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The performance and environmental durability of pultruded glass fibre composite rebars
thesis
posted on 2010-11-25, 12:36 authored by J. ZhangThe work reported is a study of the performance of pultruded unidirectional glass fibre
composite rebars, in order to understand and quantify the environmental degradation of
the materials in water and alkali solution with, and without, stress. The rebars have been
proposed as possible candidates for replacing reinforcing steel in concrete structures.
Firstly, the interfacial strength, mechanical properties and dynamic mechanical
properties of the rebar composites were investigated using ILSS and a three point
bending test, in conjunction with SEM and dynamic mechanical thermal analysis
(DMTA). It was concluded that the surface treatments on glass fibres played a major role
in the ILSS of the composites. Likewise, the flexural properties and failure behaviour of
the rebars were also affected and all were related to the ILSS values. With increasing
ILSS, the flexural strength and modulus increased and the failure features varied from
compressive, to mixed compressive-tensile, to tensile. This was because higher
interphase strengths delayed the occurrence of fibre microbuckling and increased the
instability of glass fibres in the matrix. It was found that the glass transition temperature
(Tg), as measured by DMTA, can be used to assess interfacial strength. A strong
interphase resulted in a relatively higher Tg (and vice versa). This appears to have been
caused by the more efficient transfer of the "restraining effect of glass fibres" on
polymer chain mobility. The rate and magnitude of flexural property
degradation in alkali solution was similar to that in water, except that at 80°C, the
modulus was considerably reduced. This was caused by the corrosion of defect
inclusions introduced during rebar manufacturing process. The results suggest that the
hydroxyl ions in the alkali solution do not diffuse into the polymer matrix. Addition of
alkali into water did not lead to a significant difference in water absorption dynamics and
DMTA behaviour of pure Atlac 580 vinylester resin.
Thirdly, fractured glass rebars, subjected to stress and water or alkali solution at 40°C,
were studied. It was observed that low stresses resulted in relatively planar cracks normal
to the applied tensile stress but did not pose significant damage to the interphase. The
opposite was true for rebars under high-levels of stress. Alkali solutions accelerated the
occurrence of stress corrosion in terms of failure times. It was found that crosslinked
vinylester resin exhibited a diphasic structure as detected by modulated temperature
differential scanning calorimetry (MDSC). Based on these results, it is proposed that
microcracks form in the polymer matrix of the composite (under low stresses) due to the
different responses of the two phases to the stress field at crack tips. Microcracking then
allows transport of aqueous media into the composite by a percolation process.
History
School
- Aeronautical, Automotive, Chemical and Materials Engineering
Department
- Materials
Publisher
© J. ZhangPublication date
2000Notes
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.EThOS Persistent ID
uk.bl.ethos.343667Language
- en
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Keywords
Pultruded glass compositesComposite interphaseInterphase degradationEnvironmental durabilityStress corrosionMicro-phase separationDynamic mechanical thermal analysis (DMTAModulated temperature differential scanning calorimetry (MDSC)Interlaminar shear strength (ILSS)Materials Engineering not elsewhere classified
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