Handbook on Concrete Mixes

IS SP Part 23 - Scope: Key Formulas, Tables & Specifications

The scope covers concrete materials, properties, testing, and durability parameters. Key highlights:

1. Assumed Standard Deviation & Characteristic Strength (Clause 4.1.2, Tables 29 & 30):

Formula for characteristic strength:

[ f_k = \mu - k \times \sigma ]

• (f_k) = characteristic strength
• (\mu) = mean strength
• (\sigma) = standard deviation
• (k) = factor from Table 30

2. Water Impurities Limits (Table 16):

• Sodium & potassium carbonates: max 1000 ppm
• Sodium chloride: max 20,000 ppm
• Sulphates: max 10,000 ppm
• Calcium chloride: max 2% by cement weight (plain concrete)
• Silt & suspended particles: max 2000 ppm

3. Admixtures Physical Requirements (Table 18):

Key Formulas, Tables & Specs for Cements (IS SP Part 23):

1. Chemical Composition of Ordinary Portland Cement (Table 2)

2. Heat Evolution of Cement Compounds (cal/g) (Table 3)

3. Physical & Chemical Requirements for Various Cements (Table 4)

• Fineness (Specific surface): 2250 - 3500 cm²/g (varies by cement type)
• Setting Time: Initial ≥ 30 min; Final ≤ 10 hrs
• Soundness (Le-Chatelier expansion): Max 10 mm
• Compressive Strength (Ordinary Portland Cement):
  • 3 days: ≥ 160 kgf/cm²
  • 7 days: ≥ 220 kgf/cm²

IS SP Part 23: Aggregates - Classification & Properties

1. Classification of Aggregates (Clause 2.2.1)

• Coarse Aggregate: Particles > 2.36 mm (Clause 2.36)
• Fine Aggregate (Sand): 2.36 mm to 150 µm
• Natural Aggregates: Classified based on origin and particle size.

2. Key Properties of Natural Aggregates (Clause 2.2.2)

• Fineness Modulus (FM): Indicates aggregate gradation.

  [ \text{FM} = \frac{\text{Sum of cumulative % retained on standard sieves}}{100} ]

• Void Content (%): Influences water demand in concrete.

• Clay Content (%): Affects compressive strength; higher clay reduces strength (Fig. 11).

• Alkali Reactivity: Measured by reduction in alkalinity of 1N NaOH solution (Rc) and silica dissolved (Sc).

3. Important Figures

• Fig. 9: Shows effect of mixing time on FM of sand and gravel.
• Fig. 10: Void content vs. mixing water requirement.
• Fig. 11: Clay content vs. 28-day compressive strength.

4. Specifications Summary

flowchart LR
    A[Aggregates] --> B[Coarse (>2.36 mm)]
    A --> C[Fine (2.36 mm - 150 µm)]
    B --> D[Properties: Size, Shape, Strength]
    C --> E[Properties: Fineness Modulus, Void Content, Clay %]
    E --> F[Influences Water Demand & Strength]

Note: Refer to IS SP 23 for detailed test methods and limits on deleterious materials.

Workability of Concrete (IS SP Part 23 - Clause 3.1.3)

Workability ensures concrete can be placed and compacted easily without segregation or bleeding. It depends on:

• Compacting equipment
• Section size and reinforcement concentration
• Aggregate size (nominal max size 20mm considered in tables)

Key Parameters & Recommended Ranges (Table 22 summary for 20mm aggregates)

Important Notes:

• Workability increases with aggregate size.
• Minimum workability consistent with proper compaction is ideal.
• Insufficient workability → incomplete compaction → reduced strength and durability.
• Vibration effectiveness affects required workability.

Related Formulas & Relations:

• Relative Water Content vs Slump (Table 21):

• Workability is often measured by Slump, Compacting Factor, and Vee-Bee Time.

Summary Diagram: Workability Parameters

flowchart LR
    A[Concrete Mix] --> B[Workability]
    B --> C[Slump Test]
    B --> D[Compacting Factor]
    B --> E[Vee-Bee Time]
    C --> F{Workability Range}
    D --> F
    E --> F
    F --> G[Easy to Place & Compact]
    F --> H[Moderate Difficulty]
    F --> I[Difficult Placement]

References:

• IS SP Part 23 Clause

Key Principles & Formulas for Concrete Mix Design (IS SP Part 23)

1. Basic Parameters

• Characteristic Strength (fck) at 28 days (N/mm²)
• Water-Cement Ratio (w/c): Critical for strength & durability
• Maximum Aggregate Size: Typically 20 mm or 40 mm
• Workability: Slump range (e.g., 0-10 mm for low workability)
• Quality Control & Compaction Method

2. Water-Cement Ratio & Strength Relationship

From Fig. 43 & 46 (Teychenne et al.):

Lower w/c → higher strength but less workability.

