some properties of fiber-cement composites with selected fibers

Conferência Brasileira de Materiais e Tecnologias Não-Convencionais: 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 PhD Student, Instituto Tecnológico de Aeronaútica – CTA [email protected]

2 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,


Anais. Conferência Brasileira de Materiais e Tecnologias Não-Convencionais – Habitações e Infra-Estrutura de Interesse Social – Brasil NOCMAT, Pirassununga, 29/10 a 03/11/2004.

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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 shrinkage-resisting 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



35

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 Elkem-920D 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]

Density (g/cm3) 2.65

Source: Laboratory of Microstructure/PCC - Escola Politécnica – USP, Brazil.

TABLE 2 - PROPERTIES OF SYNTHETIC FIBERS

Sample Length (µµµµm)

Diameter (µµµµm)

Density (g.cm-3)

MOE (GPa)

Extension at Break

(mm/mm) PVA 6000 14 1.300 3.8-19.8 0.13 Polypropylene (PP) 5600 26 0.916 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



36

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.)

Description Synthetic

Fiber

Cellulose

Fiber

OPC

CPIIE

Carbonate

Filler

Silica Fume

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

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.

1

2

LL

R = (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.



37

RESULTS PVA Fiber composites 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.

0,000 0,005 0,010 0,015 0,020 0,025 0,030 0,035 0,0400123456789

1011121314151617

Hydration Date: 28 Days

PVA2.16 PVA2.70 PVA3.23 PVA3.76 PVA4.28

Str

ess

(MP

a)

Strain (mm/mm)

0,000 0,005 0,010 0,015 0,020 0,025 0,030 0,035 0,0400123456789

1011121314151617

Accelerated Aging Test - 50 Cycles

PVA 2.16 PVA 2.70 PVA 3.23 PVA 3.76 PVA 4.28

Stre

ss (M

Pa)

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) AP (% by volume) BD (g/cm3) Formulation

28 days 50 cycles 28 days 50 cycles 28 days 50 cycles PVA2.16 19.6 ± 1.3 16.8 ± 1.4 32.3 ± 1.2 27.8 ± 1.7 1.65 ± 0.05 1.65 ± 0.04 PVA2.70 21.6 ± 0.8 19.5 ± 1.5 34.1 ± 0.6 31.2 ± 1.9 1.58 ± 0.03 1.60 ± 0.03 PVA3.23 19.4 ± 1.0 18.2 ± 1.6 32.2 ± 1.0 30.4 ± 1.8 1.66 ± 0.04 1.67 ± 0.05 PVA3.76 19.1 ± 0.6 15.9 ± 1.0 31.3 ± 0.7 23.4 ± 1.5 1.65 ± 0.02 1.66 ± 0.02 PVA4.28 19.1 ± 0.6 17.8 ± 0.9 31.3 ± 0.6 29.4 ± 1.3 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



38

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 MOR (MPa) Toughness (kJ/m2) Formulation

28 Days 50 Cycles p 28 Days 50 Cycles P PVA2.16 9.68 ± 1.15 10.04 ± 2.41 0.68 2.03 ± 0.48 0.46 ± 0.11 7.93E-9 PVA2.70 8.31 ± 1.92 9.31 ± 1.29 0.19 2.52 ± 0.86 0.89 ± 0.48 5.23E-5 PVA3.23 12.47 ± 1.33 10.44 ± 1.64 7.03E-3 2.95 ± 0.58 0.82 ± 0.30 6.11E-9 PVA3.76 10.99 ± 0.67 10.24 ± 1.39 0.16 2.46 ± 0.68 1.18 ± 0.49 2.00E-3 PVA4.28 11.04 ± 2.18 10.83 ± 1.36 0.82 3.49 ± 0.79 1.83 ± 0.41 2.81E-5

PP Fiber Composites 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.

0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,080123456789

1011121314151617

Hydration Date: 28 Days

Strain (mm/mm)

Stre

ss (M

Pa)

PP 2.16 PP 2.70 PP 3.23 PP 3.76 PP 4.28

0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08

0123456789

1011121314151617

Accelerated aging test - 50 Cycles

PP 2.16 PP 2.70 PP 3.23 PP 3.76 PP 4.28

Stre

ss (M

Pa)

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.



39

TABLE 6 - MECHANICAL PROPERTIES OF THE PP FORMULATIONS AFTER 28 DAYS OR 50 AGING CYCLES MOR (MPa) Toughness (kJ/m2) Formulation

28 days 50 cycles p 28 days 50 cycles p PP2.16 6.52 ± 1.20 7.64 ± 1.78 0.12 1.18 ± 0.53 0.45 ± 0.39 2.69E-3 PP2.70 5.96 ± 1.47 9.38 ± 0.97 8.51 E-6 1.07 ± 0.33 1.31 ± 0.55 0.26 PP3.23 7.14 ± 1.15 8.09 ± 0.88 0.05 1.84 ± 0.47 1.70 ± 0.44 0.49 PP3.76 9.88 ± 1.01 8.78 ± 1.84 0.12 2.12 ± 0.82 1.93 ± 0.48 0.54 PP4.28 7.78 ± 0.82 9.26 ± 1.56 0.02 2.17 ± 0.35 2.21 ± 0.40 0.80

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.

