Cement vs. Lime Treatment
Cement vs. Lime Treatment
(OP)
I need some advice on subgrade stabilization. I have been asked to prepare some recommendations for lime treatment of some subgrade soil. I have generally been taught over the years that lime is typically most effective on clayey soils with a PI>20 and cement treatment is usually used on granular soils with less fines having a PI<20. I have used both methods several times to improve subgrade soils at numerous sites.
However, on this particular site, there are upto 5 thin soil layers in the upper 15 feet that include clayey gravels, clayey sands, sands, and even clays with less than 10% passing the #200 sieve and a PI around 22. Since there will be significant cuts to reach grade on this project, I would like to chose one method that would be effectrive on all these types of soil.
I am guessing that lime is not the best option here because of the sands and gravels. Would cement or fly ash be a better option for treatment? If so, would cement be effective in treating the clay soils with a PI=22?
However, on this particular site, there are upto 5 thin soil layers in the upper 15 feet that include clayey gravels, clayey sands, sands, and even clays with less than 10% passing the #200 sieve and a PI around 22. Since there will be significant cuts to reach grade on this project, I would like to chose one method that would be effectrive on all these types of soil.
I am guessing that lime is not the best option here because of the sands and gravels. Would cement or fly ash be a better option for treatment? If so, would cement be effective in treating the clay soils with a PI=22?





RE: Cement vs. Lime Treatment
also what part of the world is the job located?
RE: Cement vs. Lime Treatment
RE: Cement vs. Lime Treatment
contact a local firm and get their thouhts since they're familiar with the local soils. around here, the driving factor is the fines (and mica) in the soil. you gain a little if there is coarse material, so we've actually added a little GAB or pulverized ashpalt and incorporated it in to the material prior to adding cement so that the %cement could be lowered. this game works especially well for RAP.
try this link and go to the bookstore--search for soil cement or lime stabilization...there's several free publications to help.
http://www.cement.org/index.asp
RE: Cement vs. Lime Treatment
RE: Cement vs. Lime Treatment
if you have a large area, try a reclamation contractor (here's one that i've worked with in my part of the country-- http://www.millergroup.ca/index.html) that can pulverize large areas at a time. having jimmy joe bob grading to "tooth up" the area with his bobcat and throwing the cement by hand might work for potholes, but large areas require knowledgable contractors with the appropriate equipment to do the work efficiently.
RE: Cement vs. Lime Treatment
Years ago I did some work on predominantly granular soils (GM, GC, SC, SM) to find out if lime treatment would provide sufficient improvement from a structural perspective. Simply, when the fine content was low, and/or the fines were silty without much clay, we could only get a reaction by adding flyash - the flyash was the pozzzolan. As I recall, even with significant percentages of flyash, the strength gained was not very great.
Since you have lots of variability, select from the ends of the spectrum and work with the admixture (flyash and lime or cement and flyash) to get the strength gain you need. Just make sure it works for both ends of the soil spectrum.
RE: Cement vs. Lime Treatment
When you start to add lime to a soil, it has two intial effects, firstly it uses some water to hydrate [and generate heat which reduces moisture - increases performance] and increase the pH. Once the pH reaches a maximum [typically around 12.4] then any additional lime begins to break down the clay minerals and allow the formation of calcium-silicate-hydrates and calcium-allumina-hydrates [i.e. cement]. By only adding cement, you end up using some of it to only increase the pH, which is why when cements are used, often lime will also be added. If you use PFA, this contains the allumina and silica which is present in clay soils [with a PI of over 20, or 15 in the UK].
Depending upon what the problems with the soils are [too wet/too weak etc...] and cost implications, a balance can be made between cost and end-perfromance.