Tentative Guidelines on Cement-Fly Ash Concrete for Rigid Pavement Construction

IRC 68: Introduction to Cement-Fly Ash Concrete for Pavements

Key Points:

• Cement-fly ash concrete replaces 15-20% of cement and ~10% of sand with fly ash, producing economical mixes with equivalent strength to plain cement concrete.
• Fly ash must conform to IS: 3812 (Part I)-1966, with lime-reactivity ≥ 40 kg/cm², Blaine surface area ≥ 3200 cm²/g, and carbon content ≤ 12%.
• Cement used should comply with IS: 269-1976 or IS: 8112-1976.
• Fly ash concrete mix design is indirect:
  • Design a plain cement concrete mix (W:C:S:A).
  • Calculate equivalent cement-fly ash mix (W':C':F:S':A') using replacement factors.

Mix Design Formulae

Where:

• ( p_c ) = 0.85 (typical cement replacement factor)
• ( p_s ) = 0.90 (typical sand replacement factor)
• ( S_c, S_s, S_f ) = specific gravities of cement, sand, fly ash respectively

Material Specific Gravities (Example)

Quality Control Highlights

• Fly ash moisture content checked daily.
• Mixing sequence: water → fly ash

Key Specifications & Formulas for Materials in Cement-Fly Ash Concrete (IRC 68)

1. Materials Specifications:

• Fly Ash:

  • Conforms to IS: 3812 (Part I)-1966.
  • Lime reactivity ≥ 40 kg/cm².
  • Blaine specific surface area ≥ 3200 cm²/g.
  • Carbon content ≤ 12%.
  • MgO ≤ 5%, SO₃ ≤ 3% (for lignite fly ash).
  • Moisture content checked daily.

• Cement:

  • Ordinary Portland Cement as per IS: 269-1976 or IS: 8112-1976.

• Water:

  • As per IRC: 15-1970 para 2.3.

• Aggregates:

  • Saturated surface dry basis weights.
  • Specific gravities: Cement (3.15), Sand (~2.687), Coarse Aggregate (~2.9), Fly Ash (~2.25).

2. Mix Design Method:

Given plain cement concrete mix: W:C:S:A (water, cement, sand, aggregate in kg/m³).

Equivalent Cement-Fly Ash mix: W':C':F:S':A'

• Cement and sand replaced by fly ash: [ C' = p_c \times C, \quad S' = p_s \times S ] Typical values: [ p_c = 0.85, \quad p_s = 0.90 ]

• Fly ash quantity (equal volume replacement): [ F = (C - C') / S_c + (S - S') / S_s ] where (S_c, S_s) = specific gravities of cement and sand.

• Water adjusted to maintain water-to-binder ratio: [ W' = W \times \frac{C' + F}{C} ]

• Aggregate adjusted for volume changes: [ A' = A + (W - W') \times \rho_w ] where (\rho_w) = density of water (1000 kg/m³).

3. Mixing Procedure:

• Add water first.
• Add fly ash to form slurry.
• Add cement and aggregates.
• Ensure thorough

Cement-Fly Ash Concrete Mix Design (IRC 68 Highlights)

1. Mix Design Procedure (Clause 3.3 IRC 68):

   • Start with a plain cement concrete mix: ( W:C:S:A ) (Water, Cement, Sand, Aggregate in kg/m³).
   • Equivalent cement-fly ash mix: ( W':C':F:S':A' ).
   • Cement and sand replaced by fly ash by volume: [ C' = p_c \times C, \quad S' = p_s \times S ] where typical values: [ p_c = 0.85, \quad p_s = 0.90 ]
   • Fly ash quantity: [ F = (C - C') + (S - S') \times S_f ] where ( S_f ) = specific gravity of fly ash.
   • Water adjusted to maintain water to effective binder ratio: [ \frac{W}{C + F} = \frac{W'}{C' + F} ]
   • Aggregate adjusted for volume: [ A' = A + (W - W') ]

2. Material Specifications:

   • Fly ash per IS: 3812 (Part I) - lime reactivity ≥ 40 kg/cm², Blaine fineness ≥ 3200 cm²/g, carbon ≤ 12%.
   • Cement per IS: 269 or IS: 8112.
   • Water per IRC: 15-1970.

