Due to the transition towards a circular economy, sustainable design strategies are growing in importance. An example of such a strategy is IFD: Industrial, Flexible and Demountable design. This design strategy has been developed recently and focuses on modular designs that can be changed in shape and whose components can be demounted and reused. This thesis aims to investigate how the principles of IFD can be applied in the design of a sustainable superstructure for an overpass. The goal is to assess which structural system is best for use in a sustainable IFD overpass and to determine how the overpass can be converted into a modular overpass by focusing on connections and module dimensions. To demonstrate the potential of the IFD design, the sustainability benefits of the overpass are evaluated.

Through a review of literature on IFD and similar design strategies, guidelines were formulated that are relevant for overpasses. Based on the guidelines, designs for three structural systems were developed using a preliminary design approach. These designs were assessed on their environmental impact and compliance with IFD principles, using an Environmental Cost Indicator and Multi-Criteria Assessment respectively. Due to its good behaviour on both aspects, the Composite alternative was found to be the best.
Then, a literature study on the connections was performed to investigate the different options. The number of relevant shear connectors was reduced to four by considering the tolerances for assembly and the protrusion of connectors from the main elements of the structure. A finite-element model was made to evaluate the effects of the four different shear connectors on the structural behaviour. To be able to use the connectors in the model, an elastic limit was imposed to ensure demountability and reusability; small adjustments were made on the reported behaviour of the connectors using a parametric study. From the four remaining connectors, the Embedded Coupler Device connection without injected resin was found to be the most favourable, due to it requiring the lowest number of connectors in the serviceability limit state. For the steel girder connection, a shear-loaded bolted connection was proposed; shear keys were found to be a good solution for the deck connection. Moreover, module dimensions were determined based on sustainability considerations and IFD principles, leading to the final design.

The proposed design shows that IFD principles can successfully be applied to come to a design for an overpass. The use of a small selection of modular elements and demountable connections creates a flexible design, which complies with all the IFD principles. By application of a structural system with a low environmental impact, sustainability of the design is also accounted for.

The IFD design is competitive in situations where the overpass is extended or when it is disassembled and reassembled, since for these scenarios it ends up with the lowest overall environmental impact. This leads to the recommendation to use IFD design in situations where flexibility and reusability are advantageous.

Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) is a promising material for different applications such as bridge deck strengthening due to its improved strength and durability properties. Especially the tensile strength and ductility is heavily dependent on the distribution and orientation of the steel fibers within the element. This fiber behaviour can be unpredictable, causing a large scatter in material properties. This scatter is inconvenient for predicting the material properties. The novelty of the material is the main reason that UHPFRC is not included in the Eurocode. Certain countries like Switzerland and France have developed their own UHPFRC norms.

In order to increase the knowledge and understanding of the fiber distribution and orientation, a non-destructive testing method has been developed. Two types of magnetic probes have been developed: the C-shaped ferrite probe and the single ferrite probe. These probes are based on other probes developed at the University of Milan and Porto. The C-shaped ferrite probe is most suitable for measuring the total fiber content and fiber orientation. The single ferrite probe is able to take fiber content measurements closer to the edge making it more efficient for fiber distribution measurements. This can result in a reliable prediction of the peak-tensile strength. The addition of UHPFRC specific design rules and this non-destructive testing method will make UHPFRC and its applications more attractive.

In this research, 27 different UHPFRC plates were cast with the same dimensions of 10x200x200 mm3. These plates were cast horizontally or vertically with either 1%, 2%, 3% or 4% fiber content. Seven plates were vibrated after casting in order to analyse the influence of vibration. Each fiber content resulted in a relatively homogeneous fiber distribution and random fiber orientation. Horizontal casting of UHPFRC plates usually result in a more homogeneous fiber distribution and more random fiber orientation compared to vertically cast plates. The best distribution and orientation was reached when the elements were not vibrated at all. Vibration can result in severe fiber segregation along the element height and vertical orientation of the fibers. These conclusions hold for longer UHPFRC elements where the element height and the element thickness remains constant.

One of the main pitfalls in this research is the small thickness of the plates. The length of the fibers exceeds the plate thickness, which makes casting very difficult. During casting, fibers will get stuck at the top of the mould, which also influences the results. Moreover, it is important to continuously keep mixing the UHPFRC mixture in order to equally divide the fibers over all plates and to use a mixture that is castable yet not too flowable. High workability mixtures are more prone to fiber segregation.

