Effect of fibres on early age cracking of concrete tunnel lining. Part I: Laboratory ring test

In the first part of this study (part I: Laboratory test), ring tests are performed to investigate the sensitivity of concrete to cracking due to both shrinkage strain and fibre type (two organic fibres and one steel fibre have been studied). Results obtained show that the use of polypropylene microfibres does not delay the age at which the first crack appears but does slightly reduce crack opening. Polypropylene and steel macrofibres have a greater effect since cracking is delayed and the crack opening is significantly reduced. Tensile strength results indicate that a portion of the cracking delay may be attributed to the tensile strength increase resulting from fibre reinforcement.