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Here we report on a study of a rheological behavior of sodium alginate and montmorillonite suspension. We find that viscoelastic behavior of this suspension is dramatically affected with increasing volume fraction of montmorillonite platelets. Addition of montmorillonite generally leads to gel formation, which is attributed to interactions of montmorillonite and alginate via H-bonding and attraction between the positive edges of the platelets and the anionic backbone of the biopolymer. A critical concentration for the measured system was observed at 20 wt.% montmorillonite, where a crossover to a gel-like structure was detected. The observed gel has a rubber plateau, which develops further with higher montmorillonite concentration. In this physical gel the relaxation maximum was detected, which is associated with the breaking and reformation of the bonds between the platelets and the biopolymer. For this transient behavior, we find that a Maxwell type viscoelasticity quite well describes the relaxation time and the observed G'-G" crossover. We believe that this gel-like behavior plays an important role in formation of highly ordered nanostructures that develop during the drying of these bio-nanocomposite suspensions., Materials and Environment, ChemE/Advanced Soft Matter, ChemE/O&O groep

Here we report on a study of a rheological behavior of sodium alginate and montmorillonite suspension. We find that viscoelastic behavior of this suspension is dramatically affected with increasing volume fraction of montmorillonite platelets. Addition of montmorillonite generally leads to gel formation, which is attributed to interactions of montmorillonite and alginate via H-bonding and attraction between the positive edges of the platelets and the anionic backbone of the biopolymer. A critical concentration for the measured system was observed at 20 wt.% montmorillonite, where a crossover to a gel-like structure was detected. The observed gel has a rubber plateau, which develops further with higher montmorillonite concentration. In this physical gel the relaxation maximum was detected, which is associated with the breaking and reformation of the bonds between the platelets and the biopolymer. For this transient behavior, we find that a Maxwell type viscoelasticity quite well describes the relaxation time and the observed G'-G" crossover. We believe that this gel-like behavior plays an important role in formation of highly ordered nanostructures that develop during the drying of these bio-nanocomposite suspensions., Materials and Environment, ChemE/Advanced Soft Matter, ChemE/O&O groep

The present invention is in the field of a composition for forming a bio-compatible membrane applicable to building material, such as steel, stainless steel, iron alloy, cast steel, etc., to a method of applying said composition for forming a bio-compatible membrane, a biocompatible membrane, use of said membrane for various purposes, and to building material comprising said membrane., Structural Engineering, Civil Engineering and Geosciences

The present invention is in the field of a composition for forming a bio-compatible membrane applicable to building material, such as concrete, cement, etc., to a meth od of applying said composition for forming a bio-compatible membrane, a biocompatible membrane, use of said membrane for various purposes, and to building material comprising said membrane., Structural Engineering, Civil Engineering and Geosciences

Chloride-induced corrosion is a point of big concern in reinforced concrete (RC) structures. To monitor the actual health and to predict the remaining service-life of structures, it is important to understand the structural behaviour and the failure mechanism of structures exposed to chlorides under fatigue loading conditions. A beam test, whereby two RC beam are loaded dynamically, was developed to investigate the behaviour of a RC structure between first loading and structural failure. A parallel rebar test, whereby a plain rebar is loaded dynamically, was performed to focus on the behaviour of a plain rebar in a chloride environment. The results of both tests show that corrosion reduces the maximum number of iterations until failure. Deflections of the beams and elongations of the rebars show a significant increase close to failure. A finite element model is developed to simulate the impact of corrosion on the structural performance of a plain rebar. Preliminary calculation results show high local stresses close to the damaged interfaces. These high stresses result in local fatigue damage, which can initiate global failure of the structure., Structural Engineering, Civil Engineering and Geosciences

The present invention is in the field of a composition for forming a bio-compatible membrane applicable to building material, such as steel, stainless steel, iron alloy, cast steel, etc., to a method of applying said composition for forming a bio-compatible membrane, a biocompatible membrane, use of said membrane for various purposes, and to building material comprising said membrane., Structural Engineering, Civil Engineering and Geosciences

The present invention is in the field of a composition for forming a bio-compatible membrane applicable to building material, such as concrete, cement, etc., to a meth od of applying said composition for forming a bio-compatible membrane, a biocompatible membrane, use of said membrane for various purposes, and to building material comprising said membrane., Structural Engineering, Civil Engineering and Geosciences

Chloride-induced corrosion is a point of big concern in reinforced concrete (RC) structures. To monitor the actual health and to predict the remaining service-life of structures, it is important to understand the structural behaviour and the failure mechanism of structures exposed to chlorides under fatigue loading conditions. A beam test, whereby two RC beam are loaded dynamically, was developed to investigate the behaviour of a RC structure between first loading and structural failure. A parallel rebar test, whereby a plain rebar is loaded dynamically, was performed to focus on the behaviour of a plain rebar in a chloride environment. The results of both tests show that corrosion reduces the maximum number of iterations until failure. Deflections of the beams and elongations of the rebars show a significant increase close to failure. A finite element model is developed to simulate the impact of corrosion on the structural performance of a plain rebar. Preliminary calculation results show high local stresses close to the damaged interfaces. These high stresses result in local fatigue damage, which can initiate global failure of the structure., Structural Engineering, Civil Engineering and Geosciences