The pressing challenges of climate change and the increasing surplus of concrete waste is making it increasingly important to fully recycle concrete in a sustainable way. Since cement is by far the component that contributes most to the environmental footprint of concrete, it is of great importance to investigate the potential of upcycling secondary cementitious materials. Modern recycling techniques such as the Smart Liberator make it possible to efficiently separate the coarse and fine fractions in concrete waste. It also makes is possible to produce a fine powder fraction that shows potential to replace primary cement, which helps to mitigate CO2 emissions. This study explores to which extent recycled concrete fines (RCF), obtained from advanced recycling technologies such as the Smart Liberator, can replace ordinary Portland cement (OPC) in mortar mixtures. It is assumed that the RCF consist mostly of cementitious materials. The aim of this study is to assess the performance of RCF when replacing OPC in different mortar mixtures. Several treatment methods were applied to enhance the reactivity of the RCF.
To be able to assess the performance of the RCF as replacement of ordinary Portland cement at mortar level, three reference mortar mixtures, made from CEM I, CEM II/B-V and CEM III/B, were prepared for comparison. Portland cement with strength class 52.5 R was used in for preparation of the reference mixtures. The used RCF were the 0-63 μm fraction obtained from the Smart Liberator. It is expected that the RCF are from CEM III origin based on documentation from the company Rutte Groep. However, due to limited stock, some of the mortar mixtures had to be prepared with a different type of RCF, consisting of RCF with a CEM I and CEM III origin that were mixed in a 1:1 ratio. The OPC in the reference mixtures was replaced with RCF at 50%, 75% and 100% ratios.
Grinding, carbonation, conventional heating and flash calcination were applied as treatments to enhance the reactivity of the RCF. Thermogravimetric analyses were used to assess the effects of the treatments on the decomposition of the compounds of the RCF. Mortar prisms made with treated and untreated RCF were tested for flexural and compressive strength after 28 days of curing, and their performance was compared to the reference mortars.
The results showed that the untreated RCF performed best when used in combination with blast furnace slag. This combination was the only one in which a 100% replacement resulted in measurable strengths and the measured strengths at the other replacement ratios were the highest, reaching up to 70% of the compressive strength of the reference prisms at 50% replacement. This indicates that the RCF are a suitable activator for blast furnace slag.
The effects of the treatments differed in the different mixtures and also varied across the replacement ratios. Grinding of the RCF improved their performance at the 50% and 75% replacement ratios in the CEM I variant, while their performance in the CEM II and CEM III variants was similar to or lower than the untreated RCF. The same conclusions are drawn from the results after carbonation. Heating of the RCF up to 900 °C for 30 minutes in a regular chamber furnace resulted in better results for the CEM I variants at all replacement ratios, while no significant improvements were measured for the CEM II variants. For the CEM III variants, only the 75% replacement ratio had a significant improvement. Lastly, flash calcination resulted in the most significant improvements for the CEM I and CEM II variants at all replacement ratios. For the CEM III variants, flash calcination significantly improved the strengths at the 100% and 75% replacement ratio, but not at the 50% replacement ratio. Since this does not align with each other, it is necessary to reconfirm these results.
As a conclusion, this study demonstrated that untreated RCF shows potential to BFS, while flash calcination is the most promising treatment for boosting RCF reactivity across most mixtures. Conventional heating also showed potential, especially for CEM I. However, grinding and carbonation had mixed results, with limited benefits for BFS combinations due to carbonation effects. Future research should confirm these findings and explore ways to optimize the treatment methods.

