Cement Treated Subgrade
Cement Treated Subgrade
(OP)
Hi I need some help. I am looking at doing road reconstruction in my City and am wondering if I can use cement treated subgrade in lieu of base course. If this is not a good engineering option because of life cycle and maintenance concerns, I need to know before proceeding with these improvements. I am mostly looking to do this on collector roadways which receive a fair amount of traffic including school buses and tractor trailers. Any help that you could afford me would be greatly appreciated.





RE: Cement Treated Subgrade
B/c you say "base course" I'm inclined to think you mean asphalt.
I wouldn't recommend replacing your base course of asphalt with cement treated aggregate unless your traffic counts are in the tens of cars daily.
First, you may have issues just getting your DOT to approve it, assuming it's a DOT road. I know that Virginia DOT would have kittens if I recommended it.
Second, the structural numbers for CTA stone and asphalt are different and you'd have to redesign and regrade with whole roadway, very likely with a much thicker stone base.
That's my two cents.
RE: Cement Treated Subgrade
RE: Cement Treated Subgrade
One similar alternative is lime-treatment or lime fly-ash, which also allows you to reduce the thickness of the pavement section and increase the base strength. Local conditions and geotech data should dictate your ultimate choice. Factors such as freeze/thaw weather, truck traffic, construction schedule, aggregate availability, available budgets, etc., come into play when considering this alternative.
RE: Cement Treated Subgrade
PELS hit a few good points...you can play with lime, lime/cement, cement, add flyash, etc...simply said, there's million different things you can do...i suggest checking with local folks and see what works best and is most economical for the use...so stay away from very complicated combinations if possible. i have had luck with reclaimed asphalt and base course in the mix since the strength seems to do better due to the larger aggregate. same goes for full depth reclamation. i have not dealt much with lime here other than drying back subgrade materials simply because cement performs better in my area. for cement (and i'm sure lime) PCA has very general correlations (and other manuals on the subject) between subgrade materials and the amount of cementitous materials needed so that cost estimates can be looked at on the front end. you local geotech may have more specific information (i have a pool of job test results relative to pill strength and it seems to do very well...it's sort of a homemade analysis and takes in to account several parameters).
my last point of advice is this: you should not plan to use soil cement to "bridge" over crap. i've seen people try this before and ended up spending a lot of money on cement and installation just to take it up again because they insisted that 8" would bridge over the 2' of crap below. if it's crap below, you likely will not be able to get the necessary compaction and the soil cement layer may "break" and fall out, in a sense of course.
these guys are about the best around: http://www.millergroup.ca/
few links:
http://www.apwa.net/ (search FDR--full depth reclamation)
www.arra.org
good luck.
RE: Cement Treated Subgrade
subgrade is the natural soil at excavation level
subbase is a layer(s) of imported material on top of the subgrade
roadbase is a high specification of imported material on top of the subbase.
base course is the first layer of asphalt or bitumen macadam
wearing course is the final layer of asphalt or bitumen macadam
RE: Cement Treated Subgrade
Personally, I would strengthen subgrade (meaning the natural subgrade) in order to reduce the thickness of subbase and base - but I would NOT do without subbase and base - unless, of course, the subgrade is a well graded sand and gravel - with a high CBR value !!!! Don't forget that a properly designed subbase will also act in drainage - keeping water out of the base and asphalt (by draining it away or by interception).
RE: Cement Treated Subgrade
RE: Cement Treated Subgrade