Retarder in bridge deck concrete
Retarder in bridge deck concrete
(OP)
Good day.
We know retarders are used in concrete to delay the setting time.
The diagram above shows the deck pouring sequence of a slab-on-girder bridge. In one day, segments 1A, 1B and 1C will be poured. When the concrete gains at least 25 MPa strength, segments 2A and 2B will be poured.
Designer has asked that only for segments 1A and 1B, the concrete needs to have retarder up to the duration of the completion of 1B.
No retarder is needed for other segments.
Can anyone please explain the reason behind it? At first, I thought that the reason for using retarder is to avoid cold joints. But using it only for two positive moments regions indicate there might be other reason (deflection, unbalanced moment) behind it. So, I wonder if any one can explain.
Thank you
Talk To Other Members
RE: Retarder in bridge deck concrete
Rod Smith, P.E., The artist formerly known as HotRod10
RE: Retarder in bridge deck concrete
Typically, we like to pour the deck as quickly as possible. However, it doesn't always work out. Sometimes the placement a placement is large, or it gets slowed down, or it's delayed, which means some concrete may take the initial set before everything is placed. This leads to deflection cracks; to avoid/minimize the problem retarder is used. This way everything is (or is almost) placed before the initial set.
One question: Is it intended for 1A & 1B to be placed simultaneously? If not, look into uplift restraints at the opposite abutment from where the placement begins.
RE: Retarder in bridge deck concrete
The effect on 1A from the placement of 1B, would typically be negligible.
Rod Smith, P.E., The artist formerly known as HotRod10
RE: Retarder in bridge deck concrete
@bridgebuster: No, 1A and 1B are not simultaneous. There are no uplift restraints used to hold down girders.
@BridgeSmith: If 1C is poured first, as you suggested, then uplift at abutments may be a possibility. We don't pour 1C first because of limited reach of available concrete pumps.
RE: Retarder in bridge deck concrete
Rod Smith, P.E., The artist formerly known as HotRod10