PCC Paving with no subbase

[BubbaJ]

Does anyone have experience with PCC Paving with no subbase?

I have a design build project, I am the structural engineer, where the GC has a parking lot paving design without a subbase and wants to use it because it is cheaper. I am not familiar with this practice and some issues at the site concern me, as they do the Arch on the project.

The site has a high water table as well as a steep slope down to the paving area. Lean clays and silty to sandy clays are present in the top 4 feet of the site and could possibly be uncompacted fill.

I do not have the slab design or the site prep that is proposed to be followed.

Just looking for general opinions on the practice.

 

[civilperson]

Works good in Nebraska using 95% compacted subgrade and then a grade trimmer. Slipform 18-24' wide pavement and then saw in transverse crack control joints after 7 hrs. Or using forms and a power screed. ealy application of curing compound is necessary for moisture retention.

 

[emmgjld]

I have done and seen quite a bit in Western Colorado. I am a real stickler for subgrade preparation though. My experience is that slabs don't always care if the subgrade is somewhat soft or very hard BUT, it should all be similar. I do recommend a thin gravel base for a leveling surface. The clients generally try to do without the gravel, until grade problems start occurring.

 

[GeoPaveTraffic]

I too have seen concrete pavement placed on soil subgrade; not a big fan of it, but it can work. Several things in your discussion concern me however. First is the high groundwater table. Drainage is always important in a pavement; if the groundwater is high I would either use a drainable base or install french drains below the pavement.

Second, is the steep slope down to the pavement. With no base the pavement could slide at the soil concrete interface.

Third, is you comment that you don't have the site prep that is to be used. As pointed out previously a consistant subgrade is very important with no base.

 

[ACtrafficengr]

In addition to the high water table, you have silty soils. Add some winter weather, and you've got a recipe for frost heaves.

If you are in an area with prolonged below freezing weather, you'll need to either lower the water table, replace the unsuitable material, or both to prevent heaving. Since drains tend to get clogged, I'd lean towards replacing the native soil with a sand/gravel base course.

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