S. Verbruggen | Vrije Universiteit Brussel (original) (raw)

Papers by S. Verbruggen

Applied Mathematical Modelling, 2016

Abstract The advantages of high performance composite materials have stimulated their use as rein... more Abstract The advantages of high performance composite materials have stimulated their use as reinforcement in concrete structures as well as the research on hybrid composite-concrete elements. For the design of these hybrid structures – with often complex geometries – the standard concrete calculation rules, based on official codes such as Eurocode 2, are often not elaborated enough. Moreover, these standard models are limited or simplified to a linear behaviour and do not even allow the integration of nonlinear reinforcement behaviour. In this paper, the authors propose a general calculation methodology to simulate analytically the structural behaviour of hybrid beams, including their ultimate loadbearing capacity and deflection. This methodology introduces an original search algorithm that reduces the computation time significantly without losing accuracy. The analytical model is validated by ten experiments on 3-m-span hybrid beams with differing geometry. The experiments demonstrate the accurate prediction of the analytical model both for the load–deflection behaviour and for the occurring strains, and confirm the model assumptions made. Moreover, the structural feasibility of the proposed hybrid beams is demonstrated as they exhibit a sufficient loadbearing capacity and stiffness. This structural performance in combination with the ability to predict the behaviour reveals a great potential for future structural applications.

Journal of Nondestructive Evaluation, 2015

The use of composites such as textile reinforced cements (TRCs) and fibre reinforced polymers (FR... more The use of composites such as textile reinforced cements (TRCs) and fibre reinforced polymers (FRPs) enables the development of lightweight structures. Such a lightweight solution for floor renovation consists of a hybrid composite-concrete cross section: prefabricated beams (TRC–CFRP reinforced hollow boxes with concrete on top) support sandwich panels together with a finishing concrete compression layer creating a monolithic hybrid floor. As the hybrid beams are the main structural element of this floor system, their load-bearing and failure behaviour should be fully understood. In order to examine the optimal design of these structures in terms of load bearing capacity, the beams are separately tested in four point bending while the amount of CFRP reinforcement and the concrete thickness are varied. The digital image correlation (DIC) and acoustic emission (AE) measuring techniques are applied in a complimentary way to monitor the bending and failure behaviour of the full scale hybrid beams. DIC visualises the development of surface strain fields together with the exact cracking patterns in relation to the applied load. AE contributes in defining the load at the onset of serious cracking activity. Furthermore, AE characterizes the contribution of the different fracture modes that may vary from concrete cracking, delamination between the successive layers of the TRC or debonding at the interphase between the TRC hollow box and the concrete on the one hand and the CFRP on the other hand.

Construction and Building Materials, 2016

h i g h l i g h t s Two 3 m span hybrid composite-concrete floors are tested under four point ben... more h i g h l i g h t s Two 3 m span hybrid composite-concrete floors are tested under four point bending. The load-deflection behaviour of hybrid floors is analytically modelled. A good agreement is found between experiments and the analytical model. All tested hybrid floors fulfil the SLS deflection and ULS loadbearing requirements.

Composite Structures, 2016

Abstract The combination of high performance composites and concrete results in hybrid composite-... more Abstract The combination of high performance composites and concrete results in hybrid composite-concrete elements which no longer resemble the traditional reinforced concrete structures. Consequently, these hybrid elements have a different structural behaviour that requires new evaluation procedures. This paper focusses on hybrid TRC-composite-concrete elements which are used as a substitute for reinforced concrete beams within a floor system. Their shear behaviour is experimentally investigated by the examination of ten short-span hybrid beams with different geometries. Visual inspection shows that shear failure occurs by an inclined flexural shear crack in the concrete. A rosette strain gauge analysis proves that the principal strain and stress orientations are in accordance with theoretical predictions. Finally, the small influence of shear deformation on the total deflection of these beams is illustrated.

