Can bars made out of PET be used to reinforce concrete?

Question

I watched a video, in which a man shows how to make something that looks like a rebar out of PET bottle strips. This made me wonder: can something like this be used to reinforce concrete when constructing buildings?

The Wikipedia article about rebars only mentions fibre-reinforced plastic rebars, but I am wondering about rebars made purely from PET. I tried to find reasons why PET can't be used.

According to this article, coefficient of thermal expansion of concrete ranges from 7 to 13 x 10^-6/°C, and according to this document, coefficient of thermal expansion of PET ranges from 20 to 80 x 10^-6/°C, so there is going to be more differential stress than with steel.

Making rebars the way that was shown in the video would also be very labor intensive.

Are there any other reasons why PET can't be used to make rebars?

Answer 1

Your big issue is stiffness.

Steel works as a good reinforcement for concrete because steel is much stronger AND stiffer than concrete.

Apply a tensile stress to some steel reinforced concrete and the concrete will stretch a tiny amount, but more than the steel. So the steel will end up supporting most of the load. Which is what you want, because steel is strong in tension, but concrete is not.

To put it another way, the stiff steel stops the mixture of concrete and steel from elongating much, and so the brittle concrete will not crack.

PET can be much stronger than concrete in tension, at least for the same cross-section. But it is not anywhere near as stiff as steel.

Elastic modulus for steel E = 210 GPa. Tensile strength 250 MPa or more For concrete E = 30-50 GPa Tensile strength 2-5 MPa For PET 2 GPa Tensile strength 5-90 MPa

So you can see that the PET is stronger than concrete, but less stiff. Under a tensile load the PET will not break, but will stretch and the concrete will crack and crumple around it.

There are polymers that are stiff enough to reinforce concrete, but they are generally the very high stiffness fibres like Kevlar.