ARTICLE IN PRESS
Building and Environment 42 (2007) 1151–1157
www.elsevier.com/locate/buildenv
Performance of ‘‘Agave lecheguilla’’ natural fiber in portland cement
composites exposed to severe environment conditions
César Juárez, Alejandro Durán, Pedro Valdez, Gerardo Fajardo
Academic Group of Concrete Technology, School of Civil Engineering, Universidad Autónoma de Nuevo León, Monterrey, México
Received 11 October 2005; received in revised form 8 November 2005; accepted 2 December 2005
Abstract
The main objective of the present research was to provide the housing alternatives to istle zone rural areas in México, which represent
about 10% of the national territory. The proposed solution involved a sustainable portland cement-based composite material, reinforced
with high tensile strength natural fibers of ‘‘Agave lecheguilla’’.
The results indicated that the ‘‘Agave lecheguilla’’ or simply lechuguilla fiber shows a high tensile capacity, but can be severely
deteriorated in the alkaline environment of the composite. However, if the fiber is protected with paraffin and the composite matrix is
modified with a pozzolan admixture such as fly ash, the composite performs acceptably well at exposure to aggressive environments and
variations in humidity and temperature.
r 2005 Elsevier Ltd. All rights reserved.
Keywords: Natural fiber; Reinforcement; Composite; Durability; Sustainability; Fly ash; Flexural strength; Deterioration
1. Introduction
Historically, natural vegetable fibers or simply natural
fibers (NF) were empirically used to reinforce several
construction materials, as the case for the production of
textile material. However, only recently scientists start to
study the application of this type of fiber as concrete
reinforcement [1]. NF can be obtained at a low price using
locally available manual labor and adequate techniques.
These fibers are usually known as unprocessed NF.
However, NF can be chemically or mechanically processed
to enhance their properties; usually, these fibers are based
on wood derivate cellulose. Such chemical or mechanical
processes are commonly utilized in the developed countries; whereas, because of relatively high costs of processing, these technologies are rarely adopted in developing
countries [1].
Natural fibers are readily available in large quantities in
many countries and they represent a continuous renewable
source. At the end of the 1970s, a systematic evaluation of
engineering properties of NF was performed, including the
Corresponding author.
E-mail address: cjuarez@fic.uanl.mx (C. Juárez).
0360-1323/$ - see front matter r 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.buildenv.2005.12.005
performance of portland-cement-based composites containing these fibers. Even the results of flexural and impact
strength were encouraging, the deficiencies related to the
long-term performance of NF reinforcement were also
reported [1]. These deficiencies are related to a degradation
of the fiber by the alkaline cement paste environment and
the increase of fiber dimensions related to variations in
humidity [2].
Durability is related to concrete ability to resist damage
caused by external factors (variations in environment
humidity and temperature, sulfate or chloride attack,
etc.) and internal factors (chemical reaction between the
ingredients, high water/cement ratio, and volumetric
changes due to paste hydration).
Canovas et al. [3], studied possible ways to prevent the
damage of sisal fibers in alkaline environment. According
to their results, fiber strength is reduced due to the
extraction process and the chemical reaction with the
alkaline environment affects the inner structure of fiber.
