Conferência Brasileira de Materiais e Tecnologias NãoConvencionais: Habitações e Infra-Estrutura de Interesse Social
Brasil-NOCMAT 2004
Pirassununga, SP, Brasil, 29 de outubro – 3 de novembro, 2004
SOME PROPERTIES OF FIBER-CEMENT COMPOSITES
WITH SELECTED FIBERS
Eduardo Marcelo Bezerra 1,MSc., Ana Paula Joaquim 2, Dr., Holmer Savastano Jr.3, Prof. Dr.
1
2
PhD Student, Instituto Tecnológico de Aeronaútica – CTA edumarcel@fzea.usp.br
Researcher, Faculdade de Zootecnia e Engenharia de Alimentos, Universidade de São Paulo,
Brasil
3
Associate Professor, Faculdade de Zootecnia e Engenharia de Alimentos, Universidade de
São Paulo
ABSTRACT
The main objective of this work was to evaluate the effect of the incorporation of different
types of synthetic fibers and cellulose pulp in the toughness and strength of fiber reinforced
cementitious composites. The studies included an assessment of the mechanical and physical
behavior and the fiber-matrix interface using scanning electron microscopy at 28 days of age
and after accelerated aging test. Ten formulations were prepared with different amounts of
synthetic fibers (2.16-4.28% by volume of solid raw materials). The specimens were produced
in laboratory by slurring the raw material in water solution (20% of solids) followed by a
vacuum drainage of the excess water and pressing. Ten specimens of each formulation were
subjected to wet curing for seven days and air cure until the age of 28 days when the
mechanical and physical performances were assessed. Other ten specimens for each
formulation were exposed to the accelerated aging test (wet-dry cycles). The composites with
polyvinyl alcohol (PVA) fibers showed toughness and flexural strength higher than
polypropylene (PP) fibers also used in this study. The polyvinyl alcohol fibers formed a
strong bond with cementitious matrix due to their hydrophilic nature and geometric
characteristics. The results showed that formulations containing PVA fibers presented higher
values of MOR than those with the same volumetric percentage of PP fibers at 28 days and
after accelerated aging tests. Furthermore, the PVA fibers distribution in the matrix was more
homogeneous due to fiber dispersion as shown in the SEM analysis for the fiber amounts
under consideration.
KEYWORDS: polypropylene fiber, polyvinyl alcohol fiber, silica fume, cementitious matrix.
INTRODUCTION
Many studies have been carried out to substitute asbestos fibers in the fiber–reinforced cement
(FRC) industry [1]. Asbestos, which represents serious health hazards [2] to workers when it
is not used under proper conditions, has been prohibited in some countries. The most
frequently used reinforcements fibers include organic fibers (acrylic, polyvinyl alcohol,
SOME PROPERTIES OF FIBER-CEMENT COMPOSITES WITH SELECTED FIBERS
polyolefin and sometimes, polyethylene-polypropylene copolymers), natural cellulose
(hardwood and softwood pulps) and inorganic fibers (alkali-resistant glass and carbon, e.g.).
Flexible fibers with hydrophilic nature have been developed with high tensile strength. PVA
fibers present a diameter of 10-20µm and a tensile strength of 2,000-2,500 MPa [3]. The type,
geometry, distribution, orientation and volumetric concentration of fibers in the matrix are
factors that affect the mechanical behavior of the composites [4]. According to the
terminology adopted by the American Concrete Institute (ACI) Committee 544, Fiber
Reinforced Concrete (FRC), there are four categories of FRC based on the fiber material type
[4]. These are SFRC, for steel fiber reinforced concrete, GFRC, for glass fiber reinforced
concrete, SNFRC, for synthetic fiber reinforced concrete including carbon fibers, and NFRC,
for natural fiber reinforced concrete [5,6]. Fibers with a small average diameter have
corresponding low flexural stiffness and thus have a certain ability to conform to the shape of
the space they occupy in the paste phase of the concrete mixture between aggregate particles.
