Most of the bridges and viaducts in the Netherlands were built in the sixties and seventies of the last century, and an increasing number of them will have to be replaced due to technical or functional reasons. The Netherlands is not an exception, many industrialized countries will face a similar replacement task in the near future. With the increased traffic intensities and the importance of mobility, the design and construction strategies for new bridges have to be different from that in the past. New methods need to ensure that traffic hindrance due to construction works and (future) maintenance activities are minimized. At the Delft University of Technology, a SMART bridge concept is being developed for fast and hindrance-free infrastructural replacement. The optimal advantage is achieved by utilizing innovative but proven technologies, and by bringing academic research into practice. A combination of recent innovations in construction technology, such as advanced cementitious materials (ACM), structural health monitoring (SHM) techniques, advanced design methods (ADM), and accelerated bridge construction (ABC) is being used. These innovations represent a step towards the next generation of infrastructure where fast construction, intelligent bridge design, sustainability, zero-energy, no/low maintenance, and aesthetics are key features@en

This paper presents a comparative study based on a thorough beam bending test.The intention is to obtain the relationship between the nominal elastic wave velocity obtained from Acoustic Emission tomography analysis and the physical damage of the RC beam in terms of crack opening. The crack width of the specimen was determined by both Digital Image Correlation and the conventional LVDT measurements. The study shows that globally the nominal wave speed derived from AE tomography is related to the crack development of the specimen when the crack width is limited. It is also shown that the scatter of the AE tomography results can be improved by averaging the nominal wave velocity of the cells along the cracked section.@en

Existing bridges with large uncertainties can be assessed with a proof load test. In a proof load test, a load representative of the factored live load is applied to the bridge at the critical position. If the bridge can carry this load without distress, the proof load test shows experimentally that the bridge fulfills the requirements of the code. Because large loads are applied during proof load tests, the structure or element that is tested needs to be carefully monitored during the test. The monitored structural responses are interpreted in terms of stop criteria. Existing stop criteria for flexure in reinforced concrete can be extended with theoretical considerations. These proposed stop criteria are then verified with experimental results: reinforced concrete beams failing in flexure and tested in the laboratory, a collapse test on an existing reinforced concrete slab bridge that reached flexural distress, and the pilot proof load tests that were carried out in the Netherlands and in which no distress was observed. The tests in which failure was obtained are used to evaluate the margin of safety provided by the proposed stop criteria. The available pilot proof load tests are analyzed to see if the proposed stop criteria are not overly conservative. The result of this comparison is that the stop criteria are never exceeded. Therefore, the proposed stop criteria can be used for proof load tests for the failure mode of bending moment in reinforced concrete structures.@en

In the Netherlands, existing bridges are being assessed to investigate whether they are still capable to resist current and future traffic loads. A part of these bridges consists of prestressed I-and T-shaped girders with a low shear reinforcement ratio. This ratio is low because the principle stress criterion was used to verify sufficient shear resistance at the time of engineering. These bridges are now assessed with the present Eurocode. It appears that it is difficult to demonstrate sufficient shear tension resistance. In this paper it is investigated whether existing models can accurately predict shear tension resistance for girders with a low shear reinforcement ratio. The model used in the CSA was found to predict this resistance conservatively and consistent. However, for single span girders with low shear reinforcement ratios, it was also found that it is difficult to demonstrate additional capacity compared to the resistance to diagonal tension cracking.@en

In a proof load test, a load representative of the factored live load is applied to the bridge. Since the applied load is large, stop criteria are important. Stop criteria for shear and flexure are proposed based on existing codes and guidelines, laboratory experiments, and theoretical considerations. This proposal is verified with the results from pilot proof load tests. The result of this comparison is that the stop criteria are never exceeded, or that they are exceeded only in the last load step. The proposed stop criteria are thus not overly conservative for application to field testing. However, information about the available margin of safety is not always available, especially for shear failures, and will need further experimental validation.@en

As an important aspect in the asset management of the existing concrete bridges, a proper evaluation of the conditions of the concrete, especially the width and the distribution of cracks in the concrete structure turns out to be rather important. Conventional approaches usually require onsite investigations and are labour intensive. On the other hand, it has been recognized since long time that the elastic wave transfer properties through solid can reflect the change of properties inside the material. Smart Aggregate (SA) is a newly developed ultrasonic sensor based on this effect. Casted into the target structures, these sensors make it possible to detect the change of ultrasonic wave transfer properties and evaluate the damages of the structures from the inside. This paper presents a structure condition assessment strategy by making use of SA grid through a lab test on a scaled specimen.