3. Mixing Sequence (Clause 8.4 IRC 68):

   • Add water → add fly ash to form slurry → add cement → add aggregates.
   • Ensure thorough mixing for uniform dispersion.

4. Quality Control:

   • Check fly ash quality initially and for each batch.
   • Monitor moisture content daily.
   • Follow IRC SP: 11-1973 for overall quality control.

Example Table for Specific Gravities & Replacement Ratios

IRC 68: Related Specifications & Practices for Cement-Fly Ash Concrete Pavements

Key Specifications:

• Fly Ash: Must conform to IS: 3812-1966 (Part I) with:

  • Lime reactivity ≥ 40 kg/cm²
  • Blaine surface area ≥ 3200 cm²/g
  • Carbon content ≤ 12%
  • MgO ≤ 5%, SO₃ ≤ 3% (for lignite fly ash)

• Cement: Ordinary Portland Cement as per IS: 269-1976 or IS: 8112-1976 (High Strength OPC)

• Aggregates: As per IRC: 15-1970, para 2.2

Mixing Practice (Clause 8.4):

• Water added first
• Followed by fly ash to form slurry
• Then cement and aggregates added
• Ensures uniform fly ash dispersion

Quality Control (Clause 6):

• Follow IRC SP: 11-1973 for general QC
• Check fly ash quality per IS: 3812 initially and for each consignment
• Monitor moisture content daily
• Ensure thorough mixing

Example: Equivalent Cement-Fly Ash Concrete Mix Design

• Specific gravities: Cement (3.15), Sand (2.687), Coarse Aggregate (2.9), Fly Ash (2.25)

Summary Table of Key Standards

Key Specifications & Formulas for Cement-Fly Ash Concrete Construction (IRC 68)

1. Materials:

• Fly Ash: IS 3812-1966 compliant, lime reactivity ≥ 40 kg/cm², Blaine surface area ≥ 3200 cm²/g, carbon content ≤ 12%.
• Cement: Ordinary Portland Cement as per IS 269-1976 or IS 8112-1976.
• Water: As per IRC: 15-1970, para 2.3.
• Aggregates: Saturated surface dry basis.

2. Mix Design Procedure:

• Start with plain cement concrete mix (W:C:S:A).
• Replace cement and sand partially by fly ash:
  • Cement replacement (p_c): 15-20% (typical 0.85 for trial).
  • Sand replacement (p_s): ~10% (typical 0.90 for trial).

3. Equivalent Mix Quantities:

[ C' = p_c \times C ] [ S' = p_s \times S ] [ F = (C - C') \times \frac{S_c}{S_f} + (S - S') \times \frac{S_s}{S_f} ]

Where:

• (C, S) = original cement and sand weights (kg)
• (C', S') = adjusted cement and sand weights
• (F) = fly ash weight replacing cement and sand (kg)
• (S_c, S_s, S_f) = specific gravities of cement, sand, and fly ash respectively

4. Water and Aggregate Adjustments:

• Maintain water to effective binder ratio:

[ W' = W \times \frac{C' + F}{C} ]

• Adjust coarse aggregate for volume changes:

[ A' = A + (W - W') \times \rho_w ]

((\rho_w) is water density, approx 1000 kg/m³)

5. Construction Notes:

• Follow IRC: 15-1970 for batching, mixing, placing.
• Mix water first with fly ash to form slurry, then add cement and aggregates.
• Fly ash batching by weight; account for moisture content.
• Store fly ash covered or bagged to prevent airborne dust.

Summary Table: Typical Mix Proportions

Quality Control for Cement-Fly Ash Concrete (IRC 68)

Key Points from Clause 6:

• Fly Ash Quality:

  • Check as per IS: 3812 (Part I)-1966 initially and for each fresh consignment.
  • Monitor moisture content once or twice daily.

• Mixing Procedure (Clause 8.4):

  • Add water first, then fly ash to form slurry, followed by cement and aggregates.
  • Ensure thorough dispersion of fly ash.

