5.86% and 9.23% respectively. These figures
378 indicate, that the mortar reinforced with 0.5% palm fiber
Fig. 4. Effect of palm fiber ratio on water absorption capacity of mortar samples.
Fig. 3. Effect of palm fiber ratio on drying shrinkage.
i Fiber Ratio I
Fig. 5. Effect of palm fiber ratio on sorptivity of mortar samples.
has the highest water absorption capacity and water 379
absorption rate whereas the lowest water absorption capac- 380
ity and water absorption rate are given by the reference 381
sample. For the mortar mixes reinforced with 1.0% and 382
2.0% palm fiber (i.e. mixes 3 and 4 respectively), it can be 383
observed that the water absorption rate and capacity 384
decreased with increasing weight percent of palm fiber. 385
Although, these results differ from some published studies 386
(Aggarwal, 1995; Abdullah et al., 2011; Abdullah et al., 387
2013), they are consistent with those of other studies 388
(Ghavami, 1995; Filho et al., 2003; Bilba and Arsene, 389
2008; Savastano et al., 2001; Juarez et al., 2007; Parveen 390
et al., 2012) and suggest that alkali treatment applied on 391
natural fibers reduces the water absorption capacity by 392
removing hemicellulose and lignin or by imparting 393
hydrophobicity. 394
3.3. Mechanical testing 395
The mechanical test results including compressive 396
strength, flexural strength and split tensile strength of 397
mortars are presented in Figs. 6 and 7. For compression 398
test, two types of samples were tested viz. 5 x 5 x 5 cm 399
cubic samples and 10 x 20 cm cylindrical samples. 400
As seen in these figures, the compressive strength is 401
slightly increased in value with low fiber content as 402
compared with the control mix. High compaction between 403
the fibers and the cement matrix was likely achieved 404
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Fig. 6. The effect of palm fiber ratio on the compressive strength for cube mortar samples (the level of accuracy ranged between 3.53% and 15.22%).
Fig. 9. The effect of palm fiber ratio on split tensile strength of mortar samples after 7 and 28 days (the level of accuracy varied between 3.28% and 17.86%).
Palm Fiber Ratio (%) 3l
Fig. 7. The effect of palm fiber ratio on the compressive strength of
cylinder mortar samples (the level of accuracy ranged between 3.53% and 0.5
15.22%).
leading to good homogeneity in mix with 0.5% fiber inclusion, and this finding corroborates with the findings of Ismail (2005) who showed that the compressive strength and bulk density slightly improved with low fiber content in the range of 0.3-1.5%. However, if the fiber content exceeds the value of 0.5%, the compressive strength of mortar samples decreases which also seems to be consistent with other studies (Shimizu and Jorillo Jr., 1992; Sorovshian and Khan, 1992; Islam et al., 2011; Awwad et al., 2011).
Fig. 8 represents the results of flexural strength test performed on 4 x 4 x 16 cm prism mortar samples. The estimated error ranged between 1.80% and 11.72%. The results corroborate the findings of compressive strength test results, i.e. flexural strength increases with lower fiber content, 0.5% and 1% as compared with the control mix, and decreases with higher fiber content.
-♦-■Control Mix —■— 0.5% Palm Hber
—A— 1% Palm Hber —O— 2% Palm Hber
/' \ X--A
i L j
J ^ 'Vr--1 " \ "-Il
MJA^IJ
0 7 14 21 28 56 91 105 120 Immersion Period (days)
Fig. 10. Length change due to sulfate attack vs. immersion period.
The average splitting tensile strength at 7 and 28 days is shown in Fig. 9. Trend similar to compressive strength results was observed in this case. These results are consistent with those reported by other researchers which found that splitting tensile and flexural strength increases up to 1% of natural fiber volume (Ahmad and Ibrahim, 2010; Dawood and Ramli, 2011; Ahmad and Nurazuwa, 2008).
3.4. Durability studies
Fig. 10 presents the results of resistance against sulfate attack of conventional control mortar and palm fiber reinforced mortar samples in different ratios. The results are based on the average values obtained from six test specimens per mix. The highest length change at 120 days of immersion is observed in the control mix as well as mortar reinforced with low percentage of palm fiber (i.e. 0.5%); while, mixes with 1.0% and 2.0% appear to be more resilient to length changes. Hence, it can be inferred that higher inclusion of palm fibers within mortars offers better long term durability performance and advantage in resisting sulfate attack.