The stability of chloride ion selective electrodes in highly alkaline solutions is an important aspect when reliability and feasibility within reinforced concrete applications are concerned. The sensitivity of these electrodes largely depends on the properties of the AgCl layer, including uniformity, porosity, orientation, thickness, etc. These can be varied for optimum performance through adjusting the current density and anodizing time. In this study the Ag|AgCl electrodes were prepared in four different current density regimes and the resulting microstructural properties of the AgCl layer were correlated to potentiometric response in chloride-containing solutions, including synthetic concrete pore solution and cement extract. It was found out that lower level of the current density within the anodization process results later on in increased sensitivity and stability of the electrodes.., Materials and Environment

In this paper a performance-based method for the design of granular-paste mixtures will be proposed. Focus will be on the selection and proportioning of constituents to produce a mixture with a pre-defined shape holding ability. Shape holding ability of mixtures will be characterized by the shape preservation factor SPF. This SPF shows the ability of a mixture to preserve its shape after being demolded from a slump test. SPF is the ratio of the cross sectional area of a sample after and before demolding. By increasing the flowability of a mixture, the SPF decreases. In this study a mixture is first decomposed into aggregate, void paste and excess paste. Then a combination of the consistency of the paste and excess paste volume is determined for a required SPF. Finally, depending on the aggregate grading, the volumes of paste and aggregates in the system are determined., Structural Engineering, Civil Engineering and Geosciences

Coupled reactive-transport processes in cementitious materials play a crucial role in the aging process pf building materials. Up to now, the effect of aging on microstructure and evolution of it’s properties, in three dimensions, was studied only by dissolution of certain phases at random locations. In this paper we present a new 3D reactive-transport model and results of leaching-induced aging simulations performed on virtual cementitious microstructures generated by Hymostruc model. The outputs are the morphology of the aged 3D microstructure together with aged properties characterised by fuzzy state of each voxel at different times. This allows to simulate the evolution of properties as a function of time as well as a function of the location within the microstructure., Structural Engineering, Civil Engineering and Geosciences

Structural Health Monitoring (SHM) systems are frequently used in civil infrastructures. One important durability property in reinforced concrete (RC) structures is the level of steel bar corrosion. In a dynamic four-point-bending test, two beams are loaded simultaneously, in which corrosion is accelerated in one of them. Since geophones are commonly used in SHM systems to monitor vertical deformations and to calculate modal properties, the first natural frequency of both beams are analysed in this paper. It is discovered that many properties, like temperature and moisture, may influence natural frequencies. Besides this, calculated natural frequencies may fluctuate. Experiments showed that the first natural frequency in the corroded beam decreases while it remains almost constant in the uncorroded situation., Structural Engineering, Civil Engineering and Geosciences

Service life of reinforced concrete structures exposed to chloride enriched environment is well known to be mainly determined by steel passivity breakdown in the event of chloride-induced corrosion initiation and propagation. Since Cl- induced (localized) corrosion is caused by the free (water-soluble) chloride, present in the pore network of a reinforced concrete structure, quantifying the level of free chloride locally, e.g. via embedded Ag/AgCl electrodes (chloride sensors), is a generally accepted and applicable approach to monitor the time to corrosion initiation. The measurement is essentially a potential (voltage) reading over time and as such logically depends, among other factors, on the electrical and microstructural properties of the surrounding medium. Therefore, an accurate determination of the time to corrosion initiation significantly depends on the properties of relevant interfaces, such as the steel|cement paste interface and/or the Ag|AgCl|cement paste interface. In this paper, steel rods were coupled with Ag/AgCl sensors and embedded in cement paste cylinders. The specimens were immersed in simulated pore solution, containing 855 mM chloride concentration. Electrochemical impedance spectroscopy (EIS) was employed for quali-/quantification of the corrosion process on the steel surface (medium to low frequency response), while simultaneously providing information for the electrical properties of the bulk cement-based matrix through the high frequency response. The open circuit potential (OCP) values of both sensors and steel rods were recorded for more than 30 days. The results show a good agreement between sensor readings and steel electrochemical response i.e. time to corrosion initiation was recorded via steel OCP readings, whereas the relevant chloride content was estimated via the sensors’ OCP readings., Materials and Environment

