Guidelines for the Use of Dry Lean Concrete as Sub-base for Rigid Pavement (First Revision)

IRC SP 49 — Introduction: Key Specifications & Tables

1. Introduction Overview

• Defines scope and purpose of Lean Concrete Sub-base (DLC) for highways.
• Specifies materials, construction, curing, and testing protocols.

Key Tables & Specifications

Table 1: Grading of Aggregates (Clause 3.2.1)

Opening to Traffic (Clause 7.11)

• No heavy vehicles on DLC sub-base immediately after construction.
• Light vehicles allowed only after 7 days with Engineer's approval.

Annexure A: Curing Compound Test

• Mortar slab size: 150 x 300 x 50 mm
• Mix: Cement:sand = 1:3, w/c = 0.40-0.44
• Test: Weight loss after 72h at 38°C, 35% RH to evaluate curing efficiency.

Annexure B: DLC Mix Proportions & Test Results

• Cement:Aggregate ratios from 1:12 to 1:18.
• Water content: 6.5%
• Dry density ~2300-2400 kg/m³
• 7-day compressive strength: 4.0 to 14.4 MPa depending on mix.

Summary Diagram of DLC Construction Process

flowchart TD
    A[Material Selection] --> B[Mix Proportioning]
    B --> C[Batching & Mixing]
    C --> D[Transporting]
    D --> E[Placing]
    E --> F[Compaction]
    F --> G[Joints Formation]
    G --> H[Curing]
    H --> I[Opening to Traffic (

IRC SP 49: Width and Thickness of DLC Sub-base

Though the exact clause on width and thickness is not explicitly stated, the following key points and guidelines are derived from IRC SP 49 and related standards:

Width of DLC Sub-base

• Should match the full width of the pavement including shoulders.
• Ensure coverage beyond the pavement edges to provide structural support.

Thickness of DLC Sub-base

• Typical thickness ranges from 75 mm to 150 mm depending on traffic and subgrade conditions.
• Thickness must ensure adequate load distribution and durability.
• Thickness selection should consider:
  • Subgrade strength (minimum 97% modified Proctor density)
  • Traffic loading
  • Drainage requirements

Moisture Content & Compaction

• Optimum moisture content for DLC is between 5.0% to 7.0% (trial mixes at 5.0, 5.5, 6.0, 6.5, 7.0%).
• Use moisture-density curves to find optimum compaction.
• DLC may have 1% higher moisture during laying on main carriageway to compensate evaporation.

Drainage Layer

• Provide a Granular Sub-base (GSB) below DLC for drainage (refer IRC:58).
• Subgrade must be well compacted and stable before DLC placement.

Summary Table (Typical Values)

References for Further Details

• IRC SP 49 (Clause 6.5, Clause 5)
• IRC:58 for drainage layer specifications
• IS:2720 (Part 8) for subgrade compaction

flowchart TD
    A[Subgrade Preparation] --> B[Drainage Layer (GSB)]
    B --> C[DLC Sub-base Placement]
    C --> D[Pavement Layers]
    style C fill:#f9f,stroke:#333,stroke-width:2px

This ensures

IRC SP 49: Materials - Key Specifications & Tables

1. Cement

• Use Ordinary Portland Cement (OPC), Portland Slag Cement (PSC), or Pozzolana Portland Cement (PPC) as per mix design.
• Water-cement ratio: ~0.40 to 0.44 for mortar (Annexure-A).

2. Aggregates

• Grading of fine aggregate per IRC:15 or IS:383.
• Combined aggregate grading (Table 1):

3. Water

• Clean, potable water free from impurities.

4. Mix Proportions (Annexure-B)

• Cement:Aggregate ratios vary from 1:12 to 1:18.
• Water content ~6.5% by weight of cement.
• Typical dry density: 2300-2400 kg/m³.
• 7-day compressive strength ranges from 4.0 MPa to 14.4 MPa depending on mix.

5. Curing Compound Test (Annexure-A)

• Mortar slab 150x300x50 mm.
• Water retention efficiency tested at 38℃ and 35% RH for 72 hours.
• Ensures reduced evaporation and improved strength.

This summary covers essential material specs and grading for lean concrete sub-base per IRC SP 49. For detailed mix design and testing, refer to Annexures A & B.

