Strain Hardening UHPFRC

Abstract

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.