meeting, Short and long term performance of lime/short and long term...Lule å meeting, november...
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Luleå meeting, november 2010 1/33 Short and long term performance of lime and cement stabilised soils Olivier CUISINIER, Associate Professor Laboratoire Environnement, Géomécanique & Ouvrages Soil mechanics group Ecole Nationale Supérieure de Géologie Nancy – Université France
Transcript of meeting, Short and long term performance of lime/short and long term...Lule å meeting, november...
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Short and long term performance of lime
and cement stabilised soils
Olivier CUISINIER, Associate ProfessorLaboratoire Environnement, Géomécanique & Ouvrages
Soil mechanics group
Ecole Nationale Supérieure de GéologieNancy – Université
France
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Layout
• Stabilisation basic principles• Short term performance
– Presence of potential deleterious compounds• Long term performance
– Definition of durability– Impact of water circulation– Influence of successive wetting and drying
• Conclusions• Perspectives
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Stabilisation basic principles
• Mixing soil and few % of binder (lime /cement) to: – Permit the construction of the structure:
• Reduce water content, plasticity• Improve workability• Ease the building of backfill, compacted layer,
etc. – Improve design characteristics:
• Increase shear strength properties• Lower compressibility• Lower swelling and shrinkage
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Lime stabilisation : how does it work?Physico-chemical processes
• Immediate effects of lime addition :– Hydration of quicklime
• CaO + H2O Ca(OH)2 + 12 kJ.mol-1decrease of water content
– Increase of [Ca2+] and pH • pH of saturated solution of portlandite = 12.4
Cation exchange, modification of clay particles electrical charges aggregation of clay particles
Results in short term: improvement of workability and decrease of swelling/shrinkage potential
Stabilisation basic principles
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Lime stabilisation : how does it work?Physico-chemical processes
• Time-dependant effects of lime addition:
Increase of silicon and aluminium solubility in high-pH environment
Stabilisation basic principles
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Lime stabilisation : how does it work?Physico-chemical processes
• Time-dependant effects of lime addition:– �pH release of [Si] and [Al]
• Si + Al + Ca + OH CAH + CSH + CASH
Cementitious compounds
Stabilisation basic principles
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Binder stabilization
• Fundamental processes: hydraulic setting reactions– Clinker reacts with water to form cementitious
compounds (CSH CASH, etc.)
Stabilisation basic principles
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Soil stabilisation in the field
• Earthworks:
Stabilisation basic principles
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Soil stabilisation in the field• Deep mixing: a ground improvement method
Stabilisation basic principles
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Layout
• Stabilisation basic principles• Short term performance
– Presence of potential deleterious compounds• Long term performance
– Definition of durability– Impact of water circulation– Influence of successive wetting and drying
• Conclusions• Perspectives
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Short term performance: influence of potential deleterious compounds
• Presence of some chemicals may alter the setting reactions:– Sulphur formation of ettringite that lead to
excessive swelling – Nitrates lower UCS, delay ?– Phosphates Retarders of hydration– Chlorides accelerate hydration but lead to the
formation of Friedel’s salt and decrease – Other minerals (micas) prevent setting
reactions, swelling• Key issues:
– Concentration thresholds– Experimental procedures to determine how to use
soils containing deleterious compounds
Deleterious compounds
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Soils with a high content in sulphate can be successfully stabilized with cement but…
Compaction Curing at constantwater content
Testing
0 50 100 150 2000
2
4
6
8
10U
CS
(MPa
)
Curing period (days)
Rc Limon + 14 % sulfate 20°C Rc Limon + 14 % sulfate 40°C Rc Limon 40°C Rc Limon 20°C
0 50 100 150 2000
2
4
6
8
10U
CS
(MPa
)
Curing period (days)
Rc Limon + 14 % sulfate 20°C Rc Limon + 14 % sulfate 40°C Rc Limon 40°C Rc Limon 20°C
Influence of gypsum on performance at constant water content
Deleterious compounds
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Immersion leads to exessive swelling and loss of performance
Compaction Immersion at 20°C 1 hour after compaction
Testing
Impact of immersion Deleterious compounds
0 10 200
1
2
3
4
5
6
7
8
UC
S (M
Pa)
Days after immersion
Rc Limon + sulfate Rc Limon
0
5
10
15
20
25
30
Sw
ellin
g (%
)
Gv Limon + sulfate Gv Limon
T = 20°C
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Role of delayed immersionDeleterious compounds
CompactionImmersion after 1, 7 or 28
days at constant water content
Testing
0 10 20 300
1
2
3
4
5
6
7
8
LVE + Gypsum+ CaO + CEM II
LVE + CaO + CEM II
UC
S (M
Pa)
Curing time before immersion (days)
1 day of immersion 28 days of immersion90 days of immersion1 day of immersion 28 days of immersion 90 days of immersion
0 10 20 300
5
10
15
20
25
30
LVE + Gypsum + CaO + CEM IISw
ellin
g (%
)
Curing time before immersion (days))
1 days of immersion 28 days of immersion 90 days of immersion
Delayed immersion permitted to: lower swellingincrease UCS up to satisfactory value
Sulphate can be managed for design concern by preventing wettingin the short term (first month)
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Conclusion about deleterious compounds
• Several compounds can alter the efficiency of cement/lime stabilisation (fertilizers, chloride, sulphate, sulphide)
• The impact of a compound is a function of:– Concentration (threshold between 0,01% up to 1% for S)– Curing conditions– Cement type– Etc…
• Issues: – How to predict in the lab the impact of stabilisation in
the field (design step)?– What about long term behaviour (leaching with high-
sulphate water, low pH water, freeze/thaw, etc.) ?
