Lime Stabilized, Cement Stab. Sand, or Cr. Agg. Base?

[TieGuy07]

I've got a proprosed 6ft wide reinf concrete sidewalk I've been told to beef up (and then some) to ensure that the frequent truck traffic does not break it up. I've been told to use a 10" thick reinf. conc. section. The soils in the area are typically clayey with high PIs (past 20). Given the overkill with the concrete thickness I plan to use a 6-inch thick base of either: lime stabilized subgrade, cement stabilized sand, or crushed aggregate? I'm not sure why picking say cement stabilized sand is better/worse than cr. agg. -don't think lime stab is the way to go with a 6ft width but it's typically used in this locale -help would be appreciated.

 

[csd72]

cement stabilised sand does not require compaction, but as this is only 6" thick it probably wouldnt make any difference.

I doubt that the 6" sub-base is really going to do much under a 10" pavement anyhow.

I believe lime stabilisation is more to minimise shrink/swell than to strengthen the foundation - I could be wrong though.

csd

 

[TieGuy07]

Ok, thanks csd72.

We do however typically call out 95% compaction for the cem. stab. sand here in east TX. Still not sure what to use though I've got to think that cement stab sand is the best choice due to ease of construction and any movement shouldn't break up our concrete sidewalk just move it around an acceptable amount.

 

[DarthSoilsGuy]

tieguy,

sorry, i don't have a resource readily available to me or the time this morning.

The lime and cement options traditionally have been used for remediation as an afterthought once problems were encountered on-site to get a stable subgrade.

The one field that I know where these techniques are used in typical initial pavement cross-section design is in airport runway and taxiway design. There is a whole lot of public design information such as case studies on different types of treated subgrades and thicknesses available to look at on the web. At the very least, it will give perspective on the upperside of overdesign.

 

[csd72]

I have designed ground slabs for 10 ton cranes in factories and never gone thicker than 10", so I dont think there will be an issue with your pavement thhickness unless there is really bad soil.

Make sure that it is a fairly high strength mix for abrasion as well as flexural strength.

csd

 

[TieGuy07]

DarthSoilsGuy,

Ok, thanks for jogging my memory this AM. I actually have some experience with RW/TWs. I pulled out a set of plans designed for small airplanes. We used a 7" reinf. PCC over 4" Cr. Agg. Base over 6" of compacted sungrade (exist. soil). Problem we had was wet conditions made subgrade near impossible to compact to 95% and the 4" base compaction to 100% proved impossible as well. We had high PI soils but due to high sulfate content couldn't stab w/ lime per the geotech. Geotech eventually lowered there reqmts to 98% compaction on the 4" base - best we could achieve.

Given all that -I'll call out 95% compacted (exist) subgrade under 95% compacted 6" cr. agg. base., over 10" reinf PCC (I was told to use 10", can't deviate..).

csd72 -I'll call out 4,000 psi mix for the 10" section (typ. 4" sidewalk uses 3K psi). If you think can get away with 3K psi in the 10" section let me know. For airport paving we'd typically require a certain flexural strength, but figure this is too much for a sidewalk contractor to handle.