Fiber Reinforced Concrete

[abusementpark]

What are the primary uses for Fiber Reinforced Concrete?

Does anyone have any good experience with FRC?

Any good references would be greatly appreciated.

 

[msquared48]

Small Crack control, and to create fuzzy, hairy concrete. (smile)

Mike McCann
MMC Engineering

 

[Ron]

abusementpark....fiber is good to enhance the properties of concrete, but not to replace rebar. Steel fiber does a good job of increasing the modulus of rupture for flexural strength. It also increases the compressive strength, but not in the same proportion.

Polypropylene fibers, in my opinion, are oversold. They do not do as much for the concrete as the manufacturers would have you believe. Yes, they will decrease the early crack potential. This means that the space between cracks will increase, but also the width of cracks will increase. They do not stop cracking altogether.

I have had good experience with steel fibers in concrete, not so good with polypropylene. I know of one pavement section used as a loading dock and dumpster pad that I designed over 20 years ago and it is still performing quite well, with no cracks other than at control joints. We added steel fiber to the asphalt on the same project. The asphalt has performed amazingly well for over twenty years.

 

[SlideRuleEra]

See thread507-240248

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[abusementpark]

Ron, what specific problems have you had with polypropylene fibers?

 

[Ron]

ABP...just that many ready mix producers will use poly fibers to cure their mix deficiencies (high water-cement ratio particularly). Shrinkage of the mixes has been high, resulting in wide, but longer spaced shrinkage cracks.

Workability is often an issue with any fiber.

 

[thruthefence]

http://www.fibrebond.com/

precast shelters

 

[concretemasonry]

One reason for the variable answers is the wide range of ability to handle the fibers and use the correct mix design. Some producers treat the fibers as a generic commodity despite the range of fibers and their configuration.

One major problem is the mixing time. Too short, you get poor distribution. Too much mixing time, they can ball up and cause problems.

A good ready mix producer may have mix designs for use with the specific fibers used. Some even adjust the plant/yard mixing time depending on the distance/time to the job site.

The fuzz can be eliminated by a quick singe with a torch a few days or more after placement.

fibers are not intended to be a substitute for rebar or WWF.

I had a driveway installed with 4500 psi air entrained concrete with WWF and joints sawed late the same day. Since I did not have a broom finish, I did not find any fuzz, but may have found some if I really hunted. The concrete was from a small local plant within a mile of the huge Lafarge cement plant, so he had all the cooperation and testing he needed, since he frequently allowed Lafarge into the plant for promotional purposes.

For the sidewalk (easement) and the apron to the street,I could not use rebar or WWF due to the city code written to make access to utilities easier, used the smae mix design. Water and sewer were too shallow, so repairs were frequent if you did not keep the water trickling in the winter.

There is definitely a place for them, but there is a wide range of fibers and configurations that frequently get lost in the promotion.

Dick

 

[hokie66]

Promotion. That's the word. I've always just called it sales spin.