Abstract
The purpose of this work is to evaluate mechanical behavior of sisal fiber reinforced cement mortar. The composite material was produced from a mixture of sand, cement and water. Sisal fibers were added to the mixture in two different lengths. Mechanical characterization of the composite and the plain mortar was carried out using three point bend, compression and impact tests. Specimens containing parallel sided notches of different root radii were loaded in three point bending in order to determine the effect of the fibers on the material fracture toughness in the presence of discontinuities. According to the results, while fiber reinforcement leads to a decrease in compressive strength, J-integral calculations at maximum load for the different notch root radii have indicated, particularly for the case of long fibers, a significant superiority of the reinforced material in comparison with the plain cement mortar, in consistence with the impact test data.
composite material; impact energy; fracture initiation; J-integral
1 Introduction
It is well known that the presence of short randomly dispersed fibers in a cementitious matrix can result in an appreciable improvement in the mechanical behavior of the produced composite. This improvement is clearly manifested by the significant superiority of the composite’s toughness in comparison with that of the plain matrix. The increase in toughness, due to the incorporation of fibers, can be attributed, largely, to the fiber bridging mechanism, whereby the fibers take an active part in supporting tensile loading, in controlling matrix microcracking and in reducing the rate of crack propagation. The fiber reinforced concrete will, therefore, exhibit a pseudoductile behavior, maintaining considerable load carrying capacity after cracking of the matrix.
Different types of fibers, both metallic and nonmetallic, have been used as reinforced
elements in cementitious matrices. More specifically, a number of investigations11. Sivakumar A and Santhanam M. Mechanical properties of high strength concrete
reinforced with metallic and non-metallic fibers. Cement and Concrete Composites. 2007;
29(8):603-608. http://dx.doi.org/10.1016/j.cemconcomp.2007.03.006.
http://dx.doi.org/10.1016/j.cemconcomp.2...
2. Qian CX and Stroeven P. Development of hybrid
polypropylene-steel-fiber-reinforced concrete. Cement and Concrete Research. 2000; 30(1):63-69.
http://dx.doi.org/10.1016/S0008-8846(99)00202-1.
http://dx.doi.org/10.1016/S0008-8846(99)...
3. Abu-Lebdeh TM, Fini E and Lumpkin M. Flexural and tensile characteristics of
microfiber-reinforced very high strength concrete thin panels. American Journal of Engineering
and Applied Science. 2012; 5(2):184-197.
http://dx.doi.org/10.3844/ajeassp.2012.184.197.
http://dx.doi.org/10.3844/ajeassp.2012.1...
-44. Kitamura S. Experimental study of the influence of fiber content and specimen
dimensions on the split tensile strength and its relationship with the flexural strength.
[Dissertation]. Rio de Janeiro: Fluminense Federal University; 2006.
Portuguese. were conducted using randomly dispersed short steel fibers, polymeric
fibers and hybrid combinations of both. One could verify that the presence of fibers in, for
example, high strength concrete resulted in enhancing both its flexural strength and toughness.
This was attributed to energy absorbing mechanism (bridging action) and to delay in microcrack
formation11. Sivakumar A and Santhanam M. Mechanical properties of high strength concrete
reinforced with metallic and non-metallic fibers. Cement and Concrete Composites. 2007;
29(8):603-608. http://dx.doi.org/10.1016/j.cemconcomp.2007.03.006.
http://dx.doi.org/10.1016/j.cemconcomp.2...
.
Environmental awareness and an increasing concern with greenhouse effect have stimulated
several industries to look for sustainable substitutes that can replace conventional synthetic
fibers. In this respect, natural fibers seem to be a good alternative to steel and polymeric
fibers since they are readily available in fibrous form and can be easily extracted from their
proper plants at very low cost55. Silva FA, Chawla N and Toledo Filho RD. Tensile behavior of high performance
natural (sisal) fibers. Composites Science and Technology. 2008; 68(15-16):3438-3443.
http://dx.doi.org/10.1016/j.compscitech.2008.10.001.
http://dx.doi.org/10.1016/j.compscitech....
