Cold joints 1

[longisland]

Hi,
A post tensioned girder was poured with cold joints formed &
there is no proper construction joints. The incident happened
when one truck of the concrete was rejected since the slump
was only 2 inch. The next pour was 2 hours later but they claimed
it's okay since set retarders was added. The joint is visible at
35 degree across the beam. I have advised this beam is to be
abandoned but the contractor insisted the beam can be stressed.
This is the first time I've dealt with such a messy job.
What's going to happen if the beam is stressed?

Furthermore, I would like to know if there is any side effects
on the concrete if the plasticiser is overdosed. The contractor
poured 2 litres of plasticisers into the mixer truck loaded with
5 cubic yards of concrete when the slump was too low at 3 inch height.
The target 28 day strength of the concrete is 7000 psi.

Thanks for the input

 

[haynewp]

If you don't get any responses, may want to try this question in the Structural Engineering Other Topics forum or the Concrete Engineering forum.

 

[VoyageofDiscovery]

Hi longisland,

Check over the specs, check the mix design, any deviation from the spec is the Contractor's liability, they are by nature gamblers, so test the concrete to spec, if it doesn't meet, then make him remove it entirely. The truck being turned away is not you problem, it's his.

If it's not in the spec, well, you have a contract problem, and someone will have to pay for the possible deficiency.
Have the design engineer review and comment on the as-built situation.

HTH

VOD

 

[haynewp]

Shear across the joint has to be able to be transmitted. For a regular reinforced concrete beam, the beam can crack due to shear, however there is supposed to be a combination of vertical or inclined stirrups plus longitudinal reinforcing to complete the force transfer across the crack.

For your case, I'm sure there are no stirrups crossing the joint plane. If they were not required to be there in the first place due to the strength of the concrete section alone, they have to be there now if there is a discontinuity in the concrete.

Beams without web reinforcement will fail when a crack occurs or shortly after. There is now a very weakened plane there. I don't think I would approve the use of a set retarder in this case. Before I abandon the girder, I would look at other methods to reinforce across this plane, bolting steel to the side faces of the girder, etc. or this crack may open up.