• Reference for Quality Control:
  Follow Chapter 6 of IRC SP: 11-1973 ("Handbook of Quality Control for Construction of Roads and Runways").

Example: Equivalent Cement-Fly Ash Concrete Mix Design

Important Specifications for Fly Ash:

• Lime reactivity ≥ 40 kg/cm²
• Blaine surface area ≥ 3200 cm²/g
• Carbon content ≤ 12%
• MgO ≤ 5%, SO₃ ≤ 3% (for lignite fly ash)

Summary Table: Fly Ash Concrete Quality Control

flowchart TD
    A[Water] --> B[Add Fly Ash → Form Slurry]
    B --> C[Add Cement]
    C --> D[Add Aggregates]
    D --> E[Thorough Mixing]
   

Equivalent Cement-Fly Ash Concrete Mix Design (IRC 68 - Clause 8.4 & Example)

Given Plain Cement Concrete Mix (per m³):

Replacement Parameters:

• Cement replaced by fly ash = 15% by weight
• Sand replaced by fly ash = 10% by weight
• Specific gravity of fly ash (Sf) = 2.25

Stepwise Procedure:

1. Calculate reduced cement and sand:

   [ C' = p_c \times C, \quad S' = p_s \times S ]

   Where typical trial values are: [ p_c = 0.85, \quad p_s = 0.90 ]

2. Calculate fly ash quantities replacing cement and sand by equal volume:

   [ F_c = (C - C') / S_c, \quad F_s = (S - S') / S_f ]

   Total fly ash,

   [ F = F_c + F_s ]

3. Adjust water to maintain water/effective binder ratio:

   [ W' = W \times \frac{C' + F}{C} ]

4. Adjust coarse aggregate for volume change:

   [ A' = A + (W - W') \times S_a ]

Example Calculation Summary:

Notes:

• Mix trials are essential

Batching and Mixing Procedures (IRC 68 - Clause 8.4 & related)

Batching:

• Fly ash, cement, sand, and aggregates are batched by weight.
• Water may be batched by volume using calibrated containers.
• Fly ash moisture content must be checked; adjust weight accordingly.
• For small batches, weigh fly ash on a pan balance and add directly.

Mixing Sequence:

1. Add water first into the mixer.
2. Add fly ash to form a slurry.
3. Add cement.
4. Add aggregates (sand and coarse aggregate).
5. Ensure thorough mixing for uniform dispersion of fly ash.

Equivalent Cement-Fly Ash Concrete Mix Design

Given a plain cement concrete mix with:

Specific Gravities:

Key Formulas for Equivalent Mix (Cement replaced by fly ash)

• Cement replacement factor: ( C' = p_c \times C )
• Sand replacement factor: ( S' = p_s \times S )

Typical values:
( p_c = 0.85 ), ( p_s = 0.90 )

• Fly ash quantity:
  [ F = (C - C') \times \frac{S_c}{S_f} + (S - S') \times \frac{S_s}{S_f} ]

• Water adjusted to maintain water-to-effective binder ratio:
  [ W' = W \times \frac{C' + F}{C} ]

• Adjusted coarse aggregate:
  [ A' = A + (W - W') ]

Quality Control Highlights

• Fly ash must conform to IS: 3812 (Part I)-1966.
• Moisture content of fly ash checked once or twice daily.
• Thorough mixing per IRC

Storage and Handling of Fly Ash (IRC 68 Highlights)

• Storage: Fly ash, being very fine and airborne, should be stored in:
  • Bagged form, or
  • Rectangular trapezoidal pits dug specifically for fly ash storage.
• Covering: Top of storage pits must be covered with tarpaulins or suitable covers to prevent dust dispersion.
• Handling during Transport: Either bagged or soaked with water at the top to reduce dust.
• Batching:
  • Fly ash should be batched by weight.
  • Moisture content must be checked regularly; adjust batching weight accordingly if fly ash is wet.
  • For small batches, weigh fly ash separately and feed directly into the mixer.

