The effect of fibre distribution characteristics on the flexural strength of steel fibre-reinforced ultra high strength concrete

Fibre distribution characteristics were evaluated to investigate their effect on the flexural strength of steel fibre-reinforced ultra high strength concrete in conjunction with the direction of placement. For this purpose, an image processing technique developed in this study was employed. Flexural tests were carried out to quantify the effect of fibre distribution characteristics on flexural strength. It was found that the image processing technique developed in this study could quantitatively evaluate the fibre distribution property by the use of the distribution coefficient, the number of fibres in a unit area, the packing density of the fibre image, and fibre orientation. It was also found that the fibre distribution characteristics were dependent on the direction of placing. Fibre distribution characteristics were revealed to strongly affect the ultimate flexural strength, while hardly affecting the first cracking strength. The validity of the current test results was verified through comparison with a theoretical model of flexural strength.

Research highlights
► We studied the effect of fibre distribution on the flexural strength of SFR-UHSC.
► An image processing program was developed to find the actual fibre distribution.
► The initial cracking strength was relatively less influenced by fibre distribution.
► The flexural strength was remarkably affected by fibre distribution.
► Assumption of uniform distribution causes large error in predicting the strength.