Horizon 2020 Marie Skłodowska-Curie Innovative Training Network

Sofia Antonopoulou

BSc, MSc
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Sofia Antonopoulou 2018-09-09T15:11:25+00:00
Early Stage Researcher
University College Dublin (UCD)

Project 1: Reliability of concrete structures reinforced with braided FRP

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Research Interests:

Materials science & engineering; Environmental & earth science; Geophysics & engineering geology; GeoMaterials technology; Building materials

Biography:

She holds a BSc in Geology & Geo-Environment from National & Kapodistrian University of Athens and she obtained her MSc degree in Materials Science & Engineering from National Technical University of Athens.

During her studies, she successfully completed her thesis in the field of Materials Technology and she joined in university’s internship program.

Then, she worked as a geotechnical engineer in the private sector and she participated as a research associate in three scientific projects and international conferences before joining TRUSS ITN in September 2015. A summary of her research highlights and training, dissemination and outreach activities in TRUSS  other than network-wide events, is provided in the pdf below, followed by more detailed info on her research outputs.

ESR1_Summary

Research Outputs:

  • Stamatakis, M., Antonopoulou, S., Kavouri, S., Stamatakis, G., Papavlasopoulou, N. and Anastasatou, M. (2014), “Biogenic Micro – Silica: A multifunctional raw material in environmentally friendly applications”, in Proceedings of 22nd International Conference on Materials and Technology, Portorose, Slovenia.
  • Antonopoulou, S., Badogiannis, E. and Tsivilis, S. (2013), “Comparison of geopolymers and cement mortars as concrete repairing materials”, in Proceedings of 9th National Scientific Conference on Chemical Engineering, Athens, Greece.
  • Stamatakis, M., Fragoulis, D., Stamatakis, G. and Antonopoulou, S. (2010), “The opaline silica-rich sedimentary rocks of Milos Island, Greece and their behavior as pozzolanas in the manufacture of cement”, Advances in Cement Research, 22 (3): 171 – 183. [DOI]

Selected presentations from TRUSS dissemination events

1st TRUSS Symposium (Portoroz (Slovenia), 21st June 2017)
TRUSS Workshop (Dublin (Ireland), 29th August 2018)