Curing is the process of controlling the rate and extent of moisture loss from the surface of cement based materials. It is the final stage in the production of cement-based materials and it is the essential part for achieving continuous hydration of cement, while avoiding cracking due to drying shrinkage. Continuous cement hydration also guarantees a strong bond between aggregate, fewer voids, and depercoliation of capillary pores. Thus, a properly cured cement-based material is prepared for a long service life. Using environmentally friendly, water based bio-polymers could help to achieve more durable cement-based materials, and, therefore preventing a premature end of service life of building materials. Rapid Chloride Migration tests and Environmental Scanning Microscope are employed to investigate the functional properties, e.g. transport property, and microstructure properties, respectively. Mortar samples were cured in air and applied by water-based curing compound, made of sodium alginate. We observed strong beneficial effects of applying sodium alginate as a curing compound in terms of microstructure and hydration development. Based on these results, a less porous microstructure and an improved durable cement-based material was achieved that was prepared for longer service life., Structural Engineering, Civil Engineering and Geosciences

The level of free chloride concentration in reinforced concrete structures essentially determines the onset of steel corrosion initiation and further propagation. One of the well-known methods for monitoring free chloride concentration is using silver/silver chloride electrodes (Ag/AgCl). These electrodes are sensitive mainly to chloride ions and establish a certain electrochemical potential depending on the chloride ion activity in the environment. Although the functioning principles of these electrodes are well-established, their use in concrete is challenging when durability and practical engineering issues are considered. In order to be able to accurately determine free chloride content in concrete, it is important to evaluate the performance of Ag/AgCl electrodes (sensors) in strong alkaline environments i.e. those existing in non-carbonated concrete (pH~12–13.5). Furthermore the linear response of these sensors to a wide range of chloride concentrations in highly alkaline medium, as well as their sensitivity to pH changes, need a more in-depth investigation. In this paper the response of Ag/AgCl electrodes in simulated pore solutions having different chloride concentrations and different pH values was studied. The electrodes were calibrated in cement extract solution, distilled-water and simulated pore solution. The results show that at chloride concentrations of > 4 mM the effect of pH on the response of the sensors is insignificant which makes using Ag/AgCl sensors in concrete feasible i.e. this concentration is much lower than the generally reported thresholds for corrosion initiation. Keywords: Ag/AgCl electrode, cement extract solution, free chloride, pH value, pore solution., Structural Engineering, Civil Engineering and Geosciences

The remaining service life of concrete structures strongly depends on the corrosion level of the reinforcement bars. It explains that measuring the corrosion rate is a key issue in monitoring the structural health of concrete structures. A common and appropriate technique used to evaluate the instantaneous corrosion rate of steel reinforcement is by Linear Polarization Resistance (LPR). A dynamic loaded, four-point-bending test on a reinforced concrete (RC) beam was developed to measure dynamic responses and stiffness changes due to corrosion. The test setup can load two beams with a comparable structural behaviour simultaneously, while exposed to the same ambient conditions. To expedite corrosion in one of the beams, a water-chloride solution bath was mounted on top of it. As a reference, a tap water bath was placed on top of the other beam. A wetting cycle of two days wet and five days dry was carried out to simulate real-time situations and to accelerate the corrosion process. During this test, the responses of both beams were measured by Linear Variable Differential Transformers (LVDTs) and results were filed automatically. Furthermore, the corrosion rates of both RC beams were automatically measured by LPR every day. The results of these measurements show differences in corrosion rate between both beams with time. After beam failure, brief forensic engineering was executed to analyse the corrosion of the reinforcement bars. Visual observations show a good correlation with the corrosion behaviour measured by the LPR method., Structural Engineering, Civil Engineering and Geosciences

Stray current is essentially an electrical current “leakage” from metal conductors and electrical installations. When it flows through cement-based systems, electrical energy is converted to thermal energy that causes increasing temperature due to Joule heating phenomena. The aim of this paper is to shed light on the influence of electrical current flow on cement hydration, morphological and structural changes of cement-based systems, emphasizing on the potentially altered temperature effects when electrical current flow is involved. Calorimetry tests show that degree of cement hydration increases as a results of temperature increase due to electrical current flow through cement-based systems. To evaluate the influence of electrical current on the hydration mechanisms in cement-based systems, HYMOSTRUC will be used as a modelling approach, where temperature effects due to electrical current flow are implemented in the existing numerical simulation., Structural Engineering, Civil Engineering and Geosciences

De-icing salts, used on roads in heavy winters, may enter reinforced concrete (RC) structures via its capillary pore system or via cracks, initiating reinforcement corrosion and reducing its remaining service-life. Vehicles passing real bridges exert a dynamic impact action that might activate a fatigue failure mechanism. In order to generate more knowledge on the interaction between corrosion and fatigue, a four-point-bending test setup is developed where two lab-scale RC beams are loaded simultaneously. In this setup, RC beams are loaded dynamically, while for one of the beams, corrosion is accelerated by means of a chloridesolution bath mounted on top of it. The second beam, which is the control, is only exposed to tap water. Many test repetitions are foreseen, but so far, three tests are conducted using two different loading levels. It turned out that the reinforcement bar, which corroded due to chloride exposure, failed first in all cases. This paper reports results of the failure mechanism whereby forensic engineering was used to examine the interaction between corrosion and fatigue, and that this might result in a harmful undesirable failure mechanism. The results, therefore, should also be considered for service-life design predictions of infrastructure., Structural Engineering, Civil Engineering and Geosciences