. Further,
their adoption as reinforcing elements is also associated with overall reduction in
CO2 emissions as well as reduced amounts of energy needs55. Silva FA, Chawla N and Toledo Filho RD. Tensile behavior of high performance
natural (sisal) fibers. Composites Science and Technology. 2008; 68(15-16):3438-3443.
http://dx.doi.org/10.1016/j.compscitech.2008.10.001.
http://dx.doi.org/10.1016/j.compscitech....
.
Starting early seventies, a number of studies66. Fujiyama RT. Sisal fiber reinforced cement mortar-mechanical and
microstructural characterization. [Dissertation]. Rio de Janeiro: Catholic University of Rio de
Janeiro; 1997. Portuguese.
7. Brescansin J. Fracture behavior of bamboo pulp reinforced cementitious
matrix. [Dissertation]. Rio de Janeiro: Catholic University of Rio de Janeiro; 2003.
Portuguese.
8. Toledo Filho RD. Natural fiber reinforced mortar composites: experimental
characterization. [Thesis]. Rio de Janeiro: Catholic University of Rio de Janeiro;
1997.
9. Campello EF. Fatigue behavior of bamboo pulp reinforced cementitious
composites. [Dissertation]. Rio de Janeiro: Catholic University of Rio de Janeiro; 2006.
Portuguese.-1010. Okafor FO, Eze-Uzomaka OJ and Egbuniwe N. The structural properties and
optimum mix proportions of palmnut fibre-reinforced mortar composite. Cement and Concrete
Research. 1996; 26(7):1045-1055.
http://dx.doi.org/10.1016/0008-8846(96)00087-7.
http://dx.doi.org/10.1016/0008-8846(96)0...
have been
made regarding the use of natural fibers, such as sisal and bamboo, as reinforcing elements in
cement mortars and in concretes. The focus in these works has been on the evaluation of the
mechanical properties of the resulting composites as a function of the characteristics of their
constituents, and the results obtained have indicated the viability of using natural fibers as
reinforcing agents. Cement composite laminates reinforced with long sisal fibers, manufactured
using a cast hand lay up technique, were found to exhibit high energy absorbing capacity
reflected in high toughness values under tension and bending loads1111. Silva FA, Mobasher B and Toledo Filho RD. Cracking mechanisms in durable
sisal fiber reinforced cement composites. Cement and Concrete Composites. 2009; 31(10):721-730.
http://dx.doi.org/10.1016/j.cemconcomp.2009.07.004.
http://dx.doi.org/10.1016/j.cemconcomp.2...
. Ultimate strength, on the other hand, achieved average levels
of 12 and 25 MPa for tensile and bend loading, respectively1111. Silva FA, Mobasher B and Toledo Filho RD. Cracking mechanisms in durable
sisal fiber reinforced cement composites. Cement and Concrete Composites. 2009; 31(10):721-730.
http://dx.doi.org/10.1016/j.cemconcomp.2009.07.004.
http://dx.doi.org/10.1016/j.cemconcomp.2...
.
It can thus be stated that, despite a tolerable degradation in their compressive strength,
flexural strength and fracture toughness of the reinforced composites were significantly
enhanced due to the presence of natural fibers, consistent with experimental data reported by
Abu-Lebdeh and co-authors33. Abu-Lebdeh TM, Fini E and Lumpkin M. Flexural and tensile characteristics of
microfiber-reinforced very high strength concrete thin panels. American Journal of Engineering
and Applied Science. 2012; 5(2):184-197.
http://dx.doi.org/10.3844/ajeassp.2012.184.197.
http://dx.doi.org/10.3844/ajeassp.2012.1...
. It is to be
noted, though, that the susceptibility of natural fibers to degradation, due to ambient and
biological factors, requires appropriate surface treatment in order to improve their durability.
For example, long term embrittlement can be markedly reduced by immersing sisal and coconut
fibers in a silica fume slurry prior to their incorporation by the cementitious matrix1212. Toledo Filho RD, Ghavami K, England GL and Scrivener K. Development of
vegetable fibre-mortar composites of improved durability. Cement and Concrete Composites. 2003;
25(2):185-196. http://dx.doi.org/10.1016/S0958-9465(02)00018-5.
http://dx.doi.org/10.1016/S0958-9465(02)...