Key Specifications and Formulas for Cement (IRC SP 49):

Cement Types (Clause 3.1)

• OPC: IS:8112, IS:12269
• PPC: IS:1489 (Part 1)
• PSC: IS:455
• Sulphate Resisting Cement: IS:12330 (or PSC with slag up to 50%) for soils with >0.5% soluble sulphates.

Concrete Mix Proportions (Clause 4.2)

• Max Aggregate:Cement ratio:
  • OPC: 14:1
  • PPC/PSC: 12:1
• Minimum Cementitious Content: ≥ 140 kg/m³
• Increase cement content if specified strength not achieved.
• Flyash (IS:3812 Part 1): 15-30% by weight of cementitious material.
• GBFS (IS:12089): 25-50% by weight of cementitious material.
• OPC content with flyash/GBFS ≥ 100 kg/m³.
• Uniform blending via mechanized batching/mixing plant mandatory for admixtures.

Summary Table: Cementitious Content and Ratios

Notes:

• Ensure proper storage to avoid contamination.
• Adjust cement content based on strength requirements.
• Use sulphate resisting cement in aggressive soils.

flowchart LR
    A[Cement Types] --> B[OPC (IS:8112,12269)]
    A --> C[PPC (IS:1489)]
    A --> D[PSC (IS:455)]
    A --> E[Sulphate Resisting Cement (IS:12330)]
    F[Concrete Mix Proportion] --> G[Max Agg:Cement Ratio]
    G --> H[OPC: 14:1]
    G --> I[PPC/PSC: 12:

Key Specifications & Tables for Aggregates (IRC SP 49)

1. Grading of Aggregates (Clause 3.2.1)

• Fine aggregates must conform to grading zones I-IV as per IRC:15 or IS:383.
• Maximum coarse aggregate size: 26.5 mm.
• Water absorption of aggregates ≤ 3%.
• Aggregates must be clean, hard, dense, non-porous, and free from deleterious materials (clay, mica, organic matter).

2. Aggregate Quality Requirements (Clause 3.2 & 26.5)

• Coarse aggregate: crushed stone or gravel, free from flaky, elongated, or soft particles.
• Fine aggregate: natural or crushed sand, clean and free from impurities.
• Alkali-reactive aggregates are prohibited.
• Washing and draining for 72 hours if aggregates contain dirt.

3. Water Absorption Limit

• Maximum water absorption allowed: 3%.

Summary Diagram: Aggregate Grading Flow

flowchart TD
    A[Start: Aggregate Sampling] --> B{Check Sieve Sizes}
    B -->|Passes| C[Measure % Passing]
    C --> D{Conforms to Table 1?}
    D -->|Yes| E[Use Aggregate]
    D -->|No| F[Reject or Reprocess]

References:

• IS:383 for aggregate grading & quality.
• IRC:15 for fine aggregate grading zones.
• Maximum size and absorption limits ensure durability and strength of lean concrete.

IRC SP 49: Key Specifications & Formulas for Water in Concrete

Water Quality (Clause 3.3)

• Must be clean, free from harmful substances: oil, salt, acid, alkali, sugar, vegetable matter.
• Should meet IS:456 standards.
• Potable water is generally acceptable.
• Allowed pH range: up to 9.

Curing Compound Test (Annexure-A)

• Mortar slab size: 150 x 300 mm (top), 145 x 295 mm (bottom), 50 mm depth.
• Mix: Ordinary Portland Cement : Sand = 1:3, water-cement ratio = 0.40 - 0.44.
• Flow: 35 ± 5% in 10 drops (flow table).
• Specimens cured at 38°C, 35% RH for 72 hours.
• Efficiency = % retention of mixing water (less evaporation → better curing).

Opening to Traffic (Clause 7.11)

• No heavy vehicles on lean concrete sub-base.
• Light vehicles allowed only after 7 days with Engineer's approval.

Water Content in Mix (From Annexure-B Table Summary)

Summary Diagram: Water Role in Concrete

flowchart LR
    Water -->|Mixing| Concrete
    Water -->|Curing| Strength
    Water -.->|Impurities| Deterioration
    Concrete -->|Proper Water| Durability

Note: Use potable water, maintain pH ≤ 9, and ensure curing compounds reduce evaporation as per Annexure-A test for durable lean concrete sub-base.

