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

IRC 88: Scope & Key Specifications for Lime-Flyash-Soil Stabilization

1. Scope Summary

• Stabilization of soil using lime and flyash to improve strength and durability of subgrade and base layers in road construction.
• Applicable for black cotton and other soils.

2. Key Mix Design Parameters (Clause 7.3 & 7.4)

• Minimum strength after curing (28 days + 4 days soaking):
  • Unconfined Compressive Strength (UCS): 7.5 kg/cm²
  • CBR: 25%
• For 7 days curing + 4 days soaking:
  • UCS = 3 kg/cm², CBR = 10%

3. Laboratory Testing (Clause 7.5 & 7.6)

• Compaction Test: IS 2720 (Part VIII), Heavy compaction effort.
• Strength Tests:
  • UCS: IS 2720 (Part X), specimen size:
    • Fine-grained/sandy: 50 mm dia × 100 mm height
    • Coarser: 100 mm dia × 200 mm height
  • CBR: IS 2720 (Part XVI), curing 7 or 28 days + soaking 4 days.

4. Degree of Pulverisation (Clause 8.3)

IRC 88 - Materials: Key Formulas, Tables & Specifications

1. Mix Design & Proportioning (Clause 7.3 - 7.6)

• Minimum Strength Requirements:

• Trial Mix Ratios (Lime:Flyash:Soil) (Clause 7.4):

• Lime quantity ≥ 2% by weight for effective mixing (Clause 2.5).

2. Compaction & Testing (Clause 7.5 - 7.6)

• Use Heavy Compaction as per IS: 2720 (Part VIII).
• Determine Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) from compaction tests.
• Strength testing options:
  • Unconfined Compressive Strength (UCS): IS: 2720 (Part X)
    • Specimen size: 50 mm dia × 100 mm height (fine soils)
    • 100 mm dia × 200 mm height (coarser soils, < 20 mm particles)
  • CBR Test: IS: 2720 (Part XVI)
    • Curing: 7 or 28 days + 4 days soaking

3. Degree of Pulverisation (Clause 8.3)

| Sieve Size (

IRC 88: Properties of Lime-Flyash-Soil Mixes

Key Strength Ranges (Compressive Strength in kg/cm²)

Important Notes:

• These values represent compacted and cured lime-flyash-soil mixtures.
• Strength depends on factors like mix proportions, curing time, compaction effort, and soil type.
• Higher gravel content generally yields higher strength.
• These strengths guide the design of stabilized pavement layers.

Design Implications:

• Use these strength ranges to estimate bearing capacity and layer thickness.
• Adjust lime and flyash content to optimize strength based on soil type.

flowchart LR
    A[Soil Type] --> B{Mix Proportions}
    B --> C[Compaction]
    C --> D[Curing]
    D --> E[Strength (kg/cm²)]
    E --> F[Design Pavement Layer]

For detailed mix design, refer to curing period (usually 7-28 days) and optimum moisture content per IRC guidelines.

IRC 88 - Mix Design and Proportioning (Clause 7)

Key Specifications:

• Strength Requirements (after curing and soaking):
  • 28 days curing + 4 days soaking:
    • Unconfined Compressive Strength (UCS) ≥ 7.5 kg/cm²
    • CBR ≥ 25%
  • 7 days curing + 4 days soaking:
    • UCS ≥ 3 kg/cm²
    • CBR ≥ 10%
  • Curing temperature: 30°C to 38°C

Mix Proportions (Lime: Flyash: Soil by weight parts):

• Lime content < 2% not recommended for proper mixing.

Testing & Control:

• Perform Heavy Compaction tests per IS:2720 (Part VIII) to find:
  • Maximum Dry Density (MDD)
  • Optimum Moisture Content (OMC)
• Strength tests:
  • UCS test per IS:2720 (Part X), specimen sizes:
    • Fine/sandy soils: 50 mm dia × 100 mm height
    • Coarser soils (<20 mm particles): 100 mm dia × 200 mm height
  • CBR test per IS:2720 (Part XVI), curing 7 or 28 days + 4 days soaking
• Select mix meeting minimum strength at lowest lime content or cost-effective ratio.
• Define Control Density as MDD at heavy compaction for final mix.