Despite stringent safety standards, concrete is prone to various forms of deterioration over time, and the occurrence of cracks is not uncommon. Therefore, the detection and monitoring of deformations in concrete are essential to mitigate the risks associated with structural failure. Implementing a real-time Structural Health Monitoring (SHM) system can play a crucial role in identifying early signs of damage, such as corrosion in reinforcement, thus enhancing the efficiency of maintenance and repair interventions and ultimately prolonging the lifespan of the structure. The data collected through SHM techniques also contribute to the validation of design practices employed in the structure and further advancements in the field. In a broader context, the integration of SHM supports the development of sustainable infrastructure, ensuring the longevity and safety of concrete structures.
Along with visual inspection, SHM techniques are deployed to conduct a thorough analysis of structural behaviour. However, many traditional methods involve tedious installation processes. Several techniques utilize a wide spectrum of radiations, such as ultraviolet pulses, infrared radiations, and X-rays, and rely on sophisticated equipment that demands trained personnel for data analysis. In
this study, a novel approach is proposed for SHM by utilizing magnetic fields for
crack monitoring. Currently, this technique is used to monitor cracks in steel structures.
The aim of this work is to explore and adapt this idea to integrate the sensor system into the field of structural health monitoring for concrete structures. The scientific contributions made in this study include the investigation of the effects of crack propagation on the magnetic field, the modeling of the behavior using analytical and numerical methods, the construction of a prototype, the validation of the structural health monitoring technique, and the demonstration of the feasibility of this method.

This thesis explores a suitable method and appropriate input to determine the failure probability of thermal shrinkage cracking in a steel fibre-reinforced underwater concrete floor by examining the factors that influence this failure probability.

An underwater concrete (UWC) floor is a common construction type in the Netherlands that is often applied to create building pits under the groundwater table. Usually, these (generally unreinforced) UWC floors only function as a watertight bottom layer of the building pit with only a temporary sealing function. Water tightness and crack prevention are very important aspects of this type of construction. A permanent reinforced structural top floor is frequently used on top of the temporary UWC floor to make a completely watertight construction, which is not the most sustainable and cost-efficient solution. Advances in concrete technology such as fibre-reinforced concrete have made it possible to integrate both the UWC and structural top floor or even use the UWC floor as the permanent structural floor. In these cases, the UWC floor should already function as a watertight barrier and controlling leakage by limiting the crack width becomes even more important. The addition of fibres to concrete may prevent through crack formation in the UWC slab and the possible consequent leakage. An important cause of cracking in UWC floors is thermal shrinkage during the cooling phase of the hardening reaction shortly after casting the UWC floor.

Currently, there are no guidelines for the construction of fibre-reinforced concrete (FRC) floors and the prevention or limitation of thermal shrinkage cracking. A CROW-committee "Steel fibre reinforced underwater concrete (SFRUWC) floor as permanent structural floor" has been formed. This committee aims to set up a design recommendation and part of that is addressing the thermal shrinkage cracking problem. There is a lot of uncertainty in geometry, material properties and boundary conditions associated with SFRUWC floor design and construction. Because of this, there is a need for a probabilistic approach to investigate the influence of these uncertainties and tolerances on crack formation in SFRUWC floors during the hardening phase. This research aims to determine a suitable probabilistic method to investigate the failure probability of SFRUWC floors and the parameters that influence this.

In order to achieve this, a finite element model was developed that determines the shrinkage cracking behaviour in a part of a UWC floor in a building pit. Before this model could be developed, all the necessary input parameters and design equations were collected from literature and existing guidelines. To set up a model, first the behaviour of UWC floors was studied, followed by the development of a finite element model that includes the hardening behaviour and strength development of young concrete. An important aspect of this finite element model is the use of random fields to introduce spatial variation in the strength properties of the SFRUWC floor, which is a first step to include stochastic variation in the model for the probabilistic analysis. A probabilistic sensitivity study was performed with the finite element model by calculating multiple samples for each set of input parameters. Separate input parameters were varied and the influence on the results was investigated. The parameters that were considered, include the random field properties, material properties and thermal properties. Finally, a full Monte Carlo analysis was performed to give a proof of concept on how to calculate the failure probability regarding thermal shrinkage cracking in SFRUWC floors.

In order to prevent leaking cracks and satisfy the crack width criterion, the tension-hardening behaviour of FRC has to be utilised. Tension hardening behaviour will lead to a distributed cracking pattern, consisting of multiple small cracks which can satisfy the crack width criterion as opposed to a single large separation crack which does not satisfy the maximum allowable crack width criterion. It was found that the tensile behaviour of FRC and the use of random fields to model this tensile behaviour were major parameters that influenced the crack width and the occurrence of a distributed crack pattern. An important parameter is the standard deviation of the random field, which influences the difference between the maximum and minimum tensile strength in different locations in the slab. Looking at material behaviour, the main conclusion was that the introduction of a small hardening branch in the tensile material model was the governing influence factor. Both the standard deviation of the random field and the introduction of a hardening branch in the tensile behaviour affect the ratio between the tensile strength of the ordinary concrete and the residual tensile strength of the fibre-reinforced concrete. These two factors in combination with the model that was used, turned out to be dominating the results in such a way that the other input parameters only had a relatively small influence on the crack widths.

