Numerical evaluation the effect of specimen thickness on fibre orientation in self-consolidating engineered cementitious composites

The orientation of distributed synthetic fibres in the matrix of engineered cementitious composites (ECCs) governs their capability of bearing stress and bridging micro-cracks. Understanding the orientation of synthetic fibres in ECCs matrix of different thickness specimens, therefore, is necessary. In the present work, the effect of specimen thickness on the orientation of synthetic fibres in self-consolidating (SC) ECC, a typical member of family ECC materials, is numerically investigated through the simulation of the casting of fresh SC-ECC into different thicknesses of moulds. The moulding of fresh SC-ECC, which is discretised by a limit number of separated mortar and fibre particles, is simulated using the mesh-free smoothed particle hydrodynamics (SPH) method. The synthetic fibre utilised in SC-ECC is considered as flexible fibre and virtually connected by a drag force between two adjacent fibre particles. The SPH allows tracking the movement of mortar and fibre particle during their flow, thus providing the real image of flexible synthetic fibres orientation in specimens during the casting process. A simple method is proposed to evaluate the orientation of flexible synthetic fibres at various sections of specimens after the SC-ECC stop flowing in the moulds. The results of this study reveal that thin specimens tend to have higher fibre orientation factors than thick specimens. Synthetic fibres tend to parallel with the longitudinal direction of specimens at the bottom of the formwork and rotate freely at the top surface of specimens.