3.5. Microstructure examinations
Fig. 11 depicts some of the SEM micrographs obtained from this study which sheds some light on the tensile failure
Days 0 28 Days
0.0 0.5 1.0 2.0 Palm Fiber Ratio (°/o)
Fig. 8. The effect of palm fiber ratio on flexural strength of mortar samples.
8 N.G. Ozerkan et al. / International Journal of Sustainable Built Environment xxx (2014) xxx-xxx
Untested Failed sample undergone
Sample type tensile testing
_ H [4f w Kw
r- ' J*
. _ „1»^.: Ji B ÂMSiMi
ê'PÎÉmtr iÛ vil
Untreated bundled fiber MMfiftr iWJ jjK -4m^m m f ImfâjL iilMI 4/28/2013 mag WD HV del mode -200 pm-
0.173% Ca(OH)2 treated y ' M UmU jé / AwfnPÊ^
bundled fiber fil! -'M'iMïà
MwlldiTMIFl rT IiMIIILr.ki'iJy.....„!,-■ .......... Il Imi .•..■ ' ■ »vu.™
0.173% NaOH treated il • vw ■ !■ . M"
bundled fiber BB j^f ^ r1 J 4/28/2013 mai WD HV del mode - 200 pm —
mJIOIVM IT 1 IMII ,1. ,-„■. ',!•, ,■
__ 1 )
2.0% NaOH treated bundled 1
fiber H man WT1 HV tint mnrte -XIO 11m-
IL-LMinilllMNIIHII M
Fig. 11. Typical SEM micrographs for representative untreated and treated bundled fibers at x500 magnification.
445 behavior of the treated and untreated bundled fibers. It can
446 be observed that as the concentration of the treatment
447 increased (i.e. 2.0% NaOH), the fibers became more brittle
448 and this agrees with the tensile stress-strain profiles
449 reported in the previous sections. Also, while comparing
450 the failure morphologies of the 0.173% Ca(OH)2 vs. the
451 0.173% NaOH, the contribution of the individual bundle
452 fibers in resisting the tension is more conspicuous in the
former samples; a behavior that is considered favorable 453
for mortar and concrete applications. This supports our 454
choice of 0.173% Ca(OH)2 treatment for mortar studies. 455
Typical SEM micrographs from the mortar mix cured 456
up to 28 days have been presented in Fig. 12. The abun- 457
dance of fiber bundles is observed to increase progressively 458
with their inclusion in the mixes. Moreover, the treated 459
fibers appear to remain intact within the cement matrix. 460
N.G. Ozerkan et al. /International Journal of Sustainable Built Environment xxx (2014) xxx-xxx 9
Fig. 12. Scanning electron micrographs of the 28-day mortar mixes (with and without fiber inclusion) at two different magnifications.
461 Also, the dense morphology of the CSH gel which is the
462 product of complete hydration of cement is visible in the
463 images indicating that the hydration progressed normally
464 despite the inclusion of the fibers in the mixes.
465 X-ray diffraction of the mortar mixes cured up to
466 28 days has been compared in Fig. 13. Although some
467 peaks of early hydration products such as portlandite (p),
ettringite (e) and gypsum (g) were observed, their relative 468
intensities were significantly low again supporting the 469
above argument that the treated fibers remained within 470
the cement matrix without hindering the hydration 471
processes. Calcite (c) peaks were observed which can be 472
attributed to carbonation while the conspicuous peaks of 473
quartz (q) can be attributed to the sand (i.e. fine 474
N.G. Ozerkan et al. /International Journal of Sustainable Built Environment xxx (2014) xxx-xxx
Fig. 13. X-ray diffractograms for mortar mixes (with and without fiber inclusion) at 28 days.
Angular Range (
Fig. 14. X-ray diffractograms for mortar mixes (with and without fiber inclusion) subjected to sulfate attack at 120 days.
475 aggregates) present in the mortar mixes. Hence, although
476 the preferential orientation/crystallinity was slightly differ-
477 ent, no phase change was observed between the mixes.