Fibers with high average diameter have greater flexural stiffness than those with small
diameter and will have a corresponding greater effect on consolidation of aggregates during
the process of mixing and placement. The fiber aspect ratio is a measure of the slenderness of
individual fibers. It is computed as the fiber length divided by the equivalent fiber diameter
for an individual fiber. Fibers for FRC can have an aspect ratio varying from approximately
40 to 1000 but typically less than 300 as proposed by Zollo [4]. The concrete, one of the most
commonly used construction material, is being developed towards high performance, i.e.,
high strength, high toughness, high durability, and good workability. Shrinkage and
permeability of the concrete are important properties relating to the durability. An important
consequence of reducing concrete permeability is enhancing the capability to resist shrinkage
and cracking. For concrete consisting of hardened cement, aggregates, pore and micro cracks
of different sizes, reinforcing effect of a monofiber is limited. Hybrid fibers of different sizes
and types may play important roles in resisting cracking at different scales to achieve high
performance. Sun et al. [7] reported that the shrinkage-resisting effect of hybrid fibers was
primarily related to factors such as: (1) fiber volume fraction (Vf), (2) fiber diameter and
length (df, lf) and (3) fiber elastic modulus (Ef). The incorporation of expansive agent in
proper content caused an improvement of the interfacial interaction between shrinkageresisting components (aggregates and fibers) and concrete matrix especially in the early
hydration period. The use of hybrid fibers of different types and sizes can bring about
reduction of the size and amount of cracking at different scales. In the first stages of the
cement hydration, the smaller fibers are the main factors affecting the resistance to shrinkage
and crack initiation. The incorporation of the hybrid fibers resulted in an increase in the
micropores (φ<50nm), and reduction of the larger pores (φ≥ 50nm) and the total porosity.
Fiber reinforcement is used often to increase both the toughness and the mechanical strength
of brittle matrices [8]. Reinhardt & Naaman 9] have shown that at high fiber volume fraction
(in the range of 7-10 by volume) both the toughness and strength can be simultaneously
improved. However, the incorporation of high volumetric concentration of fibers can lead to
processing difficulties because the dispersion of the fibers in cementitious matrix is a complex
process [10]. The fibers are being used for reinforcement of the cementitious matrix, to
enhance its tensile strength and toughness and reduce its tendency of cracking. In general, the
better the bond between fiber and matrix, the more efficient the load transfer to the fiber and
the stiffer the composite. Several authors reported positive experiments using short fibers with
special shape to improve anchorage [11]. The fiber extremities remain anchored in the matrix,
and the process of cracks propagation becomes more difficult. According to Oyang et al. [12],
another important factor to be considered is the dispersion of the fibers in the composite. Jain
& Wetherhold [13] have observed that ductile fibers may play important roles in resisting
cracks at different scales to achieve high performance. This work has as objective to study the
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SOME PROPERTIES OF FIBER-CEMENT COMPOSITES WITH SELECTED FIBERS
effect of the different fiber content and types in the physical and mechanical performance of
the composites relating to microstructural characterization.
EXPERIMENTAL WORK
The matrix was composed of ordinary Portland cement (OPC) CPII E type (NBR 11578),
whose specific surface area of the cement is 0.36 m2/g. Carbonate filler with specific surface
area of 0.45 m2/g was used as an aggregate. The characteristics of the silica fume Elkem920D type are described in Table 1 and the specific surface area is 22.5 m2/g. One type of
cellulose pulp was used to assist with filtering in the fiber cement production and
reinforcement in the hardened composite: Brazilian Pinus taeda unbleached kraft pulp with
Kappa number of ~ 45 and °SR equal 65. The Kappa number (Appita P201 m-86) is an
indirect measurement of lignin content. It is of special interest in the characterization of
unbleached kraft pulps. The Schopper-Riegler (°SR) number of a pulp is a measurement of
the freeness of a suspension of pulp in water, determined and expressed as specified in
SCAN-C19: 65. The refinement of the cellulose pulp was realized using PFI mill. The types
of synthetic fibers used in this work are described in Table 2.
TABLE 1 – PHYSICAL CHARACTERISTICS OF THE SILICA FUME
Physical Properties
Silica Fume
Average Diameter (µm)
0.5
Specific Surface (m2/g)
22.5
Pozzolanic Activity (mg/g)
813.83[14]
3
Density (g/cm )
2.65
Source: Laboratory of Microstructure/PCC - Escola Politécnica – USP, Brazil.
Sample
PVA
Polypropylene
(PP)
TABLE 2 - PROPERTIES OF SYNTHETIC FIBERS
Length
(µ
µm)
Diameter
(µ
µm)
Density
(g.cm-3)
6000
14
1.300
5600
26
0.916
MOE
(GPa)
Extension
at Break
(mm/mm)
3.8-19.8
0.13
1.3
1.97
Source: (1) Radici-Group, SJCampos-Brasil; (2) Laboratory of Microstructure/PCC –
Escola Politécnica – USP, Brazil.
