Guidelines for Cement Grouted Bituminous Mix Surfacing for Urban Roads
2019 Edition

1. Overview of CGBM

• Integration of high air void bituminous mix with cementitious grout.
• Optimization of grout flow characteristics and strength for complete infiltration and durability.

2. Fundamental Mix Design Equations

• Maximum Theoretical Specific Gravity (Gmm):

Where:

• A = Dry sample mass in air (g)

• B = Mass of bowl under water (g)

• C = Mass of bowl plus sample under water (g)

• D, E = Masses of lid, bowl, flask with and without sample (g)

• Air Voids (Va) and Voids in Mineral Aggregate (VMA):

[ Va = \left(1 - \frac{G_{mb}}{G_{mm}}\right) \times 100 ]

[ VMA = 100 - \frac{G_{mb} \times P_s}{G_{sb}} ]

Where:

• (G_{mb}) = Bulk specific gravity of compacted mix
• (G_{mm}) = Maximum theoretical specific gravity
• (P_s) = Percentage of aggregate in mix
• (G_{sb}) = Bulk specific gravity of aggregate

3. Summary of Recommended CGBM Properties

Scope of IRC SP 125

• Governs the design, testing, and quality control aspects of Cement Grouted Bituminous Mix (CGBM) used for urban road surfacing.

Key Formulas for Specific Gravity Determination

Essential Specifications and Tables

Material Requirements as per IRC SP 125:2019

Aggregates

• Typical bulk specific gravity (Gsb) around 2.7; if exceeding 2.7, binder content may be reduced accordingly.
• Gradations classified as CGBM Gr-I, Gr-II, or Gr-III targeting 25-35% air voids.

Bitumen

• Minimum binder content of 3.25% or as dictated by drain down evaluations.

Cementitious Grout

• Cement: OPC 43 or OPC 53 as per IS 8112 and IS 12269.
• Fly ash conforming to IS 3812 Part 2 with at least 65% passing 45 micron sieve.
• Initial setting time between 4-5 hours and final setting ranging 6-10 hours (IS 4031 Part 5).
• Compressive strength at 28 days from 40 to 100 N/mm² (ASTM C109).
• Flexural strength at 28 days between 5 and 7 N/mm² (IS 4031 Part 8).
• Flowability (Marsh Flow Value) ranging 20-50 seconds (ASTM C939).

Composite Properties of CGBM

Coarse Aggregate Criteria per IRC SP 125

• Size: Retained on 2.36 mm sieve; aggregates should be cubical, clean, hard, durable, and free from dust or deleterious substances.

• Physical Requirements (IS:2386 Parts 1, 3, 4, 5):

• Notes:
  • Polished Stone Value testing is not mandatory for 19 mm size CGBM aggregates.
  • Apply anti-stripping agents if retained tensile strength is below 80%.
  • Ensure abrasion and impact values are within limits to avoid crushing during compaction.

Fine Aggregate Specifications per IRC SP 125

• Particle Size: Passing 2.36 mm sieve and retained on 75 µm sieve (IS:2386 Part 1).
• Source: Entirely crushed, manufactured sand derived from stone crushing.
• Quality Attributes:
  • Clean, hard, durable with reasonably cubical particles.
  • Free from soft fragments, organic matter, or harmful impurities.
• Test Limits:
  • Sand Equivalent (IS:2720 Part 37): Minimum 50.
  • Plasticity Index for fraction passing 0.425 mm sieve (IS:2720 Part 5): Not exceeding 4.

Supplementary Physical Requirements (Referencing Coarse Aggregate Table 1)

Plasticity Index Calculation

[ PI = LL - PL ] Where:

• LL = Liquid Limit
• PL = Plastic Limit

For fine aggregates passing 0.425 mm sieve, PI should be ≤ 4.

flowchart LR
    FineAggregate --> SizeRange[2.36 mm to 75 µm]
    FineAggregate --> Source[100% Crushed Stone Sand]
    FineAggregate --> Quality[Clean, Hard, Durable]
    FineAggregate --> Tests[Sand Equivalent ≥ 50]

Bitumen Requirements and Mix Design Parameters (IRC SP 125)

Bitumen Type

• Use Viscosity Grade bitumen VG-30 or VG-40 complying with IS:73.
• Alternatively, Polymer Modified Bitumen (PMB) Grade 40 as per IRC SP 53.

Formulas for Mix Design

• Air Voids (Va):

[ Va = \left(1 - \frac{G_{mb}}{G_{mm}}\right) \times 100 ]

• Voids in Mineral Aggregate (VMA):

[ VMA = 100 \times \left(1 - \frac{G_{mb}}{P_s \times G_{sb}}\right) ]

Where:

• (G_{mb}): Bulk specific gravity of compacted mix.
• (G_{mm}): Theoretical maximum specific gravity.
• (G_{sb}): Bulk specific gravity of aggregates.
• (P_s): Percent aggregate in mix.

Binder Content

• Minimum binder quantity should be 3.25% or as determined via drain down testing.
• Binder content may be reduced if aggregate specific gravity is greater than 2.7.

