bridge deck pouring sequence

huangyhg

bridge deck pouring sequence
i have a contractor who has requested a change to the approved pouring sequence specified in the bridge plans in an effort to save time.
the bridge is a three span continuous curved steel plate girder superstructure that is integral with the substructure. the integral bent caps are also post-tensioned. the pt'd caps use 5 ksi concrete. the bridge deck uses 4 ksi concrete. the plans call for the deck concrete in the region over the bent to be 5 ksi, and call for construction joints to be used to separate the two regions. this part of the sequence would require 3 pours, and the screed to have to make multiple passes.
  
the request is for the final stage of the pouring sequence. it is in the negative moment region over the interior bents. the contractor would like to eliminate construction joints and excessive screed movement by making a continuous pour of the 4ksi then 5ksi then 4 ksi  without construction joints.  i am uncomfortable with this for many different reasons,(control of what is being poured in the field being the biggest) and i have requested he solve the problem by using the higher strength over the entire pour length(faster but $$).
i wanted to know if anyone had encountered this practice and if they would take issue with it as i do?
hmmm...this could be an interesting discussion on a couple of different levels.
one perspective is the contractor bid the work knowing full well that construction joints would be required in the deck at the integral pier bents.  if the owner feels that construction joints will provide better quality control and there is no cost sharing mechanism for this change then why should they entertain the request at all?
on the other hand, many owners have experienced premature deck cracking and spalls at deck contruction joints and because of this they prefer to pour continuosly whenever possible.  
i personally would prefer the continuous pour if the pour volume were small enough and the concrete would remain plastic throughout.
how large is the final stage pour?  
i assume the bent cap is intended to be monolithic without and horizontal construction joints at the deck level?  
why couldn't the contractor pour the 4 ksi on both sides of the pier bent and then pour the integral bent last with the 5 ksi concrete?  
in general, i would agree with your recommendation of using the 5 ksi throughout as long as the other important concrete properties meet or exceed those of the 4 ksi mix.
if the pour volume is small enough the contractor should very open to your recommendation is it will save them a waiting period, pump truck rental etc...
i would take issue with this request also, for several reasons not all of them technical:
1. what does the owner gain from this? is early completion an advantage (for the owner)?
2. has the contractor offered to share an cost savings (reduced contractor labor costs) with the owner?
3. what does the engineer of record have to say about this proposal (assuming that is not you).
4. at what stage of construction did the contractor make this proposal? for example:
   a. contract just awarded, with plenty of time for planning.
   b. an early construction phase "test" (of you) to see what he can "get away with" in the future.
   c. a spur of the moment decision that he wants to do "next week"
although i like to keep an open mind on contractor proposals, this one sounds "half-baked". if the contractor is unwilling to provide a real incentive, sometimes the best answer is... "no".
sorry of the typos...i need to learn to take more time to proof before hitting submit!
thanks for the responses.
some more details. the contractor is facing big liquidated damages penalties for not meeting the schedule on this job, and he is rushing the construction and not letting little details like the construction documents and dot standard specs get in the way.
this is not the first request of this nature, at this point all of the request are last minute, and need to be implemented in the immediate future. we are the eor and we have worked with the contractor on many of these issues, but i feel the client will not be served by the contractor shortcutting the contract documents and risk significant deck cracking and our reputation with the dot.  
slideruleera, i had the same impression when i read the proposal. the reasoning in the proposal talked about the time required to grind the proposed const. jts. and time to needed move the screed around to accomplish the job that he bid and won based on the plans he is now asking me to change. we also had a note in the plans that allowed him to eliminate the joints by using the higher strength concrete. i do try to keep an open mind on his requests but i feel i need to pick my battles and this is one that i don't want to budge on for the reasons previoisly stated.
thanks for your posts and i'll let you know if there are any developments.
bridge deck pours are often sequenced to avoid cracking over the negative moment regions.  while its always preferable to avoid joints of any kind in decks, you do have to sequence pours so as to avoid plastic tension/shrinkage cracks by placing concrete in the wrong sequence.
i would suggest running this by the dot as they usually have a strong opinion of things like this.  
one other thought - if the dot says no problem, and you are heading towards letting the contractor do an on-the-fly changeover in the f'c - move the location of the 4000-5000 psi interface further out by 10 feet or so.  also make the contractor submit and stick to a written plan as to how they will control, manage, record and verify that the proper mix is place in the proper place.  this will take some doing but if you give in to them on this you should strongly demand accountability from them.