WA (%) AP (%) BD (g/cm3) Formulation 28 days 50 cycles 28 days 50 cycles 28 days 50 cycles

PP2.16 20.2 ± 0.6 18.0 ± 1.5 32.9 ± 0.9 29.7 ± 1.9 1.63 ± 0.02 1.66 ± 0.05 PP2.70 20.1 ± 1.3 18.2 ± 0.9 32.5 ± 1.2 30.5 ± 1.2 1.62 ± 0.05 1.68 ± 0.02 PP3.23 20.1 ± 1.4 18.2 ± 1.0 32.6 ± 1.2 30.1 ± 1.2 1.63 ± 0.05 1.65 ± 0.03 PP3.76 18.7 ± 0.9 19.6 ± 1.8 30.7 ± 0.9 31.5 ± 1.7 1.64 ± 0.03 1.61 ± 0.06 PP4.28 21.2 ± 2.4 18.2 ± 1.1 33.2 ± 2.6 29.5 ± 1.2 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).



40

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

4.28

3.76

3.23

2.70

2.16

Fiber Content, %Vf

Toug

hnes

s (k

J/m

2 )

PVA - 28 DAYS PP - 28 DAYS PVA - 50 CYCLES PP - 50 CYCLES

(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)

PVA PP

2.16 0.84 0.92 2.70 0.91 1.29 3.23 0.72 0.97 3.76 0.83 0.73 4.28 0.82 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.

0

2

4

6

8

10

12

14

4.28

3.76

3.23

2.16

2.70

MO

R (M

Pa)

Fiber Content, %Vf

PVA - 28 DAYS PP - 28 DAYS PVA - 50 CYCLES PP - 50 CYCLES



41

(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



42

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. REFERENCES 1. Daude G., Lasnier JM., Guillabert B., Filliatre C., Sabouraud A., Guilhemat R. Extraction and identification of organic fibres from fibre-reinforced cement composites without asbestos. Cement and Concrete Research 1996; 26[5]: 791-798. 2. European Commision Directorate-General Health and Consumer Protection. Directorate C – Scientific Opinions. Scientific Committee on Toxicity, Ecotoxicity and the Environment. Brussels, 17 December 2002. 3. Kanda T., Li V., Member ASCE. Interface property and apparent strength of high-strengthhydrophilic fiber in cement matrix. Journal of Materials in Civil Engineering 1998; 5-13. 4. Zollo RF. Fiber-reinforced Concrete: an Overview after 30 Years of Development. Cement and Concrete Composites 1997; 19:107-122. 5. Soroushian P., Lee CD. Distribution and orientation of fibers in steel fiber reinforced concrete. ACI Mater. J. 1990; 87[5]:433-439. 6. Balaguru P., Naharari R., Patel M. Flexural toughness of steel fiber concrete. ACI Mater. J. 1992; 89(6):541-546. 7. Sun W., Chen H., Luo X., Qian H. The effect of hybrid fibers and expansive agent on the shrinkage and permeability of high-performance concrete. Cement and Concrete Research 2001; 31:595-601. 8. Ostertag C.P., Yi C.K., Vondran G. Tensile strength enhancement in interground fiber cement composites. Cement & Concrete Composites 2001; 23:419-425. 9. Reinhardt HW, Naaman AE. High performance fiber reinforced cement composites. In: Proceedings of the RILEM/ACI Workshop, 1992. 10. Betterman L.R., Ouyang C., Shah S.P. Fiber-matrix interaction in microfiber-reinforced mortar. J. Advanced Cement Based Mat. 1995; 2: 53-61. 11. Wetherhold, R.C., Bös, J. Ductile reinforcements for enhancing fracture resistance in composite materials. Theoretical and Applied Fracture Mechanics 2000; 33:83-91. 12. Ouyang C., Pacios A., Shah S.P. Pullout of inclined fibers from cementitious matrix. J. Eng. Mech. 1994; 120:2641.



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13. Jain L.K., Wetherhold R.C. Effect of fiber orientation on the fracture toughness of brittle matrix composites. Acta. Metall. Mater. 1992; 40:1135-1143. 14. NBR 9774/87 (MB-2570)-Agregado-Verificação da Reatividade Potencial pelo Método Químico, item 4.3 b – purificação do bórax através da recristalização. 15. Eusebio D.A., Cabangon R.J., Warden P.G., Coutts R.S.P. The Manufacture of Wood Fiber Reinforced Cement Composites from Eucalyptus pellita and Acacia mangium Chemithermomechanical Pulp. Proceedings of the 4th Pacific Rim Bio-Based Composites Symposium, Bogor Agricultural University, Bogor, Philippines, 1998. p.428-436. 16. Savastano Jr. H., Warden P.G., Coutts R.S.P. Ground iron blast furnace slag as a matrix for cellulose-cement materials. Cement & Concrete Composites 2001, 23:389-397. 17. Kong H.J., Bike S.C., Li V.C. Constitutive rheological control to develop a self-consolidating engineered cementitious composite reinforced with hydrophilic poly(vynil alcohol) fibers. Cement & Concrete Composites 2003, 25: 333-341. 18. Bentur A. Role of Interfaces in Controlling Durability of Fiber-Reinforced Cements. Journal of Materials in Civil Engineering 2000, 12[1] 2-7.

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some properties of fiber-cement composites with selected fibers