Structural Engineering, Civil Engineering and Geosciences

One of the reported problems associated with the performance of Ag/AgCl electrodes in alkaline environment, as concrete pore water, has been their poor stability. Open circuit potentials are typically observed to be stable for a time period of a few minutes to some days depending on the thickness and microstructure of the sparingly soluble AgCl and the subsequently developed mixed potentials at the electrode/solution interface. In this paper the open circuit potential of the chloride sensors were monitored over time in simulated pore solution with and without chloride and their electrochemical response recorded via electrochemical impedance spectroscopy (EIS). The alterations in response of the sensors can be denoted to transformation of the AgCl layer to Ag2O in chloride-free high pH environment as in concrete pore water. Recovery of the AgCl layer takes place in chloridecontaining medium, where establishing of sensor stability is determined by the chloride concentration., Structural Engineering, Civil Engineering and Geosciences

One of the key-elements in Structural Health Monitoring of reinforced concrete structures is the level of rebar corrosion and the way in which it affects the structural performance. A dynamic four-point-bending test was developed to help understanding the deflections of concrete structures under corrod-ed conditions. With this test, two equivalent beams are loaded under equal conditions. To generate corrosion, one beam was exposed to a chloride-water solution. The other beam was exposed to tap water only, in order to act as a reference. This paper reports and discusses seven weeks of experi-mental data, including deflections and crack widths. Although there was not yet a significant effect of corrosion, some changes in crack widths and in deflections were observed. Furthermore, the influence of temperature and surface wetting exposure on the structural behaviour will be discussed., Structural Engineering, Civil Engineering and Geosciences

For understanding the actual state of durability of concrete structures, it is important to know its response due to external loading. This response mainly depends on the actual structural and material properties of the structure, while loaded. Mechanical and chemical degradation are the main mechanisms that may affect these properties with time. Strain sensors can be used to measure elongations, deflections and accelerations, which monitor the combined effect of temperature, prestressing forces, loading forces and local strain variation, while vibration sensors can be used to measure the dynamic response of a structure. Natural frequencies and mode properties can be calculated from monitored data and show the critical dynamic response behaviour of structures. However, this response behaviour can also be calculated using structural finite element models. A full-scale sensor network is installed underneath the first span of a concrete bridge in The Netherlands. Natural frequencies and mode shapes are calculated using both monitored data and a structural finite element model. Calculation results from both methods show good agreement. Understanding the impact of chemical degradation on the mode shape properties is considered experimentally. A test-setup is currently under development in the Stevin II laboratory of Delft University of Technology and is capable of testing the response of a dynamically loaded fourpoint-bending beam with a chloride solution bath mounted on top of it. During dynamic excitation, the chlorides penetrate into the cracks and accelerate corrosion of the reinforcement. Strain, deflection, crackwidth, and corrosion rate will be measured during this test., Structural Engineering, Civil Engineering and Geosciences

In this paper, a conceptual model for analyzing the plastic part of autogenous deformation of cement paste based on the Arrhenius rate theory will be presented. The autogenous deformation will be calculated from the elastic deformations with inclusion of creep. Different kinds of cement paste with a water cement ratio 0.3 are tested and studied, and experimental result compare the model calculation. The results lead to the conclusion that early age creep plays a very important role in the autogenous deformation of hydrating cement paste and should not be neglected in simulation models., Structural Engineering, Civil Engineering and Geosciences

Service life of reinforced concrete structures exposed to chloride enriched environment is well known to be mainly determined by steel passivity breakdown in the event of chloride-induced corrosion initiation and propagation. Since Cl- induced (localized) corrosion is caused by the free (water-soluble) chloride, present in the pore network of a reinforced concrete structure, quantifying the level of free chloride locally, e.g. via embedded Ag/AgCl electrodes (chloride sensors), is a generally accepted and applicable approach to monitor the time to corrosion initiation. The measurement is essentially a potential (voltage) reading over time and as such logically depends, among other factors, on the electrical and microstructural properties of the surrounding medium. Therefore, an accurate determination of the time to corrosion initiation significantly depends on the properties of relevant interfaces, such as the steel|cement paste interface and/or the Ag|AgCl|cement paste interface. In this paper, steel rods were coupled with Ag/AgCl sensors and embedded in cement paste cylinders. The specimens were immersed in simulated pore solution, containing 855 mM chloride concentration. Electrochemical impedance spectroscopy (EIS) was employed for quali-/quantification of the corrosion process on the steel surface (medium to low frequency response), while simultaneously providing information for the electrical properties of the bulk cement-based matrix through the high frequency response. The open circuit potential (OCP) values of both sensors and steel rods were recorded for more than 30 days. The results show a good agreement between sensor readings and steel electrochemical response i.e. time to corrosion initiation was recorded via steel OCP readings, whereas the relevant chloride content was estimated via the sensors’ OCP readings., Materials and Environment