Recommended Properties

Cementitious Grout Specifications (IRC SP 125 Clause 3.5)

• Constituents: Cement, fine sand passing 600 µm sieve, micro silica (silica fume), fly ash, water, superplasticizers, and optional polymer additives.

• Typical Mix Ratios (by weight):

  • Cement : Sand : Micro silica : Fly ash = 40 : 40 : 10 : 10
  • Water to binder ratio (w/b): 0.55
  • Superplasticizer dosage: 0.5% by dry powder weight

• Alternative Mix:

  • Cement : Sand : Micro silica : Fly ash = 38 : 10 : 10 : 42
  • Water/cement ratio (w/c): 0.25
  • Superplasticizer dose: 0.3%

• Performance Metrics:

  • Flowability (ASTM C939 Marsh Flow Cone): 45-50 seconds
  • Compressive strength at 28 days: 40-100 MPa (ASTM C109 on 50 mm cubes)
  • Flexural strength at 28 days: Approximately 10 MPa (IS 4031 Part 8)
  • Initial and final setting times as per IS 4031 Part 6

• Design Considerations:

  • Balance sand and fly ash proportion for optimal fluidity and strength.
  • Use superplasticizers to maintain flow while minimizing water content.
  • Polymer additives enhance early strength gain.
  • Conduct multiple trial mixes to accommodate material variations.

Summary Table of Grout Characteristics

Cementitious Grout Design Guidelines (IRC SP 125 Clause 3.5)

• Composition includes cement, fine sand (passing 600 µm), mineral additives (fly ash, micro silica), chemical admixtures (superplasticizer 0.3-0.5% by dry powder weight), and polymers.
• Water to binder ratio ranges approximately between 0.25 and 0.55 depending on mix design.

• Key Performance Parameters:

  • Flowability (Marsh Flow Cone, ASTM C939): 23-50 seconds
  • Initial setting time (IS 4031 Part 5): 4-5 hours
  • Final setting time (IS 4031 Part 5): 6-8 hours
  • Compressive strength at 28 days (ASTM C109): 40-100 MPa
  • Flexural strength at 28 days (IS 4031 Part 8): 5.4-10 MPa
  • Voids in CGBM at 7 days (ASTM D3203): approximately 2.2-2.86%

• Testing Notes:

  • Flowability is determined by Marsh Cone with water flow baseline of 8.0±1.0 seconds.
  • Strength tests are averages of a minimum of three specimens.
  • Multiple trial mixes are encouraged to accommodate material variability.

Design Process Flowchart

flowchart TD
    SelectMaterials[Select Materials] --> ProportionMix[Proportion Mix: Cement, Sand, Fly Ash, Micro silica]
    ProportionMix --> AddWater[Add Water and Superplasticizer]
    AddWater --> Mix[Mix to Desired Consistency]
    Mix --> TestFlow[Perform Flow Test (ASTM C939)]
    TestFlow -->|Flow Adequate| ApplyGrout[Apply Grout to Bituminous Mix]
    TestFlow -->|Flow Inadequate| AdjustMix[Modify Mix and Retest]

Essential Formulas and Criteria for Bituminous Mix Design (IRC SP 125)

1. Air Voids (Va) and Voids in Mineral Aggregate (VMA):

[ Va = \left(1 - \frac{Gmb}{Gmm}\right) \times 100 ]

[ VMA = 100 - \left( \frac{Gmb \times P_s}{Gsb} \right) ]

Where:

• Gmb = Bulk specific gravity of compacted mix
• Gmm = Theoretical maximum specific gravity
• Gsb = Bulk specific gravity of aggregate
• Ps = Percentage of aggregate in mix

2. Aggregate Gradation:

• Utilize CGBM Gr-I, Gr-II, or Gr-III gradations targeting air voids between 25% and 35%.
• If aggregate specific gravity surpasses 2.7, adjust binder content accordingly.

3. Binder Content:

• Maintain a minimum of 3.25% binder content or as indicated by drain down tests.

4. Grout Material Specifications:

5. Composite CGBM Requirements:

Guidelines for Optimizing Grout Properties (IRC SP 125)

• Key Equations for Mix Parameters:

[ Va = \left(1 - \frac{G_{mb}}{G_{mm}}\right) \times 100 ]

[ VMA = 100 - \frac{G_{mb} \times P_s}{G_{sb}} ]

Where:

• (G_{mb}): Bulk specific gravity of compacted mix

• (G_{mm}): Theoretical maximum specific gravity

• (P_s): Aggregate percentage

• (G_{sb}): Bulk specific gravity of aggregates

• Grout Optimization:

  • Achieve balance between grout flowability and compressive strength.
  • Minimize mixing water while ensuring grout fully penetrates the bituminous mix voids.
  • Target Marsh Flow Value between 20 and 50 seconds (ASTM C939) for appropriate fluidity.
  • Compressive strength goals range from 40 to 100 N/mm² at 28 days (ASTM C109).
  • Refer to IRC SP 125 Fig.1 for grout flow versus water content relationships.

