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Title: Mechanical properties of blended steel fibre reinforced concrete using manufactured and recycled fibres from tyres
Author: Hu, Hang
ISNI:       0000 0004 7233 9011
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2018
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The construction industry is capable of mitigating the global environmental problems through the utilisation of waste materials in concrete. The use of sorted steel fibres recycled from end-of-life tyres (RTSF) and steel cords recycled from un-vulcanised rubber belt off-cuts (RTSC), as a viable alternative to manufactured steel fibres (MSF) in concrete applications, may lead to significant environmental benefits and enhanced structural performance. This study aims to understand the mechanical (compressive and flexural) behaviour of steel fibre reinforced concrete (SFRC) using blended MSF and RTSF, as well as recycled-fibre blends (RTSC and RTSF), leading to design-oriented models for blended SFRC at total dosages (=45 kgm3) typical for concrete slab applications such as slabs-on-grade and suspended slabs. An extensive experimental programme including compressive, 3-point bending and round panel tests on SFRC specimens was undertaken as part of this study, along with direct tensile and pull-out tests on RTSC. About 500 tests were conducted and 18 SFRC mixes examined. For SFRC using MSF and RTSF, a strong correlation is found in the flexural behaviour of the SFRC prism and round panel specimens, and conversion equations are proposed. It is found that the mechanical properties of blended mixes using RTSF vary depending on dosages, but are comparable with those of MSF-only mixes at the same fibre dosage. For blended mixes containing 10 kg/m3 of RTSF, a positive synergetic effect is obtained, with RTSF making a positive contribution at the early stages of cracking. RTSC possess a high tensile strength (>2600 MPa) and exhibit a good bond to concrete matrix. Through pull-out tests, the critical embedded length of RTSC is found to be in the range of 25-40 mm. RTSC are found to be extremely well mobilised at larger crack widths and the post-cracking strength of recycled-fibre mixes (RTSC on their own or blended with RTSF) is significantly higher (more than double) than MSF-only mixes at the same total fibre dosage. In addition, the flexural performance of concrete reinforced with recycled fibre blends improves with increasing amounts of RTSC. Utilising the extensive experimental work, the accuracy of the σ-ε relations proposed by current design guidelines (RILEM TC 162-TDF and Model Code 2010) for SFRC is assessed. These are found to have significant inaccuracies and a simplified trilinear relation is proposed for blended SFRC at low dosages. It is found that the tensile strength of SFRC with RTSF at a low total fibre dosage is only marginally improved by fibre addition, and the post-cracking tensile strengths at different strains can be determined directly from residual flexural tensile strengths (fRi) of prisms. The proposed σ-ε relations can be used directly for the design of slabs-on-grade and other SFRC applications.
Supervisor: Pilakoutas, Kypros ; Guadagnini, Maurizio Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available