FRP Bars vs TMT Bars: Where Each One Belongs

FRP bar is the product people ask about with the wrong question. They ask, "Is it stronger than TMT?" The better question is, "What problem am I trying to solve?"

FRP (fibre reinforced polymer) bar is made of glass fibre set in resin. It looks like a pale rod with a ribbed or sand-coated surface. It is not steel and it does not behave like steel. That is the point.

What FRP does better

• It does not rust. There is no steel to corrode, so there is nothing to expand and crack the concrete from inside.
• It is light. About a quarter of the weight of steel for the same diameter. One person carries a bundle.
• It does not conduct electricity and does not interfere with magnetic or radio signals.
• It resists salt and chemicals. That matters near drains, tanks, marine work and chemical sheds.
• Tensile strength is high. Per unit area, glass FRP is stronger in tension than mild steel.

What TMT does better

• It bends on site. TMT is cut and bent into stirrups and cranks with a bar bender. FRP bars cannot be bent on site. Bent shapes must be made at the factory.
• It is ductile. Steel yields and gives warning. FRP does not yield. It stretches elastically and then breaks suddenly.
• It has a higher stiffness. Glass FRP is less stiff than steel, so slabs reinforced with it deflect more and need a different design.
• Standards are mature. Design codes, sizes and test methods for TMT are well known to every site engineer.

Where each belongs

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The fence post story

Much of the FRP we sell goes to farms. A 4, 5 or 6 foot FRP rod makes a post that does not rust in the soil, weighs next to nothing and is driven in by hand. Strung with barbed wire or jhatka wire, it is a clean fence for orchards and fields. This is why FRP also sits in our fencing material range.

Common lengths in our stock are 4 ft, 5 ft and 6 ft. The weights we have on file for a post rod (about 530 g, 660 g and 790 g) belong to a particular diameter and model, which we confirm when you ask. They do not apply across the 6 mm to 20 mm range.

What to ask before you buy

1. What is it for? Reinforcement for a slab needs a structural design. A fence post does not.
2. What diameter? 6 mm to 20 mm. Thicker bars are for reinforcement. Thin ones for posts.
3. Who designed it? If it goes inside a building slab, your engineer must specify it.
4. Which surface? Sand-coated or ribbed bars bond better with concrete.

Never substitute FRP for steel in a structural member without the engineer's approval. The two materials are designed differently.

See FRP bars and ask us for the sizes in stock.

FAQs

Can FRP replace TMT in a house slab?
Not on its own decision. The slab must be designed for FRP, because it is less stiff and not ductile. Ask your structural engineer.

Is FRP bar stronger than steel?
In tension, per unit area, glass FRP is stronger than mild steel. It is also less stiff and it does not yield, so strength alone is not the whole story.

Does FRP rust?
No. It is made from glass fibre and resin.

Can FRP bars be cut?
Yes, with a hacksaw or a cutting disc. Wear a mask because the dust irritates.

What is FRP used for in farms?
Fence posts and crop supports. It does not rust in soil and it is light to carry.