This research looks at utilising an optimum quantity of rubber crumb as an air entraining admixture in concrete, thus providing maximum freeze thaw protection and maximum strength.Microscopic and chemical analysis was carried out on the rubber sample to investigate how rubber crumb entrains air and reacts with the surrounding concrete. The work contained two pilot studies that informed the main test methodology. The pilot studies examined the air content/compressive strength relationship (1) and freeze/thaw cycle durations (2). Pilot study

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PurposeEstablishing toughness performance in concrete using steel fibres is well understood, and design guides are available to assist with this process. What is less readily understood is the use of Type 2 synthetic fibres to provide toughness. This problem is exacerbated by the wide range of synthetic fibres available, with each different fibre providing different structural properties. This paper seeks to address this issue.Design/methodology/approachThe paper examines the relative pull‐out values of two single fibre types, i.e. steel and Type 2 synthetic fibres. The pull‐out test results have informed the doses of fibre additions to beams which have been used to equate near equal toughness performance for each fibre type.FindingsThe results show that synthetic Type 2 fibres, when used at a prescribed additional volume, can provide toughness equal to steel fibre concrete.Originality/valueThe scientific study of fibre pull‐out behaviour is well understood and described herein under additional reading. Practical testing to show contractors and clients how to balance the dose of fibres in concrete, so that synthetic fibres could be used as a steel fibre replacement, is not well researched. This paper bridges the information gap.