DGA as SubGrade Material
DGA as SubGrade Material
(OP)
I am structural engineer working on a new supermarket project. The client is particularly concerned about curling of the concrete slab on grade. Originally, we had specified a 3" sand layer below the 5" fiber-reinforced slab. Now, the client wants to change to a 4" slab on DGA material. Also, after discussion with the geotechnical engineer, the client and the design team have decided to eliminate the vapor barrier. I am not familiar with DGA, so my questions are: What is it? Are there any drawbacks? Is it appropriate for this application? Any helpful information would be greatly appreciated.
As an alternative, they are thinking of placing the slab on a stone subgrade. Are there any advantages to using DGA vs. stone?
As an alternative, they are thinking of placing the slab on a stone subgrade. Are there any advantages to using DGA vs. stone?





RE: DGA as SubGrade Material
Where is your site?
I wouldn't eliminate the vapor barrier, particularly if this site is in southern California...
Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See FAQ158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"
RE: DGA as SubGrade Material
The site is in Central New Jersey.
As far as the elimination of the vapor barrier goes, the owner, the contractor, and the geotech discussed this at length before deciding to do away with it.
RE: DGA as SubGrade Material
RE: DGA as SubGrade Material
I would bet DGA is NJDOT's equivalent of PennDOT 2A...ask around.
RE: DGA as SubGrade Material
RE: DGA as SubGrade Material
The decision has been made. So what are the possible consequences?
Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See FAQ158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"
RE: DGA as SubGrade Material
I believe a vapor barrier is essential in the reduction of moisture transmission from the subgrade through the concrete slab, particularly if any finishes are to be installed on the slab.
I would leave the vapor barrier in place, pour the slab as stiff as possible, make sure to thoughly wet cure the slab for at least seven (7) days and then use a high solids cure-n-seal agent that will be compatible with the floor finishes. Call the local reps from W.R. Grace, Sonoborn-Chemrex, and Master Builders and discuss it with them. Do a test pour of about 20'x20' in a maintenence area of the building utilizing the recommended finishing, curing and cure-n-seal products to verify the methods.
RE: DGA as SubGrade Material
As well, a quick check indicates that a reduction in thickness of 1" is not justified by the change in base material.
Also, dense graded aggregate is just that, dense graded, and does not prevent water from coming in contact with the u/s of the slab. In fact, the coefficient of drainage is lower than sand, which would provide relatively the same structural support.
Leave it at 5", cure well, use any base you want, but use a proper water barrier. Reduce the chance of curling by reducing joint spacing. Yes - I read the part of the post that said the floor was fiber-reinforced. You will still get cracking. Trust me...