The samples of cement composites were produced in laboratory scale, in an attempt to
roughly simulate the Hatschek method for sheeting fabrication, by slurring the raw material in
water solution (20% of solids) followed by vacuum drainage of the excess water and pressing
(3.2 MPa). Hardened pads were wet diamond sawn with dimensions of 40 x 160 mm. Test
specimen depth was the thickness of the pad, which was in the region of 5 mm. These
procedures observed the experimental work carried out by Eusebio et al. [15]. Ten
formulations were prepared with different amounts of silica fume and synthetic fiber
according to Table 3. Ten specimens for each formulation were subjected to wet curing for
seven days and air cure in an environment of 23 ± 2°C and 50 ± 5% of relative humidity until
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SOME PROPERTIES OF FIBER-CEMENT COMPOSITES WITH SELECTED FIBERS
the age of 28 days when the mechanical and physical performances were assessed. Other ten
specimens for each formulation were cured in the same way until the completion of 28 days
of age and after submitted to the accelerated aging test (soak-dry cycles). This test consists of
submerging the specimens into water for 18 h and after they are put into an oven at 60o C of
temperature during 6 h, to complete 24 h. The aging test was composed of 50 cycles and it
was based on the methodology of the European Standards/EN – 494 section 7.3.5.
TABLE 3 – VOLUMETRIC CONCENTRATIONS IN THE FORMULATIONS (% VOL OF SOLID RAW MATERIAL.)
Synthetic
Cellulose
OPC
Carbonate
Fiber
Fiber
CPIIE
Filler
PVA2.16 or PP2.16
2.16
9.38
68.23
13.78
6.45
PVA2.70 or PP2.70
2.70
9.38
68.23
13.78
5.91
PVA3.23 or PP3.23
3.23
9.38
68.23
13.78
5.38
PVA3.76 or PP3.76
3.76
9.38
68.23
13.78
4.85
PVA4.28 or PP4.28
4.28
9.38
68.23
13.78
4.33
Description
Silica Fume
Composites characterization
Mechanical and Physical Characterization
Water absorption (WA), apparent porosity (AP) and bulk density were determined according
to the procedures specified in the Brazilian Standard NBR-6470 at 28 days and after
accelerated aging test. The mechanical characterization was based on the Rilem
recommendations 49 TFR and was performed with a four point bending configuration. A span
of 135 mm and a deflection rate of 1.5 mm/min were used for all tests in an Emic DL30000
universal testing machine equipped with load cell of 1 kN. Additional information regarding
these tests were provided by Savastano Jr. et al. [16]. Modulus of rupture (MOR) and
toughness were evaluated at 28 days and after accelerated aging test. The degradation of the
composites was estimated by the R factor, which was obtained from Eqn. 1. The Standard
EN-494 establishes the R-factor to be equal or above 0.7.
R=
L2
L1
(1)
Where:
L1 = average strength of non-aged (28 days) specimens (+) 0.58 (x) the standard deviation of
results;
L2 = average strength of aged specimens (-) 0.58 (x) the standard deviation of results;
R = parameter of degradation measurement of specimens after 50 cycles.
Scanning Electron Microscopy
The surface topography of the composites by cementitious matrix reinforced with natural and
synthetic fibers was analyzed without preparation of the samples. The microstructures were
examined by scanning electron microscopy (SEM) (Zeiss model DSM950) using
backscattering electrons image.
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SOME PROPERTIES OF FIBER-CEMENT COMPOSITES WITH SELECTED FIBERS
RESULTS
PVA Fiber composites
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0,000
Hydration Date: 28 Days
PVA2.16
PVA2.70
PVA3.23
PVA3.76
PVA4.28
Stress (MPa)
Stress (MPa)
The results of the mechanical behavior of the specimens at 28 days are shown in Figure 1(a).
The formulations with PVA fibers content of 3.23% by volume presented better mechanical
behavior at 28 days. The fibers offer stiffness and strength to the matrix after initial cracking.
