Recommended Practice for Lime Flyash Stabilised Soil Base/Sub-Base in Pavement Construction
1984 Edition

Overview of Lime-Flyash-Soil Stabilization Scope

1.1 Purpose and Coverage

• Application of lime and flyash for enhancing soil strength and durability in subgrade and base layers of road pavements.
• Applicable primarily to black cotton and other expansive soils.

1.2 Mix Design Parameters (Clauses 7.3 & 7.4)

• Strength targets after curing (28 days curing + 4 days soaking):
  • UCS ≥ 7.5 kg/cm²
  • CBR ≥ 25%
• For shorter curing (7 days + 4 days soaking):
  • UCS ≥ 3 kg/cm²
  • CBR ≥ 10%

1.3 Laboratory Testing (Clauses 7.5 & 7.6)

• Compaction: IS 2720 Part VIII with heavy compaction energy.
• Strength Tests:
  • UCS per IS 2720 Part X with specimen sizes:
    • Fine/sandy soils: 50 mm diameter × 100 mm height
    • Coarser soils (<20 mm particles): 100 mm diameter × 200 mm height
  • CBR test as per IS 2720 Part XVI with specified curing and soaking.

1.4 Soil Pulverisation Requirements (Clause 8.3)

Material Requirements and Mix Proportions

2.1 Mix Design and Strength Criteria (Clauses 7.3 - 7.6)

• Minimum strength criteria:

• Typical trial mix ratios (Lime:Flyash:Soil by weight):

• Lime content should not be less than 2% by weight to ensure effective stabilization.

2.2 Compaction and Testing Procedures (Clauses 7.5 - 7.6)

• Heavy compaction as per IS 2720 Part VIII.
• Determine maximum dry density (MDD) and optimum moisture content (OMC).
• Strength evaluation via UCS (IS 2720 Part X) and CBR (IS 2720 Part XVI).

2.3 Soil Pulverisation Criteria (Clause 8.3)

Properties of Stabilized Soil Mixtures

Compressive Strength Ranges (kg/cm²)

Important Considerations:

• Values apply to compacted and cured lime-flyash-soil blends.
• Strength is influenced by mix ratios, curing duration, compaction effort, and soil type.
• Higher gravel percentages generally increase strength.
• These ranges assist in designing stabilized pavement layers.

Design Implications:

• Use strength data for bearing capacity and thickness calculations.
• Adjust lime and flyash quantities based on soil classification.

flowchart LR
    SoilType --> MixDesign
    MixDesign --> Compaction
    Compaction --> Curing
    Curing --> Strength
    Strength --> PavementDesign

Mixing and Proportioning Requirements (Clause 7)

Strength Benchmarks:

• After 28 days curing + 4 days soaking:
  • UCS ≥ 7.5 kg/cm²
  • CBR ≥ 25%
• After 7 days curing + 4 days soaking:
  • UCS ≥ 3 kg/cm²
  • CBR ≥ 10%
• Recommended curing temperatures: 30°C to 38°C

Mix Proportions by Weight (Lime:Flyash:Soil):

• Lime content below 2% is discouraged to ensure proper binding.

Testing & Quality Control:

• Heavy compaction tests per IS 2720 Part VIII for MDD and OMC.
• UCS and CBR tests as per IS 2720 Parts X and XVI respectively.
• Select economical mix that meets minimum strength criteria.
• Define control density as MDD under heavy compaction.

Pulverisation Requirements (IS 460):

Laboratory Evaluation of Lime-Flyash-Soil Blends

Strength Targets:

• After 28 days curing + 4 days soaking:
  • UCS ≥ 7.5 kg/cm²
  • CBR ≥ 25%
• After 7 days curing + 4 days soaking:
  • UCS ≥ 3 kg/cm²
  • CBR ≥ 10%
• Curing temperature: 30°C to 38°C

Mix Ratios:

• Minimum lime content: 2%

Testing Methods:

• Compaction tests (IS 2720 Part VIII) with heavy effort to determine MDD and OMC.
• Strength tests:
  • UCS per IS 2720 Part X with appropriate specimen sizes.
  • CBR per IS 2720 Part XVI after curing and soaking.