Pulverisation Requirements (IS:460):

IRC 88: Laboratory Testing Procedures for Lime-Flyash-Soil Mix

Key Specifications:

• Minimum Strength Requirements (after curing & soaking):
  • 28 days curing + 4 days soaking:
    • Unconfined Compressive Strength (UCS) ≥ 7.5 kg/cm²
    • CBR ≥ 25%
  • 7 days curing + 4 days soaking:
    • UCS ≥ 3 kg/cm²
    • CBR ≥ 10%
• Curing Temperature: 30°C to 38°C

Mix Proportions (Lime:Flyash:Soil by weight)

• Lime content < 2% not recommended.

Testing Methods:

• Compaction Test: IS 2720 (Part VIII) - Heavy compaction effort to find Maximum Dry Density & Optimum Moisture Content (OMC).
• Strength Tests:
  • UCS: IS 2720 (Part X)
    • Specimen size:
      • Fine/sandy soils: 50 mm dia × 100 mm height
      • Coarser soils (<20 mm max particle): 100 mm dia × 200 mm height
  • CBR: IS 2720 (Part XVI)
    • Curing: 7 or 28 days + 4 days soaking

Control Density:

• Maximum dry density at heavy compaction used for field compaction.

Pulverisation Requirements (IS 460):

Moisture

Key Strength Requirements per IRC 88 for Lime-Flyash-Soil Mix:

1. Minimum Strength Criteria (Clause 7.3)

Curing temperature: 30°C to 38°C.

2. Mix Proportions (Clause 7.4)

3. Testing & Compaction (Clauses 7.5 & 7.6)

• Use Heavy Compaction per IS:2720 (Part VIII).
• Determine Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) from compaction curves.
• Strength tests:
  • UCS per IS:2720 (Part X) on specimens (50mm dia × 100mm height for fine soils; 100mm dia × 200mm height for coarser).
  • CBR per IS:2720 (Part XVI) after curing and soaking.
• Select mix ratio meeting minimum strength with least lime content or cost.

4. Degree of Pulverization (Clause 8.3)

Key Formulas, Tables & Specifications for Construction Operations (IRC 88)

1. Batching and Mixing (Clause 4.75)

• Batching by weight is preferred; volume batching allowed only if unavoidable.
• Materials must be thoroughly pulverized before mixing.
• Mixing methods:
  • Mix lime, flyash, and soil together then spread.
  • Spread pulverized soil, then lime and flyash, and mix on subgrade.
• Tolerance limits (by weight):

2. Plant for Construction (Clause 8.6)

• Use mix-in-place mechanical plants (single-pass or multi-pass).
• Control mixing depth and rotor speed for uniformity.
• Multi-pass: pulverize soil → spread stabilizer → dry mix → add water → wet mix → compact.

3. Manual Mixing (Clause 8.7)

• Pulverize soil manually.
• Spread stabilizer, dry mix thoroughly.
• Adjust moisture and level before compaction.

4. Layer Thickness (Clause 8.8)

• Max compacted layer thickness: 100 mm.
• Lime-flyash-soil layer minimum thickness: 150 mm (laid in two layers).
• Roughen first layer before second to ensure bonding.

5. Moisture Content & Compaction (Clause 8.9)

• Moisture at compaction: Optimum Moisture Content (OMC) ≤ moisture ≤ OMC + 2% (per IS: 2720 Part VII).
• Use 8-10 tonne smooth wheel rollers.
• Achieve at least 100% maximum dry density (IS: 2720 Part VII).
• Complete compaction within 4 hours of mixing.

6. Construction Joint (Clause 8.11)

• Chamfer edge at ~30° at end of day.
• Scarify, moisten, and blend joint before resuming.

