Plastic bar chairs in cover concrete 1

[sdz]

What is the current thinking on using plastic bar chairs in a surface facing a high corrosion zone; b1 B1 or greater?
My understanding is that these can create a path that will enable the surrounding environment to permeate through the cover zone and so should not be used. (AS 3735—2001 - 4.4.4.4(c))

However this site shows that many engineers still recommend plastic chairs in these environments.

 

[hokie66]

Is there a better option?

 

[sdz]

hokie66, there are concrete bar chairs available. Certainly not plastic tipped wire bar chairs.

 

[LittleWheels]

We swapped to specifying only cementitious bar chairs a few years back.

 

[bugbus]

TfNSW B80 has the following, which I find pretty confusing. At first I read this to mean plastic was OK for up to B2, but they seem to prefer concrete.

 

[sdz]

TfNSW B80 = TRANSPORT FOR NSW (TfNSW) QA SPECIFICATION B80 . CONCRETE WORK FOR BRIDGES

Ok that's specifically for bridges but it's good guidance.

I notice it refers to "individual plastic bar chairs" which would exclude those that support multiple bars, including trench mesh supports.