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Abstract

Ultra-high-performance fibre-reinforced concrete (UHPFRC) represents an emerging category of cementitious material with notable characteristics. It showcases exceptional durability and long-term stability, alongside impressive compressive and tensile strength attributes, outperforming traditional concrete. The incorporation of high-strength steel fibres into the mixture serves to enhance the mechanical characteristics of this unique ultra-high-performance concrete. In fact, UHPFRC can achieve compressive strengths exceeding 150 MPa, setting it apart as a superior choice when compared to various other forms of reinforced and fibre-reinforced concretes. Several factors assist this material to gaining this relatively high compressive and tensile strength. One of the factors that could influence its mechanical behaviour is fibre content percentage.
This study aimed to investigates through experimental studies to investigate the mechanical behaviour of UHPFRC 2% and 4% fibre content samples in both tension and compression and then simulate them in FEA software. Compression test was performed on cubes with 50mm*50mm*50mm dimension while tensile test ran on Dog-bone shaped specimen after 14th day of casting the concrete. Also, a four-point bending test (4BP) was conducted on a beam of 50mm*50mm*200mm in both samples to identify the stress–strain curve and post peak behaviour of beam and then the graph was compared with the LUSAS program to verify the validity.
The experimental results reveal substantial improvements in the mechanical properties of Ultra-High-Performance Fibre-Reinforced Concrete (UHPFRC) with varying steel fibre content. In the compressive test, the inclusion of steel fibres had a pronounced effect. The 4% fibre content sample exhibited a remarkable increase in compressive strength, reaching 148 MPa, compared to 122 MPa for the 2% fibre content sample. This 26 MPa difference underscores the significant enhancement in compressive strength with a mere 2% increase in fibre content. Moving to the direct tensile test, the influence of steel fibres becomes more pronounced, particularly in the fibre activation stage. The 4% fibre content sample demonstrated a significantly higher tensile strength of 9 MPa, compared to 6 MPa for the 2% fibre content sample. This 3 MPa increase highlights the substantial impact of higher fibre content on tensile strength. Regarding the elastic modulus, the 4% fibre content sample displayed a slightly higher modulus of 47 GPa, compared to the 44 GPa of the 2% fibre content sample. While this difference is modest, it signifies increased stiffness in the material with higher fibre content. Furthermore, the fracture energy measurements are indicative of the material's toughness and energy-absorbing capabilities. The 4% fibre content sample exhibited a notably higher fracture energy of 38 KJ/m^2 compared to 27 KJ/m^2 for the 2% fibre content sample. This demonstrates that the higher fibre content enhances the material's ability to absorb energy before failure, reflecting improved toughness and ductility.
Future research should focus on optimizing fibre content in UHPFRC to meet specific application requirements while considering factors such as strength, cost-effectiveness, and workability. Addressing the brittleness of UHPFRC under compression is crucial, and efforts to enhance ductility without compromising tensile strength should be explored. Additionally, investigating the environmental sustainability of UHPFRC production and its life cycle analysis is essential to reduce the carbon footprint without sacrificing mechanical properties

Course: Civil Engineering - MSc - C0618

Date Deposited: 2023-11-07

URI/permalink: https://library.port.ac.uk/dissert/dis14265.html