Publications in TRUSS

Conference contributions
 Inspections and maintenance of infrastructure are expensive. In some cases, overdue or insufficient maintenance/monitoring can lead to an unacceptable risk of collapse and to a tragic failure as the Morandi bridge in Genoa, Italy, on 14th August 2018. An accurate assessment of the safety of a structure is a difficult task due to uncertainties associated with the aging and response of the structure, with the operational and environmental loads, and with their interaction. During the period from 2015 to 2019, the project TRUSS (Training in Reducing Uncertainty in Structural Safety) ITN (Innovative Training Network), funded by the EU H2020 Marie Curie-Skłodowska Action (MSCA) programme, has worked towards improving the structural assessment of buildings, energy, marine, and transport infrastructure. Fourteen Early Stage Researchers (ESRs) have been recruited to carry out related research on new materials, testing methods, improved and more efficient modelling methods and management strategies, and sensor and algorithm development for Structural Health Monitoring (SHM) purposes. This research has been enhanced by an advanced program of scientific and professional training delivered via a collaboration between 6 Universities, 1 research institute and 11 companies from 5 European countries. The high proportion of companies participating in TRUSS ITN has ensured significant industrial expertise and has introduced a diverse range of perspectives to the consortium on the activities necessary to do business in the structural safety sector. 
This study compares the physical properties and tensile behaviour of two different basalt fibre reinforced polymer (BFRP) rebar designs. Both types are developed using basalt fibres and epoxy resin as reinforcement and matrix respectively; composites with a constant cross section of 8 mm diameter are manufactured using a vacuum assisted resin infusion technique. The first configuration consists of eight braided layers at various angles, while the second one combines a unidirectional core with four outer braided layers. The latter hybrid design is introduced to improve the elastic modulus of braided BFRP reinforcement used in concrete structures. Tensile performance of all BFRP rebars produced in UCD laboratory is numerically and experimentally evaluated, and results for both approaches are compared. The effective longitudinal in-plane modulus and the fibre volume fractions (φf) of each sample is calculated using the classical laminate theory and then, tensile tests are performed in accordance to the B2_ACI 440.3R-04 standard to experimentally validate the numerical results. Initial findings indicate that the elastic modulus of BFRP rebar can be enhanced by combining braiding with a unidirectional fibre core while a sufficient tensile strength is obtained, but additional research towards an optimal hybrid design is required.
Basalt Fibre Reinforced Polymer composites were recently introduced as a possible replacement to steel in civil engineering applications due to both their excellent corrosion resistance and their high strength-­to-­weight ratio. These materials also have the potential to provide long-­term durability, while minimising maintenance costs. However, limited data are available in the literature regarding their fatigue performance, and most of them are focused either on their static behaviour or on aerospace applications rather than structural ones. The aim of this research is to experimentally evaluate the mechanical properties, and more specifically, the tensile fatigue performance of braided Basalt Fiber Reinforced Polymer (BFRP) reinforcement. Three different rebar designs with a 5, 8 and 10 mm diameter are manufactured, using braiding and a vacuum assisted resin infusion technique. All types are developed using basalt fibres and epoxy resin as reinforcement and matrix respectively. Tensile fatigue tests on BFRP samples are performed using Instron 500 Universal Testing Machine in accordance to B7_ACI 440.3R-­04 standard. All samples are tested under a fixed load ratio of 0.1 and a loading frequency of 4 Hz. The minimum and maximum load vary accordingly, with the latter ranging from 20 to 60% of the quasi-­static tensile strength. Throughout the whole duration of the fatigue cycling test, the applied load, displacement and specimen elongation are electronically recorded every 10th cycle. The number of repeated loading cycles to failure and stress applied is then used to generate S-­N curves for each sample. A reference specimen of each type is also used for the evaluation of the static tensile performance following the B2_ACI 440.3R-­04 standard. Initial results confirmed a sufficient fatigue performance of braided BFRP rebars with a high stiffness retention at low fatigue loads and good damping properties. Moreover, composites with a lower fiber volume fraction and a higher void content seem to exhibit an increased fatigue stress sensitivity with a reduction of the fatigue limit at elevated fatigue cycles. 
This paper focuses on the use of micro computed tomography (CT) methods for fibre
composite material analysis and evaluation of braided Basalt Fiber Reinforced Polymer (BFRP) reinforcement. More specifically, a combined experimental and computational study towards a complete 3D geometrical model of braided BFRP rebars is presented here. Rebars are designed using basalt fibres and epoxy resin as reinforcement and matrix respectively;; composites are developed in three different sizes and configurations, using braiding and a vacuum assisted resin infusion technique. All samples are scanned using micro-­CT imaging and their microstructure is assessed. Geometrical consistency is validated, including measurements on layer thickness, braiding angle and fibre orientation;; yarn cross section deviations from the idealized elliptical shape along the yarn path and nesting effects were observed. Defect and void development, yarn damage and calculation of fibre volume fractions, is completed with VG Studio Max image processing software. In addition, realistic geometrical modelling of braided composites based on these measurements is carried out using TexGen software, towards simulation of their mechanical response with FEA methods.

There is multitude of models available to assess structural safety based on a set of input parameters. As the degree of complexity of the models increases, the uncertainty of their output tends to decrease. However, more complex models typically require more input parameters, which may contain a higher degree of uncertainty. Therefore, it becomes necessary to find the balance that, for a particular scenario, will reduce the overall uncertainty (model + parameters) in structural safety. The latter is the objective of the Marie Skłodowska-Curie Innovative Training Network titled TRUSS (Training in Reducing Uncertainty in Structural Safety) funded by the EU Horizon 2020 research and innovation programme (http://trussitn.eu). This paper describes how TRUSS addresses uncertainty in: (a) structural reliability of materials such as basalt fiber reinforced polymer, (b) testing techniques in the assessment of concrete strength in buildings, (c) numerical methods in computing the non-linear response of submerged nuclear components subjected to an earthquake, (d) estimation of life of wind turbines, (e) the optimal inspection times and management strategies for ships, (f) characterization of the dynamic response of ship unloaders and (g) the relationship between vehicles fuel consumption and pavement condition. -> Link to full text in repository

