Full list of Nuggets
Over the decades, ground-supported floor slabs have been designed and built using steel to enhance concrete properties. In some cases a combination of the two types of steel and synthetic micro-fibres has been used. As fibres vary from one supplier to another, guidance on the method of use and potential benefits should be sought from the particular supplier used. Micro-fires do not provide residual post crack ductility ie do not control cracking in hardened concrete.
Steel fibres, and more recently macro-synthetic fibres, are used in ground-supported slabs for two main reasons.
1) To control the formation and development of cracks caused by early age plastic shrinkage and restrained long-term drying shrinkage.
2) To provide a degree of post-cracking load-carrying capacity, i.e. an ability of the slab to carry load after the first crack has formed during slab flexure.
For large area pour construction, sawn induced contraction grooves are cut into the slab surface at 6 to 8m centres, both ways. When some steel fibre types are used and dosage is high enough, large area pours can be constructed without joints except for a perimeter construction joint. This is often called `jointless` slab construction.
Polypropylene micro-fibres have been used in ground-supported floor slabs for some years to enhance the properties of concrete, particularly in its plastic state. An enhancement of slab surface properties and a reduction of the risk of plastic shrinkage cracking and crazing is possible with some micro-fibre types.
Acknowledgement: The Concrete Society
Concrete Bookshop - Members receive 40% discount on Concrete Society publications