3. Mix Proportioning Steps (Fig. 42)

1. Select target mean strength (fck + margin for variability)
2. Determine w/c from strength requirement
3. Choose max aggregate size & grading zone
4. Estimate water content (kg/m³) for required workability
5. Calculate cement content = water content / w/c
6. Determine fine aggregate % (Fig. 45) based on grading zone
7. Calculate coarse aggregate by difference
8. Adjust for moisture & batching conditions

4. Water & Aggregate Content (Typical Values)

5. Statistical Concepts (Clause 4.2)

• Target mean strength = fck + k × standard deviation (k ≈ 1.65 for 95% confidence)

6. Additional Notes

• Compacting factor changes by 0.1 → adjust mix accordingly
• Chemical attack and concrete mass size influence mix design
• Use saturated surface dry (SSD) basis

IS SP Part 23 - Clause 4.2: Statistical Concepts in Concrete Mix Design

• Target Mean Strength (fₜ):
  The mix design must ensure the target mean strength is achieved during trial mixes.

• Standard Deviation (σ):

  • Use either:
    • An assumed σ based on control level, or
    • A calculated σ from past test data (preferred).
  • If no past data, use values from Table 29 (IS SP Part 23).
  • Once ≥30 test results are available, use the actual σ to revise the mix.

• Key Formula for Target Mean Strength:
  [ f_t = f_k + k \times \sigma ] Where:

  • ( f_k ) = Characteristic strength (e.g., 28-day strength)
  • ( k ) = Statistical constant (usually 1.65 for 5% risk)
  • ( \sigma ) = Standard deviation

• Table 29 (Typical Standard Deviation Values):

  Quality Control Level	Standard Deviation (σ), N/mm²
  Good	3-4
  Moderate	4-5
  Poor	5-6

• Procedure Summary:

  1. Select initial σ (assumed or from Table 29).
  2. Calculate target mean strength ( f_t ).
  3. Conduct trial mixes and testing.
  4. Update σ with actual test results (≥30 samples).
  5. Adjust mix design accordingly.

Visual: Target Mean Strength Calculation Flow

flowchart TD
    A[Select characteristic strength \(f_k\)] --> B[Determine standard deviation \(\sigma\)]
    B --> C[Calculate target mean strength \(f_t = f_k + k\sigma\)]
    C --> D[Conduct trial mixes and testing]
    D --> E{≥ 30 test results?}
    E -- Yes --> F[Calculate actual \(\sigma\)]
    F --> G[Revise mix design using actual \(\sigma\)]
    E -- No --> H[Continue with assumed \(\sigma\)]
``

IS SP 23 Part 23: Effects of Temperature and Cold Weather Concreting

Key Points from Clauses 7.2 & 7.2.1

• Cold Weather Effects:
  • Delayed setting below ~5°C.
  • Early freezing causes permanent damage; strength may reduce by 50% if frozen before pre-hardening.
  • Pre-hardening period varies: 24 hours to 3 days or until strength reaches 35-70 kgf/cm².
  • Temperature differentials cause cracking and durability issues.

Recommended Minimum Formwork Removal Times at ~3°C (Clause 7.2.2.5)

Practical Guidelines

• Use test cubes cured under site conditions to decide formwork removal.
• Protect concrete from freezing until sufficient strength is attained.
• Avoid large temperature gradients to minimize cracking.

Typical Strength Development Impact (Qualitative)

graph LR
A[Normal Temp (~23°C)] --> B[Standard Strength Gain]
C[Cold Temp (~5°C)] --> D[Slower Strength Gain]
E[Freezing Before Pre-hardening] --> F[Strength Loss up to 50%]

For detailed temperature-strength curves and mix water temperature adjustments, refer to figures 49-53 in the code. Use heated mixing water or insulation to maintain concrete temperature above freezing during curing.

Key Formulas and Tables for Proportioning Concrete Ingredients (IS SP Part 23)

1. Water-Cement Ratio & Compressive Strength

• Relationship (Table 31 & Fig. 46):

2. Mixing Water Requirements (kg/m³)

(Table 32: for slump & max aggregate size)

3. Aggregate Proportioning

• Volume of dry-rodded coarse aggregate per unit concrete volume (Table 33):

4. Adjustment in Mix Proportions (Table 36)

Use of Admixtures as per IS SP Part 23 & IS 9103-1979

Types of Admixtures:

• Accelerating: Speeds up setting and early strength.
• Retarding: Delays setting to allow longer workability.
• Water-reducing: Reduces water content (5-12%) for same workability or increases strength (~10%).
• Air-entraining: Improves workability and durability by entraining air.