Control Density:

• Use MDD from heavy compaction as field control density.

Pulverisation Criteria (IS 460):

Strength Requirements per IRC 88

Minimum Strength Values (Clause 7.3):

Curing temperature range: 30°C to 38°C.

Mix Proportions (Clause 7.4):

Testing and Compaction (Clauses 7.5 & 7.6):

• Heavy compaction per IS 2720 Part VIII.
• Determine MDD and OMC.
• Conduct UCS and CBR tests on standardized specimens.
• Choose economical mix meeting strength requirements.

Pulverisation (Clause 8.3):

Guidelines for Construction Operations

7.1 Batching and Mixing (Clause 4.75)

• Weight batching is preferred; volume batching only if unavoidable.
• Soil must be thoroughly pulverized before mixing.
• Mixing approaches:
  • Combine lime, flyash, and soil uniformly before spreading.
  • Spread pulverized soil first, then add lime and flyash and mix in place.
• Allowable tolerances by weight:

7.2 Mechanical Mixing Equipment (Clause 8.6)

• Use mix-in-place mechanical plants with control over depth and rotor speed.
• Multi-pass mixing involves pulverizing soil, spreading stabilizers, dry mixing, adding water, wet mixing, and compacting.

7.3 Manual Mixing (Clause 8.7)

• Pulverize soil manually using appropriate tools.
• Spread stabilizers uniformly and dry mix thoroughly.
• Adjust moisture and level before compaction.

7.4 Layer Thickness (Clause 8.8)

• Maximum compacted thickness per layer: 100 mm.
• Minimum total thickness: 150 mm, applied in two layers.
• Roughen first layer surface prior to second layer placement.

7.5 Moisture and Compaction (Clause 8.9)

• Moisture content during compaction: within OMC to OMC + 2%.
• Use 8-10 tonne smooth wheel rollers.
• Achieve ≥ 100% of maximum dry density.
• Complete compaction within 4 hours of mixing.

7.6 Construction Joints (Clause 8.11)

• Chamfer edges at approximately 30° at end of workday.
• Scarify, moisten, and blend joints before resuming operations.

Subgrade Preparation Procedures per IRC 88

Key Requirements:

• Pulverisation standards (Clause 8.3):

• Mix proportions (Clause 7.4): Trial lime:flyash ratios include 1:2, 1:3, and 1:4 with soil; e.g., for 1:2 ratio: 2.5% lime, 5% flyash, 92.5% soil.

• Batching and mixing (Clause 8.4): Weight batching preferred; thorough pulverisation; mixing either before or after spreading.

• Layer thickness (Clause 8.8): Maximum compacted layer thickness of 100 mm; minimum total thickness of 150 mm in two layers with roughened interface.

• Moisture content at compaction (Clause 8.9): Within OMC ± 2%, per IS 2720 Part VII.

• Compaction (Clause 8.9): Use 8-10 tonne smooth wheel rollers; achieve at least 100% max dry density; complete compaction within 4 hours.

• Construction joints (Clause 8.11): Chamfer edges at 30°; scarify and moisten before continuation.

Process Flowchart:

flowchart TD
    SoilSampling --> Pulverisation
    Pulverisation --> Batching
    Batching --> Mixing
    Mixing --> LayerSpreading
    LayerSpreading --> MoistureAdjustment
    MoistureAdjustment --> Compaction
    Compaction --> DensityCheck
    DensityCheck --> SurfaceFinishing

Weather Considerations for Lime-Flyash-Soil Stabilization

Key Requirement:

• Stabilization activities must not be carried out when ambient shaded air temperature falls below 10°C (Clause 8.2).

