continuous deck pour with a concrete retarder?

[justhumm]

I just responded to a construction RFI and am l

It's a re-decking project for an existing continuous, 4-span steel bridge being done in two stages (Stage 1: Northbound Lanes, Stage 2: Southbound Lanes) with a longitudinal joint in between. The contract plans have a deck pour sequence that shows the positive moment regions being poured before the negative moment regions.

On paper, the contractor's RFI requested to do a continuous pour for each stage. So the obvious, short answer was, "No."

In conversation, the contractor claims to have used a concrete retarder for continuous pours on similar projects.

Does anyone know if any studies / reports (FHWA, NCHRP, ACI, etc.) exist, regarding the use of retarders for crack control in continuous concrete deck pours?

...or something like that...

Thanks!

 

[TehMightyEngineer]

None that I'm aware of. I'd continue to tell him "no".

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[SlideRuleEra]

Agree, the answer is "No"...for now.
If the contractor refuses to accept "no" for an answer:

The contract plans have a deck pour sequence...
...contractor claims to have used a concrete retarder for continuous pours on similar projects.

Have him submit any studies/reports for your review. Chances are that will end the issue... or just maybe he is right. Either way, don't make his request your problem. Make him prove the request is reasonable.

If the request turns out to be reasonable... then get into how $$$ savings will be shared with the owner. Note: There will be savings, otherwise no request.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[PEinc]

There is more to consider than just crack control. Pouring concrete deck spans continuously from one abutment to another can cause superstructure uplift problems. I got involved in a project where the contractor was removing deck concrete starting at one abutment and proceeding toward the other. When he got to the 2nd span, the first span steel framing rose several feet off the abutment while the 2nd span started deflecting downward toward traffic below. The DOT wasn't very happy. Loading or unloading spans in an improper order can overstress the bridge girders.

http://www.PeirceEngineering.com

 

[BridgeSmith]

PEinc, that definitely a consideration for girders with free ends.

 

[justhumm]

Thanks for the responses, all!

PEinc, wow! I know uplift is something you have to check for, but I didn't know it actually ever happened. On the bright side, at least the sole plate weld on the rocker bearings held up. :-D

 

[BridgeSmith]

We had girders pop up like that on a new bridge under construction. We designed tie-down clamps to anchor the girder ends to the abutment, but instead of casting the anchor bolts in like we detailed it, the contractor conveniently 'forgot' and epoxied them in after. They didn't clean the holes, so the epoxy couldn't bond to the concrete, and pop go the anchors when the center girder piece is released from the crane...what a mess! Now we give them U bolts to cast in for situations like that...

 

[PEinc]

The problem for the above pictured bridge was magnified by the fact that the girder "splices" in Span 2, near the Pier 1, were pinned hanger connections.

http://www.PeirceEngineering.com

 

[BridgeSmith]

Interesting, PEinc. Looks like the was a tiny splice plate on the bottom flange, that of course fractured. No way it was going to restrain that girder, and if it did, it would defeat the purpose of the pin and hanger, which is to allow for expansion. I'm sure you know all this...I'm just musing about what could have possibly been the purpose of that little plate.

 

[bridgebuster]

interesting pictures PE, thanks for posting them.

Back on topic, it can be done & I've seen it done but you got to be careful. Do you really trust the contractor with a set retarder? Besides, concrete's nature is to crack regardless. I had a project recently - deck replacement on a mile long viaduct; 18 continuous stringer units - and in some stages we called for casting the deck for some units in one shot. It was a constructability and access issue. The rule of thumb in this area is if the pour is 360 yards or less (5 trucks per hour for 8 hours) try to do it one shot.

Fortunately in my case, the deck was changed to panels instead of cast-in-place.

 

[PEinc]

HotRod10, yes, the small flange plate is strange. Maybe the plate was used for alignment purposes during original erection and pin placement? The plate is also very rusty; so it failed a long time before this construction project began. I took the photos about 1 hour after the problem arose.

http://www.PeirceEngineering.com

 

[BridgeSmith]

"...it failed a long time before this construction project began."

My guess would be the first time the temperature dropped after it was erected.

 

[bridgebuster]

It could have been used for alignment then cut afterwards. We would have to look at the original plans or some ancient inspection reports, assuming they exist.

 

[dik]

Make him prove the request is reasonable.

and a report from an independent engineer, who takes responsibility.