Key Specifications (Table 18 Summary):

Important Notes:

• Chloride content in admixtures must be declared; avoid high chloride to prevent reinforcement corrosion.
• Pozzolanic materials (fly ash, burnt clay) improve workability and durability but act also as cement replacement.
• Air content optimum depends on aggregate size (see Table 19):

Practical Use:

• Evaluate admixture performance by comparing concrete properties with and without admixture.
• Adjust mix design to optimize cement, water, and admixture dosage for desired workability and strength.

Strength and Durability Considerations as per IS SP Part 23

Key Formulas & Relationships:

• Water-Cement Ratio vs Compressive Strength (Table 31):

• Minimum Cement Content for Durability (Table 23): Depends on exposure class; e.g., for sulphate exposure, cement content and type must be adjusted.

• Chloride Ion Limits (Table 27):

• Optimum Air Content for Aggregate Size (Table 19):

Specifications & Notes:

• Use low water-cement ratio to enhance strength and durability; adjust cement content based on exposure severity (e.g., sulphate attack).

• Admixtures must comply with physical requirements (Table 18) to ensure durability without compromising strength.

• Mix design should consider aggregate properties (Tables

IS SP Part 23: Testing and Quality Control of Concrete — Key Highlights

1. Sampling & Frequency (Clause 8.1 & 8.2)

• Sampling as per IS 1199.
• Frequency depends on work size and type; minimum 1 sample per 50 m³ or per 500 m² slab.

2. Workability Tests (Clause 8.3)

• Slump Test (IS 1199)
• Compacting Factor Test (IS 1199)
• Vee-Bee Test (IS 1199)

3. Air Content (Table 19)

4. Setting Time (Clause 8.6)

• Initial and final setting times as per IS 4031 (Part 5).

5. Strength Tests (Clause 8.7)

• Compressive strength by 150 mm cubes at 7, 28 days (IS 516).
• Standard deviation and control limits from Table 28 and 29.
• Relationship between water-cement ratio and compressive strength (Table 31):

[ f_{ck} = \frac{A}{B + (w/c)} ]

Where (f_{ck}) = compressive strength, (w/c) = water-cement ratio, A and B are constants from Table 31.

6. Admixtures (Table 18)

• Physical requirements and effects on setting time, strength, bleeding.
• Example: Water-reducing admixture reduces water content by up to 5%.

7. Water Quality (Tables 16 & 17)

• Limits on impurities like chlorides (max 2000 mg/l for plain concrete).
• Testing required if impurities exceed limits.

Summary Diagram: Concrete Quality Control Workflow

flowchart TD
    A[Sampling] --> B[Workability Tests]
    B --> C[Air Content

Key IS Code Specifications for Special Considerations in Prestressed Concrete (IS SP Part 23):

1. Minimum Cement Content & Max Water-Cement Ratio (Table 25)

• Adjust cement content by ±10% for aggregate size changes (12.5 mm or 40 mm).

2. Sulphate Attack Resistance (Table 26)

• Cement type and mix requirements depend on sulphate concentration in soil/groundwater.
• Use Ordinary Portland Cement or Portland Slag Cement with specified minimum cement content and max water-cement ratio.
• For higher sulphate, use OPC with C3A ≤ 5% and 2C3A + C4AF ≤ 20%.

3. Chloride Ion Limits (Table 27)

4. Water-Cement Ratio vs Strength (Table 31)

• Typical max water-cement ratio for 28-day compressive strength ranges from 0.38 (450 kg/cm²) to 0.80 (150 kg/cm²).

5. Mix Proportion Adjustments

• Refer Tables 32-36 for water, aggregate, and admixture adjustments based on slump, aggregate size, air content, and sand fineness.

Summary Formula for Durability:

[ \text{Water-Cement Ratio} \leq \text{Max W/C from Table 25 or 26} ] [ \text{Cement Content} \geq \text{Min Cement Content from Tables} ]

flowchart TD
    A[Exposure Condition] --> B{Mild/Moderate/Severe}
    B -->|Mild| C[Min Cement 300 kg/m³, W/C ≤ 0.65]
    B -->|Moderate| D[Min

IS SP Part 23 - References and Bibliography: Key Tables & Specifications

This part provides comprehensive tables and data essential for concrete technology and mix design. Key highlights include:

Important Tables:

Key Specifications:

• Chloride Ion Limits in Concrete (Table 27):
  • Prestressed concrete: max 0.06% by cement mass
  • Reinforced concrete in moist chloride environment: max 0.10%
• Water Quality: Impurities beyond permissible limits require testing for setting and strength.
• Admixture Effects: Accelerating admixtures can increase early strength (125% at 3 days), retarders reduce strength slightly.
• Air Content: Higher air content reduces strength but improves durability; optimize per aggregate size.

Formula: Approximate Water Content Adjustment (Table 36)