Workability is measured with the LCL consistometer. The device is an open rectangular mould with an external vibrator and a removable vertical partition dividing it into two compartments. When the partition is removed, the vibrator is triggered at the same time as a chronometer. The time, t, that the concrete takes to flow to a reference line is measured.
For a matrix with a given composition (mortar and concrete), we study how workability varies when the percentage of fibres increases. The curves thus obtained take the form Ln(t)= A + B %. We show that the value of coefficient A is linked to the matrix composition while coefficient B is especially sensitive to the type of fibre used and to the gravel -fibre interaction.
Mortar and concrete compositions reinforced by fibres of very different types with different lengths and geometries (rods or ribbons) are tested and are used to validate the proposed model. The types of fibres studied are: glass fibres coated with thermoplastic, PVC fibres, steel fibres and amorphous cast iron fibres. The results can be used to optimize the geometry of very different types of fibres and thus obtain a better workability.