Engineering Structures, 2014

Cement-based composites are emerging as strengthening and repair materials for concrete structure... more Cement-based composites are emerging as strengthening and repair materials for concrete structures, because of their advantages related to fire safety and their relatively low cost. To be able to compete with the existing Carbon Fibre Reinforced Polymer (CFRP) solutions, the cement matrix must be reinforced with textiles in high fibre volume fractions. Extensive experimental verification of the contribution of these Textile Reinforced Cements (TRC) as external reinforcement with regard to the load bearing and cracking behaviour of reinforced concrete beams is still necessary. This paper compares the existing CFRP and TRC solutions with a strong focus on the cracking behaviour by performing seventeen bending experiments monitored with Digital Image Correlation (DIC). It shows that the TRC-reinforced beams exhibit a similar cracking behaviour to the CFRP-reinforced beams. Moreover, precracking of the concrete beams before the application of the external reinforcement reduces only the initial high stiffness, but does not influence the cracking behaviour, failure mode or ultimate load. These test results indicate the relevance of non-precracked tests that have been performed in the past.

Composite Structures, 2016

Construction and Building Materials, 2013

ABSTRACT Characterization of the damage mechanisms of a structure in real time is a challenging e... more ABSTRACT Characterization of the damage mechanisms of a structure in real time is a challenging engineering task. Several nondestructive testing techniques have been used according to their capabilities and the target problem. Acoustic emission (AE) is one of them, enabling to record the elastic waves due to propagating cracks and to evaluate the criticality of the condition. Information on the location of the cracking sources, their mode and severity can be supplied by proper analysis of AE parameters and trends. However, in certain cases assumptions are inevitable and many times the experience of the user is essential in order to explain the AE trends according to the actual damage mechanism occurring at the moments when AE changes are registered. In the present case AE is used for monitoring the bending failure of concrete beams reinforced by external layers of different composite materials. The monitoring is complemented by Digital Image Correlation (DIC) which gives a clear depiction of the surface strain field and its transient changes according to stress redistribution which occurs after fracture moments. Results of AE are thus benchmarked and certain trends reliably attributed to specific processes. Conclusions on the mechanical performance of the different reinforcing materials on the beams, which is another major aim of the study, are also drawn.

Concrete Solutions 2014, 2014

Loadbearing insulating sandwich panels with Textile Reinforced Cement (TRC) faces can combine the... more Loadbearing insulating sandwich panels with Textile Reinforced Cement (TRC) faces can combine the structural and insulating performance of a conventional wall configuration in one lightweight element. This makes them very suitable as a new type of wall element for low- and high rise residential buildings. By combining 2D and 3D textiles in the TRC faces the performance of the panels can even be improved. This paper presents a preliminary investigation of the buckling behaviour of large-scale sandwich panels with combined 3D and 2D TRC faces. The large-scale experiment is compared with an analytical model. This paper shows that further in depth investigations are needed with regard to the experimental test set-up (boundary conditions) in order to establish a better agreement with the analytical model.

The use of a recently developed inorganic phosphate cement with grain sizes less than 100 microme... more The use of a recently developed inorganic phosphate cement with grain sizes less than 100 micrometer in combination with an adapted manufacturing process creates the possibility to obtain cement composites with a never been seen fiber volume ratio (Vf) of up to 25-30%, a factor 2 to 10 times higher than conventional cement composites. The forthcoming gain in tensile strength enables the material to be used in high performance building applications such as sandwich panels, structural claddings and concrete repair. This paper presents a concept for a lightweight stayin-place cement composite formwork taking advantage of this new promising material. Full scale tests analyzing the structural behavior indicate the opportunities of this innovative forming technique. Results also show an improved mechanical behavior of the composite (concrete-formwork) beam as the micro cracking phenomenon of concrete in tension is better controlled and crack propagation is delayed compared to a traditiona...

The last couple of years, the importance and potential of textile reinforced cementitious composi... more The last couple of years, the importance and potential of textile reinforced cementitious composites (TRC’s) has been investigated and proven in literature. The research has mainly been performed on thin-layered specimens made of individual fibre textile layers impregnated by a matrix. The drawback of this manufacturing technique however is the time-consuming process. A solution is the transition towards a three dimensional, rigid fibre textile, fully immersed in the matrix, which would drastically decrease the production time and thus improve the market uptake of these materials.