Deleterious compounds
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Layout
• Stabilisation basic principles• Short term performance
– Presence of potential deleterious compounds• Long term performance
– Definition of durability– Impact of water circulation– Influence of successive wetting and drying
• Conclusions• Perspectives
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Water
Definition of durability
• After construction: external stresses could alter design performance during the service life– Example : River levee in soil stabilized with
lime/cement
River levee in soil stabilized with lime/cement
Key characteristics that must be maintained:
1- permeability2- shear strength
Key features: 1- lixiviation 2- decrease of pH
Durability = Is the required performance preserved over the service life ?
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Layout
• Stabilisation basic principles• Short term performance
– Presence of potential deleterious compounds• Long term performance
– Definition of durability– Influence of successive wetting and drying– Impact of water circulation
• Conclusions• Perspectives
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Case 1: Effects of wet/dry cycles on a lime-stabilised clayey soils
• A34 clay (wL = 98,1 %, Ip = 61 %)• Short term effect of lime treatment
100 1000 10000
-4
-2
0
2
4
6
8
10
12
14
Sw
ellin
g %
Time (min)100 1000 10000
-4
-2
0
2
4
6
8
10
12
14
Sw
ellin
g (%
)
Time (min)
Without quicklime 3 % quicklime, 28 days of curing
Effect of successive wet/dry periods ?
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How to simulate wet/dry cycles in the laboratory ?
1 : Oven – full saturationDisappearance of lime-stabilisation benefits after 2/3 cycles (Khattab et al. 2007; Guney et. al 2007)
Remarks : • Not representative of
actual wet/dry cycles due to seasons alternation
• Extreme cycles (kinetic, gradient…)
2 – Unsaturated soil mechanic technique
• Perfect control of water content conditions
• Amplitude of the wet/dry cycles more representative of actual wet/dry cycles due to seasons
• Unsaturated soil mechanic techniques– Osmotic technique (suctions comprised between 0 and 8.5 MPa)– Salt solutions (above suction of 8.5 MPa)
• Unsaturated soil mechanic techniques– Osmotic technique (suctions comprised between 0 and 8.5 MPa)– Salt solutions (above suction of 8.5 MPa)
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Basic principle of the osmotic method
• Osmotic principle
M
BA
waterC0
Initial
M
h
BA Final
Cf
• Osmotic oedometer
Soil sample
Vertical stress σv
Semi-permeable membrane
Contrôle des échanges d’eau
PompePEG 6000 solution
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Influence of successive wet/dry cycles
• Samples prepared in the laboratory :
0 2000 4000 6000 8000 10000-5
0
5
10
15
Sw
ellin
g (%
)
Suction (kPa)
w ≈ 50 %
w ≈ 25 %w ≈ 30 %
Unstabilized
0 2000 4000 6000 8000 100-5
0
5
10
15
Sw
ellin
g (%
)Suction (kPa)
w ≈ 30 %w ≈ 25 %
w ≈ 35 %
3 % CaO, 1 month at 40°C
• Short term efficiency of lime-stabilisation regarding swelling and shrinkage
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Influence of successive wet/dry cycles• Samples taken in the field (7 years after construction) :
0 200 400 600 800 1000 1200-10
-8
-6
-4
-2
0
2
4
6
8
10
Sw
ellin
g (%
)
Suction (kPa)
Cycles between 0 and 1 MPa
w ≈ 43 %w ≈ 50 %
Swell/shrink potential ≈ null
0 2000 4000 6000 8000-10
-8
-6
-4
-2
0
2
4
6
8
10
Sw
ellin
g (%
)Suction (kPa)
w ≈ 30 %
w ≈ 43 %
w ≈ 43 %
Cycles between 0 and 8.5 MPa
Swell/shrink potential ≈ 8 %
The efficiency of lime stabilization has to be regardedas a function of the range of variation of the water content
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Effects of wet/dry cycles on a lime-stabilised clayey soils
• Conclusions – Unsaturated soil mechanics techniques are able to
reproduce field conditions– The use of osmotic method demonstrated the
ability of stabilized soil to resist to wet/dry cycles– Major role of the amplitude of the wet/dry cycles
on durability• Issues to assess durability of a lime-stabilised
structure– Prevision of the service life ?– Wet/dry cycles amplitude ?– Impact of the initial conditions ?