The chemical reactions are initiated at temperature changes
and on the exposure to humidity and highly alkaline
environment. One of the most important works related to
durability of NF was performed by Gram [4,5], who
studied sisal fibers in the Concrete and Cement Research
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Institute, Stockholm, Sweden. He stated that the decomposition of the main structural component of fiber–cellulose in an alkaline environment, and hemicelluloses as well
as separation of lignin, could progress according to two
different mechanisms. The first one was related to fiber
removal and separation, which occurred when lineal
glucose chains of cellulose were dissolved due to their
reaction with hydroxyl-ions; OH , resulting in methanol
radicals (–CH2OH), which could be easily liberated from
the molecular chain, causing decomposition of the cellulose
molecular structure. Therefore, the separation of fiber was
continuous process and it happened at exposure to alkaline
environment and at temperatures lower than 75 1C. The
second mechanism of cellulose decomposing was related to
alkaline hydrolysis. This process involved the division of
molecular chain, and was combined with chain separation,
since the division of chain provided further exposure to
inner structure of the fiber. Usually, this process was
realized at temperatures around 100 1C. Also, Gram [4,5]
performed tensile tests on fibers subjected to a concentrated solution of calcium hydroxide and water. In both
cases, the tensile strength was considerably reduced. In the
first case, this reduction was due to an effect of alkaline
environment and, in the second, due to the microbiological
action. It was detected that when the composite was
subjected to humidity variations, strength was substantially
reduced. It was observed that in carbonated concrete with a
pH of less than 9, fibers preserved their flexibility and
strength, but in noncarbonated zones, the fibers were
fragile.
As other developing countries, Mexico has a large
production of NF. Meanwhile, this country has an
inadequate infrastructure and housing deficit demanded
by growing population. Despite of this fact there were only
few scientific research related to the rational utilization of
such viable resource as NF. Belmares [6], used ‘‘Yucca
carnerosana’’, a vegetable fiber available in the State of
Coahuila, México to reinforce the polyester matrices. The
study carried out by Castro and Naaman [7], concluded
that it was possible to reinforce portland cement mortars
with maguey fibers, since this fiber has an adequate
physical and mechanical properties. The northeast part of
Mexico is represented by the States of Coahuila, Zacatecas,
Nuevo León, San Luis Potosı́, and Tamaulipas and is
known as the istle zone. This region is propitious for grow
of lechuguilla plant, on which thousands of families
inhabiting these zones rely.
The wide availability of this plant in México [8] and the
potential use of lechuguilla fiber in materials, were the main
reasons of the research conducted at UANL. This paper
focuses on the application of the lechuguilla fiber as
reinforcement in portland cement composites.
2. Research significance
Thousands of families reside in arid and semiarid zones
of Mexico, living in a precarious economic situation. This
is mainly the result of the deficient agrarian investments
through the years, which motivated farmers to abandon
their fields and immigrate to the big cities looking for new
opportunities, in most cases without success. The remaining population suffers because of extreme drought and lack
of financial support, both reducing their harvest production and lack of affordable housing. Therefore the research
of technical alternatives aiming to improve rural housing
and use of local materials are required.
3. Experimental program
3.1. Materials
Natural fiber ‘‘Agave lecheguilla’’, portland cement CPC
30R, fly ash (FA) and local limestone aggregates were used
in the experimental program. FA is a pozzolan, which
came from burning charcoal, used by the Rio Escondido
power plant, located in Piedras Negras, Coahuila. The
chemical composition of FA is shown in Table 1. Fly ash
was used at dosage of 60% by cement weight for composite
with the W/C ratio of 0.65 and 15% by cement weight for
composite with the W/C ratio of 0.35. The proportioning
of fine aggregate was provided according ASTM C 33-97
[9] and the grading of the sand is given in Table 2. Natural
fibers with length of 20–30 mm were used at dosage of 1%
by volume. Commercially available sulfonated naphthalene-based superplasticizer admixture was used at a dosage
of 1% of cement weight, for FA mix with W/C ratio of 0.35
the dosage was 1.2% of cement weight. These contents of
superplasticizer were selected to maintain a 1271 cm
slump of all mixtures.