478 In contrast, X-ray diffraction of the mortar mixes sub-
479 jected to sulfate attack was carried out and compared in
480 Fig. 14. The samples collected for this analysis were
481 obtained from mix specimens aged up to 120 days while 482Q11 being immersed in sodium sulfate solution. In addition to
483 some of the phases reported earlier, presence of ettringite
484 (e) and strong peaks of gypsum (g) especially at 11.6° 20
485 were conspicuous which, are typical products formed as a
486 result of sodium sulfate attack in cement mortars (Prasad
487 et al., 2006). Weak peaks of portlandite (p) were also pres-
488 ent; which could imply the possibility of conversion of
489 calcium hydroxide into the aforesaid sulfate products.
490 However, the overall trend seems to suggest that with
491 increased fiber inclusion in the mixes, the intensities of
492 products of sulfate attack became low thereby implying
493 that such mixes offer better resistance to sulfate attack.
494 This is in agreement with the previous observations that
495 mixes 1.0% and 2.0% fiber inclusion are more resilient to
496 length changes.
497 Nevertheless, it is recommended to investigate exposure
498 times much longer than 120 days as well as higher sodium
499 sulfate concentrations to better understand the deteriorating
effects on the mortar mixes as well as the influence of date 500
palm fibers on improving the durability. 501
4. Conclusions 502
The tensile performance of Portland cement mortars 503
and concrete had been reported to be enhanced via the 504
inclusion of certain fibers in sufficient quantities. Natural 505
fibers such as those obtained are known to exhibit high 506
tensile strength and a low modulus of elasticity despite high 507
variation. Date palm trees are native to the middle-east 508
region; their fibers can be easily and abundantly found in 509
countries like the State of Qatar. 510
The results in this paper are based on laboratory exper- 511
iments with four mortar mixes reinforced with varying 512
percentages of treated natural date palm fiber up to 513
2.0%. For fiber inclusions greater than 2.0%, poor work- 514
ability as well as difficulty in preparing and obtaining 515
monolithic compacted samples due to excessive separation 516 of mortar components was encountered. Hence, it is rec- Q12517
ommended that such date palm fiber inclusion in mortars 518
has to be limited to less than 2.0% by weight. 519
Fibers treated with 0.173% Ca(OH)2 displayed better 520
tensile strengths and stiffness properties than those treated 521
with NaOH and hence, the former was chosen as preferred 522
N.G. Ozerkan et al. /International Journal of Sustainable Built Environment xxx (2014) xxx-xxx 11
523 pre-treatment for the bundled fibers used in the mortar
524 mixes. This was further supported by the microstructural
525 examination on the hardened mortars which, revealed that
526 the integrity of treated fibers remained intact within the
527 cement matrix without hindering the hydration processes.
528 The setting time of the mortar pastes was observed to be
529 prolonged with the increase in the fiber content. Water
530 absorption rate and capacity decreased with increasing
531 weight percent of palm fiber in the mixes. Results also indi-
532 cated that inclusion of fibers improves the flexural
533 strengths. However, the cylinder and cube compressive
534 strengths decreased with the increase in treated fiber
535 inclusion.
536 Nevertheless, the results of the durability performance
537 of the studied mixes clearly suggest that incorporation of
538 1.0-2.0% of date palm fibers improved the resistance of
539 the mortar against sulfate attack. Also, the drying shrink-
540 age performance of the mixes improved with increased
541 fiber inclusion.
542 Based on this study, it can be concluded that inclusion
543 of treated palm fibers in cement mortars do offer flexural
544 strengths and durability performance improvements. How-
545 ever, these advantages come as a trade-off in the form of
546 initial loss in workability and subsequent poor compressive
547 strengths.
548 Although, the work reported in this paper was carried
549 out on cement mortars, conclusions are expected to be rel-
550 evant to fiber reinforced concrete employing treated natu-
551 ral fibers. Yet, for practical purposes, it is recommended
552 to conduct thorough feasibility studies on the use of such
553 natural fibers based on the actual application as well as
554 the desired final properties of the resulting cement
555 composites.
556 5. Uncited reference
557Q13 ACI Committee 544 (2002).
558 Acknowledgements
559 The joint initiative and financial backing of the Qatar
560 University (QU), Texas A&M University at Qatar (TAM-
561 UQ) and Qatar Energy & Environment Research Institute
562 (QEERI) for this collaborative study is duly acknowledged.
563 In particular, the authors are grateful to Dr. Eyad Masad
564 (TAMUQ), Dr. Mariam Ali (QU) and Dr. Fahhad Alharbi
565 (QEERI) for their strong support.
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