Proceedings of The Eighteenth International Conference of Experimental Mechanics, May 27, 2018

Loadbearing sandwich panels used as wall elements are a promising development since they combine ... more Loadbearing sandwich panels used as wall elements are a promising development since they combine structural and energy efficiency. Composite behaviour needs to be ensured so that the sandwich panel works as one element under a flexural load (meaning that the shear forces due to bending are transferred from one face to the other). To assure this full composite behaviour, an investigation of the bond strength between the faces and the core of the sandwich panel is necessary. Therefore, two different bond test setups were performed on sandwich panels with Textile Reinforced Cement (TRC) faces and an Extruded Polystyrene (XPS) insulating foam core. The two bond test setups were compared and revealed that one of the setups showed a combination of bond and shear failure of the core so that a clear conclusion on the bond strength couldn't be obtained. The second setup showed clear bond failure and gave a good estimation of the bond strength between TRC and XPS.

Proceedings, May 15, 2018

Textile reinforced cements (TRC), combining a cementitious matrix with fibre textiles, are a well... more Textile reinforced cements (TRC), combining a cementitious matrix with fibre textiles, are a well-researched subject in literature. The material offers several advantages such as the design of low-weight, slender structures. However, one of the main drawbacks of this composite material is the time consuming manufacturing process using two dimensional fibre textiles. Three dimensional fibre textile architectures offer a solution to this problem, while retaining the TRC advantages. Most 3D fibre textiles use distance holders to bridge two, or more textile layers at a certain distance from each other. The influence of this distance holder on the mechanical properties of the whole TRC remains relatively unstudied in literature and will be the research topic of this paper. This research will present the results of three point bending experiments, performed on short TRC beams with a length to thickness ratio of approximately 4 to 1. A comparison is drawn between 3D TRC with fully operational 3D fibre textiles and 2D TRC with the same textile geometry and orientation, but without distance holders. A positive influence on the flexural response is witnessed for the 3D fibre textile, with an increased flexural stiffness up to 35%.

Proceedings

Fire-testing of Textile Reinforced Concrete (TRC) is an interesting field in which quite limited ... more Fire-testing of Textile Reinforced Concrete (TRC) is an interesting field in which quite limited research has been conducted so far. In this paper some preliminary tests are presented, where mortars used as binders are heated to 850 °C and their residual strength is tested, while the Ultrasonic Pulse Velocity (UPV) is also measured, before and after heating, and compared. Additionally, TRC specimens are subjected to flame exposure with a simple set-up and the residual strength is also tested by flexural tests. It is concluded that even with simple set-ups, interesting results can be obtained regarding the structural degradation of the material.

Smart Structures and Systems, 2016

One of the most commonly used techniques to strengthen steel reinforced concrete structures is th... more One of the most commonly used techniques to strengthen steel reinforced concrete structures is the application of externally bonded patches in the form of carbon fiber reinforced polymers (CFRP) or recently, textile reinforced cements (TRC). These external patches undertake the tensile stress of bending constraining concrete cracking. Development of full-field inspection methodologies for fracture monitoring are important since the reinforcing layers are not transparent, hindering visual observation of the material condition underneath. In the present study acoustic emission (AE) and digital image correlation (DIC) are applied during four-point bending tests of large beams to follow the damage accumulation. AE helps to determine the onset of fracture as well as the different damage mechanisms through the registered shifts in AE rate, location of active sources and change in waveform parameters. The effect of wave propagation distance, which in large components and in-situ can well mask the original information as emitted by the fracture incidents is also discussed. Simultaneously, crucial information is supplied by DIC concerning the moments of stress release of the patches due to debonding, benchmarking the trends monitored by AE. From the point of view of mechanics, conclusions on the reinforcing contribution of the different repair methodologies are also drawn.

Materials and Structures, 2016

This paper presents the experimental study of concrete beams in bending, externally strengthened ... more This paper presents the experimental study of concrete beams in bending, externally strengthened with Textile Reinforced Cementitious materials (TRC) with varying contact area with the concrete. In order to study the pure influence of the TRC on the concrete substrate, only non-internally-reinforced concrete beams are considered. The crack pattern evolution is monitored with Digital Image Correlation, and the influence of the contact width between the concrete substrate and the external reinforcement is investigated. The results show that the TRC reinforcement has an important crack bridging capacity, and consequently that its application over the full beam width is beneficial for the loadbearing capacity and the limitation of the crack widths of the concrete beam.

