Combining the high strength of Ultra High Performance Concrete (UHPC) and the strain capacity of Strain Hardening Cementitious Composites (SHCC), Strain Hardening Ultra High Performance Fibre Reinforced Concrete (SH­UHPFRC) could be a promising material for the application of strengthening RC elements. This research describes the development of an SH­UHPFRC mixture, using Ultra High Molecular Weight Polyethylene (UHMWPE) fibres. The benefits of using this material as a strengthening material were analysed using a numerical model and the environmental impact of the SH­UHPFRC was evaluated. During the material development the effects of different material types and the applied ratios were considered. The flowability of the mixture, compressive strength and tensile response were tested to determine the mixture design. The effect of different cement types and amount of superplasticizer played a significant role in the increasing of the workability of the mixture. The effect of using UHMWPE fibres over steel fibres was investigated, as well as the effect the amount of UHMWPE fibres had on different properties. The material properties of the material research were implemented in a numerical model using ATENA software, representing a strengthened reinforced concrete (RC) beam subjected to a three­point bending test. In addition to the modelling of a RC beam strengthened with SH­UHPFRC, a parameter study was executed to determine the effect of increased strain capacity in the strengthening material. This was done by adjusting the tensile stress­strain relation in the material model. Three levels of strain were tested and the capacity and cracking behaviour of the strengthened beam were compared. The environmental impact was evaluated using the CUR Groen Beton calculation tool. The mixture design of SH­UHPFRC was compared to that of relevant concrete types. The environmental impact per volume is high for SH­UHPFRC, but the mechanical properties are superior which leads to a lower required volume to achieve similar mechanical results. Comparing a strengthened beam to a RC beam demonstrated the contribution of SH­UHPFRC, proving that, including the environmental impact, SH­UHPFRC could outperform NC as a strengthening material. The developed mixture granted a compressive strength of nearly 120 MPa, a tensile strength of 8.9 MPa and a tensile strain capacity over 2%. The use of this material for the strengthening of a RC beam lead to an increase in shear capacity of 78%, following from the numerical model. Evaluating the environmental impact, the use of SH­UHPFRC overcomes the use of NC to strengthen a shear­deficient beam. It is recommended to conduct further research on specific aspects of the material optimization of SH­UHPFRC. For the numerical modal the resemblance to practice could be improved and the range of parameters expanded. The environmental impact of a beam strengthened with SH­UHPFRC proved to be lower compared to an RC beam with equal shear capacity, showing the benefit of this superior material. An analysis of the full life cycle of an element strengthened with SH­UHPFRC could be done to get a better estimation of the environmental effect of using this material for strengthening purposes over NC.

The growing need for strengthening of concrete structures to improve their structural performance challenges structural engineers to come up with strengthening techniques that is most suitable and effective for a structural system in its deteriorated state. Although there are quite a few techniques in practice for strengthening of concrete structures -reinforced or prestressed, various factors limit their efficiency and performance. Use of novel concrete-based materials such as Ultra High Performance Fibre Reinforced Composite (UHPFRC) can lead to an effective strengthening system due to the exceptional material properties of UHPFRC. In particular, the strain hardening behavior of UHPFRC in tension and its excellent durability. Out of the two main mechanisms of failure in concrete elements namely flexure failure and shear failure, shear failure is the most critical due to the abrupt nature of its mechanisms that leads to complete collapse of the structures with no sign of warning. This makes shear strengthening of prestressed concrete structures, that typically form the supporting elements in large infrastructural units such as bridges, a very essential course of action. To investigate the effectiveness of using UHPFRC in shear strengthening of prestressed concrete elements, the post-tensioned T girders of Helperzoom bridge, Groningen, Netherlands are chosen as reference beams which are strengthened with UHPFRC. The reference beams are subjected to a 3-point bending test to determine their failure mechanism and structural capacity. The reference beam is modelled, and tests are simulated by finite element analysis using ATENA. Since the simulated beam failure in shear compression rather than shear tension by localization of the shear tension crack. In order to understand this behavior and the failure mechanism and to check if the results from the simulations are reasonable, a detailed analysis is performed. The influence of shear reinforcement and prestressing, active in the critical shear region, on the shear capacity and the final failure mode are investigated. The results from the numerical analysis are compared to the results from experimental shear tests performed on existing post-tensioned girders which exhibit a similar mode of failure as observed in the reference T beams. The shear capacity of the reference T beam is also calculated from the Flexural Shear Crack Model proposed by Huber et.al and it is seen that the shear capacity from the numerical analysis from ATENA is in close match to that obtained from the analytical model. The contribution of the arching effect to the shear capacity calculated from the model is between 77% and 87% for the beams tested in this research and the contribution is between 28% and 58% in the beams tested in the experiment. In the last step, the effectiveness of strengthening the reference beam with UHPFRC is determined. The results show that the effect of strengthening with UHPFRC is maximum in the reference beam without stirrups and prestressing both in terms of shear capacity and ductility.