7. Degree of Pulverisation (Clause 8.3)

| Sieve Size

Preparation of Subgrade as per IRC 88

Key Specifications & Steps:

• Pulverisation Requirements (Clause 8.3):

• Mixing Proportions (Clause 7.4):
  Trial lime:flyash ratios: 1:2, 1:3, 1:4 with soil; e.g., for 1:2 → Lime 2.5%, Flyash 5%, Soil 92.5%.

• Batching & Mixing (Clause 8.4):
  Batch by weight; thorough pulverisation; mix lime, flyash, and soil either before or after spreading.

• Layer Thickness (Clause 8.8):
  Max compacted layer thickness: 100 mm; minimum total layer thickness: 150 mm, laid in two layers with roughened surface between layers.

• Moisture Content (Clause 8.9):
  At compaction, moisture = OMC (IS 2720 Part VII) ± 2%.

• Compaction (Clause 8.9):
  Use 8-10 tonne smooth wheel rollers; achieve ≥100% max dry density (IS 2720 Part VII); compaction within 4 hours after mixing.

• Construction Joint (Clause 8.11):
  Chamfer edge at 30°; scarify and moisten joint before continuing.

Summary Flowchart of Subgrade Preparation:

flowchart TD
    A[Soil Sampling & Clearing] --> B[Pulverisation to Specified Degree]
    B --> C[Batching Lime, Flyash & Soil by Weight]
    C --> D[Mixing (Manual or Mechanical)]
    D --> E[Spreading Mixed Material in Layers ≤100mm]
    E --> F[Adjust Moisture Content (OMC ± 2%)]
    F --> G[Compaction with Rollers]
    G --> H[Check Density ≥ 100% Max Dry Density]
    H --> I[Surface Finishing & Construction Joint Preparation]

References:

• IS

IRC 88 - Weather Limitations for Lime-Flyash-Soil Stabilization

Key Specification:

• Minimum Air Temperature: Stabilization shall NOT be done when air temperature in the shade is below 10°C (Clause 8.2).

Related Construction & Curing Guidelines

• Moisture Content at Compaction: Between Optimum Moisture Content (OMC) and OMC + 2% (Clause 8.9).
• Compaction: Achieve at least 100% maximum dry density as per IS: 2720 (Part VII).
• Curing Temperature: Laboratory curing at 30°C to 38°C (Clause 7.6).
• Curing Period: Minimum 28 days recommended for strength development.
• Curing Methods:
  • Cover with bituminous coating (MC-30 or emulsion) to retain moisture.
  • Alternatively, moist straw/sand with frequent water sprinkling (5-6 times/day).
• Traffic Restrictions: No traffic or heavy equipment on stabilized layer until curing is complete.

Summary Table: Weather & Curing Conditions

flowchart TD
    A[Start Stabilization] --> B{Is Air Temp ≥ 10°C?}
    B -- No --> C[Delay Stabilization]
    B -- Yes --> D[Prepare Soil Mix]
    D --> E[Compaction at OMC to OMC+2%]
    E --> F[Curing for 28 days at 30-38°C]
    F --> G{Curing Complete?}
    G -- No --> F
    G -- Yes --> H[Allow Traffic]

Note: Avoid stabilization in cold or damp weather to ensure proper pozzolanic reaction and strength gain.

Degree of Pulverisation (IRC 88)

For lime-flyash-soil stabilization, soil must be pulverised to meet the following gradation as per IS:460:

Key Specifications:

• Soil pulverisation ensures proper mixing and reaction with lime and flyash.
• Pulverised soil must pass the above sieve sizes by weight percentage.
• This gradation ensures uniform compaction and strength development.

Related Mix Design & Strength Criteria:

• Curing: 28 days at 30°–38°C, moisture maintained.
• Testing: IS 2720 (Part X for UCS, Part XVI for CBR).

