Chemical Subgrade Stabilization

[fattdad]

Do you consider the blending of flyash, portland cement or lime into a subgrade for a building pad a form of chemical stabilization? Just an informal poll. . . .

f-d

¡papá gordo ain’t no madre flaca!

 

[cvg]

technically it is a chemical stabilization, but I usually call it just lime or cement stabilization. have not used fly ash, other than as a replacement for portland cement in soil cement.

 

[TDAA]

Technically, you are changing the soil chemically. That is why it behaves differently. It is not like you are adding sand / rock / fabric / grid for mechanical stabilization.

 

[msucog]

lime and cement stabilization. don't completely recall about fly ash since it's not used a lot here even though we did have a presentation from a supplier a couple years back. it seems vaguely familiar that the fly ash provides similar properties to the soil at the higher concentrations than that for lime and cement. and it also seems "fuzzy" that the different fly ashes perform dramatically different at the same percentage. so, with all that being said, i'd consider fly ash the same as lime and cement.

 

[moe333]

I believe they both are forms of chemical stabilization since you are changing the chemistry of the soil, there are chemical reactions taking place.

 

[msucog]

to add to my response since it might not be clear...yes, chemical stabilization.

 

[Panars]

Yes, I consider adding cement, lime, flyash, etc. to the soil as chemical stabilization.

 

[fattdad]

Thanks folks! I would certainly agree with the term "Soil Stabilization" as it relates to blending of ash, PC or lime into the soil. I was just taken somewhat off guard by the addition of "Chemical". Must just be me. . . .

f-d

¡papá gordo ain’t no madre flaca!

 

[geohec]

Yes, depending on the fly ash type, you could just use between 10 to 15% fly ash to stabilize a subgrade soil or for embankment construction. The reaction of the stabilization depends on many factors suh as: water content on the mixture, amount of fly ash, soil type, clay minerallogy, etc.

 

[JML4TCM]

The term "Soil stabilization" would include chemical or mechanical stabilization methods.

 

[LCruiser]

Yes. The fly ash is a substitute for soils that will react with lime. If you just use lime in silty soils it doesn't help that much. It needs some pozzolanic action - that's where the fly ash comes in. Mix the lime, keep it wet, then if you have some silty soils mix in fly ash 4 or 5 days later. If it's all silt there's no need to wait. Type "C" fly ash has it's own lime in it (concentration varies depending on where you are and which spec you're using. Type "F" fly ash has no lime in it and you need to add it separately.

 

[iandig]

Just one more thing to add to the previous comments. In the UK we have adopted similar terminology to mean different things. When we are using hydraulic binders for geotechnical improvement [lime, cement, PFA, GGBS etc...] it can either be:
? 'modification' = short-term improvement, reduce moisture content.
? 'stabilisation' = long term strength gain and formation of cementitious product.
However when we talk about remediation, we use similar names for two distinct processes defined as stabilisation and solidification but they 'mean' something quite different.
For remediation:
? substitute stabilisation for solidification [solidify material].
? stabilisation is now the chemical binding of a contaminant to the soil thus preventing leachate etc...
Therefore when considering remediation, a stabilised soil may not have good geotechnical properties, strength, stiffness, deformation resistance etc...This confusion of terminology is currently under review, but it highlights the importance of understanding what is meant by the various terms, chemical stabilisation may not mean an improvement in strength, but a binding of a contaminant using a binder.