Mineral Admixtures per IRC SP 49

Key Specifications (Clause 3.4)

• Fly Ash: 15–30% by weight of cementitious material (conforms to IS:3812 Part 1)
• Ground Granulated Blast Furnace Slag (GBFS): 25–50% by weight (conforms to IS:12089)
• Minimum OPC content: ≥ 100 kg/m³ concrete when mineral admixtures are used.
• Site mixing: Allowed only with mechanized uniform blending and automated batching/mixing plant.

Concrete Mix Proportioning (Clause 4.2)

• Max aggregate:cement ratio:
  • OPC: 14:1
  • PPC/PSC: 12:1
• Minimum cementitious content: 140 kg/m³ (increase if required for strength)
• Mineral admixture content: Flyash 15–30%, GBFS 25–50% by weight of cementitious materials.

Mix Proportion Example (Annexure-B summary)

Notes:

• Use IS:3812 and IS:12089 for detailed quality requirements.
• Maintain proper storage to avoid contamination.
• Ensure curing compound efficiency as per Annexure-A for moisture retention.
• Avoid heavy traffic on lean concrete sub-base before 7 days (Clause

IRC SP 49: Concrete Compressive Strength & Mix Proportioning

1. Concrete Compressive Strength (Clause 4.1)

• The concrete compressive strength shall meet the design requirements as specified.
• Strength is typically determined by standard cube tests at 28 days.

2. Concrete Mix Proportioning (Clause 4.2)

• Maximum Aggregate:Cement Ratio:
  • OPC: 14:1
  • PPC/PSC: 12:1
• Minimum Cementitious Material Content:
  ≥ 140 kg/m³ of concrete (increase if required to achieve strength)
• Mineral Admixtures Content (Clause 3.4):
  • Fly Ash: 15-30% by weight of cementitious materials
  • GBFS (Ground Granulated Blast Furnace Slag): 25-50% by weight of cementitious materials

Notes:

• Mix proportions are validated by CRRI test results (Annexure-B).
• Adjust cement content if minimum does not achieve target strength.

Summary Table

flowchart LR
    A[Concrete Mix Design] --> B[Select Cement Type (OPC/PPC/PSC)]
    B --> C{Aggregate:Cement Ratio}
    C -->|OPC| D[Max 14:1]
    C -->|PPC/PSC| E[Max 12:1]
    A --> F[Minimum Cementitious Content ≥ 140 kg/m³]
    A --> G[Add Mineral Admixtures]
    G --> H[Fly Ash 15-30%]
    G --> I[GBFS 25-50%]

This ensures concrete meets strength and durability requirements per IRC SP 49.

IRC SP 49: Concrete Compressive Strength Key Points

• Clause 4.1: Specifies concrete compressive strength requirements.
• Clause 5.5:
  • Average compressive strength of every 5 consecutive cubes ≥ 7 MPa at 7 days
  • Strength of any individual cube ≥ 5.5 MPa at 7 days

Concrete Mix Proportioning (Summary)

• Design mix must ensure above strength criteria before starting work.
• Use mineral admixtures per Clause 3.4 to improve strength/durability if required.

Typical Strength Check Formula

[ f_{ck,7} \geq 7 \text{ MPa (average of 5 cubes)} \quad \text{and} \quad f_{ck,7}^{(individual)} \geq 5.5 \text{ MPa} ]

Practical Notes:

• Cube size: 150 mm × 150 mm × 150 mm (standard)
• Testing at 7 days for early strength confirmation
• Adjust water-cement ratio, admixtures, and curing to meet strength

flowchart LR
    Start[Start Concrete Mix Design]
    --> MixProportion[Design Mix Proportion]
    --> CastCubes[Cast 5 Concrete Cubes]
    --> Cure7Days[Cure for 7 Days]
    --> TestStrength[Test Compressive Strength]
    --> CheckAvg{Avg Strength ≥ 7 MPa?}
    --> CheckInd{All Individual ≥ 5.5 MPa?}
    CheckAvg -- No --> ReviseMix[Revise Mix Design]
    CheckInd -- No --> ReviseMix
    CheckAvg -- Yes --> CheckInd
    CheckInd -- Yes --> Approve[Approve Mix & Proceed]

This ensures concrete meets IRC SP 49 strength criteria for safety and durability.