. Long term properties of the treated specimens
were thus found to be very proximate to those of 28 days untreated apecimens1212. Toledo Filho RD, Ghavami K, England GL and Scrivener K. Development of
vegetable fibre-mortar composites of improved durability. Cement and Concrete Composites. 2003;
25(2):185-196. http://dx.doi.org/10.1016/S0958-9465(02)00018-5.
http://dx.doi.org/10.1016/S0958-9465(02)...
.
In view of their numerous advantages, natural fiber reinforced composites have been considered as potential candidates for structural applications, such as low cost residential compounds in developing countries. Structural components are expected to support the applied loads without suffering critical or subcritical fracture during their projected lifetime, and since the presence of discontinuities (notches and cracks) can lead to premature failure, the cement base composite should be tolerant to such defects. The notch sensitivity exhibited by a given material depends on its toughness level and this in turn can be expressed by appropriate parameters such as the value of the J-integral at physically significant events (for example, fracture initiation and maximum load attainment). Higher toughness signifies lower notch sensitivity; however, one should point out that toughness level depends on the notch geometry, particularly the notch root radius.
The present work was initiated with the purpose of evaluating the effect of sisal fibers on the compressive strength and fracture resistance of hardened cement mortar. As the presence of natural fibers is generally detrimental to the compressive strength, it is imperative to strike a good balance of properties, so as to guarantee adequate toughness level together with acceptable compressive strength. For evaluating the fracture toughness, the J-integral approach was adopted and specimens containing deep notches of different root radii were cast in appropriate molds, cured and then loaded in three point bending. The J-integral values at maximum load were determined and correlated with the notch root radius, for both plain and reinforced mortars. Finally, the J-integral results are also correlated with the impact energy of unnotched prismatic bars having the Charpy dimensions.
2 Material and Methods
The mortar mixture used in the present study was composed of Portland cement PC 32, washed dry sand and tap water, in the proportions of 1:1: 0.4, respectively. The sand had fineness modulus of about 3.33, a maximum particle size of 2 mm and an apparent density of 1.6 g/cm3.
As to the production of the reinforced mortars, 25 and 45 mm long sisal fibers, amounting to
3% of the combined weight of cement and sand, were thoroughly dispersed throughout the dry
mixture before water was gradually added. The fibers had an average specific weight of 9.1
kN/m3 and average mechanical properties of 400 MPa tensile strength, 4% elongation
and 18 GPa elastic modulus55. Silva FA, Chawla N and Toledo Filho RD. Tensile behavior of high performance
natural (sisal) fibers. Composites Science and Technology. 2008; 68(15-16):3438-3443.
http://dx.doi.org/10.1016/j.compscitech.2008.10.001.
http://dx.doi.org/10.1016/j.compscitech....
.
The mixing process resulted in a homogeneous pulp which was cast in appropriate molds for compression and bend test specimens. Twenty four hours later, the specimens were taken off the molds and then immersed in water for 35 days. The hardened specimens of the reinforced mortars had a fiber volume fraction of about 0.081, corresponding to the quantity of fibers incorporated by the matrix.
Compressive strength of the mortars in question was determined using cylindrical specimens (50 mm in diameter and 100 mm in length) which were loaded at room temperature (23 °C) in a universal testing machine with a cross-head speed of 10–5 m/s.
The fracture resistance of the mortars was evaluated making use of notched prismatic specimens (50×50×300 mm) which were submitted to three point bending, with 270 mm loading span. The bend test was carried out at room temperature at a cross head speed of 2x10–5 m/s and load-displacement (P-δ) curves were obtained for both plain and reinforced mortars. The bend specimens contained a 25 mm deep parallel sided notch with 0.5, 1, 1.5, 2 and 2.4 mm root radius. Unnotched specimens with a geometry identical to that of the notched bars were also tested in three point bending.
