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

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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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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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

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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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

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

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

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

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

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

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

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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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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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

Modern society and infrastructure are facing an increased demand for fast construction. A number of viaducts are aged and will need to be replaced in near future. When considering this replacement task, lightweight, slender bridge is the solution. Dead load reduction and high-strength to weight ratio are the main advantages when using the lightweight aggregate concrete (LWAC). Still, structural applications of LWAC are lacking. The main disadvantage of LWAC compared to regular concrete, which refrains its wider structural application, is its brittleness and uncontrolled crack propagation, especially when LWAC is exposed to compression. One of the ways to improve brittleness and increase the ductility of concrete is by addition of fibers. In this research, preliminary study is performed where fiber reinforced LWAC mixture was designed and tested. The mix consisted of lightweight aggregate Stalite, leading to high-strength LWAC and polyvinyl alcohol fibers (PVA) providing reduced brittleness and explosive failure. Results on fracture behavior and compressive strength with the increased amount of fibers were investigated and showed promising behavior. In future, structural tests (e.g. compression tests on prisms and beams) will be performed to further verify the benefits of combining aggregate Stalite with PVA fibers for structural applications of high-strength LWAC.@en

Nowadays, finite element analyses provide information about the performance of a structure, but they are more or less simplified. Therefore, load tests are the only way to find the “real” behavior of an existing bridge subjected to the rating process. In this paper, the state-of-the-art concerning load tests of concrete road bridges is presented, and the problems of the execution of such tests are specified. It is pointed out that only load tests accompanied with current finite element analyses may result in a proper assessment of the level of safety of the bridge. The authors’ procedure of complex assessment of such bridges combines in-situ examination of the structure, load testing, and finite element modeling.
The paper discusses the following topics:
• Aims and fundamentals of static diagnostic and proof load tests,
• The load application method according to different codes and specifications,
• The basis for proper assessment of the target load: reliability index, partial factors approach, global rating factor approach,
• Establishing the load allowable on the bridge, based on the applied proof load,
• The proposed procedure of assessment of existing concrete road bridges by load testing.@en

When designing a concrete structure, a structural engineer often assumes that it is initially free of stresses and cracks. Serviceability limit state analyses are therefore often carried out only taking into account the structure’s self weight and the other imposed loads. As a result, initial tensile stresses and (internal) cracking that can arise from, e.g., partially restrained shrinkage is not accounted for. This might imply that service life predictions can be too optimistic since micro-cracks can promote the penetration of chlorides, with the result of an accelerated corrosion of the reinforcement. The impact of restraint can be at both the structural level (plane sections must remain plane) and the material level (concrete is a non-homogenous material from components having different shrinkage behaviour and stiffness). In this contribution the results of the numerical analysis of eigenstresses and micro-cracking due to the shrinkage of the cement paste in concrete are highlighted. The two-dimensional Delft beam lattice model (BLM) is used to simulate concrete on meso-level as a three-phase material. Stress relaxation in the cement paste is calculated with the activation energy method. For the comparison of the calculated micro-cracking the results of laboratory tests on concrete are used by which the chloride penetration is measured under different restraint conditions with different levels of micro-cracking. The results of the numerical analyses with BLM specimens showed that micro-cracking can increase the diffusion coefficient of (uncracked) concrete with a factor 1.2–1.6, depending on the magnitude of stress relaxation. The residual tensile eigenstresses in concrete reduces due to micro-cracking and stress relaxation till values in the order of 0.5–1.0 MPa which are not taken into account in global calculations and can speed up (unexpected) cracking in the concrete.@en