Construction Methodology for Dry Lean Concrete (DLC)

1. Scope & Purpose

This DLC construction methodology covers construction of Dry Lean Concrete (DLC) as a sub-base for cement concrete pavements. It includes supply of plant, materials and labour; mixing, transporting, placing, compacting, curing and testing in accordance with contract specifications and MoRTH/IS requirements.

2. Materials & Mix Design

2.1 Cement

OPC (IS:269) or PPC (IS:1489) with Engineer's approval. Minimum cement content: 150 kg/m³ (increase if required).

2.2 Aggregates

Aggregates to comply with IS:383 and MoRTH Clauses. Coarse aggregate maximum size: 25 mm. Fine aggregate: clean natural or crushed sand free from deleterious materials.

2.3 Water

Water used for mixing and curing shall be clean and comply with IS:456.

3. Trial Mixes

3.1 Procedure

1. Prepare trial mixes at moisture contents: 5.0, 5.5, 6.0, 6.5 and 7.0%.
2. Compact specimens in three layers using a vibratory hammer; determine OMC and MDD.
3. Cast six cubes at OMC and test at 3 and 7 days to establish strength.

4. Trial Length (Demonstration Strip)

Construct a trial length of minimum 60 m (full width) outside the project area to validate rolling compaction, OMC, and equipment. Perform three sand replacement tests (3 holes along a diagonal excluding 0.5 m edge zones). The average density is the Reference Density (100%).

5. Proportioning of Materials

5.1 Aggregate–Cement Ratio

Maximum aggregate:cemen ratio: 15:1.

5.2 Moisture & Cement Content

Maintain moisture between OMC and OMC + 2%. Minimum cement content: 150 kg/m³. Average compressive strength of five consecutive cubes ≥ 10 MPa (7 days); any individual cube ≥ 7.5 MPa (7 days).

6. Preparation of Base

Ensure subgrade conforms to lines/grades and is uniformly compacted. Provide drainage layer (GSB/WMM) as per MoRTH Clause 401 prior to DLC placement.

7. Batching & Mixing

Use forced-action central batching plant with separate weighing for each material. Plant capacity should be at least 25% higher than the laying requirement. Ensure accurate proportioning and uniform mixing.

8. Transporting

Transport plant-mix DLC immediately to the paver in covered tippers/dumpers. Maintain uninterrupted supply to the paver for uniform laying.

9. Placing & Spreading

Place DLC using an electronic-sensor paver capable of laying a single even layer without segregation. Prefer full-width placement; lane-by-lane is acceptable if planned. Stagger joints from overlay slab joints: transverse 500–1000 mm, longitudinal 200–400 mm.

10. Compaction

10.1 Equipment

Use double drum smooth-wheeled vibratory rollers (80–100 kN static weight).

10.2 Rolling Sequence

1. Preliminary pass without vibration to bed the material.
2. Vibratory passes until no visible movement under the roller.
3. Final pass without vibration to remove marks and smooth the surface.

11. Joints

Provide contraction and longitudinal joints per drawings. At construction joints, cut back compacted material to a vertical face unless vertical forms are used.

12. Curing

Commence curing immediately after compaction by one of the following methods:

• Apply curing compound immediately after rolling; once tackiness reduces, cover with wet hessian for 3 days.
• Cover with gunny bags/hessian and keep continuously moist for 7 days.

13. Quality Control & Frequency of Testing

14. Inspection Plan

15. Safety Measures

All operations to follow the approved EHS plan. Key controls include PPE, barricading, signboards, traffic management, trained equipment operators, emergency response and first aid facilities.