Curing is the process of controlling the rate and extent of moisture loss from the surface of cement based materials. It is the final stage in the production of cement-based materials and it is the essential part for achieving continuous hydration of cement, while avoiding cracking due to drying shrinkage. Continuous cement hydration also guarantees a strong bond between aggregate, fewer voids, and depercoliation of capillary pores. Thus, a properly cured cement-based material is prepared for a long service life. Using environmentally friendly, water based bio-polymers could help to achieve more durable cement-based materials, and, therefore preventing a premature end of service life of building materials. Rapid Chloride Migration tests and Environmental Scanning Microscope are employed to investigate the functional properties, e.g. transport property, and microstructure properties, respectively. Mortar samples were cured in air and applied by water-based curing compound, made of sodium alginate. We observed strong beneficial effects of applying sodium alginate as a curing compound in terms of microstructure and hydration development. Based on these results, a less porous microstructure and an improved durable cement-based material was achieved that was prepared for longer service life., Structural Engineering, Civil Engineering and Geosciences

The stability of chloride ion selective electrodes in highly alkaline solutions is an important aspect when reliability and feasibility within reinforced concrete applications are concerned. The sensitivity of these electrodes largely depends on the properties of the AgCl layer, including uniformity, porosity, orientation, thickness, etc. These can be varied for optimum performance through adjusting the current density and anodizing time. In this study the Ag|AgCl electrodes were prepared in four different current density regimes and the resulting microstructural properties of the AgCl layer were correlated to potentiometric response in chloride-containing solutions, including synthetic concrete pore solution and cement extract. It was found out that lower level of the current density within the anodization process results later on in increased sensitivity and stability of the electrodes.., Materials and Environment

In this paper, a conceptual model for analyzing the plastic part of autogenous deformation of cement paste based on the Arrhenius rate theory will be presented. The autogenous deformation will be calculated from the elastic deformations with inclusion of creep. Different kinds of cement paste with a water cement ratio 0.3 are tested and studied, and experimental result compare the model calculation. The results lead to the conclusion that early age creep plays a very important role in the autogenous deformation of hydrating cement paste and should not be neglected in simulation models., Structural Engineering, Civil Engineering and Geosciences

In this paper a performance-based method for the design of granular-paste mixtures will be proposed. Focus will be on the selection and proportioning of constituents to produce a mixture with a pre-defined shape holding ability. Shape holding ability of mixtures will be characterized by the shape preservation factor SPF. This SPF shows the ability of a mixture to preserve its shape after being demolded from a slump test. SPF is the ratio of the cross sectional area of a sample after and before demolding. By increasing the flowability of a mixture, the SPF decreases. In this study a mixture is first decomposed into aggregate, void paste and excess paste. Then a combination of the consistency of the paste and excess paste volume is determined for a required SPF. Finally, depending on the aggregate grading, the volumes of paste and aggregates in the system are determined., Structural Engineering, Civil Engineering and Geosciences

The level of free chloride concentration in reinforced concrete structures essentially determines the onset of steel corrosion initiation and further propagation. One of the well-known methods for monitoring free chloride concentration is using silver/silver chloride electrodes (Ag/AgCl). These electrodes are sensitive mainly to chloride ions and establish a certain electrochemical potential depending on the chloride ion activity in the environment. Although the functioning principles of these electrodes are well-established, their use in concrete is challenging when durability and practical engineering issues are considered. In order to be able to accurately determine free chloride content in concrete, it is important to evaluate the performance of Ag/AgCl electrodes (sensors) in strong alkaline environments i.e. those existing in non-carbonated concrete (pH~12–13.5). Furthermore the linear response of these sensors to a wide range of chloride concentrations in highly alkaline medium, as well as their sensitivity to pH changes, need a more in-depth investigation. In this paper the response of Ag/AgCl electrodes in simulated pore solutions having different chloride concentrations and different pH values was studied. The electrodes were calibrated in cement extract solution, distilled-water and simulated pore solution. The results show that at chloride concentrations of > 4 mM the effect of pH on the response of the sensors is insignificant which makes using Ag/AgCl sensors in concrete feasible i.e. this concentration is much lower than the generally reported thresholds for corrosion initiation. Keywords: Ag/AgCl electrode, cement extract solution, free chloride, pH value, pore solution., Structural Engineering, Civil Engineering and Geosciences

