Reinforced Concrete CTE

[ridgeline]

I am looking for a reference (preferably ACI) that details how a composite coefficient of thermal expansion (CTE) for reinforced concrete may be computed given the individual concrete and steel CTE values.

I have spent several hours searching but have been unsuccessful at finding one...

 

[jayrod12]

In my books, it shows the coefficient of structural steel to be 6.5x10^-6 per degree Fahrenheit and for concrete is is 7x10^-6. Hardly seems worth trying to blend it together?

 

[ridgeline]

Perhaps for most practical applications.

I am looking at a concrete CTE equal to 9.1x10^-6. Higher reinforcement ratios would be expected to have some measurable effect. I suspect an appropriate analytical approach must exist..

 

[jayrod12]

What kind of concrete do you have with such a high CTE? I've never seen anything higher than 9 and even that's plaster based, i.e. gypsum based. And that stuff is never structural.

 

[centondollar]

" I suspect an appropriate analytical approach must exist.. "
There are "analytical approaches" (mathematical idealizations) for a lot of things in reinforced concrete that, for most practical cases, do not produce very accurate results. The most glaring examples are shear design (strut-and-tie is only reasonably accurate for massive sections and in an "average" sense), crack width calculations and deflection estimations.

I have never once heard of an analytical approach for estimating the internal forces generated by thermal expansion difference of rebar and concrete. The obvious reason for this is given by jayrod12: the coefficients of thermal expansion are almost identical.

 

[ridgeline]

It's a HPC mix (~10ksi)

 

[jayrod12]

And what level of temperature swings are you expecting?

How did you get such an accurate CTE for the concrete?

 

[ridgeline]

+/- 25 degrees Fahrenheit. Laboratory specimens were tested for CTE. Results averaged 9.1+/-0.2x10^-6

I was able to finally track down an old ACI reference. If interested:
Berwanger, C. (1971). The modulus of concrete and the coefficient of expansion of concrete and reinforced concrete at below normal temperatures. Special Publication, 25, 191-234.