Experimental data in the unit (Table 11.3) show that the strength of fibre reinforced concrete with randomly dispersed fibres rises with aspect ratio up to a value, beyond which strength falls. That maximum useful aspect ratio is about:

1. Table 11.3 lists relative strength of fibre concrete for aspect ratios of 0, 25, 50, 75 and 100. 2. Relative strength rises from 1.00 at AR = 0 to 1.70 at AR = 75. 3. At AR = 100 the relative strength drops to 1.50, indicating the peak has been crossed. 4. The unit attributes the fall beyond AR = 75 to balling, agglomeration and non-uniform fibre distribution. 5. Hence 75 is the practical upper bound for aspect ratio in steel-fibre concrete. _Source: IGNOU Concrete Technology, Unit 11 "Special Concrete" (Light Weight, Aerated, No-Fines, High Density, Fibre Reinforced, Polymer Concrete)._