The remaining service life of concrete structures strongly depends on the corrosion level of the reinforcement bars. It explains that measuring the corrosion rate is a key issue in monitoring the structural health of concrete structures. A common and appropriate technique used to evaluate the instantaneous corrosion rate of steel reinforcement is by Linear Polarization Resistance (LPR). A dynamic loaded, four-point-bending test on a reinforced concrete (RC) beam was developed to measure dynamic responses and stiffness changes due to corrosion. The test setup can load two beams with a comparable structural behaviour simultaneously, while exposed to the same ambient conditions. To expedite corrosion in one of the beams, a water-chloride solution bath was mounted on top of it. As a reference, a tap water bath was placed on top of the other beam. A wetting cycle of two days wet and five days dry was carried out to simulate real-time situations and to accelerate the corrosion process. During this test, the responses of both beams were measured by Linear Variable Differential Transformers (LVDTs) and results were filed automatically. Furthermore, the corrosion rates of both RC beams were automatically measured by LPR every day. The results of these measurements show differences in corrosion rate between both beams with time. After beam failure, brief forensic engineering was executed to analyse the corrosion of the reinforcement bars. Visual observations show a good correlation with the corrosion behaviour measured by the LPR method., Structural Engineering, Civil Engineering and Geosciences

Coupled reactive-transport processes in cementitious materials play a crucial role in the aging process pf building materials. Up to now, the effect of aging on microstructure and evolution of it’s properties, in three dimensions, was studied only by dissolution of certain phases at random locations. In this paper we present a new 3D reactive-transport model and results of leaching-induced aging simulations performed on virtual cementitious microstructures generated by Hymostruc model. The outputs are the morphology of the aged 3D microstructure together with aged properties characterised by fuzzy state of each voxel at different times. This allows to simulate the evolution of properties as a function of time as well as a function of the location within the microstructure., Structural Engineering, Civil Engineering and Geosciences

Viscoelastic stress modeling in ageing cementitious materials is of major importance in high performance concrete of low water cement ratio (e.g. w/c ~0.35) where crack resistance due to deformation restraint needs to be determined. Total stress analysis is complicated by the occurrence of internal stresses due to shrinkage, which requires estimating the stress relaxation effect from tensile creep. This study presents a new and direct methodology for viscoelastic stress analysis based on measurement of the viscoelastic hydration modulus. Autogenous shrinkage, if restrained, creates an internal tensile stress condition which is uniform within a cross section. Autogenous shrinkage stresses develop within the porous hydration products. They are compressive stresses and if restrained by reinforcement a net tensile stress develops. Results show that the viscoelastic hydration modulus is approximately 8000-9000 MPa and is a constant material property. Total stress analysis can now be separated into two components, an elastic stress based on the Young’s modulus (typically in the range of 28000-34000 MPa) and a viscoelastic (time-dependent) stress based on measurement of timedependent strains (creep and shrinkage). The importance of reducing paste content for shrinkage stress control is demonstrated using the Pickett’s model., Structural Engineering, Civil Engineering and Geosciences

Stray current is essentially an electrical current “leakage” from metal conductors and electrical installations. When it flows through cement-based systems, electrical energy is converted to thermal energy that causes increasing temperature due to Joule heating phenomena. The aim of this paper is to shed light on the influence of electrical current flow on cement hydration, morphological and structural changes of cement-based systems, emphasizing on the potentially altered temperature effects when electrical current flow is involved. Calorimetry tests show that degree of cement hydration increases as a results of temperature increase due to electrical current flow through cement-based systems. To evaluate the influence of electrical current on the hydration mechanisms in cement-based systems, HYMOSTRUC will be used as a modelling approach, where temperature effects due to electrical current flow are implemented in the existing numerical simulation., Structural Engineering, Civil Engineering and Geosciences

De-icing salts, used on roads in heavy winters, may enter reinforced concrete (RC) structures via its capillary pore system or via cracks, initiating reinforcement corrosion and reducing its remaining service-life. Vehicles passing real bridges exert a dynamic impact action that might activate a fatigue failure mechanism. In order to generate more knowledge on the interaction between corrosion and fatigue, a four-point-bending test setup is developed where two lab-scale RC beams are loaded simultaneously. In this setup, RC beams are loaded dynamically, while for one of the beams, corrosion is accelerated by means of a chloridesolution bath mounted on top of it. The second beam, which is the control, is only exposed to tap water. Many test repetitions are foreseen, but so far, three tests are conducted using two different loading levels. It turned out that the reinforcement bar, which corroded due to chloride exposure, failed first in all cases. This paper reports results of the failure mechanism whereby forensic engineering was used to examine the interaction between corrosion and fatigue, and that this might result in a harmful undesirable failure mechanism. The results, therefore, should also be considered for service-life design predictions of infrastructure., Structural Engineering, Civil Engineering and Geosciences