3.2. Test procedures
3.2.1. Tests to assess the performance of protective agents
for enhancing the durability of fibers
This procedure was used to obtain the most effective
protective agent to reduce the water absorption of fiber
Table 1
Chemical composition of cementituos materials
Material
Fly ash
Portland cement
Chemical composition (%)
SiO2
Al2O3
Fe2O3
CaO
MgO
Na2O
63.93
17.55
24.32
4.70
4.29
1.77
2.34
64.74
0.78
1.23
0.20
0.37
Table 2
Grading of the aggregates
Aggregate type
Sand
Passing, % at a mesh (mm)
0.15
0.30
0.60
1.18
2.36
4.75
9.50
6.0
20.0
42.5
67.5
90.0
97.5
100.0
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and, in a long-term preserves the mechanical properties of
fiber in the alkaline environment of the cement matrix. In
order to reduce the water absorption and protect the fibers
in the alkaline environment, a comparison study was
carried out by using several organic water repellent
substances to figure out the most suitable one, which
should be not harmful to composite, nontoxic, as well as
inexpensive and easy for disposal. The following substances were selected [11]: linseed oil (LO), paraffin wax
(P), linseed oil/rosin (colophony) (C), and paraffin/rosin
(PR). These substances used to saturate the fibers providing the water resistance and durability against alkaline
environment. Once the fibers were treated, water absorption was determined and compared to that of untreated
fibers (UF).
In order to assess the performance of the protective
agents in composite, an alkaline environment was simulated through a concentrated calcium hydroxide solution,
with a pH of 12.5. The research program involved four
series of treated fibers and one series untreated fibers as
control. Each series had 120 randomly selected fibers.
Fibers were exposed to the calcium hydroxide solution at
23 1C. For 6 months, 12 fibers of each series were tested in
tension monthly and, thereafter, every 3 months until
completing a year. As a reference, 12 fibers of each series
were tested without exposure to the alkaline environment.
Maximum and minimum failure load were rejected, getting
an average of 10 remaining loads. All fibers were dried in
the lab environment for 24 h prior to testing and the failure
tensile stress was calculated based on the total area of the
fiber transversal section.
3.2.2. Accelerated tests to assess the durability of fiberreinforced composites
The main objective of this group of experiments was to
improve the density of cement matrix and improve the
durability of fiber-reinforced composites (FRC). In order
to realize this objective an accelerated deterioration tests
were designed to simulate natural environment [3,4,21].
The experimental program included the cement matrixes of
different density and permeability, obtained with different
W/C, 0.65 and 0.35, and addition of FA.
The mix proportions of composite are specified in Table
3. Investigated composites were mixed in a high-performance countercurrent mixer. The composite mixing,
placing and curing procedures were conducted according
to ASTM C 192-98 [12]. In case when FA was used, it was
homogenized with aggregates. All specimens were kept in
the molds for 24 h, protected from moisture loss and then
were cured at standard conditions for 7 days.
Three specimens for each group of treated fibers and an
additional three with untreated fibers as control were
produced. Besides, the FA effect on the cement matrix with
different fibers types was studied. The dimensions of the
specimens were 75 75 280 mm. Mixtures of the six
series as per as Table 3 were produced for each accelerated
test, as well as six reference series which where not
1153
Table 3
Mix proportions of fiber-reinforced composites
Materials
Composite mix proportion (kg/m3)
Series 1 Series 2 Series 3 Series 4 Series 5 Series 6
Cement
380.8
380.8
380.8
706.9
706.9
706.9
Fly ash
228.5
106.0
Sand
1540.0 1540.0 1287.5 1309.8 1309.8 1192.7
Water
247.4
247.4
247.4
240.3
240.3
238.9
Superplasticizer
7.1
7.1
8.5
Fibers untreated
6.9
6.9
Fibers treated
6.9
6.9
6.9
6.9
W/C ratio
0.65
0.65
0.65
0.35
0.35
0.35
subjected to any type of exposure. Following the curing
period, the control specimens were kept in laboratory
conditions, and were tested at 28 days age.
In order to evaluate the effect of the accelerated tests on
flexural strength of fiber composites, three specimens per
each series as per as Table 3 were tested. The following tests
were carried out, after which flexural tests were performed
according to ASTM C 78-94 [13]:
Test 1:
Test 2:
Test 3:
Test 4:
Test 5:
Exposure to 15 cycles of wetting and drying at
constant temperature. Each cycle consisted of
the exposure to a humid environment in an oven
at 70 1C for 24 h, followed by the exposure to a
dry environment in an oven at 70 1C for 24 h.