Composite Structures, 2015

The construction industry currently shows an increasing interest towards composites. However, des... more The construction industry currently shows an increasing interest towards composites. However, despite their high mechanical capacity to weight ratio their practical use in construction remains rather limited, the relatively high cost often being mentioned as the most restricting factor. This paper demonstrates how this need for minimization of both cost and mass can be tackled by a multi-objective optimization. First, a two-objective size optimization procedure is developed, and subsequently its strength is illustrated on hybrid composite-concrete beams. An original methodology combining Non-dominated Sorting Genetic Algorithm (NSGA-II) and a meta-model is used to find all optimal solutions. The optimization algorithm moreover gives insight on the influence of different parameters such as the span and the concrete class on the weight and cost of the beams, and the dominance of certain design constraints in various locations of the design space.

Proceedings of the 9th International Conference on Fracture Mechanics of Concrete and Concrete Structures, 2016

The present paper describes a collection of fracture monitoring cases in different materials. The... more The present paper describes a collection of fracture monitoring cases in different materials. The cases examined include bending of textile reinforced cement (TRC), hybrid concrete-TRC lightweight beams, granite, additive manufacturing metal components, combined loading of human femur bone and pull-out in reinforced concrete. In all cases the basic role is played by acoustic emission (AE). It is shown that certain waveform parameters exhibit strong sensitivity to the rate of fracture as well as the dominant fracture mode. Parameters like frequency content and the duration of the signals supply real time trends that in the present cases are verified by optical techniques. It is concluded that AE supplies important information and allows the prediction of how the material will behave based on the initial AE recordings and before serious damage is inflicted. AE shows a very broad application range; however, the contribution of combination with other techniques is highlighted in order to increase the reliability of the interpretation of AE results.

Cement and Concrete Composites

Engineering Fracture Mechanics

Applied Mathematical Modelling, 2016

Abstract The advantages of high performance composite materials have stimulated their use as rein... more Abstract The advantages of high performance composite materials have stimulated their use as reinforcement in concrete structures as well as the research on hybrid composite-concrete elements. For the design of these hybrid structures – with often complex geometries – the standard concrete calculation rules, based on official codes such as Eurocode 2, are often not elaborated enough. Moreover, these standard models are limited or simplified to a linear behaviour and do not even allow the integration of nonlinear reinforcement behaviour. In this paper, the authors propose a general calculation methodology to simulate analytically the structural behaviour of hybrid beams, including their ultimate loadbearing capacity and deflection. This methodology introduces an original search algorithm that reduces the computation time significantly without losing accuracy. The analytical model is validated by ten experiments on 3-m-span hybrid beams with differing geometry. The experiments demonstrate the accurate prediction of the analytical model both for the load–deflection behaviour and for the occurring strains, and confirm the model assumptions made. Moreover, the structural feasibility of the proposed hybrid beams is demonstrated as they exhibit a sufficient loadbearing capacity and stiffness. This structural performance in combination with the ability to predict the behaviour reveals a great potential for future structural applications.

Journal of Nondestructive Evaluation, 2015

The use of composites such as textile reinforced cements (TRCs) and fibre reinforced polymers (FR... more The use of composites such as textile reinforced cements (TRCs) and fibre reinforced polymers (FRPs) enables the development of lightweight structures. Such a lightweight solution for floor renovation consists of a hybrid composite-concrete cross section: prefabricated beams (TRC–CFRP reinforced hollow boxes with concrete on top) support sandwich panels together with a finishing concrete compression layer creating a monolithic hybrid floor. As the hybrid beams are the main structural element of this floor system, their load-bearing and failure behaviour should be fully understood. In order to examine the optimal design of these structures in terms of load bearing capacity, the beams are separately tested in four point bending while the amount of CFRP reinforcement and the concrete thickness are varied. The digital image correlation (DIC) and acoustic emission (AE) measuring techniques are applied in a complimentary way to monitor the bending and failure behaviour of the full scale hybrid beams. DIC visualises the development of surface strain fields together with the exact cracking patterns in relation to the applied load. AE contributes in defining the load at the onset of serious cracking activity. Furthermore, AE characterizes the contribution of the different fracture modes that may vary from concrete cracking, delamination between the successive layers of the TRC or debonding at the interphase between the TRC hollow box and the concrete on the one hand and the CFRP on the other hand.