Impact testing was carried out on unnotched prismatic specimens (10×10×50 mm), using a low capacity Charpy type impact machine appropriate for low toughness brittle materials.
3 Results and Discussion
3.1 Compressive strength
Plain mortar specimens loaded in compression suffered a highly unstable mode of failure, whereas the fiber-reinforced mortars exhibited a more stable behavior, characterized by larger deformations with a gradual drop in the applied load. This increased capacity for deformation can be attributed to the interfacial bond between the sisal fibers and the cement mortar matrix.
The values of the compressive strength were calculated from the ultimate load and are presented in Table 1, for the three mortars in question.
From this table it can be verified that the presence of sisal fibers has a deleterious
influence on the strength level. Moreover, this influence turns out to be more significant for
the long fibers in comparison with the shorter ones. This can be attributed to a decrease in
the mortar’s density, associated with an increase in its porosity1010. Okafor FO, Eze-Uzomaka OJ and Egbuniwe N. The structural properties and
optimum mix proportions of palmnut fibre-reinforced mortar composite. Cement and Concrete
Research. 1996; 26(7):1045-1055.
http://dx.doi.org/10.1016/0008-8846(96)00087-7.
http://dx.doi.org/10.1016/0008-8846(96)0...
11. Silva FA, Mobasher B and Toledo Filho RD. Cracking mechanisms in durable
sisal fiber reinforced cement composites. Cement and Concrete Composites. 2009; 31(10):721-730.
http://dx.doi.org/10.1016/j.cemconcomp.2009.07.004.
http://dx.doi.org/10.1016/j.cemconcomp.2...
12. Toledo Filho RD, Ghavami K, England GL and Scrivener K. Development of
vegetable fibre-mortar composites of improved durability. Cement and Concrete Composites. 2003;
25(2):185-196. http://dx.doi.org/10.1016/S0958-9465(02)00018-5.
http://dx.doi.org/10.1016/S0958-9465(02)...
-1313. Hughes BP and Fattuhi NI. Stress-strain curves for fibre reinforced concrete
in compression. Cement and Concrete Research. 1977; 7(2):173-183.
http://dx.doi.org/10.1016/0008-8846(77)90028-X.
http://dx.doi.org/10.1016/0008-8846(77)9...
. However, it should be mentioned that the specimen integrity
was preserved over a wider deformation range in the presence of longer fibers.
To a first approximation, the ultimate compressive strength of the composite can be estimated from the relation
where σc and σm are respectively the composite and matrix strength and Vm the matrix volume fraction given by
where Vf is the fiber volume fraction.
The validity of Equation 1 is derived from the hypothesis that the fibers do not play an active role in supporting compressive loads applied to the composite. Accordingly, for the sisal fiber volume fraction of 0.081, σc is estimated to be about 25.7 MPa, which is close to the compressive strength level of 25 MPa experimentally determined for the mortar containing the 25 mm fibers. However, for the long fibers (45 mm), the lower compressive strength of 22 MPa listed in Table 1 does not agree well with the strength level estimated by Equation 1, indicating that higher porosity can be associated with the incorporation of such fibers.
3.2 Flexural strength
As expected, the use of sisal fibers as reinforcing element resulted in a significant increase in the load carrying capacity of the unnotched bend specimens. The ultimate load values, corresponding to the average of three bend tests, amounted to 1.5, 2.2 and 2.5 kN, for the plain, 25 mm and 45 mm fiber reinforced mortar, respectively. Considering the specimen geometry and dimensions, the maximum flexural stress σ, within the linear elastic loading regime, can be related to applied load P as
where P is in kN and σ in MPa.
