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 <20 PI 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 manufacturing Cheaper but more may be needed Good 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 15 samples

When should soil subgrades be stabilized? CBR of Clays Soils are 6 or less

How much stabilizer should be used Eads and Grim Test (ASTM D 6276) The lowest amount needed to reach a pH of 12.4

Unconfined Compressive Strength, Q u, 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

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 + H 2 oCa(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 againClay will have a silty texture

Procedures (Lime Stabilization) Mellow for one day and mix again

Procedures (Lime Stabilization) Final Compaction ( hours)

Dry (hydrated lime) application Ca(OH) 2 Hydrated lime is delivered in tanker Transported to spreader truck Procedures (Hydrated Lime Stabilization)

Dry (hydrated lime) application Ca(OH) 2 Hydrated lime spread on subgrade

Dry (hydrated lime) application Water added during mixing Compaction 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 sealing Typical 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 + H 2 oCa(OH) 2 quick lime is converted to hydrated lime CaO + H 2 OCa(OH) 2 Molecular Weight CaO Ca x 1 = O x 1 = Total Molecular Weight Ca(OH 2 ) Ca x 1 = O x 2 = H 1.00 x 2 = 1.02 Total /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 directly Typical cure time sometimes shortened

Procedures (Cement Stabilization) Water applied to mixer directly

Field testing to determine long-term strengths And durability of chemically stabilized subgrades

Field testing to determine long-term strengths And 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

Percentile Test Value In Situ CBR From University of Kentucky Transportation Center

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 resist consolidation and movement, thus virtually eliminating rutting in all layers but the asphalt surface. Unstabilized Base Stabilized Base

Reduced Moisture Susceptibility High water table Unstabilized Granular Base Stabilized Base

Thank You