Construction and Building Materials, 2016

h i g h l i g h t s Two 3 m span hybrid composite-concrete floors are tested under four point ben... more h i g h l i g h t s Two 3 m span hybrid composite-concrete floors are tested under four point bending. The load-deflection behaviour of hybrid floors is analytically modelled. A good agreement is found between experiments and the analytical model. All tested hybrid floors fulfil the SLS deflection and ULS loadbearing requirements.

Composite Structures, 2016

Abstract The combination of high performance composites and concrete results in hybrid composite-... more Abstract The combination of high performance composites and concrete results in hybrid composite-concrete elements which no longer resemble the traditional reinforced concrete structures. Consequently, these hybrid elements have a different structural behaviour that requires new evaluation procedures. This paper focusses on hybrid TRC-composite-concrete elements which are used as a substitute for reinforced concrete beams within a floor system. Their shear behaviour is experimentally investigated by the examination of ten short-span hybrid beams with different geometries. Visual inspection shows that shear failure occurs by an inclined flexural shear crack in the concrete. A rosette strain gauge analysis proves that the principal strain and stress orientations are in accordance with theoretical predictions. Finally, the small influence of shear deformation on the total deflection of these beams is illustrated.

Engineering Structures, 2014

Cement-based composites are emerging as strengthening and repair materials for concrete structure... more Cement-based composites are emerging as strengthening and repair materials for concrete structures, because of their advantages related to fire safety and their relatively low cost. To be able to compete with the existing Carbon Fibre Reinforced Polymer (CFRP) solutions, the cement matrix must be reinforced with textiles in high fibre volume fractions. Extensive experimental verification of the contribution of these Textile Reinforced Cements (TRC) as external reinforcement with regard to the load bearing and cracking behaviour of reinforced concrete beams is still necessary. This paper compares the existing CFRP and TRC solutions with a strong focus on the cracking behaviour by performing seventeen bending experiments monitored with Digital Image Correlation (DIC). It shows that the TRC-reinforced beams exhibit a similar cracking behaviour to the CFRP-reinforced beams. Moreover, precracking of the concrete beams before the application of the external reinforcement reduces only the initial high stiffness, but does not influence the cracking behaviour, failure mode or ultimate load. These test results indicate the relevance of non-precracked tests that have been performed in the past.

Composite Structures, 2016

Construction and Building Materials, 2013

ABSTRACT Characterization of the damage mechanisms of a structure in real time is a challenging e... more ABSTRACT Characterization of the damage mechanisms of a structure in real time is a challenging engineering task. Several nondestructive testing techniques have been used according to their capabilities and the target problem. Acoustic emission (AE) is one of them, enabling to record the elastic waves due to propagating cracks and to evaluate the criticality of the condition. Information on the location of the cracking sources, their mode and severity can be supplied by proper analysis of AE parameters and trends. However, in certain cases assumptions are inevitable and many times the experience of the user is essential in order to explain the AE trends according to the actual damage mechanism occurring at the moments when AE changes are registered. In the present case AE is used for monitoring the bending failure of concrete beams reinforced by external layers of different composite materials. The monitoring is complemented by Digital Image Correlation (DIC) which gives a clear depiction of the surface strain field and its transient changes according to stress redistribution which occurs after fracture moments. Results of AE are thus benchmarked and certain trends reliably attributed to specific processes. Conclusions on the mechanical performance of the different reinforcing materials on the beams, which is another major aim of the study, are also drawn.

