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polypropylene fibers in concrete 3

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domdem

Civil/Environmental
May 21, 2002
13
Does anyone out there know if any research has been done with regard to fire testing on concrete with fibres.

Of particular interest is that do the thickness of multifilament fibres ie (18 micron or 32 micron)improve or reduce explosive spalling

if anybody knows anything about this please let me know
 
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When the temperature of the concrete gets to the spalling stage, it is likely the poly fibers have melted. More discussion to follow...
 
We have undertaken fire tests with the Building Research Establishment for our tunnel linings with conventional rebar, no rebar, polypropylene fibres, steel fibres and a mix of pp fibres with all of the above. The test specimens were axially loaded then a furnace applied the heat up to 1200 degrees over 2 hrs.

Result: All of the combinations which contained the pp fibres (approx 2kg/m3 of fibre) showed no spalling.
 
Ginger...thanks for the info on PP fibers in fire. Here in the US we sometimes use a wide torch to burn the trailing, exposed fibers from the surface of slabs for aesthetics. I surmised that they would not do well with surface spalling under direct flame, but evidently your study shows otherwise.

Did you get spalling with the steel fibers?

Thanks,
Ron
 
Hi Ron

We tested combinations of conventional rebar alone, fibres alone and also fibres plus rebar. In all of these cases where the polypropylene fibres were NOT included, we saw varying degrees of spalling. The inclusion of the PP fibres does appear to have significant benefits at doses between 1 & 2 kg/m3

Andy
 
Andy,
The dosages you mentioned are typical here. That's good info. Thanks again.
Ron
 
Andy

The dosages you refer to are between 1 and 2 kg per metre as i expected but is there a significant difference between say 1 kg or 2 kg in either temperature or time, i am only interested in reinforced concrete,

Many Thanks
Dominic
 
Ginger,

After the good test results, did you also apply the PP fibres in a real tunnelling project and if so were no additional fire prevention/protection measures taken?

thanks,
Jeroen
 
JeroenvD

We have used a polypropylene and steel fibre mix in a twin bore 8.9m ID road tunnel without any other fire protection measures.
 
GINGER

I noted that earlier you mentioned that you tested the fibres with and without rebar did you find that with the rebar it was more inclined to increase spalling due to the expasion of the reinforcing under temperature.Also what was the maximum temperature you tested to ie cellulose,carbon or TNO.
Regards
Dominic
 
Dominic

Yes, rebar thermal expansion was a reason for the additional spalling. We heated the concrete to 1200 degC.
 
And all this time I had been under the impression that rebar and concrete had the same expansion rates. (I need to inform my professors).

Thanks Ginger.
 
It is generally accepted now that PP fibers--or PVA--will melt out during a fire and provide a sacrificial route for trapped water vapor to escape.

Steel fibers are great at reducing normal spalling, but they can cause dangerous explosions during a fire.

With PVA fibers you get a structural fiber that can't corrode and a sacrificial fire fiber as well.

Richard
 
Ginger,

Recently we have carried out some test with a 80 N/mm2 concrete with 2 kg PP fibres reinforcement. THe concrete was exposed to a temperature of 1200 degrees (TNO). The test result of one piece was acceptabel but the other was very bad. As the steel fibres have no influence on spalling prevention but only at damage reduction you probably used more PP fibres or weaker concrete.

Jeroen
 
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