Within the Dutch infrastructure there is the challenge of having to replace or strengthen a large number of existing structures within the upcoming years. This challenge also provides the opportunity to develop new concepts. The promising concept described in this report involves the application of UHPC to redesign the decks of existing concrete bridges in combination with the reuse of existing foundations. The Twentekanaal was selected as the topic of the project, because it comprises many bridges of which various have similar characteristics and were built in the same period. Not all bridges could be considered in-depth simultaneously. Therefore, one representative bridge was selected, the Eefdesebrug, after which the results for this bridge would be generalised onto all other relevant bridges across the canal. To determine the full potential of the project, it was investigated up to what extent the results for the Eefdesebrug could be projected onto other bridges across the canal. An inventory was set up containing all bridges. These were characterised and compared based on bridge category, year of construction and dimensions. This resulted in a total of twelve bridges with similar characteristics, to which the results of the redesign of the Eefdesebrug could potentially be generalised to. After the potential of the project had been determined, the focus was placed on the redesign of the Eefdesebrug, which was carried out following a stepwise approach. After each design phase, the global goal of the project was reflected by means of a weight comparison with the existing bridge. To limit the scope of the project, the new deck should be constructed using prefabricated beams. The design would be based on the Eurocode, supplemented by the AFGC-SETRA 2013 guideline. The final design resulted in a 32% reduction of the self-weight compared to the existing bridge. This design comprises pretensioned box beams with a slenderness of 36. A global assessment of the existing foundation was subsequently carried out. A criterion for reuse of the existing foundation was formulated based on the vertical loads due to permanent and vertical variable actions in the new and existing situation. This criterion was satisfied, with which the possibility of reuse of the foundation of the Eefdesebrug had been demonstrated. It was subsequently investigated what may be expected if the solution for the Eefdesebrug would be applied onto the group of twelve aforementioned bridges. Using the results for the Eefdesebrug it was possible to estimate the dimensions for the other bridges and to consider the vertical forces acting upon the foundations. It was shown that a similar solution can be applied to all twelve bridges across the Twentekanaal with characteristics similar to those of the Eefdesebrug.

First of all, an overview was created of different problems that can occur by the construction of cast-in-situ concrete piles, discussing the mechanisms that cause these problems. From the overview it was concluded that little information is present about the exact cause of excessive bleeding. Two possible causes were identified, excess pore water pressure in the surrounding soil caused by the pile installation and concrete stability, these are further researched. Comprehensive measurement data of the hydraulic head in an intermediate confined sand layer, during the installation of displacement piles, showed a consistent trend. During the descending phase a large increase in the hydraulic head was measured which can be described by volume displacement in the sand layer. In addition, a cumulative effect in the hydraulic head was found at the start of withdrawal of the temporary casing as the excess pore water pressure, resulting from the volume displacement, was not fully dissipated. During withdrawal, two additional pore water pressure increments can be distinguished. The direct increase starting from the onset of withdrawal has been interpreted as being caused by the reaction force of the machine on the ground resulting from the pull up force on the casing necessary to get the casing in motion. Unfortunately, no conclusive cause was found for the second increase in hydraulic head regarding the processes that take place during withdrawal. This calls for further research as the hydraulic head after withdrawal will influence the interaction between the fresh concrete and the surrounding soil. Then a literature study on (excessive) bleeding in cement based materials was performed to assess how concrete stability influences the initiation of bleeding. The literature study showed that in order to capture the full bleeding phenomenon three processes can be distinguished. Sedimentation, Consolidation and Cement Hydration.