Chemical Stabilization

8/12/2019 Chemical Stabilization

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Chemical StabilizationAkram Karimian


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Stabilization

Soil stabilization is the process of maximizing the suitability of soil

for a given construction purpose.

Purpose Of Soil Stabilization:

*strength improvement

*Dust control

*Soil waterproofing

And reduce the construction cost by making best use of locally

available materials.


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Mechanical Stabilizationsoil stabilization can be achieved through physical process

by altering the physical nature of native soil particles by

either induced vibration or compaction or by incorporating

other physical properties such as barriers and nailing.

Chemical Stabilization

soil stabilization depends mainly on chemical reactions

between stabilizer(cementitious material) and soil minerals(pozzolanic materials) to achieve the desired effect such as

Hydration, Cation exchange, Pozzolanic reactions,.


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Chemical Stabilization

Through soil stabilization, unbound materials can be

stabilized with

traditional cementitious materials (cement, lime, fly

ash, bitumen or combination of these)

or

nontraditional materials (Ionic, Enzymes,

lignosulfonates, polymers, petroleum emulsions,

tree resin, salts).

The stabilized soil materials have a higher strength,

lower permeability and lower compressibility than the

native soil.


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Portland cement

Mechanical additives

Well-graded fines

Decrease plasticity

Increase strength

Decrease swelling ability

lime

CaO or Ca(OH)2 Chemical additives

Medium moderately fine soil

Fine-grained clay

Decrease plasticity

Increase strength

Decrease swelling ability

Curing day 3 to 7 days

Cement stabilized soil are usually

stronger than lime stabilized soils

No in Lime.

traditional stabilizers


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Fly Ash

Chemical additives

Silicon and aluminum compounds

Granular materials with few fines

+ lime + water

Available and cheap

Bitumen Mechanical additives

Asphalt cement and Asphalt

emulsions

Make soil stronger Increase resistant to water

and frost


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Factors Affecting the Strength of Stabilized Soil

organic matters,

sulphides ,

Compaction,

Moisture content,

Temperature.

the top layers of most soil

react with hydration product e.g.

(Ca(OH)2) resulting into low pH Delay in hydration process

Make hardening difficult

Impossible to compact


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organic matters,

sulphides

Compaction,

Moisture content,

Temperature.

sulphides in form of iron pyrites (FeS2)

2FeS2+ 2H2O +7O2= 2FeSO4+ 2H2SO4

CaCO3+ H2SO4+ H2O = CaSO4.2 H2O + CO2

greater volume than the

combined volume of reactants


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organic matters,

sulphides

Compaction,

Moisture content,

Temperature.

Stabilized mixture has lower maximum drydensity

The optimum moisture content increases with

increasing binders In cement stabilized soils, hydration process

takes place immediately. This process involveshardening of soil mix which means that it isnecessary to compact the soil mix as soon aspossible. Any delay in compaction may resultin hardening of stabilized soil mass andtherefore extra compaction effort may berequired to bring the same effect. That maylead to serious bond breakage and hence lossof strength.

Lime stabilized soil require mellowing

periodto allow lime to diffuse through

the soil thus producing maximum

effects on plasticity. After this period,lime stabilized soil may be remixed and

given its final compaction resulting into

remarkable strength.


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organic matters,

sulphides

Compaction,

Moisture content,

Temperature.

hydration process + compaction

Insufficient moisture content will

cause binders to compete with soilsin order to gain moisture from thesurrounding.

For soils with great soil-water affinity(such as clay, peat and organic soils),

the hydration process may beretarded due to insufficient moisturecontent, which will ultimately affectthe final strength.


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organic matters,

sulphides

Compaction,

Moisture content,

Temperature.

Pozzolanic reaction is sensitive to

changes in temperature.

In the field, Pozzolanic reactionsbetween binders and soil particles

will slow down at low temperature

and result into lower strength of the

stabilized mass. In cold regions, it may be advisable

to stabilize the soil during the warm

season.