Summary:

• Pulverise soil so 100% passes 25 mm sieve.
• For black cotton soil, 50% passes 4.75 mm sieve; for others, 60% passes 4.75 mm.
• Follow mix design and curing for strength compliance.

flowchart TD
    A[Soil Pulverisation] --> B{Sieve Test}
    B -->|Pass 25 mm 100%| C[Pass 4.75 mm]
    C -->|Black Cotton: 50%| D[Ready for Mixing]
    C -->|Other Soils: 60%| D
    D --> E[Mix with Lime & Flyash]
    E --> F[Curing 28 days

Key Specifications & Formulas for Curing and Moisture Control (IRC 88)

Moisture Content for Compaction (Clause 8.9)

• Moisture at compaction = Optimum Moisture Content (OMC) ± 2%
• OMC as per IS: 2720 (Part VII)
• Compaction density ≥ 100% of Maximum Dry Density (IS: 2720 Part VII)

Curing (Clause 8.13)

• Temperature range for curing: 30°C to 38°C (lab), field may vary.
• Minimum curing period: 28 days (if moist curing by sprinkling straw/sand)
• Moisture during curing: Maintain close to OMC by sprinkling water 5-6 times/day.
• Bituminous curing: Use MC-30 cut-back @ 50-60°C or emulsion @ 25-55°C at 8.3 kg/10 m².
• Light sprinkling of water before bituminous application recommended to avoid moisture loss.
• No traffic or heavy equipment allowed during curing.

Layer Thickness & Mixing (Clauses 8.8, 8.6, 8.7)

• Max compacted layer thickness: 100 mm
• Lime-flyash-soil layer minimum thickness: 150 mm (laid in two layers)
• Mixing: Mechanical preferred; manual allowed for narrow widths.

Quality Control Tests (Clause 9)

Summary Flow of Curing & Moisture Control

flowchart TD
    A[Mixing Lime, Flyash & Soil] --> B[Layer Spreading (max 100 mm)]
    B --> C[Compaction at OMC ± 2%]
    C --> D{Curing Method}
    D -->|Bituminous Coating| E[Apply MC-30 @ 50-60°C or Emulsion]
    D -->|Mo

Thickness Design of Stabilised Layers (Lime-Flyash-Soil Mix) - IRC 88

Key Specifications:

• Maximum compacted layer thickness: 100 mm per layer.
• Minimum total thickness: 150 mm, laid in two layers.
• Moisture content at compaction: Optimum Moisture Content (OMC) to OMC + 2%.
• Compaction: Achieve ≥ 100% of maximum dry density (IS: 2720 Part VII).

Mix Design & Strength Testing:

• Lime content: Minimum 2% by weight (below 2% not recommended).
• Tests for strength:
  • Unconfined Compressive Strength (IS: 2720 Part X) after 28 days curing at 30-38°C.
  • CBR test (IS: 2720 Part XVI) after 7 or 28 days curing with soaking.
• Control Density: Maximum dry density under heavy compaction.

Degree of Pulverisation (Before Stabilization):

Construction Notes:

• Mix soil, lime, and flyash by weight.
• Use mechanical mixing preferred; manual mixing allowed only for narrow widths.
• Compact with 8-10 tonne smooth wheel rollers.
• Construction joints: Chamfer edges at 30°, scarify and blend before continuing.
• Curing: Maintain moisture and temperature for proper strength gain.

Summary Formula for Layer Thickness:

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

flowchart TD
  A[Prepare Subgrade] --> B[Pulverise Soil]
  B --> C[Batch Lime & Flyash (by weight)]
  C --> D[Mix Soil + Lime + Flyash]
  D --> E[Spread & Level Mixed Material]
  E --> F[Compact (OMC to OMC+2%, 100% max dry density)]
  F --> G{Layer Thickness < 100 mm?}
  G -- Yes --> H[Proceed to Next Layer