Concrete Mix Proportioning – IRC SP 49 (Clauses 3.4 & 4.2)

• Maximum Aggregate:Cement Ratio:

  • OPC: 14:1
  • PPC/PSC: 12:1

• Minimum Cementitious Content:
  ≥ 140 kg/m³ of concrete
  (Increase if required to achieve specified strength)

• Mineral Admixtures Content:

  • Flyash: 15–30% by weight of cementitious material (IS:3812 Part 1)
  • GBFS: 25–50% by weight of cementitious material (IS:12089)
  • OPC content ≥ 100 kg/m³ when using admixtures

• Mixing Requirements:
  Uniform blending via mechanized batching and mixing plant with automated process control

Typical Mix Proportioning Formula:

[ \text{Water-Cement Ratio (w/c)} = \frac{\text{Water}}{\text{Cementitious Material}} ]

• Adjust w/c ratio to meet target compressive strength (refer to CRRI test data, Annexure-B)
• Aggregate quantities adjusted to maintain max aggregate:cement ratio

Summary Table:

flowchart TD
    A[Start: Select Cement Type] --> B{OPC or PPC/PSC?}
    B -->|OPC| C[Max Aggregate:Cement = 14:1]
    B -->|PPC/PSC| D[Max Aggregate:Cement = 12:1]
    C --> E[Check Cementitious Content ≥ 140 kg/m³]
    D --> E
    E --> F{Use Mineral Admixtures?}
    F -->|Yes| G[Flyash 15-30% or GBFS 25-50%]
    G --> H[Ensure

IRC SP 49 - Drainage Layer: Key Specifications & Formulas

1. Drainage Layer (Clause 5)

• The drainage layer is typically a lean concrete sub-base (DLC).
• Mix proportions and materials are critical to ensure permeability and strength.

2. Concrete Mix Proportions (Clause 4.2 & Annexure-B)

• Cement : Aggregate ratio varies from 1:12 to 1:18 depending on cement type (PSC, OPC, PPC).
• Water content fixed at 6.5% by weight of cement.
• Aggregate grading: 40% sand, 50% 20mm coarse aggregate, 50% 10mm coarse aggregate.

3. Control of Thickness, Density & Strength (Clause 7.10)

• Thickness tolerance: ±10 mm.
• Dry density measured via density holes per 2000 m² daily.
• Strength control by cube tests: 3 samples/1000 m² daily, tested as per IS:516.

4. Opening to Traffic (Clause 7.11)

• No heavy commercial vehicles allowed immediately after construction.
• Light vehicles only after 7 days with engineer's approval.

Summary Formula for Mix Proportioning (Example for OPC 1:14 mix)

Cement = 140 kg
Water = 140 * 6.5% = 9.1 kg
Aggregate = 1960 kg (Sand = 784 kg, Coarse Aggregate = 1176 kg)

Diagram: Drainage Layer Composition

graph LR
  A[Cement] --> B[Lean Concrete Mix]
  C[Water] --> B
  D[Sand (40%)] --> B
  E[Coarse Aggregate (60%)] --> B
  B --> F[

IRC SP 49: Construction Key Points

1. Concrete Mix Proportions (Clause 4.2)

• Cement : Aggregate ratios vary (e.g., 1:12 to 1:18).
• Water content: ~6.5% by weight.
• Aggregate grading per Table 1 (Clause 3.2.1):

2. Construction (Clause 7)

• Trial Mixes: Essential before full-scale work.
• Batching & Mixing: Accurate measurement and uniform mixing.
• Transporting: Avoid segregation and premature setting.
• Placing & Compaction: Proper layer placement and compaction to achieve design density.
• Joints: Properly constructed to avoid cracking.
• Curing: Use curing compounds tested per Annexure-A; maintain moisture for 72 hours at 38°C & 35% RH.
• Opening to Traffic (7.11): No heavy vehicles for at least 7 days; light vehicles only with approval.