Structural Engineering, Civil Engineering and Geosciences

One of the reported problems associated with the performance of Ag/AgCl electrodes in alkaline environment, as concrete pore water, has been their poor stability. Open circuit potentials are typically observed to be stable for a time period of a few minutes to some days depending on the thickness and microstructure of the sparingly soluble AgCl and the subsequently developed mixed potentials at the electrode/solution interface. In this paper the open circuit potential of the chloride sensors were monitored over time in simulated pore solution with and without chloride and their electrochemical response recorded via electrochemical impedance spectroscopy (EIS). The alterations in response of the sensors can be denoted to transformation of the AgCl layer to Ag2O in chloride-free high pH environment as in concrete pore water. Recovery of the AgCl layer takes place in chloridecontaining medium, where establishing of sensor stability is determined by the chloride concentration., Structural Engineering, Civil Engineering and Geosciences

Structural Health Monitoring (SHM) systems are frequently used in civil infrastructures. One important durability property in reinforced concrete (RC) structures is the level of steel bar corrosion. In a dynamic four-point-bending test, two beams are loaded simultaneously, in which corrosion is accelerated in one of them. Since geophones are commonly used in SHM systems to monitor vertical deformations and to calculate modal properties, the first natural frequency of both beams are analysed in this paper. It is discovered that many properties, like temperature and moisture, may influence natural frequencies. Besides this, calculated natural frequencies may fluctuate. Experiments showed that the first natural frequency in the corroded beam decreases while it remains almost constant in the uncorroded situation., Structural Engineering, Civil Engineering and Geosciences

For understanding the actual state of durability of concrete structures, it is important to know its response due to external loading. This response mainly depends on the actual structural and material properties of the structure, while loaded. Mechanical and chemical degradation are the main mechanisms that may affect these properties with time. Strain sensors can be used to measure elongations, deflections and accelerations, which monitor the combined effect of temperature, prestressing forces, loading forces and local strain variation, while vibration sensors can be used to measure the dynamic response of a structure. Natural frequencies and mode properties can be calculated from monitored data and show the critical dynamic response behaviour of structures. However, this response behaviour can also be calculated using structural finite element models. A full-scale sensor network is installed underneath the first span of a concrete bridge in The Netherlands. Natural frequencies and mode shapes are calculated using both monitored data and a structural finite element model. Calculation results from both methods show good agreement. Understanding the impact of chemical degradation on the mode shape properties is considered experimentally. A test-setup is currently under development in the Stevin II laboratory of Delft University of Technology and is capable of testing the response of a dynamically loaded fourpoint-bending beam with a chloride solution bath mounted on top of it. During dynamic excitation, the chlorides penetrate into the cracks and accelerate corrosion of the reinforcement. Strain, deflection, crackwidth, and corrosion rate will be measured during this test., Structural Engineering, Civil Engineering and Geosciences

One of the key-elements in Structural Health Monitoring of reinforced concrete structures is the level of rebar corrosion and the way in which it affects the structural performance. A dynamic four-point-bending test was developed to help understanding the deflections of concrete structures under corrod-ed conditions. With this test, two equivalent beams are loaded under equal conditions. To generate corrosion, one beam was exposed to a chloride-water solution. The other beam was exposed to tap water only, in order to act as a reference. This paper reports and discusses seven weeks of experi-mental data, including deflections and crack widths. Although there was not yet a significant effect of corrosion, some changes in crack widths and in deflections were observed. Furthermore, the influence of temperature and surface wetting exposure on the structural behaviour will be discussed., Structural Engineering, Civil Engineering and Geosciences

In this paper results are presented from a by STW funded research project “spalling of concrete due to fire exposure” between Eindhoven University of Technology and Delft University of Technology and aimed at developing an integral spalling model. In this paper two coupled Finite Element based models are presented in which the first model describes the physical behaviour of concrete and is used to determine the temperature and pore pressure development and the second model describes the fracture mechanics behaviour of concrete and is used to determine the crack development., Structural Engineering, Civil Engineering and Geosciences

In this paper, the effect of the mix composition on rheological behavior of a mixture is studied by considering a two-phase model for a mixture. A mixture is decomposed into a granular and a paste phase. Paste itself is divided into the void paste and the excess paste. The slump test is used for evaluation of rheological behavior of a mixture. The results show that the granular-cement paste mixtures can be split into three main classes viz Granular-High Paste, Granular-Intermediate Paste and Granular-Low Paste. In Granular-High Paste class, the behavior is governed by the excess paste and the capacity of deformation of mixtures is maximal. In Granular-Low Paste class, the behavior is governed by the void paste and the capacity of deformation of mixtures is minimal. In Granular-Intermediate Paste class the behavior is determined by both the excess paste and the void paste, and the deformability is in between that of the two other extreme cases., Structural Engineering, Civil Engineering and Geosciences