Exposure to 15 cycles with humidity and
temperature variations. Each cycle consisted of
exposure to a dry environment in an oven at
70 1C for 24 h, followed by water immersion at
21 1C for 24 h.
Exposure to an environment with 95% relative
humidity and 23 1C for 150 days.
Exposure to a sodium chloride solution 3%
NaCl at 23 1C for 150 days, to simulate a marine
environment.
Exposure to a sulfate solution with 10,000 ppm
concentration of sodium sulfate (Na2SO4) at
23 1C for 150 days. This condition is considered
as severe according to ACI 318-02 [14].
4. Test results and discussion
4.1. Performance of the protective agent for enhancing the
durability of fibers
According to Canovas [3], the effect caused by humidity
is related to the increase of the fiber diameter, producing an
intermolecular disorder and increase the permeability.
Coutts [15,16] mentioned that humidity had a very strong
influence mainly on the hemicelluloses and lignin, which
form the cellulose matrix. Coutts stated that with the
increase in the humidity, fiber strength dropped down to a
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1154
UF
98
100
LO
C
P
tensile strength tends to drop due to an effect of the
alkaline solution (Fig. 2). However, the fibers treated with
paraffin maintained a 53% of the tension strength, whereas
the other treatment options were capable to keep only
31%.
The treated and control fibers excluding fibers with
paraffin, became brittle after 6 month of exposure (Fig. 3),
possibly because the protection was lost in the alkaline
environment. Fibers treated with paraffin maintained a
47% of their ductility, whereas the other fibers demonstrated only 17–27% of initial value. For fiber treated with
paraffin, it is considered a positive solution to maintain
about 50% of the tensile strength and ductility in an
alkaline environment. This is an important finding since it
was reported [17–19], that NF completely deteriorates in
less than a year of exposure to an alkaline environment,
losing entirely its ductility and reinforcement capability.
4.2. Durability of fiber-reinforced composites
As any other material, natural fiber-reinforced composite is also vulnerable to the environment. When it has a
low W/C ratio and it is properly compacted and cured,
fibers are usually well protected by the cement paste.
Natural fibers and also synthetic polymers suffer the loss of
performance in the alkaline environment of the cement
matrix [1]. According to RILEM Technical Committee 19
[20], the required durability of concrete with fibers depends
on the application area. In case of structural components
of a building it may require a durability of up to 100 or
more years. However, when such concrete is used for nonstructural elements, the service life could be less. Gram
[4,5], suggests some alternatives to produce a water-proof
matrix, by means of the reduction of the W/C ratio and the
use of high content of silica fume. Silica fume is highly
reactive and reduces alkalinity of the cement paste down to
a pH of 9–10. However, it is expensive, and the reduced
alkalinity can posses a corrosion problem for the steel
reinforcement. This research was focused on obtaining a
denser matrix by reducing the water/cementitiuos ratio,
and adding FA, which is cheaper and less reactive,
PR
80
67
64
61
64
60
40
20
0
Saturation period = 24 h
Fig. 1. Water absorption of treated fibers.
400
UF
350
LO
C
60
300
Final/initial strength %
Tensile strength (MPa)
Absorption % related to fiberdry
weight
50%. This is crucial when the fiber is used in composite
exposed to high humidity environments, since strength of
the composite can be seriously reduced. Water absorption
of treated fibers is presented in Fig. 1. The research results
indicate that paraffin is the most effective protective agent,
providing significantly reduced water absorption, only
37% of that for untreated fiber. This effect can be caused
by partial sealing of the fiber pores with paraffin. Besides,
paraffin film formed over the fiber acts as water repellent,
preventing complete saturation. Canovas [3], reduced the
water absorption of sisal fibers by 53%, using colophonyturpentine, mix in a proportion of 1:6 as a sealer. However,
colophony had little effect on lechuguilla fibers, possibly
due to the lack of complete penetration of the protective
agent into the fiber pores, sealing only the larger pores or
macro-pores. Control of water absorption is important for
fiber durability; however, it cannot ensure the volumetric
stability of the fiber within the cement matrix.