3. Drainage Layer (Clause 5)

• Proper drainage under sub-base to prevent water accumulation.

Summary Diagram of Construction Process

flowchart TD
    A[Trial Mix] --> B[Batching & Mixing]
    B --> C[Transporting]
    C --> D[Placing]
    D --> E[Compaction]
    E --> F[Joints Construction]
    F --> G[Curing]
    G --> H[Opening to Traffic]

For detailed mix proportions & test results, refer Annexure-B (Clause 4.2) tables with cement-aggregate ratios and compressive strengths.

IRC SP 49: Trial Mixes Key Points & Specifications

1. Trial Mix Preparation (Clause 7.1 & 6.5)

• Prepare trial mixes at moisture contents: 5.0%, 5.5%, 6.0%, 6.5%, 7.0%.
• Use cement content as per aggregate-cement ratio from para 4.2.
• Compact in 3 layers using a vibratory hammer with square/rectangular foot.
• Cast cubes to find Optimum Moisture Content (OMC) and Maximum Dry Density.

2. Strength Testing (Clause 7.9.2 & 6.5)

• At OMC, cast 6 cubes for compressive strength tests at 3 and 7 days.
• If strength is unsatisfactory:
  • Increase cement content or
  • Use higher grade cement.
• Repeat trial mixes as needed.

3. Adjustments During Construction

• Adjust moisture content if trial section results are unsatisfactory.
• Ensure mix neither sticks to rollers nor is too dry (avoid ravelling).
• Daily check natural moisture content of aggregates to adjust mix water.

Summary Table for Trial Mix Moisture Content

Typical Trial Mix Procedure Flowchart

flowchart TD
    A[Start Trial Mix] --> B[Prepare Mixes at 5.0 to 7.0% Moisture]
    B --> C[Compact in 3 Layers with Vibratory Hammer]
    C --> D[Cast Cubes for Density & Strength Tests]
    D --> E{Strength Satisfactory?}
    E -- Yes --> F[Approve Mix Design]
    E -- No --> G[Increase Cement or Use Higher Grade Cement]
    G --> B
    F --> H[Construct Trial Section]
    H --> I{Mix Performance Satisfactory?}
    I -- Yes --> J[Start Production]
    I -- No --> K[Adjust Moisture Content & Re-test]
    K --> D

Note: Trial mixes ensure optimized

Batching and Mixing - IRC SP 49 Key Points

• Batching Plant Requirements (Clause 7.3):

  • Separate weight proportioning for each material.
  • Capacity ≥ 125% of proposed laying capacity.
  • Preferably forced action central batching & mixing plant with automatic controls.
  • Calibration: Monthly to maintain accuracy.
  • Alternative mixers allowed if proven satisfactory in trial.

• Concrete Mix Proportions (Clause 4.2):

• Cementitious content must be increased if required to achieve specified strength.

Summary Diagram of Batching Process

flowchart LR
    A[Raw Materials] --> B[Batching Plant]
    B --> C[Separate Weight Proportioning]
    C --> D[Forced Action Mixer]
    D --> E[Mixed Concrete]
    E --> F[Calibration & Quality Control]

This ensures accurate, consistent concrete quality for pavement construction.

IRC SP 49 - Transporting (Clause 7.4) Key Points

• Transporting DLC (Dry Lean Concrete):

  • Transport the lean concrete sub-base promptly to avoid initial setting.
  • Use suitable vehicles and methods to prevent segregation and loss of mix water.
  • Avoid delays and maintain uniformity in the mix during transport.

• Opening to Traffic (Clause 7.11):

  • No heavy commercial vehicles (trucks/buses) allowed on lean concrete sub-base immediately after construction.
  • Light vehicles may be permitted only after 7 days with prior Engineer approval.

• Curing Compound Efficiency (Annexure-A):

  • Tested by water evaporation reduction on standard mortar slabs.
  • Specimen: 150x300x50 mm slab, cement:sand = 1:3, w/c ratio 0.40-0.44.
  • Curing compound must harden within 30 minutes after application.
  • Specimens weighed before and after 72 hrs at 38°C & 35% RH to calculate water retention.