To determine maximum crack widths in SFRUWC floor it is essential to consider multiple samples with different random fields to find out if only a distributed crack pattern is possible or whether also single localised cracks can occur. The possibility of both these results being able to occur, leads to a large possible error in the maximum crack width. The results of this thesis have shown that the random field parameters remain uncertain and experimental research is needed to determine these correctly. Until then, it is important to investigate how significantly these parameters influence the results. It is recommended to extend this research by improving the model by making it more realistic and finding out if these two factors are still the dominating input parameters.

Conventional construction techniques are unsustainable and expensive due to longer construction time, labour-intensive work, and the use of formwork. 3D concrete printing is seen as a potential substitute to overcome these issues. However, extrusion-based 3D printed structures exhibit a weak interlayer bond, and researchers have tried to address this problem through techniques such as using cement mortar layers or vertical steel reinforcement between the layers. This study aims to address the problem of the weak interlayer bond by implementing the phenomenon of 'topological interlocking' to increase the mechanical interlocking between the layers. The study performed scale model printing in the form of mould-casting and caulk-gun extrusion to produce specimens to analyze the effect of grooving on interlayer bond strength. The results were counterintuitive to the previously observed research, and the study recommends avoiding issues that may interfere in further similar studies.

Alkali-activated material (AAM) is one of the most attractive alternatives to ordinary Portland cement (OPC). Recently, more and more research interests are devoted to durability performance. In cold areas, freeze-thaw resistance is a crucial durability factor for concrete. However, the understanding of the freeze-thaw resistance of AAMs is minimal. Accordingly, the subject of this thesis is drawn forth. The main aim of this study was to investigate the effects and mechanisms of using admixtures (SAP and AEA) to improve the freeze-thaw resistance of alkali-activated slag (AAS).
Regarding the general properties, such as workability and mechanical properties, it was found that the influence of adding SAP or AEA is acceptable. Then, the air-void systems created by SAP and AEA were reconstructed and characterized by the micro-CT scan. It was found that both SAP and AEA successfully entrained air voids into AASM, while the characteristics of the resultant air-void system were quite different. Further analysis on the surface condition of AASM undergoing 28-day sealed curing or preconditioning procedures in the CDF test, and the ASTM C672 test revealed that AASM shows a considerable surface microcracking potential. Samples sealed for 28 days showed a considerable extent of microcracking due to autogenous shrinkage. Samples that underwent 14-day drying after 7/14 days’ curing showed significant microcracking due to autogenous shrinkage and drying shrinkage. With the addition of SAP, the cracking caused by autogenous shrinkage was minimized, but the cracking caused by drying was only slightly reduced. With the addition of AEA, there was only a minor improvement in surface integrity.
The freeze-thaw resistance of AASM with or without the addition of SAP or AEA was investigated in the form of surface scaling damage by a modified CDF test. Plain AASM showed poor surface scaling resistance mainly attributed to the pre-existing surface microcracking. The addition of SAP and AEA successfully improved the surface scaling resistance of AASM. The improvement was more significant by adding SAP due to the effect of improving surface integrity. Based on the SAP mixtures, a good correlation was found between the SAP air-void system and the resultant surface scaling resistance. The final cumulative surface scaling generally decreased with higher entrained air content, denser air voids distribution, and smaller air voids size. A preliminary logarithm model was developed for the relationship between the reduction in surface scaling and the equivalent water/binder ratio and the air-void system. Finally, upscaling tests on the concrete scale also found that the addition of SAP improved the surface scaling resistance of AASC.
Overall, in this study, the freeze-thaw resistance of AAS was successfully improved by the SAP and AEA. The effects of adding SAP/AEA and the related factors on the selected properties of AASM were revealed. The mechanisms behind these observations were also understood and generated a series of further research possibilities. It is hoped that these findings and observations can give some guidance to the industrial applications of AAS and some inspiration to the scientific community.