The adhesion between the PVA fibers and cementitious matrix is one of the major factors
responsible for the efficiency of load transfer. The pullout represents the tensile strength of
the composite, and the pullout work represents the energy consumed in the failure process,
which is a measure of the toughness of the composite. The hydroxyl groups on the PVA fiber
surface cause an increase in the wettability of the fiber in the polar matrix mix, enhancing
dispersion of the fibers when coupled with mechanical agitation on mixing [17]. The
mechanical results after 50 cycles of accelerated aging test are presented in Figure 1(b). The
formulations with less content of PVA fibers were more susceptible to the degradation after
accelerated aging test. This behavior could probably be attributed to the degradation of
cellulose fibers, since they are present in proportionally higher amounts in these formulations.
0,005
0,010
0,015
0,020
0,025
0,030
0,035
0,040
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0,000
Accelerated Aging Test - 50 Cycles
PVA 2.16
PVA 2.70
PVA 3.23
PVA 3.76
PVA 4.28
0,005
0,010
0,015
0,020
0,025
0,030
0,035
0,040
Strain (mm/mm)
Strain (mm/mm)
(a)
(b)
FIGURE 1 - STRESS-STRAIN CURVES OF THE COMPOSITE REINFORCED WITH DIFFERENT CONCENTRATIONS OF
PVA FIBERS (IN % BY VOLUME OF RAW-MATERIALS) AFTER (A) 28 DAYS OF CURE AND (B) 50 CYCLES UNDER
ACCELERATED AGING TEST.
Table 4 shows the results of the physical characterization after 28 days and after accelerated
aging test. There was a reduction of the apparent porosity and water absorption results after
the accelerated aging test for all formulations.
TABLE 4 - PHYSICAL PROPERTIES OF FORMULATIONS WITH PVA FIBER AT 28 DAYS OR ACCELERATED AGING TEST
FOR ALL FORMULATIONS
WA (% by mass)
Formulation
28 days
50 cycles
PVA2.16
19.6 ± 1.3 16.8 ± 1.4
PVA2.70
21.6 ± 0.8 19.5 ± 1.5
PVA3.23
19.4 ± 1.0 18.2 ± 1.6
PVA3.76
19.1 ± 0.6 15.9 ± 1.0
PVA4.28
19.1 ± 0.6 17.8 ± 0.9
AP (% by volume)
28 days
50 cycles
32.3 ± 1.2 27.8 ± 1.7
34.1 ± 0.6 31.2 ± 1.9
32.2 ± 1.0 30.4 ± 1.8
31.3 ± 0.7 23.4 ± 1.5
31.3 ± 0.6 29.4 ± 1.3
BD (g/cm3)
28 days
50 cycles
1.65 ± 0.05 1.65 ± 0.04
1.58 ± 0.03 1.60 ± 0.03
1.66 ± 0.04 1.67 ± 0.05
1.65 ± 0.02 1.66 ± 0.02
1.64 ± 0.02 1.66 ± 0.02
The alteration of the physical performance of the composites can be associated with the
matrix carbonation and with the activation of hydration mechanism after the 50 soak-dry
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SOME PROPERTIES OF FIBER-CEMENT COMPOSITES WITH SELECTED FIBERS
cycles [18]. The reduction of the toughness after the accelerated aging test was considered
statistically significant for all formulations at the 0,05 level in the one-way analysis of
variance as shown in Table 5. The formulation PVA3.23 showed a statistically significant
reduction of the MOR after accelerated aging test. These results can be associated with the
increase of the adhesion of the fiber-matrix after soak-dry cycles due the hydroxyl groups
present in the fiber surface. The increase adhesion among the fibers and the cementitious
matrix made the pullout of these fibers more difficult; consequently resulting in the reduction
of the toughness.
TABLE 5 - MECHANICAL PROPERTIES OF THE PVA FORMULATIONS, AFTER 28 DAYS OR 50 AGING CYCLES
Formulation
PVA2.16
PVA2.70
PVA3.23
PVA3.76
PVA4.28
MOR (MPa)
Toughness (kJ/m2)
28 Days
50 Cycles
p
28 Days 50 Cycles
P
0.68
7.93E-9
9.68 ± 1.15 10.04 ± 2.41
2.03 ± 0.48 0.46 ± 0.11
0.19 2.52 ± 0.86 0.89 ± 0.48 5.23E-5
8.31 ± 1.92 9.31 ± 1.29
12.47 ± 1.33 10.44 ± 1.64 7.03E-3 2.95 ± 0.58 0.82 ± 0.30 6.11E-9
10.99 ± 0.67 10.24 ± 1.39 0.16 2.46 ± 0.68 1.18 ± 0.49 2.00E-3
11.04 ± 2.18 10.83 ± 1.36 0.82 3.49 ± 0.79 1.83 ± 0.41 2.81E-5
PP Fiber Composites
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0,00
Hydration Date: 28 Days
PP 2.16
PP 2.70
PP 3.23
PP 3.76
PP 4.28
Stress (MPa)
Stress (MPa)
Results relating to the use of polypropylene fibers are shown in Figure 2. It can be observed in
Figure 2(a) that the PP3.76 formulation showed better mechanical performance after initial
curing. This fact can be attributed to the good dispersion of the PP fibers at intermediate
volumetric fractions.