Equation 3, which is based on the theory of
beams, can be applied to the plain mortar, as it behaves essentially in an elastic manner,
yielding a flexural strength level of about 5 MPa. To a first approximation, the same equation
may also be applied to the fiber reinforced mortars, resulting in strength levels of about 7
and 8 MPa, for the 25 and 45 mm fiber reinforcement, respectively. These values are considered
to be rough estimates, in virtue of the nonlinear behavior that precedes the ultimate load
achieved by the fiber reinforced bend specimens. Accordingly, one may be able to conclude that
the reinforced mortar can achieve a flexural strength level, representing a 60% improvement
over the plain matrix of similar formulation. A common theme in the literature1414. Li VC. J-integral applications to characterization and tailoring of
cementitious materials. In: Chuang T-J, Rudnicki JW, editors. Multiscale deformation and
fracture in materials and structures. Springer; 2002. p. 385-406..
http://dx.doi.org/10.1007/0-306-46952-9_21.
http://dx.doi.org/10.1007/0-306-46952-9_...
-1515. Savastano Jr. H, Turner A, Mercer C and Soboyejo WO. Mechanical behavior of
cement-based materials reinforced with sisal fibers. Journal of Materials Science. 2006;
41(21):6938-6948. http://dx.doi.org/10.1007/s10853-006-0218-1.
http://dx.doi.org/10.1007/s10853-006-021...
refers to the notion that fibers serve as bridging elements when crack
traverse the cement matrix, thus maintaining the specimen integrity and allowing the ultimate
load and deformation capacity to increase.
The strengthening effect due to fiber presence is also related to the interfacial bond
between the fibers and cement matrix, which allows the former to take an active part in
supporting the applied load. Sisal fibers present irregular cross section with different shapes
that may be beneficial for the bond strength. Three different cross sectional geometries were
reported in the literature1616. Silva FA, Mobasher B, Soranokom C and Toledo Filho RD. Effect of fiber shape
and morphology on interfacial bond and cracking behaviors of sisal fiber cement based
composites. Cement and Concrete Composites. 2011; 33(8):814-823.
http://dx.doi.org/10.1016/j.cemconcomp.2011.05.003.
http://dx.doi.org/10.1016/j.cemconcomp.2...
: horse-shoe,
arched and twisted arch shape, with the highest bond stress related to the twisted arch fiber
type. Average adhesional bond for all three cross sectional geometries is reported to be in the
range of 0.59 to 0.67 MPa1616. Silva FA, Mobasher B, Soranokom C and Toledo Filho RD. Effect of fiber shape
and morphology on interfacial bond and cracking behaviors of sisal fiber cement based
composites. Cement and Concrete Composites. 2011; 33(8):814-823.
http://dx.doi.org/10.1016/j.cemconcomp.2011.05.003.
http://dx.doi.org/10.1016/j.cemconcomp.2...
.
Macro and micro fracture aspects of fiber reinforced bend specimens are presented in Figures 1 and 2. As
depicted in Figure 1, fracture mode of the fiber
reinforced bend specimens is characterized by a pull-out failure mechanism. This figure refers
to the profile of a 45 mm fiber reinforced specimen, showing the sisal fibers as exposed due to
fiber pull-out. Figure 2, on the other hand, presents the
fracture surface features of a 25 mm fiber reinforced bend specimen, also attesting to the
pull-out phenomenon as a dominant mode of failure. At this point, it is important to mention
that the pull-out force increases as the embedded fiber length increases1616. Silva FA, Mobasher B, Soranokom C and Toledo Filho RD. Effect of fiber shape
and morphology on interfacial bond and cracking behaviors of sisal fiber cement based
composites. Cement and Concrete Composites. 2011; 33(8):814-823.
http://dx.doi.org/10.1016/j.cemconcomp.2011.05.003.
http://dx.doi.org/10.1016/j.cemconcomp.2...
, which is seen to be consistent with the fact that long (45
mm) fibers are more effective in promoting flexural strength than the 25 mm fibers.
3.3 Fracture resistance
Examples of the load-displacement curves obtained in three point bending of the composite mortar are presented in Figure 3, for the different notch root radii. The load-displacement curves corresponding to the plain and reinforced mortars are depicted in Figures 4, 5 and 6, for the 0.5, 1.5 and 2.4 mm root radii, respectively, indicating the marked influence of the presence of sisal fibers on both load carrying capacity and deformability of the notched specimens.
