Method of making, curing and determining compressive strength of accelerated cured concrete test specimens

Scope of IS 9013: Method for Accelerated Curing and Compressive Strength Testing of Concrete

Purpose:

• To provide a reliable, fast method for assessing concrete quality by accelerated curing (warm-water and boiling-water methods) and compressive strength testing.
• Enables strength estimation within ~24 hours, predicting 28-day strength to aid timely quality control and corrective actions.

Key Points:

• Accelerated curing accelerates cement hydration, achieving ~50% of 28-day normal curing strength rapidly.
• Correlation curves between accelerated and normal curing strengths must be established for local materials (see Appendix A).
• Applicable for quality control and mix proportioning adjustments on-site.
• High-pressure steam curing excluded due to practical limitations.

Important Correlation (Appendix A)

Summary of Accelerated Curing Methods (Clause 0.5)

References for Sampling and Testing

• Sampling: IS 1199-1959
• Specimen size, compaction, capping: IS 516-1959

flowchart LR
    A[Concrete Specimen Casting] --> B[Accelerated Curing]
    B --> C{Method}
    C --> D[Warm Water (~60°C)]
    C --> E[Boiling Water (100°C)]
    D & E --> F[Compressive Strength Test (~24h)]
    F --> G[Correlation with 28-day Normal Strength]
    G --> H[Quality Control Decision]

This method ensures early detection of concrete quality, enabling timely intervention and economical mix design adjustments.

IS 9013: Apparatus and Materials - Key Points

1. Apparatus (Clause 2.3.2 & 2.3.3)

• Accelerated Curing Tank:
  • Must contain sufficient water.
  • Water temperature around specimens must be controlled and maintained at the desired level continuously, except for max 15 minutes after immersion.
  • Typical tank layout shown in Fig. 1 (IS 9013).

2. Materials

• Concrete specimens made with local materials considering:
  • Cement chemical composition.
  • Water-cement ratio.
  • Mix proportions.
• These influence hydration rate and strength development.

3. Key Specifications (Clause 10.3 & Appendix A)

• Accelerated curing (warm water or boiling water methods) achieves ~50% of 28-day normal curing strength in a shorter time.

• Correlation between accelerated and normal curing strengths is mix-dependent.

• Use regression equations from Appendix A for strength prediction:

  [ f_{ac} = k \times f_{28} ]

  where:

  • ( f_{ac} ) = strength after accelerated curing,
  • ( f_{28} ) = 28-day normal cured strength,
  • ( k \approx 0.5 ) (typical value).

4. Usage

• Accelerated curing is for early quality control (results within ~24 hours).
• Correlation curves must be developed locally due to material variability.

Summary Table: Strength Correlation

flowchart LR
A[Concrete Specimen] --> B[Accelerated Curing Tank]
B --> C{Curing Method}
C --> D[Warm Water Method]
C --> E[Boiling Water Method]
D --> F[Strength ~50% of 28-day normal]
E --> F
F --> G[Correlation with Normal Curing Strength]

Note: Always verify with local calibration curves as per Appendix A for accurate strength prediction.

Preparation of Test Specimens (IS 9013)

• Sampling & Material Prep:

  • For correlation tests (accelerated vs normal curing), follow IS 516:1959 for sampling, proportioning, mixing, workability, specimen size, compacting, and capping (Clause 3.1).
  • For control tests, sampling per IS 1199:1959; specimen size, compacting, and capping per IS 516:1959 (Clause 3.2).

• Key Specifications from IS 516:1959:

  • Specimen Sizes:
    • Cubes: 150 mm × 150 mm × 150 mm (standard)
    • Cylinders: 150 mm diameter × 300 mm height (alternate)
  • Compacting: Use standard tamping rod or vibration as per IS 516.
  • Capping: Use sulfur mortar or neoprene caps to ensure uniform load distribution.

• Workability Test: Slump test as per IS 1199.

• Accelerated Curing Setup: Refer to Fig. 1 (IS 9013) for tank layout ensuring controlled temperature and humidity.

