HIGHWAY QUALITY TEST

Dry Lean Concrete (DLC) Construction Methodology

Complete MoRTH Section 600 Compliant Guide for Highway Projects

1. Introduction to Dry Lean Concrete (DLC)

Dry Lean Concrete (DLC) is a low-cement content concrete layer laid as a sub-base for rigid pavements (PQC) in highway construction projects. It forms the structural foundation between the prepared subgrade/sub-base and the Pavement Quality Concrete (PQC) layer.

Unlike conventional concrete, DLC contains lower cement content and minimal water. It is designed primarily to:

• Provide uniform support to the PQC layer
• Prevent pumping of fines
• Improve load transfer
• Enhance pavement durability
• Ensure long-term structural stability

As per MoRTH Section 600, DLC must meet specified requirements related to grading, compaction, strength, moisture control, and curing.

2. Importance of DLC in Rigid Pavement System

In rigid pavement design, the structural layers typically include:

• Subgrade
• Granular Sub-Base (GSB)
• Dry Lean Concrete (DLC)
• Pavement Quality Concrete (PQC)

DLC performs the following critical functions:

2.1 Load Distribution

It distributes wheel loads uniformly to the subgrade and prevents stress concentration.

2.2 Working Platform

Provides a firm and level surface for PQC paving operations.

2.3 Prevention of Pumping

Reduces migration of fine particles and water under repeated loading.

2.4 Improved Durability

Minimizes differential settlement and cracking in rigid pavement.

Without proper DLC construction, PQC performance may significantly reduce.

3. Applicable Codes and Specifications

DLC construction must comply with:

• MoRTH Section 600
• Relevant IS Codes for cement and aggregates
• Project technical specifications
• Approved mix design and method statements

Typical references include:

• IS 383 – Aggregates
• IS 456 – Concrete
• IS 516 – Compressive strength test
• IS 2720 – Soil density and moisture tests
• IS 2386 – Aggregate testing

Always ensure latest revision compliance before execution.

4. Materials for DLC

4.1 Cement

• OPC or PPC permitted
• Minimum cement content: 150 kg/m³
• Fresh, lump-free, and stored properly

Cement must be used within approved shelf life.

4.2 Aggregates

• Maximum size: 25 mm
• Clean and free from deleterious material
• Well graded as per approved grading

Gradation must comply with MoRTH Table 600-1.

Daily grading checks are mandatory.

4.3 Water

• Clean and potable quality
• Free from oils, salts, and harmful substances
• Conforming to concrete quality standards

5. Mix Design and Trial Mix

DLC mix design aims to determine:

• Optimum Moisture Content (OMC)
• Maximum Dry Density (MDD)
• Cement content
• Required compressive strength

5.1 Target Strength

7-Day Compressive Strength:

• Average ≥ 10 MPa
• Individual ≥ 7.5 MPa

5.2 Trial Mix Procedure

1. Prepare mix with selected aggregate grading.
2. Vary moisture content between 5–7%.
3. Determine OMC and MDD using Modified Proctor test.
4. Cast minimum six cubes at OMC.
5. Cure and test at 3 and 7 days.
6. Adjust cement content if strength not achieved.

Approval of trial mix is mandatory before main work.

6. Demonstration Strip (Trial Length)

Before bulk construction, a demonstration strip of minimum 60 meters length must be constructed.

6.1 Objectives

• Validate equipment capability
• Finalize rolling pattern
• Establish reference density
• Verify thickness and level control

6.2 Procedure

• Construct using proposed plant and machinery.
• Use sensor paver for laying.
• Compact with proposed rollers.
• Conduct sand replacement tests at 3 locations.
• Average density becomes Reference Density (100%).

This reference density is used for future field acceptance.

7. Plant and Equipment

7.1 Batching Plant

• Central batching plant preferred
• Accurate cement weighing system
• Calibrated moisture control

7.2 Paver Machine

• Electronic sensor paver
• Automatic level control
• Ensures uniform thickness

7.3 Rollers

• Vibratory roller (80–100 kN)
• Smooth wheeled roller
• Proper overlap of 30–50%

8. Transportation of DLC

• Use dumpers with covered tarpaulin
• Avoid moisture loss
• Minimize segregation
• Avoid delay between mixing and laying

Time between mixing and compaction should be minimized.

9. Laying of DLC

9.1 Surface Preparation

• GSB must be approved and levelled
• Remove loose material
• Check cross fall and camber

9.2 Layer Thickness

• Maximum 200 mm per layer
• If thickness >200 mm, construct in multiple layers

9.3 Moisture Control

• Maintain OMC ±2%
• Excess moisture causes bleeding
• Low moisture reduces compaction

Continuous field moisture checks are essential.

10. Compaction Procedure

Compaction is critical for performance.

10.1 Rolling Pattern

1. Initial static pass
2. Vibratory passes
3. Intermediate passes alternating direction
4. Final static pass

10.2 Compaction Requirement

Minimum 98% of MDD

Field density tests must confirm compliance.

11. Joint Treatment

11.1 Longitudinal Joints

• Overlap 200–400 mm
• Ensure proper bonding

11.2 Transverse Joints

• Stagger 500–1000 mm
• Avoid cold joints

12. Curing of DLC

Immediately after compaction:

• Apply curing compound OR
• Cover with wet hessian cloth

Curing duration: Minimum 7 days.

Improper curing causes shrinkage cracks.

13. Quality Control Tests

13.1 Gradation Test

Frequency: 1 per 3000 m³

13.2 Field Density Test

Frequency: 1 per 2000 m²
Method: Sand Replacement

13.3 Moisture Content

Frequency: 1 per 250 m³

13.4 Compressive Strength

Frequency: 3 samples per 1000 m²

14. Acceptance Criteria Summary

15. Common Site Problems and Solutions

15.1 Low Density

Cause: Inadequate roller passes
Solution: Increase vibration and adjust moisture

15.2 Segregation

Cause: Poor plant control
Solution: Proper aggregate blending

15.3 Cracking

Cause: Early moisture loss
Solution: Immediate curing

15.4 Thickness Variation

Cause: Improper paver calibration
Solution: Sensor check and trial adjustment

16. Safety Measures

• PPE mandatory
• Equipment operators trained
• Barricading and traffic diversion
• Dust control measures
• Emergency first aid facility

17. Documentation Requirements

Maintain:

• Trial mix approval records
• Cube test reports
• Field density reports
• Daily progress reports
• Equipment calibration records

Proper documentation ensures audit compliance.

18. Environmental Considerations

• Control cement dust
• Avoid material spillage
• Proper disposal of waste concrete
• Noise control during night work

19. Checklist Before Concreting

✔ Approved trial mix
✔ Approved GSB level
✔ Calibrated plant
✔ Verified OMC
✔ Approved rolling pattern
✔ QC team ready

20. Conclusion

Dry Lean Concrete is a critical structural layer in rigid pavement construction. Proper mix design, moisture control, compaction, curing, and quality testing are essential to ensure pavement durability and performance.

Strict compliance with MoRTH Section 600, supported by systematic field verification and documentation, ensures long-term success of highway infrastructure projects.

About the Author

Kishor Kumar is a Highway QA/QC Engineer specializing in MoRTH compliant construction methodologies, pavement quality control, and infrastructure testing practices. He shares practical, field-oriented knowledge for engineers and contractors.