Do It Yourself Construction of Cement Stabilized Sub Base/Base
2015 Edition

Overview and Scope - Highlights of MORD 24

Objective:

• Provide guidance for rural road development under the National Rural Roads Development Agency (MoRD).

Coverage:

• Encompasses material selection, specifications, construction methods, design, quality assurance, and safety measures for stabilized materials in rural roads.

Soil-Cement Base Specifications (Clause 6.2)

• Minimum 7-day unconfined compressive strength: 3 MPa (laboratory test)
• Minimum thickness: 100 mm (refer to pavement design catalogue)
• Soil preparation: Complete pulverization and mixing (Clause 404 MoRD)
• Clayey soils: May require lime pretreatment prior to cement stabilization

Extract from Pavement Design Catalogue for Cement-Treated Bases

*Exact thickness depends on detailed design and subgrade strength.

Pavement Layer Schematic

graph TD
  A[Surface Dressing] --> B[Bituminous Macadam]
  B --> C[Crack Relief Aggregate Layer]
  C --> D[Cement Treated Base]
  D --> E[Cement Treated Subbase]
  E --> F[Subgrade Soil]

References:

• Clause 6.2, MORD 24
• IRC:SP:72-2015 Pavement Design Catalogues
• MoRD Specifications Clause 404

Guidance on Stabilizer Selection (MORD 24, Clause 2.0)

Selection depends primarily on the plasticity index (PI) and particle size distribution (% passing 0.075 mm sieve):

• PI = Plasticity Index, PP = Plasticity Percentage
• Coefficient of Uniformity (Cu) should be ≥ 5, preferably > 10 for economical stabilization.
• Soils with high plasticity and clay minerals respond better to lime stabilization.
• Cement requires pretreatment with approximately 2% lime for soils with high plasticity.

Storage and Handling (Clause 7.4)

Summary:

• Employ lime for soils with PI > 20.
• Use cement for soils with low PI and well-graded materials.
• Apply lime-pozzolana for intermediate soil conditions.
• Store stabilizers properly to minimize loss of strength.

flowchart TD
    A[Soil Sample] --> B{>25% Passing 0.075 mm?}
    B -- Yes --> C{PI < 10?}
    C -- Yes --> D[Cement or Lime-Pozzolana]
    C -- No --> E{PI between 10 and 20?}
    E -- Yes --> F[Lime or Cement]
    E -- No --> G[Lime]

Material Requirements and Testing (MORD 24 - Clauses 3.0 & 3.1)

• Material Quality:

  • The gradation and type of soil or granular material greatly influence pavement behavior.
  • Materials must meet minimum quality standards to reduce risks of carbonation and cracking.

• Strength Assessment Tests:

  • Unconfined Compressive Strength (UCS): Evaluates compressive strength without lateral confinement.
  • California Bearing Ratio (CBR): Measures load-bearing capacity of stabilized materials.

Important Test Equations:

• Unconfined Compressive Strength (UCS): [ UCS = \frac{Load_{max}}{Area} ] Where:

  • (Load_{max}) = Peak failure load (N)
  • (Area) = Cross-sectional area (mm²)

• California Bearing Ratio (CBR): [ CBR(%) = \frac{Load_{sample}}{Load_{standard}} \times 100 ] Where:

  • (Load_{sample}) = Load on stabilized soil at 2.5 mm penetration
  • (Load_{standard}) = Load on crushed stone at 2.5 mm penetration

Typical Specifications Summary:

flowchart TD
    A[Soil/Granular Material] --> B{Meets Specifications?}
    B -- Yes --> C[Stabilize with Recommended Additive]
    B -- No --> D[Increase Additive Dosage]
    C --> E[Conduct UCS & CBR Tests]
    D --> E
    E --> F{Strength Adequate?}
    F -- Yes --> G[Incorporate in Pavement]
    F -- No --> H[Revise Mix or Material]

Construction Processes (MORD 24 - Clause 4.0 and Table 8)

Critical quality control tests during construction to ensure proper stabilization and compaction:

• Mean density ≥ specified compaction level.
• Each individual test ≥ 99% of specified compaction. | | Compacted Layer Thickness| Randomly verified during construction. |

Essential Parameters:

• Compaction Degree: Achieve or exceed specified compaction, typically ≥ 95% Modified Proctor.
• Moisture Content: Maintain optimum moisture for efficient compaction.
• Layer Thickness: Adhere to design specifications, generally 150-200 mm per stabilized layer.

flowchart LR
    A[Commence Construction] --> B[Soil Pulverization Tests (≥3/day)]
    B --> C[Check Moisture Content (≥3/day)]
    C --> D[Compact Soil Layer]
    D --> E[Density Tests (≥3/day)]
    E --> F{Compaction ≥ Specified?}
    F -- Yes --> G[Random Thickness Checks]
    F -- No --> H[Rework Layer]
    G --> I[Proceed to Next Layer]
    H --> D

Rate Analysis for Cement-Treated Soil Sub-base/Base (MORD 24)

Following Clauses 5.0 and 4.6 of MORD 24 and IRC Standard Data (2014), key aspects include:

Key Information:

• Item: Cement-Treated Soil Sub-base/Base Course
• Reference: Serial number 4.6 from MORD Standard Data Book (IRC, 2014)
• Objective: To determine unit rates incorporating material, labor, and machinery costs.

