Adhesion between concrete and bare steel 3

[DataAB]

I had a discussion with a colleague regarding the pullout capacity of a bare steel pipe embedded in 25 MPa concrete. What is the adhesion value between concrete and bare steel?
How is it related to the 28 day strength of the concrete?

Any comments appreciated.

 

[PEinc]

Per FHWA Publication No. FHWA-RD-96-017, Drilled and Grouted Micropiles: State-of-Practice Review, Vol. II: Design, Page 91, a typical ultimate design bond value for a steel tube/grout interface is 1.0 to 1.5 MPa. I assume that, for concrete instead of grout, the bond would be similar.

 

[JStructsteel]

friction coeff. is 0.45, does that help any?

 

[mudflaps]

Old, old (1960's) bond value for plain rebar (not deformed) was 60 psi (80 psi for deformed bars). This of course assumed clean steel surface (no oil or paint) and only a very little evidence of surface rust. If it was good enough for large projects (Hoover Dam, etc) it must have been close to what the PHD's are allowing us today.

OLD CA SE

 

[Tomfh]

My old, old, old (1930s) Hool and Johnson Concrete Engineers handbook discusses stress development in plain bars.

It concludes that the maximum working bond stress between round bars and concrete should not exceed 4% of the 28 day concrete compressive strength (cylinder strength). This is approximately one third the value required to cause first slip of the bar, and is approximately one-fifth the maximum bond resistance.

So for 25 MPa concrete you are looking at an upper value of 1 MPa for working stress, which agrees with PEInc above.

Rust increases bond resistance by approximately 15%.

Polishing decreases resistance by approximately 65%