Summary Table: Opening to Traffic

Practical Tips:

• Transport lean concrete in covered mixers or trucks.
• Avoid re-tempering on site.
• Ensure curing compound application soon after placing to minimize water loss.

flowchart TD
    A[Mixing] --> B[Transporting]
    B --> C[Placing]
    C --> D[Curing]
    D --> E[Opening to Traffic]
    E -->|Heavy Vehicles| F[Not Allowed]
    E -->|Light Vehicles| G[Allowed after 7 days]

This ensures quality and durability of the DLC sub-base as per IRC SP 49 guidelines.

Key Specifications for Laying and Compaction (IRC SP 49):

1. Laying

• Use a hydrostatic paver capable of laying lean concrete in a single, even layer without segregation (Clause 7.5).
• For roads > 2 lanes, use two pavers in echelon, spaced 15-20 m apart.
• Transverse joints staggered by 500-1000 mm; longitudinal joints by 200-400 mm relative to overlaying concrete slabs.

2. Compaction

• Start rolling immediately after laying and leveling (Clause 7.6.1).
• Roll full width until no visible movement and surface is closed.
• Rolling starts from lower edge of camber/one side slope towards center/outer edge.
• Dry density from 3 density holes (200 mm dia) must be:
  • ≥ 97% of trial length density (average)
  • Edges (0.5 m from edge) ≥ 95% of trial density

3. Control of Thickness, Density & Strength (Clause 7.10)

• Thickness tolerance: +10 mm
• Density test: Density holes spaced along diagonal every 2000 m² daily.
• Strength: 3 cube samples per 1000 m² daily, tested per IS:516.

Summary Table

flowchart LR
    A[Laying with Hydrostatic Paver] --> B[Immediate Leveling]
    B --> C[Start Rolling from Lower Edge]
    C --> D[Roll Full Width till Surface Closed]
    D --> E[Check Dry Density (≥97% avg, ≥

IRC SP 49 - Trial Length Construction (Clause 7.9)

• Duration & Timing:

  • Construct trial length at least 14 days before main work starts.
  • Complete in 2 days.

• Dimensions:

  • Minimum length: 60 m
  • Full pavement width
  • Max length per day: 30 m

• Construction Requirements:

  • Include at least one transverse construction joint with hardened concrete.
  • Sub-base to be laid subsequently to test joint soundness.

• Location:

  • Trial length must be outside main works.

• Post-Approval:

  • After approval, no changes allowed in:
    • Materials
    • Mix proportions
    • Moisture content
    • Mixing, laying, compaction methods
    • Plant and construction procedures

Summary Table

This ensures the trial length validates construction methodology before full-scale works commence.

IRC SP 49 - Clause 7.10: Control of Thickness, Density and Strength

Thickness Control

• Tolerance: ±10 mm on the specified thickness of Dry Lean Concrete (DLC) layer.

Density Control

• Dry Density Measurement:
  • Take density holes along a diagonal line.
  • Spacing: One set per every 2000 m² or part thereof laid daily.
  • Use these samples to calculate dry density.

Strength Control

• Sampling Frequency:
  • 3 samples per 1000 m² or part thereof laid daily.
• Testing:
  • Prepare cubes from dry lean concrete samples.
  • Compact, cure, and test compressive strength per IS:516.
• Trial Mixes (Clause 6.5):
  • Moisture content tested at 5.0%, 5.5%, 6.0%, 6.5%, 7.0%.
  • Cubes cast at optimum moisture for 3 and 7-day strength.
  • Adjust cement content or grade if strength is unsatisfactory.

Summary Table for Control

Key Notes:

• Adjust moisture daily based on aggregate moisture.
• Mix should neither stick to rollers nor be too dry.
• Trial section construction per Clause 7.9 after mix approval.

flowchart TD
    A[Start Construction] --> B[Check Aggregate Moisture]
    B --> C[Prepare Trial Mixes at 5-7% Moisture]
    C --> D[Cast Cubes for Strength Test]
    D --> E{Strength Satisfactory?}
    E -- Yes --> F[Approve Mix & Construct Trial Section]
    E -- No --> G[Adjust Cement Content/Grade]
    G --> C
    F --> H[Control Thickness ±10mm]
    H --> I[Density Sampling (per 2000 m²)]
    I --> J[Strength Sampling (per 1000 m²)]
    J --> K[Test Cubes per IS:516

IRC SP 49: Opening to Traffic (Clause 7.11)

• Restriction on Vehicles:

  • No heavy commercial vehicles (trucks, buses) allowed on lean concrete sub-base immediately after construction.
  • Light vehicles allowed only after 7 days, and with prior Engineer approval.

