Do It Yourself Construction of Cement Stabilized Sub Base/Base

Introduction - MORD 24 Key Points

Purpose:

• Guide for rural road development by National Rural Roads Development Agency (MoRD).

Scope:

• Covers selection, specifications, construction, design, quality assurance, and precautions for stabilized materials in rural roads.

Key Specifications for Soil-Cement Base (Clause 6.2)

• Minimum 7-day unconfined compressive strength: 3 MPa (laboratory test)
• Minimum thickness: 100 mm (as per pavement design catalogue)
• Soil preparation: Thorough pulverization and mixing (Clause 404 MoRD)
• Clayey soils: May require lime pre-treatment before cement stabilization

Pavement Design Catalogue for Cement Treated Bases (Excerpt)

*Exact thickness depends on detailed design and subgrade strength.

Summary Diagram (Pavement Layer)

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

Selection of Stabilizer (MORD 24, Clause 2.0)

The choice depends on 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 cost-effective stabilization.
• High plasticity soils with clay minerals are better stabilized with lime.
• Cement requires pre-treatment with ~2% lime for high plasticity soils.

Storage & Handling (Clause 7.4)

Summary:

• Use lime for high PI soils (>20).
• Use cement for low PI soils and well-graded materials.
• Use lime-pozzolana for intermediate conditions.
• Ensure stabilizer storage to minimize strength loss.

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

Specifications and Test Requirements for Stabilized Materials (MORD 24 - Clause 3.0 & 3.1)

• Material Quality:

  • Gradation and soil/granular type critically affect pavement performance.
  • Materials must meet minimum quality standards to reduce carbonation and cracking risks.

• Strength Evaluation Tests:

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

Key Test Formulae:

• Unconfined Compressive Strength (UCS):
  [ UCS = \frac{P}{A} ]
  Where:

  • (P) = Maximum load at failure (N)
  • (A) = Cross-sectional area (mm²)

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

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

Typical Specifications (Summary):

flowchart TD
    A[Soil/Granular Material] --> B{Meets Spec?}
    B -- Yes --> C[Stabilize with Standard Additive]
    B -- No --> D[Increase Additive Content]
    C --> E[Perform UCS & CBR Tests]
    D --> E
    E --> F{Strength OK?}
    F -- Yes --> G[Use in Pavement]
    F -- No --> H[Modify Mix or Material]

Note: More additive may be needed if material quality is poor, increasing cracking risk. Always verify with UCS and CBR tests before construction.

Construction Operations (MORD 24 - Clause 4.0 & Table 8)

Key quality control tests during construction ensure proper soil stabilization and compaction:

Important Specifications:

• Degree of Compaction: Achieve at least the specified compaction (usually ≥ 95% of Modified Proctor).
• Moisture Content: Maintain optimum moisture for maximum compaction efficiency.
• Layer Thickness: Follow design thickness, typically 150-200 mm per layer for stabilized sub-base/base.

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

This process ensures quality stabilized pavement layers per MORD guidelines.

Analysis of Rates for Cement Treated Soil Sub-base/Base Course (MORD 24)

Based on Clause 5.0 and Clause 4.6 of MORD 24 and IRC Standard Data (2014), key points are:

Key Specifications:

• Item: Cement Treated Soil Sub-base/Base Course
• Reference: Sl no. 4.6, MORD Standard Data Book (IRC, 2014)
• Purpose: To arrive at unit rates for construction items considering material, labor, and equipment costs.

Typical Components in Analysis of Rates:

Formula for Unit Rate:

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

Example Table Extract (Indicative):

Summary:

• Refer Clause 5.0 for methodology.
• Use Sl no. 4.6 in MORD Standard Data Book for detailed unit rates.
• Include all cost components: materials, labor, equipment, overheads.
• Adjust rates as per local market conditions.

flowchart LR
    A[Material Cost] --> D

Design of Cement Stabilised Sub Base and Base (MORD 24)

Key Specifications

• Material Gradation (Table 5):

• Material Properties (Table 4):

Design Guidelines

• Use IRC SP-72 (2015) design charts for thickness based on subgrade CBR and traffic.
• Cement content should ensure adequate strength and durability.
• Grading must provide a well-closed surface finish with Cu ≥ 5.
• Plastic fines passing 425 micron should meet liquid limit and plasticity index limits.
• Thickness and grading choice depend on pavement design and Engineer-in-Charge approval.

Typical Design Flow (Simplified)

flowchart TD
    A[Determine Subgrade CBR] --> B[Select Traffic Category]
    B --> C[Use IRC SP-72 Design Charts]
    C --> D[Determine Thickness of Cement Stabilised Layer]
    D --> E[Check Material Gradation & Properties]
    E --> F[Select Cement Content & Mix Design]
    F --> G[Construction & Quality Control]

Summary: Follow grading limits, material specs, and IRC SP-72 charts to design cement stabilized sub-base/base layers ensuring durability and strength.

Quality Assurance in MORD 24 (Clause 7.0 & 7.3.1.2)

Key quality control tests during construction for stabilized materials as per Table 8:

Important Notes:

• The degree of compaction is critical for ensuring soil stability.
• Moisture content must be controlled to achieve desired compaction.
• Thickness checks ensure uniform layer compaction.

flowchart TD
    A[Start Construction] --> B[Pulverization Tests (3/day)]
    B --> C[Moisture Content Tests (3/day)]
    C --> D[In-situ Density Tests (3/day)]
    D --> E{Check Degree of Compaction}
    E -->|Average ≥ Specified| F[Accept Layer]
    E -->|Average < Specified| G[Rework Layer]
    F --> H[Thickness Check (Random)]
    G --> B

This ensures consistent quality and compliance with MORD 24 standards.

Precautions while using Stabilized Materials (IS Code MORD 24, Clause 8.0):

• Moisture Control: Maintain optimum moisture content during mixing and compaction to achieve desired strength.
• Mixing Uniformity: Ensure thorough and uniform mixing of stabilizing agents (lime, cement, bitumen) with soil.
• Curing: Provide adequate curing (minimum 7 days for cement/lime stabilization) to develop strength.
• Compaction: Achieve specified compaction (typically 95% Proctor density) to reduce voids and increase durability.
• Avoid Contamination: Prevent contamination by organic matter or salts which reduce stabilization effectiveness.
• Temperature Control: For bituminous stabilization, maintain temperature within recommended limits to avoid premature setting or poor bonding.

Specifications and Test Requirements (Clause 3.0):

Summary:

• Use optimum moisture and uniform mixing.
• Ensure proper compaction and curing.
• Test for strength, moisture, density, and durability per IS standards.
• Avoid contamination and control temperature during mixing and curing.

flowchart TD
    A[Soil Sampling] --> B[Testing for Properties]
    B --> C{Is Soil Suitable?}
    C -- Yes --> D[Add Stabilizer]
    D --> E[Mix Uniformly]
    E --> F[Control Moisture]
    F --> G[Compaction]
    G --> H[Curing]
    H --> I[Strength Testing]
    I --> J{Meets Specs?}
    J -- Yes --> K[Use in Construction]
    J -- No --> L[Adjust Mix