0,01
0,02
0,03
0,04
0,05
0,06
0,07
0,08
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0,00
Accelerated aging test - 50 Cycles
PP 2.16
PP 2.70
PP 3.23
PP 3.76
PP 4.28
0,01
0,02
0,03
0,04
0,05
0,06
0,07
0,08
Strain (mm/mm)
Strain (mm/mm)
(a)
(b)
FIGURE 2 - STRESS-STRAIN CURVES OF THE COMPOSITE REINFORCED WITH DIFFERENT CONCENTRATIONS OF PP
FIBERS (IN % BY VOLUME OF RAW-MATERIALS) AFTER (A) 28 DAYS OF CURE AND (B) 50 CYCLES UNDER
ACCELERATED AGING TEST
According to Figure 2b and the results presented in Table 6, it can be observed that the MOR
of the formulations PP2.70 and PP4.28 presented statistically significant increase at the 0,05
level in the one-way analysis of variance. The toughness of the formulation PP2.16 presented
statistically significant reduction at the 0,05 level in the one-way analysis of variance as
shown in Table 6. The formulations with smaller volumetric fraction of the PP fibers were
more affected after soak-dry cycles.
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SOME PROPERTIES OF FIBER-CEMENT COMPOSITES WITH SELECTED FIBERS
TABLE 6 - MECHANICAL PROPERTIES OF THE PP FORMULATIONS AFTER 28 DAYS OR 50 AGING CYCLES
Formulation
PP2.16
PP2.70
PP3.23
PP3.76
PP4.28
28 days
6.52 ± 1.20
5.96 ± 1.47
7.14 ± 1.15
9.88 ± 1.01
7.78 ± 0.82
MOR (MPa)
50 cycles
7.64 ± 1.78
9.38 ± 0.97
8.09 ± 0.88
8.78 ± 1.84
9.26 ± 1.56
p
0.12
8.51 E-6
0.05
0.12
0.02
Toughness (kJ/m2)
28 days
50 cycles
p
1.18 ± 0.53 0.45 ± 0.39 2.69E-3
0.26
1.07 ± 0.33 1.31 ± 0.55
0.49
1.84 ± 0.47 1.70 ± 0.44
0.54
2.12 ± 0.82 1.93 ± 0.48
0.80
2.17 ± 0.35 2.21 ± 0.40
Concerning physical characteristics, the formulation containing 3.76% of PP fibers showed
the smallest values of the apparent porosity and water absorption after 28 days of cure as it
can be seen in Table 7. This behavior is helpful in the understanding of the better mechanical
strength of this formulation.
TABLE 7 - PHYSICAL PROPERTIES OF FORMULATIONS WITH PP FIBERS AT 28 DAYS OR ACCELERATED AGING TEST.
Formulation
PP2.16
PP2.70
PP3.23
PP3.76
PP4.28
WA (%)
28 days 50 cycles
20.2 ± 0.6 18.0 ± 1.5
20.1 ± 1.3 18.2 ± 0.9
20.1 ± 1.4 18.2 ± 1.0
18.7 ± 0.9 19.6 ± 1.8
21.2 ± 2.4 18.2 ± 1.1
AP (%)
28 days 50 cycles
32.9 ± 0.9 29.7 ± 1.9
32.5 ± 1.2 30.5 ± 1.2
32.6 ± 1.2 30.1 ± 1.2
30.7 ± 0.9 31.5 ± 1.7
33.2 ± 2.6 29.5 ± 1.2
BD (g/cm3)
28 days
50 cycles
1.63 ± 0.02 1.66 ± 0.05
1.62 ± 0.05 1.68 ± 0.02
1.63 ± 0.05 1.65 ± 0.03
1.64 ± 0.03 1.61 ± 0.06
1.57 ± 0.06 1.62 ± 0.04
Comparison between the results obtained for PP and PVA reinforced composites indicates
that the modulus of rupture at 28 days is lower for all PP formulations than the correspondent
PVA formulations as it can be visualized in Figure 3(a).
