Rebar Bond Strength 2

[dik]

Does anyone have information about the bond strength of reinforcing to high early strength concrete at an early age... likely 3 or 4 days?

Thanks...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[BridgeSmith]

Presumably, you could calculate the capacity based on the strength of the concrete at the time of interest, in the same way it would be calculated for concrete with that ultimate strength. Most of the capacity for rebar is based on the tension splitting strength of the concrete, anyway, and not much related to the bond.

 

[dik]

Thanks, is there any effect caused by loading it at a very early age... like a matter of days from being cast?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

The project is the replacement slab for part of the slab removed to construct a pit. The reinforcing located in the replacement slab will be required to provide support for the top of the pit wall. To speed up operation in the plant, the contractor wants to use High Early cement (Type 3, I think, I'm not used to that designation). The rebar will not be confined... in a slab only so splitting will be a possibility.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[BridgeSmith]

There would be an effect from creep of the concrete, which would transfer more stress to the steel, which would then be 'locked in'. I believe calculating the stress in the reinforcing as you normally would, again, using the strength of the concrete at the time of load application, would be give you a good approximation.

The strength gain is fairly fast at the beginning, and tapers off, though. I worked on a project where our ultimate concrete strength requirements were 3.25 ksi (class B) and 3.75 ksi (class A), and the mix was the supplier's standard 4.5 ksi mix. The cylinder tests showed it was reaching class B strength in 3-4 days and class A strength in 7 days.

Due to the small role concrete strength plays in the bending strength of lightly to moderately reinforced flexural members, it's unlikely the increase in bending stress will be significant, unless the beam is heavily reinforced.

You might need to check the concrete shear capacity, though, since that is presumed to be linearly related to the strength of the concrete.

The deflection/deformation may also increase significantly, if you load it early, so if that's critical, you may have to recalculate the deflection using the lower strength.

 

[dik]

Thanks...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[BridgeSmith]

The rebar will not be confined... in a slab only so splitting will be a possibility.

Lap and development lengths may need to be increased, if the full loading, or something close to it, will be applied before the concrete reaches full strength.