12" foundation mat - placement size?
12" foundation mat - placement size?
(OP)
Okay, we have a 12" foundation mat, reinforced T&B with #6@8" EW. Placement will be in the next month or so. The EoR is likely to refer back to his restrictions for slab on grade placement size limits of 60 ft or 3,600 SF. Of course, the contractor (my client) would like something greater for this slab. He will also have to factor in his winter protection issues.
Any thoughts on practical limits? on cold weather curing methods?
Ralph
Structures Consulting
Northeast USA





RE: 12" foundation mat - placement size?
Also important to consider - this is NOT the finished slab - it gets covered with 6" of stone and then a 6" finished slab.
Ralph
Structures Consulting
Northeast USA
RE: 12" foundation mat - placement size?
Greg
RE: 12" foundation mat - placement size?
RE: 12" foundation mat - placement size?
beton1 - Please see the attached. Note the list at the bottom of the sketch. My contractor client and I are preparing for a meeting with the CM, excavator, owner's rep & design team next Tuesday. While I have most of my concerns & suggestions organized, I'm open to any thoughts from the collective wisdom here.
Ralph
Structures Consulting
Northeast USA
RE: 12" foundation mat - placement size?
Insulating blankets are placed on non-work areas, or better yet the bottom foot and trimming of the excavation is left until you are ready to start there. Then, as mentioned, protection of fresh concrete is needed. Not an easy task. The membrane placement also complicates it all.
RE: 12" foundation mat - placement size?
I don't understand the need for the membrane. What kind of structure is it? Could that be moved to the top of the mat slab?
Can the reinforcing steel be prefabricated in mats, then lift into place? This would greatly help in minimizing the grounds exposure to heat loss and would probably better maintain the integrity of the membrane. Once the steel is in place, ground thaw heater lines can be draped over the steel with blankets on top to keep the ground below from freezing. During concrete placement, the blankets and ground thaw lines can be removed as the pour progresses.
Benton1 brought up a good point about placement capacity. What is the maximum pour rate or quantity the concrete producer can provide while maintaining concrete temperatures?
Based on the temperatures you give, it is possible that frost is already at the depth of the final excavation. The ground may need to be thawed before any construction could begin after excavation, or possibly before final excavation.
Bottom line...how many blankets does your contractor have and how many ground thaw heaters is he willing to provide.
Greg
RE: 12" foundation mat - placement size?
To all who are following this thread: The construction is what it is. The CM and the concrete contractor (my client) are not in a position to deviate from the contract documents UNLESS there is a real benefit (time, $$, quality) AND the owner demonstrates a willingness to entertain value engineering.
I am not privy to the geotech report at this time, so I cannot comment on the existing soils at the foundation level.
This is a college classroom building. The basement contains all of the mechanicals.
Placement capacity, as well as finishing capacity will be discussed next week.
More data to follow.
Ralph
Structures Consulting
Northeast USA
RE: 12" foundation mat - placement size?
Is the EOR looking to force joints? If that is the case, and you must have construction joints that often, I would say to form it in a checkerboard fashion, using column locations ac corners, and place alternate squares. This could get you down to two main (or total) pours with proper planning.
RE: 12" foundation mat - placement size?
This is not a slab on grade. It is a mat foundation. It should be placed in the largest practical sections, with joints if required to be located near midspan where the shear is miminal.
TDAA,
This is a structural mat slab, not something you are going to sawcut. Any joints should consider how the slab works, including whether it resists hydrostatic uplift, which I assume it does due to the layers described, including the membrane.
RE: 12" foundation mat - placement size?
The key is how you organize the flow of concrete, the placement, the vibration, and the finishing (if any).
If the trucks can't get in to the site at a rate to prevent cold joints from forming, then you've got a problem.
RE: 12" foundation mat - placement size?
RE: 12" foundation mat - placement size?
Okay folks, here's where things stand:
Placement size - 5 sections, max 3,900 SF, max dimension 82 feet. It was like pulling teeth to get to that.
The entire basement is about 5' below the water table, so everyone is concerned about cracks occurring that would permit water intrusion. Even considering the waterproofing membrane underneath the mat.
Not meaning to cast a bad reflection upon a fellow engineering type, but the PM for the EoR is an EIT. I suspect he is being instructed to hold the line at what the contract documents require. Logical, practical or not.
The current hot issue is the protection & curing of the 3" mud slab below the membrane. Must achieve 300 day degrees before removing heat. Today's high is about 18 degrees F at 4:00 pm. Morning low was -1 degree F. The curious thing is I find no mention of day degrees as a criteria for curing a slab on grade in their specifications, only the statement: "Concrete shall be treated and protected immediately after concreting or cement finishing is completed, to provide continuous moist curing above 50 degrees F for at least seven days, regardless of ambient air temperatures." Day degrees requirement occurs only with regard to vertical & elevated concrete work.
This experience further confirms my decision to stay away from the estimating & sales side of construction. I could never second-guess the requirements in the contract documents and still price work so it would be competitive.
Ralph
Structures Consulting
Northeast USA