In recent years, the area of structural engineering has found new interesting prospects in the theory of waves. The acoustoelastic properties of materials are utilized in a new promising structural health monitoring (SHM) technique. The propagation of ultrasonic waves through stressed elements gives the ability to find invaluable information on the stress-state of the concerned element. This information is then analyzed with the use of Coda Wave Interferometry (CWI). This technique explores the late arrivals of the wave field, which is referred to as the coda. Due to scattering of the waves through heterogeneous elements, this part of the wave field holds additional information compared to the early arrivals, which makes it very suitable for application on concrete elements.
The use of ultrasonic waves with CWI in concrete elements has been studied enthusiastically by engineers due to its promising prospects. Nevertheless, this technique is still developing both in theory and in practice. The majority of previous similar studies have been conducted in laboratory settings, and thus conditions are very controlled. In this study, the monitoring technique is applied in conjunction with Smart Aggregate (SA) to a concrete structure for practical use. The SA sensors are positioned in groups at key location in the first concrete cast of a cast-in-situ prestressed concrete bridge, which entails two bridge spans of approximately 30 meters length. Measurements are done at different phases during the construction of the bridge, when the stress-state at the positions shifts due to change in loading and boundary conditions. The resulting data is analyzed with CWI and subsequently evaluated whether it coincides with expectations. Deviations from these expectations are rationalized or an attempt thereof is made.
The results show significant differences between field measurement results and expectations based on laboratory tests. These differences are explained by the presence of a greater amount of parameters, which influence the data gathered from field measurements. With the appropriate measures, the various factors acting on the structure are isolated and subsequently validated with laboratory data. The most prominent factors affecting the acoustoelastic properties of the structure are established to be time related. These factors involve concrete shrinkage, creep deformation and the concrete hydration process. With laboratory testing the effect of these factors on the wave propagation velocity are determined. By taking into account the additional factors, a strong correlation between changes in the stress-state and changes in the wave propagation velocity is observed when the data is read in an adjusted manner.
With a proper protocol, the use of smart aggregates in combination with CWI could be very valuable in accessing concrete structures on-site in both its construction stage and service stage. As it stands, prerequisite knowledge of the monitored structure is necessary to make use of the full potential of the SHM involving CWI and SA. The demand for prerequisite knowledge of the structure increases as the monitored structure becomes more complex, because it increases the amount of additional endeavors required to properly asses the acquired data. As such, the discussed monitoring technique in its current stage of development generally has low accessibility for practical use. But with further research and more understanding of monitoring method, the discussed SHM technique might be applicable for general use in the near future.

Orthotropic bridges can be modelled using a grillage model and an orthotropic plate model. The grillage model has some benefits (i.e.: shorter calculation time and easier to apply pre-stressing) compared to the orthotropic plate model. However, during the Blankenburgverbinding project Ballast Nedam experienced that the transverse load-spread of the grillage model can be lower compared to the orthotropic plate model. This potentially results into a less economical reinforcement design. The aim of this study is to investigate the differences in transverse load-spread of the grillage and orthotropic plate model and to make a judgement on the practical usability of the grillage model based upon the differences in reinforcement design. To test the hypothesis that the grillage model has less transverse load-spread compared to the orthotropic plate model and to quantify the impact on the reinforcement design, a case study on the bridge decks of the Blankenburgverbinding is carried out. The results of a grillage model are compared to an orthotropic plate model. In order to be able to judge whether to orthotropic plate model describes the correct behaviour of the bridge, this model is verified using a 3D plate model. In total, 3 different single-span, simply supported bridge deck layouts were modelled (straight, curved and curved with a skew angle). The results of the 3D plate model are almost equal to the results of the orthotropic plate model. Both these models show the same transverse load-spread. The grillage model shows less transverse load-spread compared to the orthotropic plate model and the 3D plate model. This difference in load-spread increases with increasing eccentricity of the applied load. The torsional and transverse shear stiffness has the biggest impact on the transverse-load spread. When these stiffnesses are higher, the transverse load-spread increases. Lowering the stiffnesses results into less load-spread. In case of the curved bridge deck, the grillage model results in about 7.3% more reinforcement compared to the orthotropic plate model. For the curved and skewed deck the grillage model results into up to 4.7% more reinforcement compared to the orthotropic plate model. The differences in design bending moments (Wood-Armer moments) are relatively small. Although the theoretical difference in amount of reinforcement is significant, the practical difference in reinforcement design between both models can be small. For example, the structural engineer is limited by the available space, detailing requirements and the available bar diameters. These limitations and rounding differences make that for some bridges it is possible to reduce for example 5% reinforcement and for some bridges such a reduction can be very hard to realise. In that case, the theoretical difference between the amount of reinforcement becomes very small or completely vanishes in practice. Eventually, it depends on the situation whether the benefits of the grillage model outweigh the theoretically less economical reinforcement design. When there are a lot of repetitive bridge decks it can be beneficial to use an orthotropic plate model. In that case, the orthotropic plate model has to be created only once and a small reduction in the amount of reinforcement of one deck can add-up to a significant reduction for the whole project. When there is only one bridge deck to model, or all spans are unique, the benefits of the grillage model most likely outweigh the practical difference in the amount of reinforcement.

