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. ... Read more

Existing reinforced concrete (RC) structures can be strengthened using Strain Hardening Cementitious Composites (SHCC). The ability of SHCC in exhibiting a ductile response under tensile load due to strain­-hardening after crack initiation makes it a viable material to be used in, both, construction and retrofitting of concrete structures. The main objective of this research is to study the shear behaviour of SHCC-strengthened RC beams using NLFEA. The shear behaviour of benchmark RC beams is analysed first. The analysis of the selected RC beams analysed using Damage-based shear retention function results in accurate predictions of peak load if a fine mesh size resulting in 30 or more elements in the height of the beam is used. However, the failure type is predicted inaccurately for both coarse and fine mesh sizes due to lack of consideration for aggregate interlock in Damage-based shear retention function. The analysis of the selected RC beams using Al-Mahaidi shear retention function results in accurate predictions of peak load if a coarse mesh size resulting in 20 elements in the height of the beam is used. The failure type is also predicted accurately using Al-Mahaidi shear retention function with the stated mesh size. The consideration for aggregate interlock implicitly in Al-Mahaidi shear retention function in the form of shear retention factor allows for accurate prediction of both peak load and failure type. After analysing the shear behaviour of RC beams, the shear behaviour of a reinforced SHCC beam is analysed using Al-Mahaidi shear retention function since it can predict both failure load and failure type accurately for RC beams. In comparison with experiment, the peak load for the reinforced SHCC beam is underestimated and the failure type is also incorrectly modelled. Use of embedded reinforcement results in excessive cracking along the reinforcement, causing convergence issues at a load lower than the experimental peak load. Such excessive cracking is not observed in RC beams since cracks more localized in concrete as compared to SHCC, which exhibits multi-cracking behaviour. Therefore, the shear behaviour of selected reinforced SHCC beam using Al-Mahaidi shear retention function is not accurately modelled. After the analysis of shear behaviour of concrete and SHCC separately, their behaviour is studied in the form of SHCC-RC hybrid beams. The solution strategy consisting of Al-Mahaidi shear retention function is used, and different types of hybrid interface are modelled. The results show that peak load and failure type are accurately predicted when a numerically perfect bond is modelled at hybrid interface for hybrid beams exhibiting no debonding during experimentation. This is in case of a mesh size resulting in 20 elements in the height of beam used. The peak load and failure type, however, are inaccurately predicted when delamination is modelled at the hybrid interface for hybrid beams failing due to delamination during experimentation, irrespective of the mesh size considered. This is due to the inability of the Coulomb friction interface model in recognising significant delamination at the hybrid interface as a reason for the failure of the hybrid beam. ... Read more