| 1. |
- Zhang, Emma, 1985, et al.
(author)
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Electrical monitoring of concrete using a novel structural sensor based on conductive cementitious mortar
- 2020
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In: ECCM 2018 - 18th European Conference on Composite Materials. - 9781510896932
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Conference paper (peer-reviewed)abstract
- This paper presents the development of a durable structural sensor based on cement-mortar modified with graphene and other carbon-based fillers. The purpose of the structural sensor is to indirectly monitor curing and service performance of concrete via electrical resistivity measurements. Electrical resistivity is an efficient parameter which can non-destructively capture intrinsic structural features of cementitious materials. The developed structural sensor is used to record electrical resistivity as a durability indicator during the whole service life of the concrete structure. To date, performance monitoring systems usually fail in the long-run before the failure of the actual monitored structure. The proposed sensor is embeddable in the interrogated structure and ensures sustainable consolidation with appropriate physico-chemical adherence and mechanical interlocking. This allows the monitoring system to surpass the expected service life of the parent concrete. Within this on-going work, the effects of different concentrations of carbon fillers on the electrical properties of cementitious mortars are reported. After an initial investigation to select the appropriate synthesis, the ability of the sensor to monitor the development of resistivity during setting and hardening was tested and the results are presented herein. Finally, the durability of the sensor was tested via electrical stability measurements under freeze-thaw cycles.
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| 2. |
- Grammatikos, Sotirios, 1985, et al.
(author)
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Concrete setting and hardening monitoring using a novel graphene-based sensor
- 2017
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In: ICF 2017 - 14th International Conference on Fracture. ; 2, s. 1204-1205
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Conference paper (peer-reviewed)abstract
- This paper presents the procedure towards the development of a durable structural sensor based on graphene and other carbon fillers, for the monitoring of structural performance of concrete. The sensor captures electrical resistivity as a strength development and durability index during the whole service life of concrete. To date, performance monitoring systems usually fail in the long-run before the failure of the actual structure. The proposed sensor is embedded in the interrogated structure and ensures sustainable consolidation via appropriate physico-chemical adherence and mechanical interlocking. This allows for an efficient performance monitoring 'build-up' expected to surpass the service life of the parent concrete structure. The effects of different concentrations of graphene and other fillers on the electrical properties of concrete were studied. After an initial investigation to select the appropriate synthesis, the ability of the sensor to monitor the development of resistivity during setting and hardening was tested and the results are presented herein.
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| 3. |
- Grammatikos, Sotirios, 1985, et al.
(author)
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Impedance spectroscopy as a tool for moisture uptake monitoring in construction composites during service
- 2018
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In: Composites Part A: Applied Science and Manufacturing. - : Elsevier BV. - 1359-835X. ; 105, s. 108-117
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Journal article (peer-reviewed)abstract
- This is a first study comparing dielectric spectroscopy and gravimetric measurements of moisture uptake in pultruded glass fibre reinforced polymers (FRPs). Specimens were subjected to sub-Tg hygrothermal aging for 224 days. Impedance spectra in the frequency range 0.1 Hz to 10 MHz were captured during exposure and compared with gravimetric measurements. Moisture concentration was found to increase the FRP's dielectric permittivity monotonically and decrease bulk resistance. High quality dielectric data was obtained as moisture uptake is independent of inherent changes suggested by mass loss which compromise gravimetry. Dielectric measurements remained sensitive to moisture despite significant mass loss, which typically distorts the weight gain process complicating the commonly adopted gravimetric methodology. Real-time dielectric measurements were obtained from FRP specimens continuously immersed in water and without making use of any additional sensing elements. The novel approach adopted is of high commercial impact as moisture uptake control is recognized as a significant problem by industry.
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| 4. |
- Grammatikos, Sotirios, 1985, et al.