Concrete Solutions 2014, 2014

Loadbearing insulating sandwich panels with Textile Reinforced Cement (TRC) faces can combine the... more Loadbearing insulating sandwich panels with Textile Reinforced Cement (TRC) faces can combine the structural and insulating performance of a conventional wall configuration in one lightweight element. This makes them very suitable as a new type of wall element for low- and high rise residential buildings. By combining 2D and 3D textiles in the TRC faces the performance of the panels can even be improved. This paper presents a preliminary investigation of the buckling behaviour of large-scale sandwich panels with combined 3D and 2D TRC faces. The large-scale experiment is compared with an analytical model. This paper shows that further in depth investigations are needed with regard to the experimental test set-up (boundary conditions) in order to establish a better agreement with the analytical model.

The use of a recently developed inorganic phosphate cement with grain sizes less than 100 microme... more The use of a recently developed inorganic phosphate cement with grain sizes less than 100 micrometer in combination with an adapted manufacturing process creates the possibility to obtain cement composites with a never been seen fiber volume ratio (Vf) of up to 25-30%, a factor 2 to 10 times higher than conventional cement composites. The forthcoming gain in tensile strength enables the material to be used in high performance building applications such as sandwich panels, structural claddings and concrete repair. This paper presents a concept for a lightweight stayin-place cement composite formwork taking advantage of this new promising material. Full scale tests analyzing the structural behavior indicate the opportunities of this innovative forming technique. Results also show an improved mechanical behavior of the composite (concrete-formwork) beam as the micro cracking phenomenon of concrete in tension is better controlled and crack propagation is delayed compared to a traditiona...

The last couple of years, the importance and potential of textile reinforced cementitious composi... more The last couple of years, the importance and potential of textile reinforced cementitious composites (TRC’s) has been investigated and proven in literature. The research has mainly been performed on thin-layered specimens made of individual fibre textile layers impregnated by a matrix. The drawback of this manufacturing technique however is the time-consuming process. A solution is the transition towards a three dimensional, rigid fibre textile, fully immersed in the matrix, which would drastically decrease the production time and thus improve the market uptake of these materials.

Proceedings of The Eighteenth International Conference of Experimental Mechanics, May 27, 2018

Loadbearing sandwich panels used as wall elements are a promising development since they combine ... more Loadbearing sandwich panels used as wall elements are a promising development since they combine structural and energy efficiency. Composite behaviour needs to be ensured so that the sandwich panel works as one element under a flexural load (meaning that the shear forces due to bending are transferred from one face to the other). To assure this full composite behaviour, an investigation of the bond strength between the faces and the core of the sandwich panel is necessary. Therefore, two different bond test setups were performed on sandwich panels with Textile Reinforced Cement (TRC) faces and an Extruded Polystyrene (XPS) insulating foam core. The two bond test setups were compared and revealed that one of the setups showed a combination of bond and shear failure of the core so that a clear conclusion on the bond strength couldn't be obtained. The second setup showed clear bond failure and gave a good estimation of the bond strength between TRC and XPS.

Proceedings, May 15, 2018

Textile reinforced cements (TRC), combining a cementitious matrix with fibre textiles, are a well... more Textile reinforced cements (TRC), combining a cementitious matrix with fibre textiles, are a well-researched subject in literature. The material offers several advantages such as the design of low-weight, slender structures. However, one of the main drawbacks of this composite material is the time consuming manufacturing process using two dimensional fibre textiles. Three dimensional fibre textile architectures offer a solution to this problem, while retaining the TRC advantages. Most 3D fibre textiles use distance holders to bridge two, or more textile layers at a certain distance from each other. The influence of this distance holder on the mechanical properties of the whole TRC remains relatively unstudied in literature and will be the research topic of this paper. This research will present the results of three point bending experiments, performed on short TRC beams with a length to thickness ratio of approximately 4 to 1. A comparison is drawn between 3D TRC with fully operational 3D fibre textiles and 2D TRC with the same textile geometry and orientation, but without distance holders. A positive influence on the flexural response is witnessed for the 3D fibre textile, with an increased flexural stiffness up to 35%.

