Título: | SHRINKAGE, CREEP AND FRACTURE OF CEMENTITIOUS COMPOSITES REINFORCED WITH BAMBOO PULP | ||||||||||||||||||||||||||||||||||||
Autor: |
ANGELA TERESA COSTA SALES |
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Colaborador(es): |
KHOSROW GHAVAMI - Orientador |
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Catalogação: | 12/JUL/2006 | Língua(s): | PORTUGUESE - BRAZIL |
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Tipo: | TEXT | Subtipo: |
THESIS
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Notas: |
[pt] Todos os dados constantes dos documentos são de inteira responsabilidade de seus autores. Os dados utilizados nas descrições dos documentos estão em conformidade com os sistemas da administração da PUC-Rio. [en] All data contained in the documents are the sole responsibility of the authors. The data used in the descriptions of the documents are in conformity with the systems of the administration of PUC-Rio. |
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Referência(s): |
[pt] https://www.maxwell.vrac.puc-rio.br/projetosEspeciais/ETDs/consultas/conteudo.php?strSecao=resultado&nrSeq=8663&idi=1 [en] https://www.maxwell.vrac.puc-rio.br/projetosEspeciais/ETDs/consultas/conteudo.php?strSecao=resultado&nrSeq=8663&idi=2 |
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DOI: | https://doi.org/10.17771/PUCRio.acad.8663 | ||||||||||||||||||||||||||||||||||||
Resumo: | |||||||||||||||||||||||||||||||||||||
The application of cimentitious composites using vegetal
fibers in substitution of
asbestos is a worldwide fact in the fiber cement industry.
Despite their good
mechanical properties and durability, the use of asbestos
fibers causes well-known
health hazards. Although vegetal fibers have relatively
poor mechanical properties
compared with synthetic fibers, they have other advantages
such as low cost and
low energy demand during manufacture. Bamboo is an
excellent fiber supplier,
due to its fast growth and the quality of its fibers.
Using vegetal pulp it is possible
to insert considerable amounts of fiber in a cement
matrix, which randomly
distributed confer isotropic characteristics to the
composite. Studies are carried
out aiming to improve the performance of composites with
vegetal fibers.
Shrinkage and creep are sorts of time depending
deformation that may
significantly reduce the durability and performance of the
cement based
composite. Cementitious composites are essentially
heterogeneous materials
subject to the presence of flaws at different levels due
to the presence of many
internal microcraks in the material prior to loading.
Therefore, the application of
fracture mechanics could become a suitable tool for the
design and control of the
integrity of these composites, since the inhibition of
crack initiation and
propagation is one of the main functions of the short
fiber reinforcement. This
work sought to analyze the behavior of cimentitious
composites reinforced with
bamboo pulp under shrinkage and creep and to provide
sufficient fracture
parameters to describe the failure mode of the material.
The results show that,
whereas the plastic shrinkage reduces, the free drying
shrinkage increases
proportionally to bamboo pulp content in the composite,
reaching a 40%
increment for a 14% pulp content, after one year. Under
restrained shrinkage, the
composite with bamboo pulp presents better performance
than unreinforced
matrix. Namely, under same boundary conditions, while the
unreinforced matrix
presents cracks after about four hours, the composites
present no cracks visible through a 10x magnifying glass,
even after forty five days of drying. Study of the
shrinkage reversibility of the composite showed that there
is contraction
deformation prevalence. Under simple compression, the
creep capacity of the
bamboo pulp composites increases proportionally with the
fiber content. Under
bending stress, there was an increase of the specific
creep in the compressed face
of the specimen, as the pulp content of the mixture
increases. The specific creep
under bending tension for the tensile face was greater for
the unreinforced matrix
than in the bamboo pulp composites. As revealed through
the assessment of
fracture behavior of composites with bamboo pulp, notched
specimens presented a
considerable improvement in bending behavior when compared
to the
unreinforced matrix. The composites with pulp became less
sensible to the notch
with the increment of pulp content. In the bamboo pulp
composites, considerable
softening was observed in the load-displacement curve, as
load gradually
decreases after the peak load and before the rupture due
to crack propagation.
Using resistance curves (R-curves) it was possible to
identify the KIR values that,
for the composites, kept certain constancy as the crack
length increased. At this
plateau of the curve, the average values for KIR reached
1,88 MPa.m1/2 and 1,84
MPa.m1/2 for composites with bamboo pulp content of 8% and
14% respectively.
In the composites, crack profiles and crack surfaces were
tortuous, while in the
unreinforced matrix the fracture mechanisms were more
intensely dominated by
the presence of the initial notch.
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