In recent years the long term durability of reinforced concrete structures has become a major concern. The effect of harsh loading conditions and aggressive environmental factors can lead to corrosion of reinforcing steel in civil engineering applications. This in turn leads to undesired repairs, additional costs and shorter service lives. Advanced composite materials, such as Basalt Fibre Reinforced Polymer (BFRP), have the capacity to significantly address this problem. These materials have enhanced physical properties such as higher mechanical and corrosion resistance, and have the potential to replace traditional steel rebars as tension reinforcement in concrete. There are however limitations that prevent their use on a larger scale, and lack of ductility is the most significant. Braiding techniques could provide the required performance benefits related to the additional ductility and flexibility needed, as well as enhancing the bond between FRP and concrete. If this is achieved, it has the potential to prevent a brittle failure and successfully meet strength, reliability and cost demands. This study focuses on the basics of materials characterization and reliability analysis of internal BFRP reinforcement for concrete structures towards design optimization for structural reliability over their service life. [DOI] -> Link to full text in repository

In recent years, degradation of reinforced concrete (RC) structures due to corrosion of reinforcing steel has become a major concern worldwide. This affects long-term durability, total service life and structural safety of RC elements. Advanced composite materials, such as Basalt Fibre Reinforced Polymer (BFRP), are currently being developed and are showing promising results as a viable alternative to steel in infrastructure applications. More specifically, these materials can offer significant advantages related to both their non-corrodible nature and their enhanced physical and mechanical properties. However, their brittle nature is considered as the main limitation preventing their use on a larger scale. A detailed investigation of manufacturing technologies and design methodologies for the optimum development of BFRP composites, indicates that braiding methods could provide the required performance benefits through increased ductility and flexibility; it can also enhance the bond between FRP and concrete.

This study focuses on exploring the potential of braided Basalt Fibre Reinforced Polymer reinforcement through design optimisation and evaluation of their structural performance. Braided BFRP preforms with different configurations were produced changing key braiding parameters in order to achieve the desired structural geometry and meet the performance characteristics of existing rebar reinforcement. Following from that, successful epoxy resin impregnation trials in regular and spiral configurations confirmed the possibility of manufacturing braided BFRP composites in complex shapes. Moreover, a theoretical numerical approach based on Classical Laminate Theory (CLT) has been developed to determine the stiffness properties of manufactured braided composites, calculating the effective longitudinal in-plane modulus of each braided sample. The relation between geometrical factors and processing conditions on the physical and mechanical properties of the braided rebars was clearly observed. Future plans include assessment of the manufacturing process for improved rebar design, advanced material analysis and characterization tests combined with experimental validation of the developed numerical approach. In addition, finite element analysis (FEA) models will be developed for braided BFRP composites in order to assess the relation between braiding parameters and rebar performance.

In recent years, the development and use of Fibre Reinforced Polymer composite materials in infrastructure have gained increasing attention worldwide. More specifically, natural mineral fibres such as basalt are currently being developed and are showing promising properties. Within an appropriate polymer matrix, their use as reinforcement in concrete structures offers performance benefits related to their environmentally friendly and non-corrodible nature. In particular, BFRPs have the potential to replace conventional internal steel rebar and thus, to be the next generation material in concrete reinforcement applications. A detailed literature review indicates that a careful selection of the appropriate manufacture technique and design methodology are required in order to prevent brittle failure on a concrete structure reinforced with FRP composite material. This paper reports on how to use the additional helical reinforcement and the braid configuration in order to increase strength, structural ductility and long term durability. Moreover, this study outlines the development of an analytical numerical model to predict the longitudinal elastic modulus of braided composites, as well as its validation by comparison of the results with available data from the literature. -> Link to full text in repository

In recent years, significant research has been conducted, by both industry and academia, into the optimum development and use of Fiber Reinforced Polymer composite materials in infrastructure. In particular, it is widely recognised that FRPs have the potential to replace conventional internal steel rebars in concrete reinforcement and offer performance benefits related to their advanced properties, such as corrosion resistance, high tensile strength etc. A review of the available literature indicates that brittle behaviour of FRP can significantly decrease the expected ultimate load capacity and, thus have a negative effect on structure’s long term durability. However, selecting braiding as manufacture technique and enhancing flexural capacity and shear strength through additional helical reinforcement, could provide structure with the additional ductility needed to prevent a brittle failure. Furthermore, the impact of deterioration mechanisms, focusing on the interaction between FRP and concrete in a structure, is an aspect for further investigation via laboratory testing and advanced analysis. This study summarises the results of research on structural design and manufacture methods of FRP composite materials by presenting new configuration and types of FRP reinforcement in order to encourage the use of these promising materials in construction industry. -> Link to full text in repository