Typical Components of Cost Analysis:

Unit Rate Formula:

[ Unit Rate = \frac{Total Cost (Materials + Labor + Equipment + Overheads)}{Quantity of Work (e.g., m^3 or m^2)} ]

Illustrative Table:

Summary:

• Refer to Clause 5.0 for methodology.
• Use Serial No. 4.6 in MORD Standard Data Book for detailed unit rates.
• Consider all cost factors: materials, labor, machinery, overheads.
• Adjust rates based on local market conditions.

flowchart LR
    A[Material Costs] --> D[Total Cost Calculation]

Design Parameters for Cement-Stabilized Sub-base and Base (MORD 24)

Material Gradation Standards (Table 5):

Material Properties (Table 4):

Design Recommendations:

• Use IRC SP-72 (2015) design charts considering subgrade CBR and traffic loads for thickness determination.
• Cement content must ensure sufficient strength and durability.
• Gradation should provide a closely graded surface finish with Cu ≥ 5.
• Fines passing 425 micron must conform to liquid limit and plasticity index requirements.
• Thickness and gradation are subject to pavement design and approval by the Engineer-in-Charge.

Simplified Design Flow

flowchart TD
    A[Assess Subgrade CBR] --> B[Identify Traffic Category]
    B --> C[Apply IRC SP-72 Design Charts]
    C --> D[Calculate Cement-Stabilized Layer Thickness]
    D --> E[Verify Material Gradation & Properties]
    E --> F[Select Cement Dosage and Mix Design]
    F --> G[Implement Construction and Quality Control]

Quality Control Measures as per MORD 24 (Clauses 7.0 & 7.3.1.2)

Essential quality control testing during construction for stabilized materials (Table 8):

• Average ≥ specified compaction.
• Each individual test ≥ (specified compaction - 1%). | | Compacted Layer Thickness| Random verifications during construction. |

Key Points:

• Achieving the specified degree of compaction is critical for soil stability.
• Moisture content must be carefully controlled to attain proper compaction.
• Thickness monitoring ensures uniformity in layer construction.

flowchart TD
    A[Begin Construction] --> B[Conduct Pulverization Tests (3/day)]
    B --> C[Perform Moisture Content Tests (3/day)]
    C --> D[Carry Out In-situ Density Tests (3/day)]
    D --> E{Is Compaction Adequate?}
    E -->|Yes| F[Accept Layer]
    E -->|No| G[Redo Layer]
    F --> H[Random Thickness Check]
    G --> B

Precautions in Using Stabilized Materials (MORD 24, Clause 8.0):

• Moisture Regulation: Maintain optimum moisture during mixing and compaction to achieve target strength.
• Uniform Mixing: Ensure thorough blending of stabilizers (lime, cement, bitumen) with soil.
• Curing: Provide adequate curing, typically a minimum of 7 days for cement or lime stabilization, to develop strength.
• Compaction: Attain specified compaction levels (usually 95% Proctor density) to reduce voids and enhance durability.
• Avoid Contamination: Prevent intrusion of organic matter or salts which can degrade stabilization effectiveness.
• Temperature Management: For bituminous stabilization, keep temperatures within recommended ranges to avoid premature setting or poor bonding.

Relevant Test Methods and Requirements (Clause 3.0):

Summary:

• Apply optimum moisture content and ensure uniform mixing.
• Achieve proper compaction and curing.
• Conduct strength, moisture, density, and durability testing as per IS standards.
• Prevent contamination and control temperature during mixing and curing.

flowchart TD
    A[Soil Sampling] --> B[Property Testing]
    B --> C{Is Soil Suitable?}
    C -- Yes --> D[Add Stabilizer]
    D --> E[Uniform Mixing]
    E --> F[Moisture Control]
    F --> G[Compaction]
    G --> H[Curing]
    H --> I[Strength Testing]
    I --> J{Meets Criteria?}
    J -- Yes --> K[Proceed with Construction]
    J -- No --> L[Adjust Mix or Method]