(author)
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Non-linear response of environmentally aged polymer composites: A physicochemical and mechanical study
- 2016
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In: ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials. - 9783000533877
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Conference paper (peer-reviewed)abstract
- In this paper, the anomalous behaviour of polymer composites subjected to hygrothermal aging is discussed in reference to the results of a characterization study on polyester matrix fibre reinforced polymer (FRP) composites. Hygrothermal aging, the combination of moisture and elevated temperatures, has been proven to affect the durability of FRPs. Significant structural degradation can be expected as a consequence of hygrothermal aging, however it has been shown that some material properties exhibit a strong non-linear and even beneficial behaviour as a consequence of hygrothermal exposure, indicating the presence of different competing mechanisms. To study these different mechanisms which control the structural performance of an exposed material, FRP samples were exposed to short-term hygrothermal aging for 112 days. Moisture absorption characteristics and mechanical performance were assessed at prescribed time frames throughout aging. With a view to examining any induced intrinsic and surface characteristics, Computed Tomography scan (CT-scan) and Scanning Electron Microscopy (SEM) were also employed. Lastly, impedance spectroscopy was used as an innovative tool to efficiently follow moisture absorption during aging.
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| 5. |
- Grammatikos, Sotirios, 1985, et al.
(author)
-
On the Mechanical Recycling of Decommisioned Insulation Polymer Composite Components
- 2020
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In: IOP Conference Series: Materials Science and Engineering. - : Institute of Physics Publishing. - 1757-8981 .- 1757-899X. ; 842:1
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Conference paper (peer-reviewed)abstract
- Fibre reinforced polymer composites (FRPs) are being increasingly used in aerospace and automotive applications due to their high specific mechanical properties. The construction industry has also started taking advantage of the potential of FRPs for both structural and non-structural purposes. The result of this remarkable absorption of FRPs within the worldwide production market, has led to an immense increase of decommissioned thermoset-matrix components. Nowadays, the majority of the decommissioned FRP components are recovered energy-wise through incineration or simply discarded in landfills around the globe. Within the framework of this paper, we present a solution for the extension of the service life of decommissioned FRP components. Decommissioned electrical insulation FRP pipes were granulated and incorporated as fillers within both cementitious and polymer matrix composites. The effect of FRP granulates on the mechanical performance of cementitious and polymer matrix composites is examined to determine the maximum granulate-filler fraction that can be recycled without compromising the mechanical performance and manufacturing process.
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| 6. |
- Grammatikos, Sotirios, 1985, et al.
(author)
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Recycling and re-purposing decommisioned construction polymer composites for construction applications
- 2018
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In: ECCM 2018 - 18th European Conference on Composite Materials. - : Applied Mechanics Laboratory. - 9781510896932
-
Conference paper (peer-reviewed)abstract
- Fibre reinforced polymer composites (FRPs) are being increasingly used in aerospace and automotive applications due to their high specific mechanical properties. The construction industry has also started taking advantage of the potential of FRPs for both structural and non-structural purposes. The result of this remarkable absorption of FRPs within the worldwide production market, has led to an immense increase of decommissioned thermoset-matrix components. Nowadays, the majority of the decommissioned FRP components are recovered energy-wise through incineration or simply discarded in landfills around the globe. Within the framework of this paper, we present a solution for the extension of the service life of decommissioned FRP components. Decommissioned electrical insulation FRP pipes were granulated and incorporated as fillers within both cementitious and polymer matrix composites. The effect of FRP granulates on the mechanical performance of cementitious and polymer matrix composites is examined to determine the maximum granulate-filler fraction that can be recycled without compromising the mechanical performance and manufacturing process.
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| 7. |
- Grammatikos, Sotirios, 1985, et al.
(author)
-
Thermal cycling effects on the durability of a pultruded GFRP material for off-shore civil engineering structures
- 2016
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In: Composite Structures. - : Elsevier BV. - 0263-8223. ; 153, s. 297-310
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Journal article (peer-reviewed)abstract
- This paper investigates the effects of thermal cycles on the structural integrity of a pultruded Glass Fibre Reinforced Polymer (GFRP). Through a critical review of current literature alongside a comprehensive experimental campaign, the material's response to cyclic thermal loading has been ascertained, defined by the rate of degradation of its physical, mechanical and visco-elastic properties. Matching sets of both dry and soaked samples conditioned in distilled water for 224 days. Freeze-thaw cycling of both dry and soaked samples was conducted between 20 °C and -10 °C for a total of 300 cycles. Computed Tomography scanning (CT-scan) was undertaken to assess the microstructural physical changes throughout freeze-thaw cycling. After exposure, GFRP samples exhibited a minor decrease in glass transition temperature (Tg) which indicated minor structural degradation. Dry GFRP sample's mechanical response exhibited negligible changes in both tensile and in-plane shear properties. However, as a result of the higher induced thermal stresses, soaked samples showed a significant degradation of their tensile and shear strengths. Yet, the soaked material's stiffness remained largely unaffected due to the potential reversible nature of plasticization, which acts to increase the material's molecular mobility when initially moisture-saturated, but is later recovered as the soaked samples lose moisture throughout freeze-thaw cycling.