Key Specifications from IRC 68 & IS 3812:

Important Notes on Mix Preparation (Clause 8.4):

• Water is first added to the mixer.
• Fly ash is added next to form a slurry.
• Cement and aggregates are added afterward.
• Ensure thorough mixing for uniform dispersion.

flowchart LR
    A[Water] --> B[Fly Ash]
    B --> C[Slurry Formation]
    C --> D[Cement + Aggregates]
    D --> E[Thorough Mixing]
    E --> F[Concrete Mix Ready]

This ensures controlled dust, consistent batching, and proper mix quality per IRC 68.

Workability and Strength Considerations for Cement-Fly Ash Concrete (IRC 68)

1. Mix Proportioning:

• Replace 15-20% cement and ~10% sand by weight with fly ash.
• Fly ash slurry preparation: Add water → fly ash → cement → aggregates.

2. Equivalent Mix Design:

3. Water and Aggregate Adjustment:

• Maintain water to effective binder ratio:
  ( W' = W \times \frac{C' + F}{C} )
• Adjust coarse aggregate:
  ( A' = A + (W - W') \times \text{specific gravity of water} )

4. Quality Control:

• Fly ash per IS: 3812 (Part I)-1966.
• Moisture content checked daily.
• Thorough mixing as per IRC: 15-1970 para 8.4.

5. Workability:

• Adjust ( p_c, p_s ) based on trial mixes to achieve desired workability.
• Use fly ash slurry to improve dispersion.

Summary Table: Mix Design Parameters

Environmental and Economic Benefits of Cement-Fly Ash Concrete (IRC 68)

• Environmental Benefits:

  • Fly ash (15-20% cement replacement) reduces cement consumption, lowering CO₂ emissions.
  • Utilizes fly ash, a waste by-product, addressing disposal issues.
  • Reduces demand for natural sand (10% replacement), conserving natural resources.

• Economic Benefits:

  • Lower cement content reduces material costs.
  • Fly ash is generally cheaper than cement.
  • Mix design allows equivalent strength with less cement, optimizing cost-efficiency.

Key Specifications & Mix Design Formulas

Equivalent Cement-Fly Ash Concrete Mix Design (from plain cement concrete mix W:C:S:A)

[ C' = p_c \times C, \quad S' = p_s \times S ]

• (p_c) (cement replacement factor): 0.85 (trial value)
• (p_s) (sand replacement factor): 0.90 (trial value)

Fly ash quantity:

[ F = (C - C') + \frac{(S - S')}{S_f} ]

Water adjusted to maintain water-to-binder ratio:

[ W' = W \times \frac{C' + F}{C} ]

Coarse aggregate adjusted for volume:

[ A' = A + (W - W') ]

Summary

• Use IS: 3812 for fly ash quality.
• Follow batching and mixing guidelines (water first, then fly ash slurry, then cement and aggregates).
• Trial mixes to adjust workability and strength.
• Significant savings in cement and sand reduce cost and environmental impact.

flowchart LR
    A[Plain Cement Concrete Mix] --> B[Calculate Cement & Sand Replacement]
    B --> C[Determine Fly Ash Quantity]
    C --> D

Key Formulas & Steps for Equivalent Cement-Fly Ash Concrete Mix Design (IRC 68 Annexure)

Given a plain cement concrete mix ( W:C:S:A ) (water, cement, sand, aggregate in kg/m³), design the equivalent cement-fly ash mix ( W':C':F:S':A' ):

1. Define variables:

2. Replacement factors (suggested trial values):

3. Calculate quantities:

[ C' = p_c \times C ] [ S' = p_s \times S ]

Fly ash quantity (F) (equal volume replacement):

[ F = (C - C') \times S_o + (S - S') \times S_s ]

Water adjusted to maintain water-to-effective binder ratio:

[ W' = W \times \frac{C' + F}{C} ]

Aggregate adjusted to maintain volume:

[ A' = A + (W - W') ]

4. Procedure:

• Start with plain mix.
• Calculate (C', S') using (p_c, p_s).
• Compute fly ash (F).
• Adjust water (W') for same water/binder ratio.
• Adjust aggregate (A').
• Trial mix and adjust (p_c, p_s) for workability and strength.

Example Table (from context):

| Material | Quantity