Thanks Ron et al for the info, just getting to grips with this site. Alot of info to look at.
Ron can see that you are not a great fan of fibres particularly synthetic.
Reading the threads there seems to be alot of generalisation about fibres - there are of course many different types all held with varying claims by the manufacturers.
1. The monofilament polyprpolene fibres that are commonly used in concrete to reduce plastic shrinkage, increase impact resistance etc etc are "non structural" and am in agreement with the general consnsus that they do nothing that a good quality concrete should do in relation to cracking etc. Although nowadays they are being used in enhancing the fire resistance of concrete.( they melt and let the water in the concrete - now steam- escape through the capillaries so reducing spalling)which is probably worth paying for in u/g structures.
2. Second type of fibre we can term is structural. As far as I am aware this is about the "post-crack performance" of concrete - so how the fibre performs after the concrete cracks. Esentially if you do a flexural test on a beam the first crack will be the same whatever the fibre reinforcement - the flexural strength is dependant on the concrete matrix not the reinforcement.
There are a number of tests that can compare the strength of fibre after cracking - known as toughness.
As for the argument for/against steel or polypropylene fibres with regard to toughness there are poly fibres on the market nowadays that can equal steel. eg
7-8kg polypropylene fibre = 40kg steel hooked end fibre.
There are obvious advantages of using poly in that they don't rust, lighter, cheaper etc etc. Whether this better than steel is upto the designer.
The issue for me is that if I take out the steel mesh what is the replacement for steel fibres.
Interested in MERBAS in thread 592-4995. What are you using the monofilament fibres in precast for?
Cheers