Structural Engineering, Civil Engineering and Geosciences

Structural Engineering, Civil Engineering and Geosciences

In the field of civil infrastructure, Structural Health Monitoring systems are implemented more and more frequently with the aim to safeguard the safety and service-life of structures such as bridges and tunnels. Changes in the integrity of the material and/or structural properties of this class of structures is known to adversely affect their performance, which can also be observed from the structures’ dynamic response, such as the natural frequencies, damping ratios and mode shapes. The procedure to obtain these response parameters is known as modal analysis. Two methods for obtaining these parameters are compared in this paper, one based on a careful analysis of measured vibration sensor data, and another one is based on a structural calculation using a Finite Element Method (FEM). The dynamic modal characteristics of a structure can be obtained by using vibration-based damage identification techniques such as Stochastic Subspace Identification (SSI). The SSI technique is capable of extracting modal parameters from output-only measurements, i.e. using raw data collected by simply monitoring a structure under its normal load. In this paper the application of SSI for the “Hollandse Brug”, which is a six-lane Dutch concrete highway bridge under in-service conditions, is described. The bridge is equipped with a sensor network of 145 sensors, including 34 vibration sensors (geo-phones). This paper demonstrates how the key modal parameters can be extracted by applying SSI to the sensor readings. To assess the quality of the sensor-based results, the modal parameters derived using SSI are compared with the results obtained from Finite Element Method (FEM) calculations. For the FEM calculation, the computer program Scia Engineer is used. The results of the two methods agree well, which shows that the SSI technique under output-only and in-service conditions is an effective tool for modal analysis, and thus a valuable method to be used in structural health monitoring syst, Structural Engineering, Civil Engineering and Geosciences

Since the early 20th century, the necessity of modeling and monitoring fresh concrete behavior has been recognized by the industry with the objective to ensure adequate mechanical properties and a proper durability of concrete structures. Due to the rapid development of computer technology, the applications of computational simulation tools in the field of concrete technology has significantly increased and help us to understand the mechanisms of rheological systems. The development of proper rheological models and suitable numerical methods are considered as basic needs for a thorough understanding of the flow properties. The main challenge is finding a quantitative correlation between the model parameters and the properties and proportions of the mix ingredients. This paper presents a numerical approach for macroscopic behavior of a fresh self-compacting mixture using Discrete Element Method (DEM). The employed research is based on a conceptual idea where the grain-paste interaction is explicitly modelled as an interactive two-phase system. Each mixture is considered to be an assembly of “grain-paste” systems, which can be characterized according to the mix composition based on the “excess paste theory”. The macroscopic behavior is evaluated based on the slump flow test results. Simulations and experimental laboratory test results show good agreement., Structural Engineering, Civil Engineering and Geosciences

The Brazilian construction industry is committed to delivering the venues and infrastructure of the Rio 2016 Olympic and Paralympic Games with zero increase in carbon dioxide emissions, reduced consumption of raw materials, increased use of renewable materials and 100% local recycling of construction waste. This in turn has led to significant research and development into using cement replacements – particularly sugar-cane ash from local ethanol production – and recycled aggregates in concrete production. This paper reports on the initial and promising results for ecological concrete mixes using up to 20% sugar-cane ash and 50% cleaned recycled aggregates from demolition waste., Structural Engineering, Civil Engineering and Geosciences

Structural Engineering, Civil Engineering and Geosciences

Structural Engineering, Civil Engineering and Geosciences

The InfraWatch project is a Dutch research project, aimed at developing novel techniques for large-scale monitoring of concrete infra-structures. The project involves a large bridge, fitted with multiple types of sensors that capture the high-resolution dynamic behavior of the bridge. With 145 sensors measuring at 100 Hz, a huge amount of data becomes available that describes various aspects of the bridge’s response to traffic and weather conditions, both long and short-term. A single truck passing the bridge already encompasses almost 50,000 readings, such that detailed modal analysis can be performed. At the same time, this data-intensive monitoring continues around the clock, as well as the calendar, such that more gradual effects like changes in temperature and traffic conditions can be tracked as well. This wealth of information is being analyzed in various ways ? which will be elaborated in this paper ? combining both computer science and civil engineering expertise. The InfraWatch project is a central project in the Dutch national research program “Integral Solutions for Sustainable Construction (IS2C)”, which is aimed at developing novel techniques for a next generation predictive simulation model for service life assessment. Other projects within this program are concerned with key degradation processes in structural concrete, such as ASR and chloride penetration. In the near future, the progress of such degradation processes will be measured by dedicated sensors, to be developed within these ‘sister projects’. Such direct degradation measurements will complement the indirect measurements currently performed, which essentially only monitor the dynamic load on the bridge. A lab experiment is currently being developed in the Stevin II laboratory of Delft University of Technology, where ASR and chloride penetration will be measured alongside with the dynamic deformations of a test beam under load while focusing on the mutual interaction of both the materials d, Structural Engineering, Civil Engineering and Geosciences

Structural Engineering, Civil Engineering and Geosciences