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Strain Hardening Cementitious Composite (SHCC) is an innovative material which, due to the special material composition and the addition of fibres, exhibits a controlled microcracking behaviour under tensile stresses. As such it might be a promising material for improvement of durability of concrete structures.

An experimental study was performed aiming to investigate the cracking behaviour of reinforced concrete beams enhanced with SHCC layers in the beam tension zone (hybrid SHCC - concrete beams). Specimens with SHCC layers of different thickness were tested. The hybrid SHCC/concrete beams were compared to regular reinforced concrete (control) beams with the same dimensions and rebar position. Specimens were tested in four-point bending while Digital Image Correlation (DIC) and an image analysis software package (ImageJ) were used to evaluate crack pattern development and crack widths. In the experiments, hybrid beams showed better cracking behaviour compared to control beams, whereas also a higher bending moment capacity was found. The thicker the SHCC layer, the higher the load capacity is. More importantly for the aim of this study, composite beams with a 70 mm SHCC layer showed a better crack width control compared to the reference beams. The maximum crack width exceeded 0.3 mm at approximately 64 kN load, whereas in the control beam it exceeded 0.3 mm at 35 kN load. In hybrid beams with a 30 mm SHCC layer, the benefits were much lower, as expected.

The study indicates that by using a combination of conventional concrete and advanced concrete (SHCC in this case), possibly optimal design of reinforced concrete structures could be achieved by eliminating the crack width as governing design parameter and thus saving on reinforcement needed for crack width control. @en

This chapter describes the proof load testing of viaduct Zijlweg at a position that is critical for bending moment and at a position that is critical for shear. The viaduct Zijlweg has cracking caused by alkali-silica reaction, and the effect of material degradation on the capacity is uncertain. Therefore, the assessment of this viaduct was carried out with a proof load test. This chapter details the preparation, execution, and evaluation of viaduct Zijlweg. The outcome of the proof load test is, according to the currently used methods for proof load testing, that the viaduct fulfills the code requirements, and that strengthening or posting is not required.@en

The sustainability of infrastructure projects is becoming increasingly important issue in engineering practice. This means that in the future the construction materials will be selected on the basis of the contribution they can make to reach sustainability requirements. Geopolymers are materials based on by-products from industries. By using geopolymer concrete technology it is possible to reduce our waste and to produce concrete in the environmental-friendly way. An 80% or greater reduction of greenhouse gases compared with Ordinary Portland Cement (OPC) can be achieved through geopolymer technology. However, there are limited practical applications and experience. For a broad and large scale industrial application of geopolymer concrete, challenges still exist in the technological and engineering aspects. The main goal of GeoCon Bridge project was to develop a geopolymer concrete mixture and to upscale it to structural application. The outputs of projects provide input for development of recommendations for structural design of geopolymer based reinforced concrete elements. Through a combination of laboratory experiments on material and structural elements, structural design and finite element simulations, and based on previous experience with OPC concrete, knowledge generated in this project provides an important step towards a “cement free” construction. The project was performed jointly by three team members: Microlab and Group of Concrete Structures from Technical University of Delft and Technical University of Eindhoven.

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In the Netherlands, existing bridges are being assessed to investigate whether they are still capable to resist current and future traffic loads. Bridges that are compiled of single span prestressed girders, appear to have insufficient resistance to diagonal tension cracking. This concerns bridges that do not contain sufficient stirrups. Consequently, diagonal tension cracking could result in an abrupt brittle failure. However, the assessments are performed using the Eurocode model and there is doubt about its accuracy. In this research the accuracy of the Eurocode model is determined by comparing predicted resistances with experimentally found resistances. Moreover the stress distribution according to the Eurocode model is compared with the stress distribution of a linear elastic finite element analysis. Based on the comparison, an alternative model is suggested, that predicts the resistance to diagonal tension cracking more accurately.@en