Proceedings

Fire-testing of Textile Reinforced Concrete (TRC) is an interesting field in which quite limited ... more Fire-testing of Textile Reinforced Concrete (TRC) is an interesting field in which quite limited research has been conducted so far. In this paper some preliminary tests are presented, where mortars used as binders are heated to 850 °C and their residual strength is tested, while the Ultrasonic Pulse Velocity (UPV) is also measured, before and after heating, and compared. Additionally, TRC specimens are subjected to flame exposure with a simple set-up and the residual strength is also tested by flexural tests. It is concluded that even with simple set-ups, interesting results can be obtained regarding the structural degradation of the material.

Smart Structures and Systems, 2016

One of the most commonly used techniques to strengthen steel reinforced concrete structures is th... more One of the most commonly used techniques to strengthen steel reinforced concrete structures is the application of externally bonded patches in the form of carbon fiber reinforced polymers (CFRP) or recently, textile reinforced cements (TRC). These external patches undertake the tensile stress of bending constraining concrete cracking. Development of full-field inspection methodologies for fracture monitoring are important since the reinforcing layers are not transparent, hindering visual observation of the material condition underneath. In the present study acoustic emission (AE) and digital image correlation (DIC) are applied during four-point bending tests of large beams to follow the damage accumulation. AE helps to determine the onset of fracture as well as the different damage mechanisms through the registered shifts in AE rate, location of active sources and change in waveform parameters. The effect of wave propagation distance, which in large components and in-situ can well mask the original information as emitted by the fracture incidents is also discussed. Simultaneously, crucial information is supplied by DIC concerning the moments of stress release of the patches due to debonding, benchmarking the trends monitored by AE. From the point of view of mechanics, conclusions on the reinforcing contribution of the different repair methodologies are also drawn.

Materials and Structures, 2016

This paper presents the experimental study of concrete beams in bending, externally strengthened ... more This paper presents the experimental study of concrete beams in bending, externally strengthened with Textile Reinforced Cementitious materials (TRC) with varying contact area with the concrete. In order to study the pure influence of the TRC on the concrete substrate, only non-internally-reinforced concrete beams are considered. The crack pattern evolution is monitored with Digital Image Correlation, and the influence of the contact width between the concrete substrate and the external reinforcement is investigated. The results show that the TRC reinforcement has an important crack bridging capacity, and consequently that its application over the full beam width is beneficial for the loadbearing capacity and the limitation of the crack widths of the concrete beam.

Composite Structures, 2015

The construction industry currently shows an increasing interest towards composites. However, des... more The construction industry currently shows an increasing interest towards composites. However, despite their high mechanical capacity to weight ratio their practical use in construction remains rather limited, the relatively high cost often being mentioned as the most restricting factor. This paper demonstrates how this need for minimization of both cost and mass can be tackled by a multi-objective optimization. First, a two-objective size optimization procedure is developed, and subsequently its strength is illustrated on hybrid composite-concrete beams. An original methodology combining Non-dominated Sorting Genetic Algorithm (NSGA-II) and a meta-model is used to find all optimal solutions. The optimization algorithm moreover gives insight on the influence of different parameters such as the span and the concrete class on the weight and cost of the beams, and the dominance of certain design constraints in various locations of the design space.

Proceedings of the 9th International Conference on Fracture Mechanics of Concrete and Concrete Structures, 2016

The present paper describes a collection of fracture monitoring cases in different materials. The... more The present paper describes a collection of fracture monitoring cases in different materials. The cases examined include bending of textile reinforced cement (TRC), hybrid concrete-TRC lightweight beams, granite, additive manufacturing metal components, combined loading of human femur bone and pull-out in reinforced concrete. In all cases the basic role is played by acoustic emission (AE). It is shown that certain waveform parameters exhibit strong sensitivity to the rate of fracture as well as the dominant fracture mode. Parameters like frequency content and the duration of the signals supply real time trends that in the present cases are verified by optical techniques. It is concluded that AE supplies important information and allows the prediction of how the material will behave based on the initial AE recordings and before serious damage is inflicted. AE shows a very broad application range; however, the contribution of combination with other techniques is highlighted in order to increase the reliability of the interpretation of AE results.

Cement and Concrete Composites

Engineering Fracture Mechanics