Design issues for concrete reinforced with steel fibers, including fibers recovered from used tires

The writers are investigating the use of steel fibers, recovered from used tires (RSF), as concrete reinforcement, aiming at the development of design recommendations. This paper presents part of this research and examines initially an existing design guideline, developed by RILEM for steel fiber-reinforced concrete (SFRC), in order to assess the suitability of the guideline for the flexural design of concrete reinforced with RSF (RSFRC). This examination indicates that, although the RILEM guideline is in general suitable for the flexural design of RSFRC, there are some fundamental issues related to the evaluation of the tensile stress-strain behavior of SFRC that affect the accuracy of the guideline. Thus, based on this conclusion, a new approach is outlined for the evaluation of the tensile stress - strain behavior of SFRC and models are derived for different types of RSF and industrially produced fibers. These models are applied to the flexural design of concrete reinforced with RSF (RSFRC) and results are compared with those obtained by using the RILEM tensile stress-strain models. It is concluded that the model proposed in this study is more conservative and accurate than the RILEM models. Recommendations are also made on values of tensile strain to be used as the ultimate limit state, when predicting the resistance capacity of SFRC and RSFRC. © 2006 ASCE

Modelling of SFRC using inverse finite element analysis

A method of inverse finite element analysis is used to determine the constitutive relationship of SFRC in tension, using primary experimental data. Based on beam bending test results and results from pull-out tests, an attempt is made to explain the physical processes taking place during the cracking stage. Basic models predicting the behaviour of SFRC in tension are proposed. © RILEM 2006

Reuse of tyre steel fibres as concrete reinforcement

To attain economically viable and environmentally friendly tyre recycling, it is necessary to develop new applications and products, which will use tyre by-products (especially the steel cord) as raw materials. The authors demonstrate that the steel fibres recovered from used tyres can be used to reinforce concrete elements. This application has a great potential, as it is estimated that more than 500000 t of high-quality steel fibres could be recovered annually from used tyres in the EU alone. This paper presents the work carried out as part of various ongoing projects on the use of steel fibres in concrete construction. The first part of the paper deals with waste management issues, the methods used to recover steel fibres from tyres, and existing applications of used tyres. The second part presents the mechanical behaviour of concrete elements reinforced with these steel fibres and discusses the relevant design and economic issues. It is concluded that the use of these steel fibres in concrete construction will benefit not only the construction industry, but also the producers and recyclers of used tyres

Stress-strain characteristic of SFRC using recycled fibres

This paper presents work from a comprehensive study on the development of a flexural design framework for concrete reinforced with steel fibres that are recovered from used tyres. The experimental flexural behaviour of notched concrete prisms reinforced with these fibres is initially presented. For comparison purposes, prisms reinforced with industrially produced fibres are also considered. An attempt to adopt an existing RILEM design framework to derive appropriate tensile stress-strain blocks is made, but problems are identified with key parameters of the framework. The influence of crack propagation and location of neutral axis depth on the tensile stress distribution is examined. Following an analytical study, it is concluded that the uniaxial stress-strain model, proposed by RILEM overestimates the load-carrying capacity and should be modified by utilising more advanced analytical techniques. © RILEM 2006

Reuse of tyre steel fibres as concrete reinforcement

To attain economically viable and environmentally friendly tyre recycling, it is necessary to develop new applications and products, which will use tyre by-products (especially the steel cord) as raw materials. The authors demonstrate that the steel fibres recovered from used tyres can be used to reinforce concrete elements. This application has a great potential, as it is estimated that more than 500000 t of high-quality steel fibres could be recovered annually from used tyres in the EU alone. This paper presents the work carried out as part of various ongoing projects on the use of steel fibres in concrete construction. The first part of the paper deals with waste management issues, the methods used to recover steel fibres from tyres, and existing applications of used tyres. The second part presents the mechanical behaviour of concrete elements reinforced with these steel fibres and discusses the relevant design and economic issues. It is concluded that the use of these steel fibres in concrete construction will benefit not only the construction industry, but also the producers and recyclers of used tyres

Stress-strain characteristic of SFRC using recycled fibres

This paper presents work from a comprehensive study on the development of a flexural design framework for concrete reinforced with steel fibres that are recovered from used tyres. The experimental flexural behaviour of notched concrete prisms reinforced with these fibres is initially presented. For comparison purposes, prisms reinforced with industrially produced fibres are also considered. An attempt to adopt an existing RILEM design framework to derive appropriate tensile stress-strain blocks is made, but problems are identified with key parameters of the framework. The influence of crack propagation and location of neutral axis depth on the tensile stress distribution is examined. Following an analytical study, it is concluded that the uniaxial stress-strain model, proposed by RILEM overestimates the load-carrying capacity and should be modified by utilising more advanced analytical techniques. © RILEM 2006

Pull-out behaviour of steel fibres recycled from used tyres

Role of Cement Science in Sustainable Development - Proceedings of the International Symposium - Celebrating Concrete: People and Practice 2003, Pages 175-184It is estimated that currently in the UK around 60,000 tonnes of steel are discarded as part of the cord and bead of used tyres. As a result of environmental legislation there is an urgent need to find alternative uses for this steel, which consists of high quality fibres, to avoid disposing it in landfills. Work at the University of Sheffield has recently demonstrated that steel fibre from recycled tyres can be used as reinforcement in concrete. To optimise the use of steel fibres in concrete and to obtain the optimum bond strength without fibre failure, the critical fibre length needs to be determined. This paper presents a study on the bond characteristics of steel fibres from used tyres. The current experimental program investigates the pull-out behaviour of different fibre types by using a double-sided pull-out test method. Single and multi-fibre pull-out set-ups are employed in these experiments. It was found that fibres from recycled used tyres have as good bond characteristics as commercially available steel fibres