Proof load testing of existing reinforced concrete bridges is becoming increasingly important as the current bridge stock is aging. In a proof load test, a load that corresponds to the factored live load is applied to a bridge structure, to directly demonstrate that a bridge fulfills the code requirements. To optimize the procedures used in proof load tests, it can be interesting to combine field testing and finite element modeling. Finite element models can for example be used to assess a tested structure after the test when the critical position could not be loaded. In this paper, the case of viaduct De Beek, a four-span reinforced concrete slab bridge, is studied. Upon assessment, it was found that the requirements for bending moment are not fulfilled for this structure. This viaduct was proof load tested in the end span. However, the middle spans are the critical spans of this structure. The initial assessment of this viaduct was carried out with increasingly refined linear finite element models. To further study the behavior of this bridge, a non-linear finite element model is used. The data from the field test (measured strains on the bottom of the concrete cross-section, as well as measured deflection profiles) are used to update the non-linear finite element model for the end span, and to improve the modeling and assessment of the critical middle spans of the structure. Similarly, an improved assessment based on a linear finite element model is carried out. The approaches shown for viaduct De Beek should be applied for other case studies before recommendations for practice can be formulated. Eventually, an optimized combination of field testing and finite element modeling will result in an approach that potentially reduces the cost of field testing.@en

This paper presents an experimental study on the development of material properties over time (up to around 2 years) and the structural behavior of reinforced beams, for two types of alkali-activated concrete (AAC). Compressive strength, flexural strength, tensile splitting strength, elastic modulus, and flexural behavior of reinforced beams are investigated. Tested material properties of AAC are compared with the properties of conventional concrete, as predicted by Eurocode. For the mixes of AAC and the conventional concretes with the same 28 days compressive strength, flexural and tensile splitting strength at 28 days are found to be similar, whereas the elastic moduli of AAC mixtures is up to 30% lower than those of conventional concrete. Related to the long term behavior, after 28 days moist-curing and subsequently exposing AAC specimens to laboratory conditions (50% RH/20°C), a reduction of flexural strength, tensile splitting strength and elastic modulus, is observed. Structural behavior of the reinforced AAC beams in four-point bending test seems not to be affected significantly by the observed decrease in material properties, and is found to be similar to that of conventional concrete beams. The acquired results indicate that the observed decrease of material properties over time might be related to drying (moisture loss). However, more research is needed to understand the phenomenon, especially related to the aimed structural application and safe upscaling of AAC.

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With the recent developments in modelling the shear behaviour of reinforcement concrete (RC) members without transverse reinforcement, the contribution of aggregate interlock has been more and more recognized as one of the critical components in the shear resistance of RC members. This paper presents a study on the aggregate interlock action utilizing laser scanned crack surfaces including the shear crack surface of a 1.2 m concrete beam. The study extends the classic aggregate interlock model proposed by Walraven to enable the possibility of employing modern measurement technology.@en

This paper presents a development of a ductile alkali-activated fly ash (FA) and ground granulated blast furnace slag (GBFS) based composite as an environmentally friendly material for structural concrete application. For this purpose, polyvinyl alcohol (PVA) fibres and sand aggregate were combined with alkali-activated paste. Workability, setting time, mechanical properties and failure mode of PVA fibres in the mixture were studied by slump test, Vicat needle test, flexural and compression tests, and Scanning Electron Microscopy (SEM) imaging, respectively. Although the mixture sets in a short period of time (less than 30 min), the workability was good and the developed fibre reinforced composite was used for a large scale application in a canoe. Casting a large volume (45 l compared to 3 l, as initially designed) did not affect the workability and the setting time of the mixture. Mechanical properties of specimens coming from “small” (3 l) and “large” (45 l) batches were tested at different ages (up to 120 days) and compared. It was shown that their flexural and compressive strength are similar, i.e. not affected by the upscaling. Furthermore, it was shown that the mixture with PVA fibres exhibits deflection hardening behaviour even with aggregate particles as large as 4 mm, although single crack localization led to failure. The SEM images of fractured surfaces indicated that combined fibre pull-out and fibre rupture occurred, with the latter one causing the final failure. The developed mixture, additionally reinforced with the plastic fiberglass mesh, was used in the 5.8 m long and 16 mm thick canoe for the student competition, which for the very first time, was constructed without the use of Ordinary Portland cement (OPC). The upscaling was successful and the results show the potential of fibre-reinforced alkali-activated FA and GBFS composite to be used as a durable and resistant material suitable for the structural application in thin shell elements, exemplified by the canoe. Such an application and a low risk project was suitable to gain the necessary experience and confidence with this innovative, “concrete like” material for which no codes or regulations are available. Furthermore, similar applications are the first step for larger scale structural applications, like structural elements in the building industry, bridges and other civil engineering structures.