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PVA - 28 DAYS
PP - 28 DAYSOF FIBER-CEMENT COMPOSITES WITH SELECTED FIBERS
SOME PROPERTIES
PVA - 50 CYCLES
PP - 50 CYCLES
14
12
MOR (MPa)
10
8
6
4
2
8
4.
2
3.
76
3
3.
2
0
2.
7
2.
16
0
Fiber Content, %Vf
PVA - 28 DAYS
PP - 28 DAYS
PVA - 50 CYCLES
PP - 50 CYCLES
4,5
4,0
2
Toughness (kJ/m )
3,5
3,0
2,5
2,0
1,5
1,0
0,5
28
4.
76
3.
23
3.
2.
2.
70
16
0,0
Fiber Content, %V f
(a)
(b)
FIGURE 3 - COMPARISON OF THE MODULUS OF RUPTURE (A) AND TOUGHNESS (B) FOR PVA AND PP REINFORCED
COMPOSITES
The results of R-value are presented in Table 8 and were calculated according to the Standard
EN-494 (Eqn. 1). Once this standard establishes that the R-factor should be equal or above
0.7, the results for all the composites under consideration are in agreement with the EN-494.
TABLE 8. R-FACTOR FOR DIFFERENT FORMULATIONS.
Synthetic fiber
(% by volume)
2.16
2.70
3.23
3.76
4.28
PVA
PP
0.84
0.91
0.72
0.83
0.82
0.92
1.29
0.97
0.73
1.01
SEM Characterization
In Figure 4 it can be observed that the PVA fibers showed homogeneous dispersion in
cementitious matrix and that considerable amounts of these fibers are well attached to the
matrix. However, the PP fibers showed inhomogeneous dispersion in the cementitious matrix
and poor anchoring, which can be attributed to the smaller embedding length of the fiber in
the matrix.
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SOME PROPERTIES OF FIBER-CEMENT COMPOSITES WITH SELECTED FIBERS
(a)
(b)
FIGURE 4 – SEM OF FRACTURE SURFACE AFTER TWENTY-EIGHT DAYS OF CURING: (A) FORMULATION PVA 4.28;
(B) FORMULATION PP4.28.
Several voids were observed in the matrix as shown in Figure 5(a). These voids are result of
the pulling out of the PP fibers. These fibers present smoother pull-out surface than the
composite with PVA fibers, resulting in poorer anchorage in the cementitious matrix. PP
fibers are easily pulled out during the load application. As a consequence, an increase of the
toughness and elongation at break has occurred with the reduction of the modulus of rupture
of the PP composites when compared to those with PVA. As observed in Figure 5(b), the
PVA fibers were not completely pulled out. This behaviour can be explained based on the
morphology of the PVA fibers. As cited before, their surface is rough and its extremities are
larger than those of PP.
(a)
(b)
FIGURE 5 - SEM OF FRACTURE SURFACE AFTER TWENTY-EIGHT DAYS OF CURING: (A) FORMULATION PP 4.28 AND
(B) FORMULATION PVA4.28.
CONCLUSIONS
Based on the presented results, it could be concluded that:
•
Formulations containing PVA fibers presented better mechanical performance than the
formulations with the same volumetric percentage of PP fibers at different ages. This
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SOME PROPERTIES OF FIBER-CEMENT COMPOSITES WITH SELECTED FIBERS
result can be associated with the better adhesion of the PVA fibers and its chemical
characteristics.
•
PVA fibers distribution in the matrix was more homogeneous due to fiber dispersion
as shown in the SEM analysis for the fiber amounts under consideration.
ACKNOWLEDGMENTS
The authors would like to aknowledge support of this work by Imbralit Ltda., Infibra Ltda.,
Fundação de Amparo à Pesquisa do Estado de São Paulo (Fapesp, Pite program, process n.
01/03833-6), Financiadora de Estudos e Projetos (Finep, Habitare program, process n.
22.201.0206.00), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Capes,
Procad program. Process n. 0125/01-6) and Conselho Nacional de Pesquisa e
Desenvolvimento (CNPq, PQ grant, process n. 305999/2003-6), Brazil. The authors also like
to acknowledge the assistance given by ITA – Institute of Aeronautics and Space – Materials
Division (IAE-AMR) regarding the SEM analysis.
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