Meaning of Pre-Cast

[BigH]

Hope to get some discussion on this:

What is the meaning/definition of precast? The drawing shows a U-shaped concrete drain for in the median of a highway - it is about 600 to 800mm deep and 500mm clear span wide. Also there are cross drains leading from the kerb to the drain - about 1.2m long, 300mm clear width and 200mm high. Specs overrule drawings overrule BOQ but BOQ mentions that the drains are to be precast. As I said there were no specific notes on drawins - or showing connecting details, etc normally associated with precast.

So, contractor wants to do cast-in-place; lots of pressure to force precast - as it meets the BOQ wording and in-situ doesn't. Can the contractor cast in situ but on an approved "casting bed", not move the unit and just leave it and call it precast - or can he do the same but shift it a few centimetres and call it precast or . . . I know this is a play on semantics and . . . but - what do you think???

 

[VAD]

BIG H:

What is the hierarchy of tender documents. Drawings generally supersede specs etc. If so then one can assume that the contractor can cast drain insitu. However, one may also saythat smnce the BOQ specifically indicated precast then the contractor should have no excuse of the intent.

Precast generally indicates that the material is manufactured in a specific facility whereby quality assurace checks can be made at times by inspectors. Sometimes the facilities also become part of the overall approval for a certified precasting plant etc. It all depends on how this is done in your particular system.

Is the quality aspect of this drain of such importance that casting it insitu would be an issue. It may be as the bottom and sides cannot be inspected as in the case of precast. On the other hand there nmay be problems asociated with field fit.

I am sure that there will be other views.

Regards

 

[jdonville]

BigH,

Sounds like it's time to submit an RFI to the designer to clarify quality issues and design intent. Many project specifications allow the designer to approve "equivalent" products - which I would take to include "means and methods", as well. If the RFI is not the way to go, the question could be couched as a value engineering proposal to cast in place rather than precast.

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

 

[DRC1]

If the higher documents allow casting in place, Then I would say it is allowed. If they are silent, then the BOQ may pervail. Generally cast in place is a little more controlled. For drains the advantage is that they can be poured monolithically by pouring upside down.Also steel forms are generally used, which give it a smoother finish and make it more efficent hydraulically. For a highway drain, I don't think that is that important.
If the engineer is a decent guy, I would talk to him. Just because something is the spec does not mean it can't be changed. If you pour it in place, You will probabably pour the floor then form and pour the walls. Even if you form and pour it all at once, you will have to let the floor get a little set before pouring the walls. This is a place where cracking & therefore leakage could occur. I would offer to put water stop in the floor pour that will continue into the walls. This would address my concern.
Good Luck!

 

[BigH]

Thanks for your inputs - really it IS a case of semantics. Hierarchy is Specifications, Drawings, BOQ. As indicated the drawings do not show any of the details that one would expect if precast is being used; but does not specifically say the work is "in situ" - but the same would be for footings, too.
The same contractor would do the precast - so there is no "precast" supplier. For the drains, it is not so much about looks - they will both look nearly the same although I admit that the precast may, if undamaged in transport and handling, look a bit better but to me its not important.
This is really a case about the measurement engineer making an issue out of the contractor casting in place and the BOQ saying it must be precast - therefore will not certify for payment!! Mainly its "internal" within the Supervisory team - but we are trying to find a way out. Engineer has not problem with in situ and apparently readily agrees that it can be in situ but measurement guy has a burr and "demands" pre-cast due to the BOQ wording even though, as indicated the drawing does not present any details about precast.
So, again, could we fine the "out" by just moving the "in situ" casting a few centimeters forward and call it precast? SEMANTICS rather than common sense.
As VAD can imagine, things are not "done" the same way over here as in North America.
to all - - and have a great 4th or, for the Canucks, hope you had a great 1st! For my part, my daughter and I went up on the roof of the house here in our West Bengali town and sang "Oh Canada" on the evening of the 1st at the top of our lungs. Tomorrow, we shall be doing the same with the "Star Spangled Banner." - we both being dual citizens.

 

[dmoler]

Never really heard of anything but precast for those types of structures. But they have to be in Florida since drainage culverts and such would be prohibited from casting in place since the water at any given time could be at or above the bottom of the culvert to begin with.

Pouring the floor and then the walls instead of all at once with a tunnel form may not be a good idea for drains. The joint between the floor and walls might not develop into a truly water tight joint, and erosion might be a problem there long term.

Hope everyone had a good 1st and 4th!

 

[jdonville]

BigH,

I would never actually recommend this, but we can dream, can't we?, the element could be demolished and removed if it won't get paid for and see how your measurements guy explains THAT to his boss!

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

 

[jheidt2543]

jdonville:

We actually did this on a small project where the Owner refused to pay for an architecural, exposed aggregate sidewalk. After fighting over the walk for 30 days, the Owner of my company issued an ultimatum, either pay for the walk or we will be over to pull it out. It wasn't until we showed up with the endloader and dump truck that the bill got paid. Sometimes, you don't bluff!

If you are in the right and an unreasonable client can't find a way to be fair, sometimes you have to lead them to a FAIR solution.