The variation of the maximum load, Pu, with the notch root radius, ρ, is presented in Figure 7, for the mortars in question. Compared to their respective unnotched counterparts, the notched specimens had a much lower load carrying capacity, as a result of the significant reduction of the specimen cross section in the notch plane. As to the influence of the notch root radius, Figure 7 indicates that Pu decreases as the notch becomes sharper and that, for a given root radius, the incorporation of the sisal fibers is associated with an appreciable increase in the load carrying capacity, with the long fibers being more effective in that respect. This is seen to be consistent with the results obtained on the flexural strength of unnotched beams, as sisal fibers contribute significantly to the tensile strength and more effectively so for longer fibers in virtue of the increase in the interfacial force, between fibers and matrix, with the increase in fiber length.
3.3.1 Toughness estimation
The J-integral values at maximum load (Jm) were calculated from
the integrated energy (U) under the load-displacement curve, using the Rice
estimation formula1717. Rice JR. A path independent integral and the approximate analysis of strain
concentrations by notches and cracks. Journal of Applied Mechanics. 1968; 35(2):379-386.
http://dx.doi.org/10.1115/1.3601206.
http://dx.doi.org/10.1115/1.3601206...
.
where B and W are the specimen cross sectional dimensions (50 x 50 mm), a the notch depth (25 mm) and U the integrated energy under the P-δ curve up to P = Pu.
At this point, it is important to mention that toughness evaluation of concrete using
fracture mechanics is considered to be applicable to large scale initially cracked
structures1818. Choi S-H, Kye H-J and Kim W-J. J-integral evaluation of concrete fracture
characteristics. International Journal of Concrete Structures and Materials. 2006;
18(3E):183-189. http://dx.doi.org/10.4334/IJCSM.2006.18.3E.183.
http://dx.doi.org/10.4334/IJCSM.2006.18....
-1919. Jun Z and Qian L. Determination of concrete fracture parameters from a
three-point bending test. Tsinghua Science and Technology. 2003; 8(6):726-733., where structural aspects, such as the size
of coarse aggregates, are to be small compared to the concrete size. Thus, the effect of
specimen size should be considered in determining the fracture toughness of concrete. For the
mortars considered in the present study, the relevant microstructural scale, which is related
to the sand used as aggregate, is in fact very small in comparison to the bend specimen
dimensions. Accordingly, Equation 4 is
considered to be applicable to toughness determination of cement mortar.
The variation of Jm with the small root radius is shown in Figure 8, for the plain mortar. One can observe that such a variation is in agreement with the effect normally detected for metallic and nonmetallic materials, where the J-integral value at fracture initiation varies linearly with the root radius. As fracture initiation in the plain mortar occurs essentially at the maximum load, Jm can, therefore, be considered a good estimate of the J-integral value corresponding to the event of failure initiation in the mortar. For small root radii (ρ ≤ 1.5 mm), though, Jm becomes independent of ρ, remaining at a constant level discriminated as JIc and considered as a material characteristic. The limiting root radius, which is equivalent approximately to 1.5 mm, is also considered a material constant of microstructural significance, apparently compatible with the fact that the sand, used as a constituent of the mortar mixture, had a maximum particle size of 2 mm.
As to the reinforced mortars, the variation of Jm with the notch root radius is presented in Figure 9, for both the 25 and 45 mm sisal fibers, in comparison with the Jm level of the plain mortar. In addition to the extremely beneficial effect of fibers on the mortar’s fracture resistance expressed by Jm, the figure also indicates that a better fracture resistance of the mortar was associated with the use of 45 mm sisal fibers. The beneficial effect on toughness is the result of an improvement in both strength and ductility of the mortar due to sisal fiber presence and as can be verified from the P-δ curves, this effect is more pronounced for the longer fibers.
The impact energy results are presented in Table 2, for the three mortars in question. The individual energy levels shown in the table correspond to the average of five tests with a standard deviation of about 12%.