The tensile strength results of treated fibers immersed in
an alkaline environment are shown in Fig. 2. According to
Gram, chemical decomposition of lignin and hemicelluloses with Ca(OH)2, is the main cause of brittle damage of
fibers in concrete [4,5]. Alkalinity of cement matrix pore
solution dissolves lignin, breaking the integrity of the
micro-cells. This explains the results, where the ultimate
250
200
150
100
UF
50
LO
C
P
PR
0
0
6
12
P
PR
53
50
40
30
31
31
30
20
10
0
Exposure period = 12 months
Exposure period (months)
Fig. 2. Tensile strength related to exposure period in an alkaline solution.
31
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UF
UF
15
LO
C
P
PR
12
9
6
3
0
0
6
Exposure period (months)
LO
C
P
PR
60
Final/initial elongation %
Tensile elogantion (mm)
18
1155
12
47
50
40
30
20
26
23
27
17
10
0
Exposure period = 12 months
Fig. 3. Elongation at fracture related to exposure period in an alkaline solution.
compared with silica fume. The Addition of FA to
composite results in a denser cement matrix, but maintains
its alkalinity. The combined use of FA with a naphthalene
superplasticizer allows the reduction of W/C ratios of 0.65
and 0.35 to water/cementitious ratios of 0.40 and 0.30,
respectively.
The proposed accelerated tests were designed to simulate
common environments in Mexico, for example, humid
climates of the central and southern parts of the country,
high temperatures with dry climates in the North West and
tropical coastal environments with humidity and temperature variations and high chloride concentrations, and the
chemical attack produced by the exposure to sulfates.
Humidity changes and temperature variations cause
cracking due to concrete shrinkage [21]. This cracking
allows the penetration of ambient moisture into concrete
reacting with the Ca(OH)2, and damaging the fibers;
besides the fibers suffer volumetric changes affecting their
adherence to the cement matrix.
In relation to Tests 1 and 2, FA paraffin-treated fiberreinforced composites, developed the highest flexural
strength compared with other composites. When FA was
added, the matrix became denser and the humidity ingress
was reduced. With the use of a superplasticizer, the initial
W/C ratios 0.65 and 0.35 were reduced to 0.40 and 0.30,
respectively, which produced a composite with an additional density and a higher strength. Test 2 turned to be the
most critical, demonstrating high values of strength loss in
all composites. Dense matrix of composite with FA prevent
the fiber deterioration caused by the humidity variations,
therefore the fibers preserved their ductility and reinforcing
capability (Fig. 4).
Humid environments are favorable for common composite, provided that humidity conditions remain unchanged.
According to Gram [4,5], transportation of the hydroxyl
ions OH or Ca2+ ions within the composite pores is very
slow when the outside environment remains constant,
which diminishes the deterioration of fiber. In the same
way, volumetric changes due to fiber contraction and
expansion are not occurring in a stable environment. The
results of Test 3 are shown in Fig. 4. It can be seen that
there is no significant difference in strength of control
specimens tested at 28 days and those specimens, which
remained 150 days in a humid environment. These findings
confirm the results of previous test, stating that stable
environments without humidity or temperature variations
allow fiber in composite to remain durable. As a result the
degradation of NF in alkaline matrix of cement was very
slow in constantly dry or humid environments. This is
important observation, since in the wet and dry cycles,
flexural strength of FA composite decreased by 14–20%,
and with exposure to constant humid environment such
reduction was only of 2%.