Global climate change has been a huge matter of concern today. While there are several factors that contribute to greenhouse gases, adversely affecting the planet, CO2 emission is one of them. It is said that 8% of total carbon dioxide emission is caused due to the production of Ordinary portland cement used for concrete in construction. The construction industry highly relies upon concrete as a major and widely used construction material. Solutions to reduce the production of Portland cement without having to entirely remove concrete as a building material has been an important discussion. A possible solution is to replace the Portland cement in concrete with industrial by-products further activating the binder with alkali activators producing a green concrete called ‘Geopolymer concrete’ (GPC) which would reduce CO2 emission.  The biggest challenge yet is that, designing any structure, a standard validated code/regulation is required and GPC doesn’t have a standard code of practice. All the concretecodes till now are formulated taking the parameters for Ordinary Portland cement concrete. This lack of design models specifically formulated for GPC restricts contractorsand engineers to use GPC in structures. This is why GPC has not gained much acceptance in practice.  This research was done in collaboration with Boskalis. A bridge (KW15-N69) has beenconstructed using geopolymer concrete in North Brabant province of the Netherlands.To make the bridge sustainable and circular, the GPC used contained no cement andaggregates were fully replaced by thermally recycled asphalt aggregates. For design ofthe bridge, Eurocode 2 for concrete structures was used and additionally regulations by Dutch ministry of transport and infrastructure was followed.This research will act asone of the pioneer studies to investigate the overall structural behaviour of geopolymerconcrete beams with respect to standard codes which should help design engineers upto some extent to execute and design structures using GPC in future.   

The Oscillating Water Column (OWC) device is one of many available technologies for generating electricity from water waves. It is a caisson-like structure, which houses a water column in an enclosed chamber with an inlet at the bottom. Waves enter the device, exciting the water column. The trapped air above is forced out through a turbine, generating electricity. The technology is relatively young compared to other sources of renewable energy, such as solar or wind energy. This makes the produced energy expensive, expressed in the Levelised Cost of Energy (LCOE). Integrating devices into breakwaters already resulted in a large reduction of the costs, as they now can be shared. During the design of such devices, main attention is given to the geometrical design. This should be based on local wave conditions to ensure the largest energy production. Having the eigenperiod match with the incident wave period enhances the resonance effect in the chamber. This research explores the potential to reduce the costs of OWC devices integrated in breakwaters through means of structural optimisation. The structural are built quite robust, leaving the thought there is room for improvement. The device in Civitavecchia, Italy was used as a case study. A new method was adopted to investigate the potential. A numerical model was constructed in STAR-CCM+, including both a fluid domain and a solid domain. The two are one-way coupled, from water to structure. The exerted wave pressures are mapped on the structure directly, resulting in a stress state in the OWC structure. Due to the transient nature of the simulations, all results are available through time. It was found, the main walls shaping the OWC device could be built with 35% less material. Variants of the original geometry were tested as well to see how these influence the results. Furthermore, the structural behaviour was investigated. Clear trends were found in position and timing of governing load combinations in the different walls. One of the most important findings was that the governing load case always was in the direction of the transverse width. The walls were found to behave more like beams in this direction. The bending moments could therefore easily be calculated using standard beam equations and the net horizontal pressure on the wall as load. This leads to the beginning of a new simplified design method where the full numerical structural analysis is not required anymore.