Flexural performance of sustainable hybrid fibre-reinforced SCC beams made of treated recycled aggregates

In this study, the flexural behaviour of steel fibre reinforced self-compacting concrete (SCC) beams made of 100% recycled aggregates (RA) was experimentally and analytically investigated. Two types of steel fibres, namely micro and hook-ended, were utilised at different volume fractions (V_f) of 0.5 and 1%. Hybrid steel fibre (a combination of micro and hooked-end) was also utilised in this investigation. A simple treatment method was implemented to enhance the properties of RAs by impregnating them in a cement-silica fume slurry (CSFS). After the treatment process was completed, a series of rectangular simply supported reinforced SCC beams were prepared and tested until failure. The performance of the tested beams was assessed considering cracking and ultimate failure loads, crack pattern, and load–deflection response. A comparative analysis was conducted to examine the validity of standard codes and analytical models proposed by researchers to predict the flexural capacity of the tested beams. The obtained results indicated that using RA lowered the ultimate flexural load of reinforced SCC beams by about 12% compared with the control beam. On the other hand, the inclusion of steel fibres resulted in comparable or even superior flexural performance when compared with the control beams, irrespective of the fibre types and volume fractions. The specimen containing 1% hybrid steel fibre had the maximum flexural capacity with a 20% improvement over the control specimen (beam without any recycled aggregates). Additionally, the use of 0.5% micro-steel fibre might be recommended as it sufficiently compensates for the inferior performance of RA concrete, hence enables the full replacement of natural aggregate (NA) with recycled aggregate in SCC beams. Furthermore, the standard codes and analytical models proposed in the literature were found to provide conservative predictions for the flexural capacity of all the tested beams. Nevertheless, these codes and models could be reasonably used to design reinforced fibrous and non-fibrous RA beams.