The analysis of Table 2 leads to conclude that the
use of sisal fibers as a reinforcing element in mortar results in a considerable increase in
the impact resistance and that such an increase is considerably more significant for the
longer fibers. Results obtained by Ramakrishna and Sundararajan2020. Ramakrishna G and Sundararajan T. Impact strength of a few natural fibre
reinforced cement mortar slabs: a comparative study. Cement and Concrete Composites. 2005;
27(5):547-553. http://dx.doi.org/10.1016/j.cemconcomp.2004.09.006.
http://dx.doi.org/10.1016/j.cemconcomp.2...
have shown that the addition of natural fibers to cement
mortar slab can increase its impact resistance by a factor ranging between 3 and 18. This
beneficial influence is attributed to the fact that, even as the matrix cracks, the load
carrying capacity is replenished by invoking fiber loading. This maintains the specimens’
integrity as they continue to deform and hence to absorb more energy. The superiority of long
fibers in promoting impact resistance is related to the higher load carrying capacity, as well
as deformability, of the mortars reinforced with such fibers.
The correlation between the impact energy levels and J-integral results is presented in Figure 10, whereby an essentially linear relationship is seen to exist between the two parameters.
Correlation between Jm and impact energy for the reinforced mortars with notch root radius of 0.5 and 2.4 mm.
4 Conclusions
Regarding the study described herein, the following conclusions can be drawn:
-
•
The use of sisal fibers decreases the mortar’s compressive strength. However, the fiber reinforced mortars exhibit retardation of the failure process, characterized by larger deformations and gradual drop in the applied load, when compared with the plain mortar.
-
•
The deleterious influence of sisal fibers on the compressive strength of reinforced mortar seems to be more significant for long fibers than for shorter ones.
-
•
The presence of sisal fibers in cement mortar considerably improves its fracture resistance. This improvement is manifested by an increase in the J-Integral values determined at maximum load in the presence of deep notches with different root radii.
-
•
Results of impact tests on unnotched specimens indicate a pronounced improvement in impact energy levels due to sisal fibers incorporated to cement mortar.
-
•
Longer sisal fibers are seen to be more effective than shorter ones in promoting fracture resistance of reinforced mortars.
References
-
1Sivakumar A and Santhanam M. Mechanical properties of high strength concrete reinforced with metallic and non-metallic fibers. Cement and Concrete Composites. 2007; 29(8):603-608. http://dx.doi.org/10.1016/j.cemconcomp.2007.03.006.
» http://dx.doi.org/10.1016/j.cemconcomp.2007.03.006 -
2Qian CX and Stroeven P. Development of hybrid polypropylene-steel-fiber-reinforced concrete. Cement and Concrete Research. 2000; 30(1):63-69. http://dx.doi.org/10.1016/S0008-8846(99)00202-1.
» http://dx.doi.org/10.1016/S0008-8846(99)00202-1 -
3Abu-Lebdeh TM, Fini E and Lumpkin M. Flexural and tensile characteristics of microfiber-reinforced very high strength concrete thin panels. American Journal of Engineering and Applied Science. 2012; 5(2):184-197. http://dx.doi.org/10.3844/ajeassp.2012.184.197.
» http://dx.doi.org/10.3844/ajeassp.2012.184.197 -
4Kitamura S. Experimental study of the influence of fiber content and specimen dimensions on the split tensile strength and its relationship with the flexural strength. [Dissertation]. Rio de Janeiro: Fluminense Federal University; 2006. Portuguese.
-
5Silva FA, Chawla N and Toledo Filho RD. Tensile behavior of high performance natural (sisal) fibers. Composites Science and Technology. 2008; 68(15-16):3438-3443. http://dx.doi.org/10.1016/j.compscitech.2008.10.001.
» http://dx.doi.org/10.1016/j.compscitech.2008.10.001 -
6Fujiyama RT. Sisal fiber reinforced cement mortar-mechanical and microstructural characterization. [Dissertation]. Rio de Janeiro: Catholic University of Rio de Janeiro; 1997. Portuguese.
-
7Brescansin J. Fracture behavior of bamboo pulp reinforced cementitious matrix. [Dissertation]. Rio de Janeiro: Catholic University of Rio de Janeiro; 2003. Portuguese.
-
8Toledo Filho RD. Natural fiber reinforced mortar composites: experimental characterization. [Thesis]. Rio de Janeiro: Catholic University of Rio de Janeiro; 1997.