Quality Control & Verification - IRC 88 Key Points

1. Material Quality Tests

• Lime Purity: CaO content ≥ 60% (IS: 1514)
• Flyash Fineness: Specific surface area ≥ 3200 cm²/g (IS: 3812-1982)
• Test frequency:
  • Lime: 1 test/5 tonnes or per consignment
  • Flyash: 1 test per consignment
• Lime/Flyash Content: Regular procedural checks
• Degree of Pulverisation: As necessary (Sieve passing per IS: 460)

  Sieve Size	Black Cotton Soil (%)	Other Soils (%)
  25 mm	100	100
  4.75 mm	50	60

2. Compaction & Strength Tests

• Density: 1 test/500 m²; achieve ≥ 100% max dry density (IS: 2720 Part VII)
• Moisture Content: 1 test/250 m²; within OMC to OMC + 2%
• Strength:
  • Unconfined compressive strength (IS: 2720 Part X)
  • CBR test (IS: 2720 Part XVI)
• Minimum strength after 28 days curing & 4 days soaking:
  • UCS ≥ 7.5 kg/cm²
  • CBR ≥ 25%
• Curing temperature: 30°C to 38°C for 28 days

3. Curing & Construction

• Cover compacted layer immediately with bituminous coating (MC-30 or emulsion)
• Alternatively, moist straw/sand + water sprinkling 5-6 times/day for 28 days
• No traffic or heavy equipment allowed during curing
• Maximum compacted layer thickness: 100 mm; lay in two layers for ≥150 mm total thickness

4. Mix Proportions (Example Ratios L:FA:Soil)

Safety and Handling Key Points from IRC 88

1. Material Batching & Mixing (Clause 4.75)

• Batching by weight is mandatory; volume batching only if unavoidable.
• Materials must be thoroughly pulverised before mixing.
• Mixing methods:
  • Mix soil, lime, flyash together before spreading.
  • Or spread pulverised soil, then add lime & flyash and mix.
• Tolerance limits (% by weight):
  • Lime: ±0.3%
  • Fly Ash: ±1.5%
  • Soil/Aggregate: ±2.0%

2. Mixing Plants (Clause 8.6)

• Prefer mix-in-place mechanical plants for uniformity.
• Equipment must control processing depth and maintain blade condition.
• Single-pass or multi-pass mixing with moisture adjustment.

3. Manual Mixing (Clause 8.7)

• Pulverise soil manually (crowbars, pick axes).
• Sprinkle water to aid pulverisation.
• Spread stabilizers uniformly and mix dry thoroughly before wet mixing.
• Layer thickness ≤ 100 mm; lime-flyash-soil min. thickness = 150 mm (laid in two layers).

4. Moisture Content & Compaction (Clause 8.9)

• Moisture at compaction: Optimum Moisture Content (OMC) ≤ moisture ≤ OMC + 2% (IS: 2720 Part VII).
• Rolling with 8-10 tonne smooth wheel rollers.
• Achieve ≥ 100% maximum dry density (IS: 2720 Part VII).
• Complete compaction within 4 hours of mixing.

5. Construction Joint (Clause 8.11)

• Chamfer existing layer edge at ~30°.
• Scarify, moisten, blend, and compact joint before resuming.

Summary Table: Tolerance Limits for Materials

Moisture Control Formula:

[ \text{Moisture at compaction} = \text{OMC} \leq \text{Moisture} \leq \text{OMC} +

IRC 88 - References and Bibliography: Key Specifications & Tables

Though IRC 88 does not explicitly list "References and Bibliography" formulas, here are critical tables and specs related to lime-flyash-soil stabilization from the code:

1. Mix Design & Proportioning (Clause 7.4)

2. Strength Requirements (Clause 7.3)

3. Degree of Pulverisation (Clause 8.3)

4. Testing Standards

• Compaction: IS: 2720 (Part VIII) - Heavy compaction for max dry density & OMC.
• Strength: IS: 2720 (Part X) - Unconfined compressive strength.
• CBR: IS: 2720 (Part XVI) - California Bearing Ratio test.

Summary Diagram: Mix Design & Testing Flow

flowchart TD
    A[Soil Sample Preparation] --> B[Pulverisation to Specified %