The fresh properties and early age performance of waste-tyre fibre reinforced self-compacting concrete

Abstract

The amount of waste generated from tyres is always on the increase leading to increased pressure on landfills all over the world. ln order to reduce the disposal of waste tyres, the secondary raw materials extracted from such waste must be transformed into a new resource. This can be achieved by finding a suitable application of the waste material extracted from tyres. Whilst rubber and steel from waste tyres have been recycled in the past, the exploitation of steel waste tyre fibres (SWTF) is a relatively new development. This study assesses the performance of waste tyre fibres which are extracted through the shredding process, in relation to their effect on the workability and early age characteristics of concrete. A self-compacting concrete (SCC) mix without any fibres was used as the control mix. Other SCC mixes containing different fibre dosages ranging from 5 to 30 kg/m3 were also produced. Eventually, standardised experimental procedures were followed to test all the mixes for their self-compacting abilities, early age characteristics and also for specific mechanical performance properties. The results obtained showed that as soon as low amounts of fibres were introduced in the concrete mix, a reduction in the self-compacting abilities of the SCC was recorded. This reduction was mainly observed in the passing ability where in some mixtures a complete loss of performance was noted. Moreover, further reduction in performance was observed as the SCC was tested at 15 minute time intervals after the mixing procedure. As expected, the performance levels were reduced, but the SCC retained certain flow characteristics. Regarding the early age characteristics, a basic environmental chamber was used in which a predetermined environmental conditions were maintained throughout all tests. A mould enabling interna! restraint was utilized, thus providing some control on the development of the crack. The results acquired show that as the SWTF dosage was increased, the time at which the concrete cracked took longer and a significant decrease in the crack width was also noted. Furthermore, the restrained concrete ring test showed that higher strains were exerted on the steel ring with the increase in fibre dosage. With regards to mechanical characteristics, the results obtained from the compressive and tensile splitting strength showed that an increase in performance was recorded over the control mix until ei peirticular fibre dosage weis reached, where a loss in both comprcssive <md tensile strength was then established. An increase in the flexural peak load and the residual strength post-crack increased as larger amounts of fibres were introduced in the SCC mixes. The research indicates that SWTF significantly contributes towards an improved early stage performance, mechanical characteristics and a potential use in self-compacting fibre reinforced concrete.