Additional Construction and Curing Conditions

• Moisture for compaction should lie between OMC and OMC + 2%.
• Compaction must achieve at least 100% of maximum dry density.
• Laboratory curing temperature ranges from 30°C to 38°C.
• Minimum curing duration is 28 days.
• Curing moisture retention methods include bituminous coatings (MC-30 or emulsion) or moist straw/sand with frequent water sprinkling.
• No traffic or heavy machinery allowed on stabilized layers until curing is complete.

Summary Table of Environmental Parameters

flowchart TD
    Start --> CheckTemperature
    CheckTemperature{Temp ≥ 10°C?} -->|No| DelayWork
    CheckTemperature -->|Yes| PrepareMix
    PrepareMix --> Compaction
    Compaction --> Curing
    Curing --> CheckCuringDone
    CheckCuringDone{Curing Complete?} -->|No| Curing
    CheckCuringDone -->|Yes| AllowTraffic

Pulverisation Requirements per IRC 88

For effective lime-flyash-soil stabilization, soil must be pulverized to meet gradation standards according to IS 460:

Key Points:

• Proper pulverisation ensures uniform mixing and reaction.
• Compliance with specified sieve passing percentages is mandatory.
• This grading supports consistent compaction and strength development.

Related Mix and Strength Parameters:

• Curing duration: 28 days at 30°–38°C with moisture retention.
• Testing as per IS 2720 Parts X and XVI.

flowchart TD
    Soil --> Pulverisation
    Pulverisation --> SieveTest
    SieveTest -->|Pass 25 mm 100%| Pass4_75mm
    Pass4_75mm -->|Black Cotton: 50%| ReadyForMix
    Pass4_75mm -->|Other Soils: 60%| ReadyForMix
    ReadyForMix --> MixWithLimeFlyash
    MixWithLimeFlyash --> Curing

Moisture and Curing Standards (IRC 88)

Moisture Content for Compaction (Clause 8.9)

• Maintain moisture within Optimum Moisture Content (OMC) ± 2% during compaction.
• OMC determined in accordance with IS 2720 Part VII.
• Achieve compaction density of at least 100% of maximum dry density.

Curing Requirements (Clause 8.13)

• Temperature for curing: 30°C to 38°C in laboratory conditions; field conditions may vary.
• Minimum curing period: 28 days under moist conditions.
• Moisture maintenance:
  • Frequent water sprinkling (5–6 times per day) or
  • Covering with bituminous coatings such as MC-30 (cut-back) or emulsion.
• Light water spraying before bituminous application is recommended to reduce moisture loss.
• No vehicular traffic or heavy equipment on the cured layer.

Layer Thickness and Mixing

• Maximum compacted layer thickness is 100 mm.
• Minimum total stabilized layer thickness is 150 mm, applied in two lifts.
• Mechanical mixing is preferred; manual mixing permissible for narrow widths.

Quality Control Tests (Clause 9)

flowchart TD
    Mix --> LayerSpreading
    LayerSpreading --> Compaction
    Compaction --> CuringMethod
    CuringMethod -->|Bituminous Coating| ApplyCoating
    CuringMethod -->|Moist Sprinkling| WaterSprinkling
    ApplyCoating --> MaintainConditions
    WaterSprinkling --> MaintainConditions
    MaintainConditions --> CuringDuration

Layer Thickness Design for Lime-Flyash-Soil Stabilized Layers

Specifications:

• Maximum compacted thickness per layer: 100 mm.
• Minimum total stabilized layer thickness: 150 mm, applied as two lifts.
• Moisture content during compaction: OMC to OMC + 2%.
• Compaction: Achieve 100% or greater of maximum dry density.

Material and Testing Requirements:

• Lime content: Not less than 2% by weight.
• Strength confirmation through UCS (IS 2720 Part X) and CBR (IS 2720 Part XVI) after curing.
• Control density based on heavy compaction MDD.

Pulverisation Guidelines (IS 460):

Construction Notes:

• Mix materials by weight.
• Mechanical mixing preferred; manual mixing acceptable for narrow sections.
• Compact using 8-10 tonne smooth wheel rollers.
• Construction joints must be chamfered at 30°, scarified, moistened, and blended before continuation.
• Maintain moisture and temperature during curing for strength development.

