Using synthetic fibres in concrete to control drying shrinkage cracking in concrete slabs-on-grade

[摘要] ENGLISH ABSTRACT: Macro synthetic fibre reinforced concrete (SynFRC) is a relatively new concrete for the purpose ofbeing used in structural elements which only require minimum reinforcement and are supportedcontinuously by sub-layers. One structural element that is of particular interest is slabs-on-gradewhich is supported by a subgrade/sub-base and requires minimum reinforcement to control theshrinkage strains which may result in cracking.The aim of this project is to investigate the potential use of macro SynFRC in the application ofcontrolling drying shrinkage cracking (DSC) in concrete slabs-on-grade. The focus is on the use ofconcrete slabs-on-grade that is intended for industrial floors.The SynFRC material parameters of interest were characterised first with the aid of variousexperimental tests. These are: flexural tests, compression tests, friction tests between the SynFRC andwooden surfaces used for full scale testing, and the shrinkage of the concrete.Next the post-cracking tensile behaviour of the SynFRC was determined by way of an inverseanalysis. These tensile responses were subsequently used to perform a series of different finiteelement analyses. These analyses were performed on specific slabs-on-grade to determine the effectsof the added tensile behaviour of the SynFRC on the DSC.The results obtained concerned: the spacing of cracks, the maximum and average crack width, and thedifference in crack width between the normal concrete (NC) and the SynFRC. These changes takeplace in accordance to the concrete age. From the analyses it was determined that the addition offibres gives the concrete a ductility that allows the concrete to crack more than NC, yet does not allowthe cracks to propagate. This applies to low fibre contents of less than 0.4% by volume and a slabthickness of 200mm, as well as to fibre contents that have Re,3 values of 0.51 and higher. Moreover, itresults in improvements seen when adding fibres if the friction is sticky, meaning when the maximumfriction between the slab and the subgrade is reached with a very small amount of movement. With astickier friction though smaller crack widths occur within both the NC and the SynFRC.

[发布机构] Stellenbosch University