Basalt Rebar

[msquared48]

Anyone used this material yet? It is fairly new in the states. Supposedly stronger than Grade 60.

Any problems seen with the material quality and reliability of uniformity of product?

Mike McCann, PE, SE (WA)

 

[TehMightyEngineer]

Interesting. First I've heard of basalt rebar.

I have used glass FRP rebar in a medium sized project. Bar quality and the fabrication was good but the contractors had a little trouble getting used to using it. Overall I'd say FRP rebar makes a great replacement for anyone who has corrosion issues or wants to develop a long-life structure without going full-stainless.

Oh, and the glass FRP itches like crazy. Baby powder helps, supposedly.

Maine Professional and Structural Engineer.

http://www.fepc.us

 

[Signious]

This looks incredibly cool. I looked up a couple videos and it is incredibly ductile - there is no way you would be able to bend the bars in shape as you do with steel reinforcement. Maybe using a heat press to soften the adhesive up during bending, but looks like any bends will need to be pre-manufactured.

I am curious if there are any special on-site requirements for cutting. Diamond or carbide blade needed? How dangerous is airborne basalt & adhesive particles.

The bars I saw ranged from regular deformations, to helical deformations down the length (almost like screw threading), to simply a very rough surface finish. I would love to see pullout test on these and compare them to regular bar.

Stepping back and looking at production of these - it seems like they are simply melting basalt, adding in lime to pull out slag, then drawing the molten rock into fibre similar to regular fibreglass production. Incredibly cool. Rock cloth!

 

[TehMightyEngineer]

All FRP bars (to my understanding) have to be prebent from the fabricator before the fiber binding agent (vinyl-ester for glass FRP bars typically).

FRP bars have to be cut with a cutting wheel. Torches or shearing cutting devices will not work (especially torches; someone tried that on the job I used it on and I bet his lungs loved it...). My understanding is a simple face mask and avoiding inhaling the dust is all that you need as it's not much of a hazard.

I looked into pullout tests and there is some variation depending on the bar's manufacturer (some are slightly better than others). Most seem to be greater or at least equal to a deformed metal bar.

The one big issue with FRP bars is elevated temperatures. While the fibers are quite fireproof the binding agent is not. This can cause loss of bond and stretching of the bars leading to excessive deflection and failures.

Maine Professional and Structural Engineer.

http://www.fepc.us

 

[TXStructural]

Basalt is NOT ductile. The bar gets some toughness from the binder, but as soon as fibers break it starts losing strength.
It is fabricated to shape (long lead times) and is still very expensive.
Obviously the steel rebar industry would want me to say these things, but as a safety and structural engineer, I think designers need to understand that glass and basalt bar have zero strength once they fail. The ductility of steel is what makes it idea when there is any risk of reaching rated strength (yield for our design purposes). The post-yield behavior is a very important part of our design philosophy and the safety inherent in reinforced concrete design. The design strategies for glass and basalt bar require design for much greater strength and a much higher margin of safety,because once it breaks, it breaks.

As to development, the surface texture of the bar is relatively less important than having larger deformations which engage the concrete in reliable ways. Low amplitude texture will be more reliant on paste flow during concrete placement and quality of concrete. If the paste does not fill in the small valleys on the bar surface, you can end up with inadequately bonded bar. There is a small amount of research using "labcrete" showing that rough texture bonds well, but having seen how unreliably paste flows around smoother bar in the field, I see this as a practical construction issue.

 

[patswfc]

msquared48,

Attached is an article on basalt rebar.

Regards

 

[patswfc]

Should have added that i dont think the paper talks about material quality and reliability of uniformity of product, and if it does it may not be relevant for the US market.
From memory, although basalt rebar has some good properties (tensile strength) it also has a few poor properties (ductility, poissons ratio - which creates issues with bar slippage within the concrete).
Personally I would try to avoid using it, until some of these issues have been overcome/improved.

 

[TehMightyEngineer]

Video on basalt FRP rebar beam test:

https://www.youtube.com/watch?v=_-FecmdM3v0

Looks like there wasn't any shear reinforcement and thus the shear failure was very brittle. Still the beam deflection and cracking seemed to be sufficiently ductile. My understanding it FRP bars get their ductility through elastic stretching of the bonding agent and bond slippage between the bar and concrete. Definitely not as ductile as steel rebar for sure. TXStructural is right that the lower ductility does require similar levels of reinforcement to steel rebar despite FRP having greater strength.

Maine Professional and Structural Engineer.

http://www.fepc.us