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Chemical Stabilization of Subgrades. Section Engineers ’ Meeting Lake Cumberland State Resort Park March 5-7, 2013 . Why should soil subgrades be stabilized?. Improve Bearing Capacity. CBR of Clays Soils are 1 to 5. CBR of Silts 4 to 10. Silts Very Susceptible to Changes in Moisture. - PowerPoint PPT Presentation
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Chemical Stabilization of Subgrades
Section Engineers’ Meeting Lake Cumberland State Resort Park
March 5-7, 2013
Why should soil subgrades be stabilized?
Improve Bearing Capacity
CBR of Clays Soils are 1 to 5
CBR of Silts 4 to 10
Silts Very Susceptible to Changes in Moisture
Stabilized Subgrade Will Last for Many Years
85% of Soils in Kentucky are Silts and Clays
Types of chemical stabilization
Lime: Lean to Fat clays Plastic Index Predominantly > 15
Cement: Sandy and Silty Soils Plastic Index <20PI 15 to 25: Lime or Cement may be used
Lime Kiln Dust: Clays
Cement Kiln Dust: Sandy Soils
Kiln Dust is byproduct from cement and lime manufacturingCheaper but more may be neededGood for drying wet soils (modification)
Types of chemical stabilization
Lime: takes longer (mellowing period initial and final mixing)
Cement: Mixed and compacted within a few hours
Kiln Dust: Lower Cost; not as much active calcium available
When should soil subgrades be stabilized?
CBR of Clays Soils are 6 or less
CBR Values KY 1303 Section 2
0
1
2
3
4
5
1 2 3 4 5 6 7 8 9 10
CBR
# of
Sam
ples
15 samples
When should soil subgrades be stabilized?
CBR of Clays Soils are 6 or lessKY 1303 Section 2
0102030405060708090
1001 2 3 4 5 6 7 8
CBR
Perc
entil
e
CBR = 2.6 @ 85th percentile
How much stabilizer should be used
Eads and Grim Test (ASTM D 6276)The lowest amount needed to reach a pH of 12.4
pH Versus Percent Stabilizer
0
2
4
6
8
10
12
14
0 1 2 3 4 5 6 7 8 9 10 11
Percent Stabilizer
pH
Unconfined Compressive Strength, Qu, test on lime stabilized sample
How much stabilizer should be used
How much stabilizer should be used?
The lowest amount needed to reach a specified strength
UCS Versus Percent Stabilizer
0
20
40
60
80
100
120
0 1 2 3 4 5 6 7 8 9 10 11
Percent Stabilizer
Unco
nfin
ed C
ompr
essi
ve S
treng
th
Procedures (Lime Stabilization)
Construct subgrade to plan elevation
Sampling before starting
• Send samples (1 per 1,000 feet min.) to Geotechnical Branch at least 3 weeks before starting stabilization
• Proctor tests may take 2 weeks• If you think a soil needs stabilization call
Geotech
Procedures (Lime Stabilization)
Quick Lime is delivered and transferred to mixing (slaking tank)CaO + H2o Ca(OH)2 Quick Lime is converted to Hydrated Lime
Procedures (Quick Lime Stabilization)
Lime Slurry is transferred to dispensing truck
Procedures (Quick Lime Stabilization)
Scarify Subgrade
Procedures ( Quick Lime Stabilization)
Apply lime slurry to scarified subgrade
Procedures (Quick Lime Stabilization)
Apply lime slurry to scarified subgrade
Procedures (Lime Stabilization)
Mix slurry and soil to specified depth
Procedures (Lime Stabilization quick lime)
Mix slurry and soil to specified depth
#4 Sieve, 1 Inch Sieve, 2 Inch Sieve
Procedures (Lime Stabilization)
Lightly Compact
Procedures (Lime Stabilization)
Mellow for one day and mix again Clay will have a silty texture
Procedures (Lime Stabilization)
Mellow for one day and mix again
Procedures (Lime Stabilization)
Final Compaction (24- 72 hours)
Dry (hydrated lime) application
Ca(OH)2 Hydrated lime is delivered in tanker Transported to spreader truck
Procedures (Hydrated Lime Stabilization)
Procedures (Hydrated Lime Stabilization)
Dry (hydrated lime) application
Ca(OH)2 Hydrated lime spread on subgrade
Dry (hydrated lime) application
Water added during mixingCompaction same as for quick lime
Procedures (Lime Stabilization)
Check compaction
Procedures (Lime Stabilization)
Cut to final grade
Procedures (Lime Stabilization)
Cut to final grade
Procedures (Lime Stabilization)
Check Depth of chemical stabilization
Lime Testing
• Soil sampler
Depth Testing
• Phenolthalein lime testing solution
Procedures (Lime Stabilization)
Depth of chemical stabilization
Procedures (Lime Stabilization)
Depth of chemical stabilization
Procedures (Lime Stabilization)
Keep moist
Procedures (Lime Stabilization)
Apply an asphalt seal No additional moisture is needed after sealingTypical cure time is seven days maximum
Why is quick lime paid at 1.25 times actual quantity?
Quick lime is delivered and transferred to mixing (slaking tank)CaO + H2o Ca(OH)2 quick lime is converted to hydrated lime
CaO + H2O Ca(OH)2
Molecular Weight CaOCa 40.08 x 1 = 40.08O 16.00 x 1 = 16.00
Total 56.08
Molecular Weight Ca(OH2)Ca 40.08 x 1 = 40.08O 16.00 x 2 = 32.00H 1.00 x 2 = 1.02Total 74.10
74.10/56.08 = 1.32 Close to 1.25?
Truck being filled with Cement
Procedures (Cement Stabilization)
Mix one time and compact soon
Dry application
Water Applied to Soil
Procedures (Cement Stabilization)
Water can be applied to mixer directlyTypical cure time sometimes shortened
Procedures (Cement Stabilization)
Water applied to mixer directly
Field testing to determine long-term strengthsAnd durability of chemically stabilized subgrades
Field testing to determine long-term strengthsAnd durability of chemically stabilized subgrades
SPT TESTS
Coring a stabilized subgrade using compressed air as cooling medium
Core of stabilized subgrade and asphalt about 30 years old
Shelby Tubes of stabilized subgrade (special tubes made)and layer below the stabilized subgrade
Field CBR test on stabilized subgrade and below stabilization
Perc
entil
e Te
st V
alue
In Situ CBRFrom University of Kentucky Transportation Center
0
10
20
30
40
50
60
70
80
90
1000 20 40 60 80 100
120
140
160
180
CBR
Perc
entil
e
Lime Cement Cement&Lime Kiln Design
DCP Tests on stabilized subgrade
Implementation
• Stabilization or modification of all new highways with CBR’s of 6 or less is recommended by Kentucky Transportation Cabinet
• Chemical stabilization is now a standard in highway construction
• Many industries and businesses use chemical stabilization
Benefits
• Economical• Prevents pavement failures during
construction• Structural credit can and is be given to
stabilized subgrade• Reduces subgrade swell• Long-term 30 years or more
Spreads Loads
Unstabilized Granular Base
Stabilized Base
100 psi
15 psi
100 psi
4 psi
Eliminates Rutting Below Surface
Rutting can occur in surface, base and subgrade of unstabilized bases due to repeated wheel loading
Stabilized bases resistconsolidation and movement,thus virtually eliminating rutting in all layers but the asphalt surface.
Unstabilized BaseStabilized
Base
Reduced Moisture SusceptibilityHigh water table
Unstabilized Granular Base Stabilized Base
Thank You