Thickness Calculation Formula:

• Total thickness ≥ 150 mm
• Each layer thickness ≤ 100 mm
• Number of layers = Ceiling (Total thickness / 100 mm)

flowchart TD
    PrepareSubgrade --> PulveriseSoil
    PulveriseSoil --> BatchMaterials
    BatchMaterials --> MixMaterials
    MixMaterials --> SpreadLayer
    SpreadLayer --> CompactLayer
    CompactLayer --> CheckThickness
    CheckThickness{Thickness ≤ 100 mm?} -->|Yes| NextLayer
    CheckThickness -->|No| AdjustLayer

Quality Assurance Highlights (IRC 88)

1. Material Testing:

• Lime purity: Minimum 60% CaO as per IS 1514.
• Flyash fineness: Specific surface area ≥ 3200 cm²/g per IS 3812-1982.
• Testing frequency:
  • Lime: At least one test per 5 tonnes or per batch.
  • Flyash: One test per batch.
• Check lime/flyash content and soil pulverisation regularly.

2. Field Testing:

• Density: One test per 500 m²; target ≥ 100% max dry density.
• Moisture content: One test per 250 m²; maintain within OMC to OMC + 2%.
• Strength:
  • UCS test (IS 2720 Part X)
  • CBR test (IS 2720 Part XVI)
• Required minimum strength after 28 days curing + 4 days soaking:
  • UCS ≥ 7.5 kg/cm²
  • CBR ≥ 25%
• Maintain curing temperature between 30°C and 38°C.

3. Curing and Layering:

• Immediately cover compacted layers with bituminous coatings (MC-30 or emulsion) or moist straw/sand with frequent water applications.
• No traffic until curing is complete.
• Maximum layer thickness: 100 mm; total thickness ≥ 150 mm requires layering.

4. Sample Mix Proportions:

Safety and Handling Guidelines (IRC 88)

14.1 Material Batching and Mixing (Clause 4.75)

• Weight batching is mandatory; volume batching only when necessary.
• Ensure thorough pulverisation of soil before mixing.
• Mixing options include combining soil, lime, and flyash prior to spreading or spreading pulverised soil then adding stabilizers and mixing in place.
• Weight tolerances:

14.2 Mixing Plants (Clause 8.6)

• Use mechanical mix-in-place plants for uniform blending.
• Control processing depth and maintain blade sharpness.
• Employ single or multiple passes with moisture adjustments.

14.3 Manual Mixing (Clause 8.7)

• Manually pulverize soil using hand tools.
• Sprinkle water to assist pulverisation.
• Spread stabilizers evenly and dry mix thoroughly before adding moisture.
• Limit layer thickness to 100 mm; minimum total thickness 150 mm in two layers.

14.4 Moisture and Compaction (Clause 8.9)

• Maintain moisture content between OMC and OMC + 2%.
• Use 8-10 tonne smooth wheel rollers.
• Achieve at least 100% maximum dry density.
• Complete compaction within four hours post mixing.

14.5 Construction Joint (Clause 8.11)

• Chamfer edges at approximately 30°.
• Scarify, moisten, blend, and compact joints before continuing.

Summary Table for Material Tolerances:

Referenced Specifications and Tables in IRC 88

Although IRC 88 does not have a dedicated section for references, key related standards and requirements include:

15.1 Mix Proportions (Clause 7.4)

15.2 Strength Requirements (Clause 7.3)

15.3 Pulverisation Gradation (Clause 8.3)

15.4 Testing Standards

• Compaction: IS 2720 Part VIII
• UCS: IS 2720 Part X
• CBR: IS 2720 Part XVI

Process Visualization

flowchart TD
    SoilSampling --> Pulverisation
    Pulverisation --> MixDesign
    MixDesign --> Compaction
    Compaction --> Curing
    Curing --> StrengthTesting