With the development of waste recovery techniques, previous research has revealed that coarse fractions of municipal solid waste incineration (MSWI) bottom ash (BA) after proper treatment could be applied in the construction sector, while the fines are seldom recovered in practice and normally landfilled. This study explores the potential application of fine MSWI BA (0–2 mm) as a supplementary cementitious material (SCM) in Portland cement (PC) mixtures. Mechanical and chemical pre-treatment approaches have been designed with various conditions to optimize the treating process. The chemical and mineralogical compositions, as well as the metallic Al content in BA were characterized before and after the pre-treatment. It was found that both methods are effective in removing the metallic Al content in BA, Moreover, BA derived from mechanical treatment exhibited more contribution to the hydration reaction in PC mixtures, as revealed by the amount of reaction products and mineral phases formed in hardened trial mixtures. BA obtained was further partially blended in PC mortars to evaluate the performance as compared to SCMs and inert fillers. It was found that treated BA resulted in a slight retarding effect on the reaction kinetics. Treated BA behaved better than the coal fly ash to contribute to the strength development, while the inclusion of BA did not lead to significant influences on the workability. ... Read more

The need to consider tunnel safety, especially with respect to fire, has been highlighted in the past by various severe tunnel fires that have occurred throughout Europe. This article provides a general overview of the current rules and regulations governing the fire resistance design of tunnel structures. Subsequently, the engineering perspective is presented, focusing on the assessment of fire severity and the resulting thermal loading on the tunnel structure, which may result in spalling of concrete. Thereafter, a scientific perspective is provided, reflecting recent advances made in numerical calculations with respect to the spalling mechanism. From the numerical results and comparison with observations from full-scale tests, it is concluded that thermal restraint is dominant for spalling. Spalling is triggered by the buckling of concrete layers loaded with strains imposed by temperature, which is a new perspective for future scientific research and innovative engineering solutions. ... Read more

Different analytical models exist to predict the shear strength of reinforced concrete members. Generally, each of these shear strength models consists of a formulation based on certain underlying theory and fitted model coefficients. The model fitting parameters are usually established from the comparison with test data. Hence, the predictive value of a shear strength model depends, to some extent, on the quality and representativeness of the used test data.
The first immersed concrete tunnel in the world is heavily deteriorated due to reinforcement corrosion. Beside its great historical importance, the tunnel is situated in the heart of Rotterdam and is one of the most important city connections. Therefore, upon discovering structural damage, a major task has been to prove that the structural safety is at a reliable and acceptable level (Blom 2013). Consequently a repair plan has been worked out to preserve this tunnel for the future and to minimise disturbance of traffic in the city centre during repair closure. This paper shows the dilemma’s and choices in realising the repair strategy.

First the conceptual consideration is shown on why removal of chloride contaminated concrete in this case is preferred above cathodic protection. Secondly, it is shown how to deal with temporarily decreased structural safety and increased probability of cracking during the repair: i.e. in the stage when chloride contaminated concrete is being removed the tunnel is still fully loaded by the ground and water loading. Finally a design plan (including testing, measuring and optimising) is presented on how a repair concrete mix should be designed to meet substrate qualities and ensure good repair quality. Laboratory tests and in situ tests have already been carried out. The paper ends with conclusions and recommendations for future projects.
This work investigates the predictive capability of several shear strength models for reinforced concrete beams without shear reinforcement. Particular attention is given to the application domain of relatively low reinforced and high depth concrete beams where limited shear test data is available. The predictive capability of the models for this area of interest is analyzed with Bayesian Inference. This probabilistic technique calculates the posterior distributions of uncertain parameters, given a set of measured test data and some prior knowledge.

The predictive capability of each shear strength model is quantified by means of a calculated model uncertainty. Furthermore, the influence of the uncertainty in model parameter values on the calculated model uncertainties is evaluated. Bayesian Inference is also used to estimate the model evidences conditionally on the used data. ... Read more

The use of high strength materials in the design of pedestrian bridges leads to slender structures with decreased mass and low stiffness. The resulting low Eigen frequency makes the bridge more susceptible to human induced vibrations. As a consequence, user comfort may decrease significantly. In some designs it has been found that the geometry has been adapted to fulfil user comfort requirements (e.g. increased height, more mass, tuned mass damping), which has a negative effect on costs and use of resources but which is unnecessary from the point of view of ultimate limit states.

Today’s codes and backgrounds do not provide extensive knowledge of the vibration source and the effect of vibrations on human comfort, nor on dynamic analyses as common design philosophy for pedestrian bridges. The city of Rotterdam has currently built some very slender pedestrian bridges not only by use of concrete material but also fiber reinforced composites. Measurements have been carried out on site and in the factory with varying bridge support conditions (e.g. clamped, simply supported). The measurement devices are low-cost widely available cell phones and movie cameras. The measurement data gives results for accelerations, speeds and displacements. Test sets were created for heel tests, moving human impulses and intentional Eigen frequency excitation. Besides that the human awareness has been recorded. The data has been evaluated by use of advanced dynamic analyses and compared with findings in codes and literature. The comparison of dynamic behavior between concrete and fiber reinforced composites is very educative. The newly developed knowledge has been applied to the design of a new UHPC pedestrian bridge. This paper shows the interesting results of the measurements, analyses, modelling and comparison with the codes and how it affects the design of a UHPC pedestrian bridge. Conclusions and recommendations will be presented. ... Read more

During inspections of several immersed tunnels in the Netherlands, damage of immersion joints has been observed. In some cases the Gina seal has moved inwards from its original location, and in other cases a permanent elongation of the entire tunnel structure has been measured. For both cases it has been hypothesised that a seasonal expansion and contraction of the tunnel elements allows sand to enter the joint gap between elements during winter, where it is compacted during summer, leading to an increasing amount of sand in the joint gap over the years. In order to study this mechanism and assess its impact, a 1:3 scale model joint gap has been designed and constructed. This setup can simulate expansion and contraction cycles of the joint and measure stresses in the joint gap and deformations of the Gina seal. First test results are presented here and show that compaction of the sand entering the joint gap indeed occurs and leads to the observed large inwards
deformations of the Gina seals. ... Read more

In een promotieonderzoek aan de TU Delft naar het spatgedrag van beton onder brand is een EEMmodel afgeleid dat zowel poriedrukken als thermische spanningen beschrijft. Dankzij deze gekoppelde benadering is dit model een waardevolle aanvulling op de huidige praktijk van brandveilig ontwerpen van tunnels. ... Read more

In the coming years numerous existing traffic bridges in cities are subject to re-evaluation. In this paper a new probabilistic traffic load model for short-span bridges is proposed. As an example, site-specific weigh-in-motion data from Rotterdam, the Netherlands, is included in the model. The method proposed in this paper allows for a very efficient computation and at the same time takes into account the stochastics in axle loads and distances. For a simply supported 6 m single lane bridge the probabilistic load model provides a design load effect that is slightly lower than currently prescribed EN 1991-2 and the Dutch Guidelines for existing structures NEN 8700 and NEN 8701. This indicates that there is possible potential for a small reduction of the traffic load for short-span city bridges compared to the current standards. However, given the questionable quality of recorded measurements, a more extensive measurement campaign using WIM measurements is needed to get an adequate quantification of the traffic load parameters for city traffic conditions. ... Read more