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Interaction of ultrasonic waves with partially-closed surface-breaking cracks in concrete structures has been studied. Measurements have been conducted on a reinforced concrete beam containing various mechanical-load-induced cracks and compared with the baseline measurements at those locations. Influence of crack width, incident angle of waves with cracks, and distance from the cracks on travel time and amplitude of the waves have been investigated when the beam was unloaded. It has been observed that a measurable part of the waves propagate through the cracks due to the acoustic coupling between the crack faces, although attenuation can be relatively high. The travel time has shown a nearly independent behavior from remaining crack opening in the measured range of 0.05 mm to 3 mm. Measurements in directions orthogonal and parallel to the crack suggest that there is substantial anisotropy in the cracking zone. Furthermore, an effective width of the micro-cracking area around the cracks has been estimated from the measurements.

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In a proof load test, a load corresponding to the factored live load is applied to a bridge, to directly demonstrate that a bridge fulfils the code requirements. The case of viaduct De Beek, a four-span reinforced concrete slab bridge that did not fulfil the requirements for bending moment after an inspection survey is studied. The middle spans, located above highway lanes, which could not be tested in the field, are the critical spans of this structure. Therefore, the observations from the field are used to check the finite element model, and improve the rating of the critical middle spans. The proposed method can be applied and further extended for proof load tests where the access to the site and the critical position of the viaduct is limited. This improvement will allow for an opti-mized combination of field testing and modelling, reducing the costs of field tests.@en

In a proof load test, the applied load is representative of the factored live load, to demonstrate experimentally that the bridge fulfils the code requirements. Signs of distress must be caught with the instrumentation by defining stop criteria. In the literature, several stop criteria for flexure are available. The German guidelines describe, amongst others, a limiting crack width and strain. However, the background of these limiting values is not clear. Therefore, a theoretical approach based on flexural theory is followed. The theoretically derived values are then compared to experimental results obtained from beam experiments. The result of this research work is a limiting value of crack widths and strains that can be used during proof load testing of concrete bridges. The arbitrary stop criteria that were used in the past can now be replaced by stop criteria that are based on the theory of concrete beams in flexure.@en

A large subset of the Dutch bridge stock consists of reinforced concrete slab bridges, for which assessment often results in low ratings. To prioritize the efforts of the bridge owner, more suitable assessment methods for slab bridges are necessary. Research efforts over the past years resulted in the development of several methods, at levels requiring increasing costs, time, and effort for increasing accuracy. The last option, when an analytical assessment is not possible due to uncertainties, is to use proof load testing to evaluate the bridge directly. To develop recommendations for the proof load testing of reinforced concrete slab bridges for the Netherlands, different methods are combined: pilot proof load tests on bridges with and without material damage, a collapse test, tests on beams taken from an existing bridge and new beams with similar dimensions cast in the laboratory, and an extensive literature review. The result of this study is a set of recommendations that describe how to prepare and execute a proof load test, and how to analyze the results. This paper summarizes the research program about proof load testing from the Netherlands and gives an overview of the currently developed recommendations and topics for further research.@en

Strain Hardening Cementitious Composite (SHCC) is an innovative material which, due to the special material composition and the addition of fibres, exhibits a controlled microcracking behaviour under tensile stresses. As such it might be a promising material for improvement of durability of concrete structures.
An experimental study was performed aiming to investigate the cracking behaviour of reinforced concrete beams enhanced with SHCC layers in the tension zone (hybrid SHCCconcrete beams). Specimens with SHCC layers of different thickness were tested. The hybrid SHCC/concrete beams were compared to regular reinforced concrete (control) beams with the same dimensions and rebar position. Specimens were tested in four-point bending while Digital Image Correlation (DIC) and an image analysis software package (ImageJ) were used to evaluate crack pattern development and crack widths. In the experiments, hybrid beams showed better cracking behaviour compared to control beams, whereas also a higher bending moment capacity was found. The study indicates that by using a combination of conventional concrete and advanced concrete (SHCC in this case), possibly optimal design of reinforced concrete structures could be achieved by eliminating the crack width as governing design parameter and thus saving on reinforcement needed for crack width control.@en