Performance of a multi-layer aligned steel fibre reinforced concrete beam: A preliminary investigation towards 3D printing

Fibre alignment and 3D concrete printing have become increasingly popular in research and industry while these technologies face a lack of deep integration. Aligning steel fibres in concrete is different from in mortar systems due to the interference originated from coarse aggregate. This paper reports the results of an experimental programme investigating manufacturing reinforced concrete by placing concrete and aligned steel fibres in multi-layer in replicating the 3D printing. The X-ray CT scan was deployed to characterise the fibre distribution by digitally colouring the fibre orientation deviation and calculating the fibre orientation efficiency which reached 0.77 in this study. 4-point bending tests were performed on beam specimens of the multi-layer aligned steel fibre reinforced concrete to assess the flexural performance. Alignment of the steel fibres resulted in 56 % increase of the ultimate load resistance compared to that being twodimensionally distributed. A model for estimating the tensile strength of multi-layer aligned steel fibre reinforced concrete was developed with consideration of the layer proximity to the neutral axis of the beam. Change of the concrete composition was observed to yield influences on the interface bond performance between the fibre layer and concrete and the influences were quantified by correlating experimental data. This study revealed that the space characteristics of the fibre distribution in multi-layer required concrete mix constituent of good rheology to develop adequate bond performance for further additive manufacturing without formwork.