Mechanical Behaviour of Eco-Efficient Ultra-High Performance Fibre Reinforced Concrete (E-UHPFRC) and Design of E-UHPFRC Screw Piles

Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) is a novel development in concrete materials that can lead to novel applications due to its excellent strength and durability potential. However, the widespread use of UHPFRC is currently limited due to its high initial cost and high carbon footprint of the cement and steel fibre constituents as well as the lack of recognised design models. The aim of this research is to develop an Eco-Efficient Ultra-High Performance Fibre Reinforced Concrete (E-UHPFRC) by utilising alternative binders (e.g. GGBS), Recycled Tyre Steel Fibres (RTSF) and Recycled Tyre Steel Cords (RTSC). This is achieved through experimental and numerical studies, as well as the development of analytical models to aid the development of design guidelines. An extensive series of tests is carried out on twelve (12) UHPFRC mixes containing either RTSC or RTSF, or blends of the two in various ratios for total fibre volumes of 2, 3 and 4%. The fresh properties of the designed E-UHPFRC mixes are examined, followed by a comprehensive analysis of the mechanical behaviour of the hardened concrete in: flexure, compression and shear. The results show that 11 of the examined mixes can offer the desired mechanical properties and meet the requirements of workability and strength to be defined as UHPFRC. The performance of the mixes containing RTSC is comparable to what is reported in the literature for mixes containing Manufactured Steel Fibres. Design models are proposed to predict the flexural and shear strengths of E-UHPFRC mixes. The complementary material efficiency study of the mixes shows that use of RTSF and RTSC in UHPFRC provides significant cost and environmental benefits. The application of the newly developed E-UHPFRC in the manufacturing of screw piles is proposed as a quick and more sustainable means of providing foundations for light weight structures, which given the limitations of ordinary concrete is currently only feasible with costlier steel piles. A detailed design guideline for E-UHPFRC screw piles is provided for two possible geometries.