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Non-traditional stabilizersIonic additives (acids and alkaline)

Alter electrolyte concentration of pore fluid -> cation

exchange -> flocculation of clay minerals Reduce the surface charge -> loss of double-water layer ->

close packing and flocculation

Reduce plasticity , swell potential, particle size

No effect in treating granular soils

Suitable for smaller clay minerals which have large double-

layer water : montmorillonite


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Non-traditional stabilizersEnzyme additives

Organic molecules : catalyze specific reactions

Depends on soil chemistry and need time for diffusion

Large organic molecules surround the clay minerals ->

neutralizing the negative charge -> reduce clays affinity for

moisture

No effect in granular soils (and silts)

Need time


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Non-traditional stabilizerslignosulfonate additives

Lignin that binds Cellulose fibers

Coat individual soil particles -> binds particles together

Cementing agents with minor chemical effects -> bonding

physically particles together

More effective in granular soils -> diminish with decreasing

particle size Deflocculated clays -> poor performance in stabilization


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Non-traditional stabilizerssalt additives

Calcium and magnesium chloride (cacl2 and mgcl2)

cation exchange and decrease double-layer and increaseflocculation

Increase pore water surface tension -> increase apparentcohesion -> improvement strength

Corrosive for metals and susceptible for leaching

granular soils: compaction and recrystallization -> weakphysical bonds between particles

Fine-grained soils : improve cohesion by preventing the soilfrom drying


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Non-traditional stabilizerspetroleum resin additives

Asphalt emulsions and synthetic isoalkane fluids

Asphalt emulsions: water adsorbs to surface + evaporation ->asphalt cement residue on soil particle surface

Coat the particle and form physical bond -> suitable forgranular soils because of low surface area

Coated particles provide excellent waterproofing

Synthetic fluids : compaction with dispersing particles andrearrangement of them + waterproofing

Do not offer chemical or physical bonding : minimalimprovement in strength


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Non-traditional stabilizerstree resin additives

By Timber and paper industries

Coat soil particles to bind them together : cementing

Suitable for granular materials


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Case Study of the use of an Enzyme stabilizerTerrazyme (In central and Eastern Europe)

Replace adsorbed water with organic cations -> neutralizing

negative charge

reduce the thickness of electrical double layer ->compacting more tightly


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Terrazyme

Resists being replaced by water -> reduce the tendency to swell

Develops cementation


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Design procedures Subgrade modification : create a working platform

no credit in design process

Subgrade stabilization : enhance the strength

increased strength take into account in design process

2 mechanisms Mixing with chemical materials

-> increase in particle size by cementation, greater strength,reduction in PI, reduced shrink/swell potential

-> absorption and chemical binding -> better compaction


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Criteria for chemical selection


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Lime required for treatmenta) .

b) .

c) .


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Cement required for treatment


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Stabilization Methods

1) In-situ stabilization

Deep mixing method

Wet mixing Dry mixing

Mass Stabilization

2) Ex-situ stabilization


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In-situ stabilization

on site soil improvement

without removing the bulk soil improving soils for deep and shallow foundations and

contaminated sites.

by injectinginto soils a cementitious material such cement

and lime in dry or wet forms.

The choice to either use dry or wet deep mixing methods

depend among other things; the in-situ soil conditions, in

situ moisture contents, effectiveness of binders to be used,

and the nature of construction to be founded.

Depending on the depth of treatment, the in situ

stabilization may be regarded as either deep mixing method

or mass stabilization.


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Deep mixing method stabilization of soils at large depth.

wet or dry binder is injected into the ground and blended with in situ soft soils (clay,

peat or organic soils) by mechanical or rotary mixing tool.

The aim is to produce the stabilized soil mass which may interactwith natural soil andNOT, to produce too stiffly stabilized soil mass like a rigid pile which may

independently carry out the design load.

Thus the design load should be distributed and carried out partlyby natural soil and

partly by stabilized soil mass (column).


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Wet mixing


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Dry mixing


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Mass stabilization is a shallow to deep

stabilization method in which the entirevolume ofsoft soil can be stabilized to a prescribed depth.

The technique is relatively new and is highly suited

for the stabilization of high moisture content such

as clay, silty, organic soils and contaminated

sediments. The method provides an alternative to traditional

method of soil improvement such as removal and

replaces techniques.

Mass stabilization


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Ex-situ stabilization

The technology involves dislodging of the soils and or

sediments from the original position and moves toother place for the purpose of amendment.

The main objectives of dredging can be either for

amending the contaminated sediments to reduce

toxicity and mobility .

Offsite treatment of the sediment can be done in

confined disposal facilities (CDF) and then be used or

disposed at designated site. Method of removal, means

of transportation, availability of treatment location,

disposal site or demand for reuse is key factors to

consider when planning for ex-situ stabilization.


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Expansive clay from Spain : PL =24.9%

LL = 43.5%UC = 0.399 MPa

free swelling : 4.65% must be less than 3% in Spain

Additives : lime (the only permitted additive in Spain)

Consolid System (CS plymer) (waste with high mineral content)


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Anti-expansive treatment


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Improve mechanical properties


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Red mud : waste material of producing alumina (35-40% bauxite)


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Chemical Stabilization