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| 8. |
- Mirzanamadi, Raheb, 1987, et al.
(author)
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Thermal properties of asphalt concrete: A numerical and experimental study
- 2018
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In: Construction and Building Materials. - : Elsevier BV. - 0950-0618. ; 158, s. 774-785
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Journal article (peer-reviewed)abstract
- The aim of this study is to investigate the effects of different design parameters of asphalt concrete and environmental conditions on the thermal properties (thermal conductivity, diffusivity and volumetric heat capacity). A two-dimensional (2-D) numerical model of the asphalt concrete was developed based on the Finite Element Method (FEM). The numerical model was validated by the experimental results using the Transient Plane Source (TPS) method. The experimental results showed that an increase in the ratio of the TPS sensor size to maximum aggregate size improves the accuracy of the thermal properties measurements. A comparison between the thermal properties obtained by the numerical model and the TPS method exhibited a relative error in the range of 2–10%. The numerical model was used to study the effects of the type of aggregates, aggregate gradation, graphite filler in the binder, air void content as well as moisture and freezing conditions on the thermal properties of asphalt concrete.
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| 9. |
- Papatzani, Styliani, et al.
(author)
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Pore-structure and microstructural investigation of organomodified/Inorganic nano-montmorillonite cementitious nanocomposites
- 2018
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In: AIP Conference Proceedings. - : Author(s). - 1551-7616 .- 0094-243X. ; 1957
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Conference paper (peer-reviewed)abstract
- In the present paper, the effect of three different types of nano-montmorillonite dispersions (nMt) on the (i) microstructure as witnessed by Scanning Electron Microscopy, (ii) long term density measurements and (iii) pore structure as determined via Mercury Intrusion Porosimetry of Portland - limestone cement formulations have been compared, in an effort to determine the upper and lower bound of nMt addition in cementitious nanocomposites. The reference formulation, contained 60% PC and 40% LS by mass of binder aiming at the minimization of clinker and maximization of other constituents. Two aqueous organomodified NMt dispersions (one dispersed with non-ionic fatty alcohol and the other with anionic alkyl aryl sulphonate) and one aqueous inorganic NMt dispersion (dispersed with sodium tripolyphosphate) were added at 0.5, 1, 2, 4 and 5.5% by mass of solids as replacement of Portland cement. The water to solids ratio was kept constant at 0.3. The inorganic nMt showed the greatest potentials for microstructural enhancement. The way in which the level of the nMt platelet separation affected the pastes was discussed. The research reported was part of a much broader project supported by the EU.
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| 10. |
- Ullah, Z., et al.
(author)
-
Multi-scale computational homogenisation to predict the long-term durability of composite structures
- 2017
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In: Computers and Structures. - : Elsevier BV. - 0045-7949. ; 181, s. 21-31
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Journal article (peer-reviewed)abstract
- A coupled hygro-thermo-mechanical computational model is proposed for fibre reinforced polymers, formulated within the framework of Computational Homogenisation (CH). At each macrostructure Gauss point, constitutive matrices for thermal, moisture transport and mechanical responses are calculated from CH of the underlying representative volume element (RVE). A degradation model, developed from experimental data relating evolution of mechanical properties over time for a given exposure temperature and moisture concentration is also developed and incorporated in the proposed computational model. A unified approach is used to impose the RVE boundary conditions, which allows convenient switching between linear Dirichlet, uniform Neumann and periodic boundary conditions. A plain weave textile composite RVE consisting of yarns embedded in a matrix is considered in this case. Matrix and yarns are considered as isotropic and transversely isotropic materials respectively. Furthermore, the computational framework utilises hierarchic basis functions and designed to take advantage of distributed memory high performance computing.
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