-
9Campello EF. Fatigue behavior of bamboo pulp reinforced cementitious composites. [Dissertation]. Rio de Janeiro: Catholic University of Rio de Janeiro; 2006. Portuguese.
-
10Okafor FO, Eze-Uzomaka OJ and Egbuniwe N. The structural properties and optimum mix proportions of palmnut fibre-reinforced mortar composite. Cement and Concrete Research. 1996; 26(7):1045-1055. http://dx.doi.org/10.1016/0008-8846(96)00087-7.
» http://dx.doi.org/10.1016/0008-8846(96)00087-7 -
11Silva FA, Mobasher B and Toledo Filho RD. Cracking mechanisms in durable sisal fiber reinforced cement composites. Cement and Concrete Composites. 2009; 31(10):721-730. http://dx.doi.org/10.1016/j.cemconcomp.2009.07.004.
» http://dx.doi.org/10.1016/j.cemconcomp.2009.07.004 -
12Toledo Filho RD, Ghavami K, England GL and Scrivener K. Development of vegetable fibre-mortar composites of improved durability. Cement and Concrete Composites. 2003; 25(2):185-196. http://dx.doi.org/10.1016/S0958-9465(02)00018-5.
» http://dx.doi.org/10.1016/S0958-9465(02)00018-5 -
13Hughes BP and Fattuhi NI. Stress-strain curves for fibre reinforced concrete in compression. Cement and Concrete Research. 1977; 7(2):173-183. http://dx.doi.org/10.1016/0008-8846(77)90028-X.
» http://dx.doi.org/10.1016/0008-8846(77)90028-X -
14Li VC. J-integral applications to characterization and tailoring of cementitious materials. In: Chuang T-J, Rudnicki JW, editors. Multiscale deformation and fracture in materials and structures. Springer; 2002. p. 385-406.. http://dx.doi.org/10.1007/0-306-46952-9_21.
» http://dx.doi.org/10.1007/0-306-46952-9_21 -
15Savastano Jr. H, Turner A, Mercer C and Soboyejo WO. Mechanical behavior of cement-based materials reinforced with sisal fibers. Journal of Materials Science. 2006; 41(21):6938-6948. http://dx.doi.org/10.1007/s10853-006-0218-1.
» http://dx.doi.org/10.1007/s10853-006-0218-1 -
16Silva FA, Mobasher B, Soranokom C and Toledo Filho RD. Effect of fiber shape and morphology on interfacial bond and cracking behaviors of sisal fiber cement based composites. Cement and Concrete Composites. 2011; 33(8):814-823. http://dx.doi.org/10.1016/j.cemconcomp.2011.05.003.
» http://dx.doi.org/10.1016/j.cemconcomp.2011.05.003 -
17Rice JR. A path independent integral and the approximate analysis of strain concentrations by notches and cracks. Journal of Applied Mechanics. 1968; 35(2):379-386. http://dx.doi.org/10.1115/1.3601206.
» http://dx.doi.org/10.1115/1.3601206 -
18Choi S-H, Kye H-J and Kim W-J. J-integral evaluation of concrete fracture characteristics. International Journal of Concrete Structures and Materials. 2006; 18(3E):183-189. http://dx.doi.org/10.4334/IJCSM.2006.18.3E.183.
» http://dx.doi.org/10.4334/IJCSM.2006.18.3E.183 -
19Jun Z and Qian L. Determination of concrete fracture parameters from a three-point bending test. Tsinghua Science and Technology. 2003; 8(6):726-733.
-
20Ramakrishna G and Sundararajan T. Impact strength of a few natural fibre reinforced cement mortar slabs: a comparative study. Cement and Concrete Composites. 2005; 27(5):547-553. http://dx.doi.org/10.1016/j.cemconcomp.2004.09.006.
» http://dx.doi.org/10.1016/j.cemconcomp.2004.09.006
Publication Dates
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Publication in this collection
Jan-Feb 2015
History
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Received
26 June 2014 -
Reviewed
07 Jan 2015