• Summary of Recommended Specifications:

Essential Recommendations for CGBM (IRC SP 125)

1. Aggregate Gradation and Mix Design:

• Adopt aggregate gradations as per CGBM Gr-I, Gr-II, or Gr-III classifications producing 25-35% air voids.
• Set binder content to a minimum of 3.25% or as verified by drain down testing.
• Calculate air voids and VMA using:

[ Va = \left(1 - \frac{G_{mb}}{G_{mm}}\right) \times 100 ]

[ VMA = 100 - \frac{G_{mb} \times P_s}{G_{sb}} ]

Where:

• Gmb = Bulk specific gravity of compacted mix
• Gmm = Maximum theoretical specific gravity
• Ps = Aggregate percentage
• Gsb = Bulk specific gravity of aggregate

2. Grout Material:

• Use OPC 43 or OPC 53 grade cement per IS 8112 and IS 12269.
• Fly ash should comply with IS 3812 Part 2 with a minimum 65% passing 45 micron sieve.
• Grout properties:
  • Initial setting time: 4-5 hours (IS 4031 Part 5)
  • Final setting time: 6-10 hours
  • Compressive strength at 28 days: 40-100 N/mm² (ASTM C109)
  • Flexural strength at 28 days: 5-7 N/mm² (IS 4031 Part 8)
  • Fluidity: 20-50 seconds (ASTM C939)

3. Composite CGBM Properties:

Key Production Parameters and Calculations (IRC SP 125)

1. Job Mix Gradation and Air Voids Calculation:

• Bulk specific gravity (Gmb) measured on compacted specimens (ASTM D3203).
• Theoretical maximum specific gravity (Gmm) of uncompacted mix.
• Air voids (Va) and VMA calculated as:

[ Va = \left(1 - \frac{Gmb}{Gmm}\right) \times 100 ]

[ VMA = 100 - \frac{Gmb \times P_s}{G_{sb}} ]

Where:

• Ps = Percentage of aggregate
• Gsb = Bulk specific gravity of aggregate

2. Grout Optimization:

• Adjust mixing water to achieve desired fluidity and strength balance.
• Ensure complete grout infiltration into bituminous mix voids.

3. Recommended Properties (Table 3 Summary):

Mechanical and Fatigue Properties of CGBM (IRC SP 125)

1. Resilient Modulus (E):

• Laboratory values range between 12,000 and 15,000 MPa measured via Indirect Tensile Test (ASTM D4123) at 35°C.
• For design considerations, a conservative modulus of 5,000 MPa is recommended to accommodate material variability and field conditions.
• Poisson’s ratio assumed as 0.25.

2. Flexural Strength (Modulus of Rupture, MB):

• Laboratory measured approximately 2.5 MPa.
• Design value for structural adequacy checks is 1.25 MPa.

3. Fatigue Life Relationship:

• Fatigue life (N) as a function of tensile stress (σ) can be expressed as:

[ N = k \left(\frac{1}{\sigma}\right)^m ]

where k and m are material-specific constants obtained from fatigue testing.

4. Recommended Properties Summary:

Pavement Design Guidelines with CGBM Layers (IRC SP 125)

1. Layer Thickness and Composition:

• Surface layer thickness:
  • 30 mm for traffic volumes up to 5 million standard axles (MSA).
  • 40-50 mm for traffic exceeding 5 MSA.
  • For renewal coats with design traffic under 30 MSA, 30 mm thickness is adequate.
• CGBM can function as surface or base course layers.

2. Material and Performance Parameters:

• Bituminous mix air voids: 25-35% to allow grout penetration.
• Grout compressive strength at 28 days: 40-100 N/mm².
• Resilient modulus approximately 5000 MPa for design purposes (lab values range 8000-15000 MPa at 35°C).
• Skid resistance: Minimum 50 BPN wet, 60 BPN dry.

3. Design Methodology:

• Employ elastic layered analysis similar to flexible pavement design.
• Input parameters include subgrade CBR, elastic moduli of granular and CGBM layers, Poisson’s ratio, and cumulative design traffic.
• Fatigue life and resilient modulus relationships derived from studies by IIT Kharagpur and CSIR-CRRI inform thickness design.

4. Construction and Quality Control:

• Prepare high void bituminous mix with optimized binder content to reduce drain down.
• Ensure grout achieves 97-100% penetration into mix voids.
• Allow curing for 7 days post grouting.
• Avoid grouting operations during adverse weather conditions such as rain or snowfall.

Fatigue Life Formula (Clause 8):

[ N = 1017.6019 \times \left(\frac{1}{e}\right)^{4.6099} \times \left(\frac{1}{E}\right)^{0.6171} ]

where:

• N = fatigue life (number of load repetitions)
• e = tensile strain at bottom of CGBM layer
• E = resilient modulus of CGBM (MPa)

Pavement Layer Design Flowchart

flowchart TD
    Subgrade[Subgrade Soil] -->|CBR| Base[Granular Base/Sub-base Layer]
    Base -->|Elastic Modulus| CGBM[CGBM Layer]
    CGBM -->|Design Inputs| PavementDesign[Structural Pavement Analysis]