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Layout
• Stabilisation basic principles• Short term performance
– Presence of potential deleterious compounds• Long term performance
– Definition of durability– Influence of successive wetting and drying– Impact of water circulation
• Conclusions• Perspectives
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Lime-stabilised silt under long term leaching
• Determine the impact of water circulation on the shear strength of lime-stabilized soil– River levee– Earth dam
Flexible wall permeameter
Distilled water circulation, equilibrated with atmosphere (80 kPa)
Latex membrane
Porous stone
Soil sample
Frame
Conf
inin
g pr
essu
re
Hydraulic head = 8 mi = 80Cell confinment = 120 kPaCirculation duration = 320 days
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Characteristics of the tested soil
• Selected soil : Jossigny silt
• Preparation of the samples• 0, 1 or 3% of quicklime• Optimum water content• Dynamic compaction
Geotechnical propertiesLiquid limit, wL (%) 37,0Plastic limit, wP (%) 18,7Index of plasticity , IP 18,3
Unit weight of solids, ρS (Mg.m-3) 2,69
Fines contents, < 2 µm (%) 29,4
50 mm
Position of blows
Compaction mold H = 100 mmΦ = 50 mm
Dynamic compaction
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Short term behaviour : impact of lime addition
– Shear strength after 90 days of curing at constant w– CU + u triaxial tests
0 100 200 300 400 500 600 700 8000
100
200
300
400
0 100 200 300 400 500 600 700 8000
100
200
300
400t (kP
a)
s' (kPa)0 100 200 300 400 500 600 700 800
0
100
200
300
400
No treatment 1 % of quicklime3 % of quicklime
Shear strength enveloppe constant from 1 to 3 % of quicklime
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Impact of water circulation after 150 days of water circulation
• Results with 1 % of quicklime
0 100 200 300 400 500 600 700 8000
100
200
300
400
0 100 200 300 400 500 600 700 8000
100
200
300
400t (kP
a)
s' (kPa)
No treatment 90 days of curingAfter 150 days of flow
0 100 200 300 400 500 600 700 8000
100
200
300
400
Total loss of the improvement brought by lime
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0 100 200 300 400 500 600 700 8000
100
200
300
400t (kP
a)
s' (kPa)
Impact of water circulation after 150 days of water circulation
• Results with 3 % of quicklime
0 100 200 300 400 500 600 700 8000
100
200
300
400
No treatment 90 days of curing220 days of flow
0 100 200 300 400 500 600 700 8000
100
200
300
400
Stability of the mechanical behaviour
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Physico-chemical processes
• Distribution of the calcium in the samplesCarbonates Free lime Ca in waterLeached calcium Cementitious compounds
0,00
0,20
0,40
0,60
0,80
1,00
1,20
1,40
T=0 T=25 T=25+150 T=25+200 T=25+320
% C
a
1 % quicklime
Curing period Leaching
0,00
0,50
1,00
1,50
2,00
2,50
3,00
T=0 T=25 T=25+150 T=25+200 T=25+320
% C
a
3 % quicklime
Curing period Leaching
Key factor = amount of Ca and pH to maintain stability, The higher the CaO content, the longer the durability
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Conclusion
• Shear strength increase brought by lime addition is reversible– Amount of binder should not only be adapted to
the short term performance but also to environmental stresses
• Key parameters : – Amount of lime added / leached calcium– Flow of water– Competition between dissolution / precipitation
processess • Further studies
– Impact of flow rate– Microstructural alteration during flow– Nature of the circulating fluid (pH, species in
solution)
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General conclusions and perspectives
• Durability is to be defined regarding certain environmental conditions (water content variation, water flux…)
• The fundamental mechanisms of degradation cannot be understood without the analysis of microstructure and physico-chemical processes
• Need : predictive models to assess long term behaviour and degradation…
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Publications• Cuisinier, O., Le Borgne, T., Deneele, D. & Masrouri, F. 2010.
Quantification of the detrimental effects of some chemical compounds on soil stabilization. Engineering Geology (accepted).
• Deneele, D., Cuisinier, O., Hallaire, V. & Masrouri, F. 2010. Microstructural evolution and physico-chemical behavior of compacted clayey soil submitted to an alkaline plume. Journal ofRock Mechanics and Geotechnical Engineering, 2 , 169-177.
• Cuisinier, O., Deneele, D & Masrouri, F. 2009. Shear strength behaviour of compacted clayey soils submitted to an alkaline plume. Engineering Geology, 108, 177-188.
• Le Runigo, B., Cuisinier, O., Cui, Y.-J., Deneele, D. & Ferber, V. 2009. Impact of the initial state on fabric and permeability of a limetreated silt under long term leaching. Canadian Geotechnical Journal, 46, 1243-1257.
• Cuisinier, O., Masrouri, F., Pelletier, M., Villiéras, F. & Mosser-Ruck, R. 2008. Microstructure of a compacted soil submitted to an alkaline plume. Applied Clay Science, vol. 40, n°1-4, 159-170.
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National project on soil stabilization
TerDOUESTTerDOUESThttp://www.cnrs-imn.fr/TerDOUEST/
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Thank you for your attention
