Glass Fiber Reinforced Concrete

[craigmcg]

I'm looking to design a concrete slab boat ramp, one that is used to launch/retreive boats in a salt-water marina. Instead of pouring a typically reinforced concrete slab, I was considering using a material such as GFRP. I don't have much experience with this material, and we have no relavent design codes in the office as of yet, so I was wondering if this is a logical idea (before I go too deep with it and order the books)? I guess my questions are as follows:

1) Is ACI 544.1R the best resource for GFRP design? This application would be more along the lines of pavement or a structural slab.

2) Will temperature/shrinkage reinforcement still be required?

Thanks in advance for everyone's input.

 

[DaveAtkins]

Are you talking about GFRC (you typed GFRP)?

I have worked with GFRC in the past--but only for wall cladding. I have never heard of using it for gravity loads.

DaveAtkins

 

[MiketheEngineer]

I have seen it used on residential driveway slabs. Seemed to work OK. Control joints were cut in. Without reinforcing - what keeps the slabs from breaking apart and moveing independently??

I'd probably keep the rebar in.

 

[concretemasonry]

Fibers in concrete in a driveway are fine for micro-cracking, but they are not a replacement for rebars or wire mesh. I used both on my own driveway, but if could only use one, it would have been mesh with control joints.

Your application is probably much different than a driveway. There could easily be more varied soil/support conditions, erosion, tides and wave action, so you need continuity that only structural reinforcement can provide. Certainly in a salt water condition, temperature differentials are not that critical, but you still have curing shrinkage.

You get some strange things happening with waves and the unusually big boat that can easily cause pumping and lack of support.

Dick

 

[civilperson]

Steel reinforcement is best. Use as epoxy coated if long life is desired. Precast and set in place is easiest.

 

[youngstructural]

Significantly off-topic, however worth mentioning given the previous mention of Epoxy coated bars.

Epoxy coated reinforcing should not be used in severe exposure, particularly saline or other chemical attack.

Any small nic in the coating provides a place where the bar can corrode. Since it is the only area corroding, the chemicals precipitating the corrosion remain in high concentration and can cause a much more severe localized corrosion. Instead of getting overall bar corrosion which can cause loss of cross section over decades, you get a localized corrosion which can cause loss of cross section in a years. Very bad for cold-climate bridges!

There is a huge industry which has tooled up around epoxy coating of reinforcing and if fighting to keep it in the market, even where inappropriate in some cases. It has a place, just be careful about exposures and site handling/fabrication.

Regards,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[hokie66]

Galvanized reinforcing doesn't suffer from the same shortcoming as epoxy coated. A small damaged area is still protected by the surrounding zinc. For information, in what geographical areas is epoxy coating used/marketed?

 

[youngstructural]

I am a strong supporter of galvanized reinforcing, and have seen some fantastic performance in the worst kinds of conditions... I've also seen some good examples of very bad epoxy performance.

I believe Epoxy bars are still marketed/available in Canada, although as of three years ago (last I was practicing there) there were definately many fewer engineers willing to specify them.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[DaveAtkins]

craigmcg,

I misunderstood your original post. You must have been talking about "fiber reinforced concrete."

GFRC is a different animal--used for cladding on buildings.

You should refer to what you are doing as fiber reinforced concrete--the fibers are not glass, but are polypropylene.

DaveAtkins

 

[hokie66]

If you are talking about polypropylene fibers as reinforcing, forget it. That's another marketing scam like epoxy coated rebar.

 

[craigmcg]

Thanks everyone for your post. To clarify, I did mean Glass Fiber Reinforced Concrete (GFRC not GFRP). I deal with FRP products frequently so its become a habit in typing.

Based on your comments and additional material I've read, I've decided to scrap the GFRC idea and simply use a simple mat that is tremie poured.

As for the off-topic post, I completely agree that epoxy-coated rebar are not for "extreme" environments such as salt water applications. I've performed numerous forensic investigations where the epoxy coating was completely negligible in its effect. The best method of corrosion protection is to ensure a proper mix design with a low w/c ratio and sufficient coverage. Our firm deals entirely with marine structures and we wouldn't even consider using epoxy rebar based on our experiences.

 

[SteveGregory]

I have used fiberglass rebar around sensitive electromagnetic equipment to replace steel rebar. There are some other uses as well. Check the link.

http://www.fiberglassrebar.com/index.html

 

[PEinc]

There seems to some confusion as to whether the OP is talking small fibers or fiberglass rebars.

 

[unclesyd]

I haven't seen a successful job using GFRC around here, the gulf coast, especially heavy driveways and 2 wide boat ramps in salt water. AS I've mentioned before the driveways have multiple origins, with many branches, from the control joint, to a chip on the edge, and just an edge.

Both first course of the boat ramps were cast above the high water mark with one being pulled in place and the other was lifted by crane. Both of these slabs were started cracking at a very young age, less than a year.

I like the product posted by SteveGregoryas it specifically mentions slat water applications.

 

[civeng80]

Agree with hokie66 polypropylene fibre reinforcement has had some very bad results for some quite large jobs. I was nearly on the point of placing some 5000m2 of concrete paving using this some 8 years ago and fortunately for me got the tip and changed my mind. When the cracking starts nothing will control it !

 

[hokie66]

IMHO polypropylene fibre should be considered only as a concrete additive, not reinforcing. It has some benefit in controlling plastic shrinkage cracking and can improve surface toughness, but that is about all. I think the benefits are not worth the effort.

 

[Qshake]

I have recently used polypropylene fibers with GFRP and CFRP in a bridge deck.

We had no problems placing it or finishing it.

So far, one year later and all is well. Very little shrinkage or temperature cracking in the deck.

I don't expect it to be morphed into a standard for epoxy coated rebar for quite some time. Prices are too high and applications just aren't enough.



Regards,
Qshake

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