• Curing Compound Efficiency (Annexure-A):

  • Test on curing compound to measure moisture retention on mortar slabs (150x300x50 mm).
  • Mortar mix: Cement:sand = 1:3, water-cement ratio 0.40-0.44.
  • Specimens cured at 38°C, 35% RH for 72 hours.
  • Calculate % retention of mixing water to assess curing effectiveness.

• Concrete Mix Proportions & Strength (Annexure-B):

  • Cement:Aggregate ratios vary (1:12 to 1:18).
  • Water content fixed at 6.5% by weight.
  • 7-day compressive strength ranges from 4.0 to 14.4 MPa depending on mix.
  • Dry density approx. 2300-2400 kg/m³.

Summary Table: Opening to Traffic

flowchart TD
    A[Lean Concrete Sub-base Constructed] --> B{Vehicle Type?}
    B -->|Heavy Vehicles| C[No Access Allowed]
    B -->|Light Vehicles| D{Days Since Construction?}
    D -->|<7 Days| C
    D -->|≥7 Days + Approval| E[Access Allowed]

This ensures protection of the sub-base strength and durability before full traffic loading.

Test on Curing Compound (IRC SP 49 - Clause 7.8 & Annexure-A)

• Curing Compound Type: White pigmented, water retention index ≥ 90%.
• Test Method:
  • Prepare 3 mortar slabs (150x300x50 mm) with OPC and standard sand (1:3), w/c ratio 0.40-0.44.
  • Mix flow: 35 ± 5% (10 drops flow table).
  • Place mortar in two layers, tamp 50 times each, finish top surface.
  • Spray curing compound within 1 hour after finishing.
  • Harden time: ≤ 30 minutes.
  • Weigh specimens with mould, cure at 38°C & 35% RH for 72 hours.
  • Reweigh and calculate water retention %:

[ \text{Water Retention %} = \frac{\text{Weight after curing}}{\text{Initial weight}} \times 100 ]

• Acceptance: Water retention index must be ≥ 90%.

Summary Table: Curing Compound Test Parameters

Curing Procedure (Clause 7.8)

• Water curing with double-layer hessian cloth, kept moist for 7 days.
• If water curing not possible, spray curing compound immediately after rolling.
• After compound loses tackiness, cover surface with wet hessian for 3 days.

flowchart TD
    A[Lean Concrete Surface Ready] --> B{Water Curing Possible?}
    B -- Yes --> C[Cover with 2 layers Hessian Cloth]
    C --> D[Keep continuously moist for 7 days]
    B -- No --> E[Spray White Pigmented Curing Compound]
    E --> F[Compound hardens within 30

DLC Test Results from CRRI (Annexure-B, IRC SP 49)

The Central Road Research Institute (CRRI) tested Dry Lean Concrete (DLC) mixes with different cement types: PSC, OPC, and PPC. Key parameters and results are tabulated below:

Notes:

• Cement:Aggregate ratio varies to optimize strength and density.
• Water content fixed at 6.5% by weight.
• Strength target for DLC sub-base is typically around 7-14 MPa at 7 days.
• PPC mixes show lower early strength but may improve later.

Usage:

• Select mix based on availability and required strength.
• Ensure proper batching, mixing, compaction, and curing as per IRC SP 49 clauses.
• Avoid heavy traffic on DLC sub-base before 7 days (Clause 7.11).

This data helps design lean concrete mixes balancing strength, density, and economy for rigid pavement sub-bases.

flowchart TD
    A[Cement Type] --> B{PSC / OPC / PPC}
    B --> C[Mix Proportioning]
    C --> D[Batching & Mixing]
    D --> E[Compaction & Curing]
    E --> F[7-day Strength Test]
    F --> G{Strength Achieved?}
    G -->|Yes| H[Use as DLC Sub-base