Neville [22] explains that the most frequent forms of
concrete chemical attack are sulfate attack, seawater, and
slightly acid water. It is possible to use different types of
cement to neutralize the chemical attack. However, in some
cases, concrete density and permeability affect its durability
to such extent that it surpasses the influence of the cement
type used. Chemical attack results in harmful physical
effects such as an increase of concrete porosity and
permeability, a decrease of its mechanical strength and
loss of covering. The results of Tests 4 and 5 are
summarized in Fig. 4. For Test 4 (exposure to chlorides),
FA paraffin- treated fiber-reinforced composites showed a
decrease of approximately 12%, while plain composites
with untreated fibers lost 30% of their original strength.
This reduction of strength is due to salt penetration into
capillary pores. When specimens dried, the solution
evaporated resulting in salt crystallization and fractures
due to crystal growth expansion inside the cement matrix.
Sulfate attack (Test 5) resulted in a reduction of flexural
strength of investigated composites (Fig. 4).
Composites made only with paraffin treated fibers lost
18% of their original strength, while composites made with
untreated fibers suffered a 30% loss. However, FA
composites made with paraffin-treated fibers lost less than
20% of their original strength after 5 months of exposure
to sulfates. It can be concluded that humidity and
temperature variations and chemical attack are the main
deterioration factors for NF reinforced composites. In
general, FA composites reinforced with paraffin treated
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Control
Test 1
Test 2
Test 3
Test 4
Test 5
8.0
6.0
Control
8.0
5.8
4.6
4.5
4.9
Test 4
4.8
4.6
4.0
2.0
2.0
0.0
Test 5
5.1
0.0
FRC with untreated fibers
Ultimate flexural strength (MPa)
Test 3
7.4
6.0
4.0
FRC with untreated fibers
8.0
8.0
6.0
6.0
5.2
4.9
7.2
7.2
6.2
5.8
5.0
5.3
4.0
2.0
2.0
0.0
5.7
5.6
6.0
4.0
5.9
0.0
FRC with treated fibers
FRC with treated fibers
8.0
6.0
Test 2
5.9
5.8
4.3
Test 1
7.4
8.0
5.9
5.1
7.0
6.9
6.2
5.8
5.3
7.1
5.3
4.9
6.0
4.0
4.0
2.0
2.0
0.0
5.7
5.6
0.0
FRC with treated fibers+ FA
FRC with treated fibers+ FA
W/C = 0.65
W/C = 0.35
Fig. 4. Effect of accelerated deterioration on flexural strength of FRC.
fiber, turned to have the best flexural strength in wetting
and drying cycles, as well as when exposed to chloride and
sulfate chemical attack. This result can be explained by the
reduction water/cementitiuos ratio, and application of FA
resulting in denser and waterproof composite.
5. Conclusions
Based on the results of this research, the following
conclusions were made:
1. Lechuguilla fibers possess high physical–mechanical
properties, such as higher tensile strength, attractive
for their application as reinforcement for composite.
2. Application of lechuguilla fiber as a reinforcement
results in a ductile post-crack behavior of composite
under bending.
3. The paraffin protective treatment allows reducing the
water absorption of fibers as well as maintaining
sufficient tensile strength even after one year of exposure
to humid and alkaline environments.
4. The initial strength of natural fiber-reinforced composites is reduced with exposure to wet and dry cycles, as
well as to aggressive chloride and sulfate environments.
5. Fly ash added to the mixture provides a denser matrix,
which protects the natural fiber-reinforced composites
from deterioration.
6. The combined effect of paraffin protection and application of fly ash, results in durable composites that may
have an economical application in construction. The
developed composites can be applied in the internal nonstructural separation walls, boards and masonry with an
adequate service life. However, the application of such
materials in structural elements reinforced with steel
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bars, as well as in roofing materials will need an
additional investigation involving performance assessment and life-cycle-cost analysis.
7. The correlation of accelerated deterioration test results
with those obtained from the specimens exposed to
natural climate variations, will allow predicting the
service life of natural fiber-reinforced composites. The
corresponding field experiments will be the subject of
our future work.
[9]
[11]
[12]
[13]
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