Summary Table: Specimen Preparation Standards

flowchart TD
    A[Sampling] --> B[Mixing & Proportioning]
    B --> C[Workability Test (Slump)]
    C --> D[Specimen Molding]
    D --> E[Compacting]
    E --> F[Capping]
    F --> G[Curing (Normal/Accelerated)]
    G --> H[Compressive Strength Test]

This ensures consistency and comparability between accelerated and normal curing test results.

IS 9013: Accelerated Curing by Warm Water Method - Key Points

1. Procedure (Clause 4 / 1.2)

• Specimens in moulds are immersed in warm water at 55 ± 2°C.
• Duration: Not less than 19 hours 50 minutes.
• After immersion, specimens are removed, demoulded, and cooled in water at 27 ± 2°C for at least 1 hour.
• Total time from start of immersion to cooling completion: within 20 hours 10 minutes.

2. Specimen Preparation (Clause 3.3)

• Immediately after moulding, cover specimens with a steel plate coated with mould oil to prevent adhesion.

3. Correlation of Strength (Appendix A)

• Accelerated curing achieves ~50% of 28-day normal curing strength at 20 hours.
• Strength depends on cement composition, water-cement ratio, and mix proportions.
• Use local correlations or experience to relate accelerated strength to normal strength.

4. Typical Regression Equation (from Appendix A)

[ R_{20} = a + b \times R_{28} ]

• Where:
  • (R_{20}) = compressive strength after 20 hours accelerated curing (N/mm²)
  • (R_{28}) = compressive strength after 28 days normal curing (N/mm²)
  • (a, b) = empirical constants based on local materials

Summary Table

flowchart TD
    A[Mould Specimens] --> B[Cover with steel plate + oil]
    B --> C[Immerse in 55±2°C water for ≥19h50m]
    C --> D[Remove & demould]
    D --> E[Cool in 27±2°C water for ≥1h]
    E --> F[Compressive strength test]

Use this method for rapid strength estimation

IS 9013: Accelerated Curing by Boiling Water Method - Key Points

1. Specimen Preparation

• Immediately after molding, cover specimens with a steel plate coated with mould oil to prevent adhesion (Clause 3.3).

2. Curing Procedure (Boiling Water Method)

• Specimens in molds are gently lowered into boiling water (100°C at sea level).
• Immersion duration: 3 hours ± 5 minutes (Clause 5.2).
• Water temperature must not drop more than 3°C after placing specimens and should return to boiling within 15 minutes.
• In confined spaces, water temperature may be kept just below boiling to reduce evaporation.

3. Post-Curing Handling (Warm Water Method Reference)

• For warm water method (not boiling), specimens are kept at 55 ± 2°C for ~20 hours (Clause 1.2).

Summary Table: Boiling Water Curing Parameters

flowchart TD
    A[Moulding of Specimens] --> B[Cover with steel plate + mould oil]
    B --> C[Lower into boiling water (100°C)]
    C --> D[Immersion for 3 hours ± 5 min]
    D --> E[Maintain water temp: max 3°C drop, recover in 15 min]
    E --> F[Remove specimens for testing]

This method accelerates strength gain by curing at boiling temperature for a short duration, simulating long-term curing in a fraction of time.

IS 9013: Testing of Specimens – Key Points

1. Sampling & Specimen Preparation

• Sampling per IS 1199:1959.
• Specimen size, compacting, and capping per IS 516:1959.
• Specimen preparation includes:
  • Material sampling, proportioning, weighing, mixing, workability test
  • Compaction and capping as per IS 516 when correlating normal and accelerated curing.

2. Test Report Requirements (Clause 8.1)

Include in test report:

• Identification mark, type, size, casting date
• Test date/time, specimen age
• Concrete particulars, compaction method, specimen size & mass
• Defects, timing of water addition, specimen making, curing & cooling immersion/removal times
• Temperature records of curing water
• Maximum crushing load & compressive strength
• Description of fractured face

3. Accelerated Curing Tank

• Follow layout as per Fig. 1 (Clause 2.3.3) for accelerated curing tanks.

Typical Compressive Strength Calculation:

[ f_c = \frac{P}{A} ]

• (f_c) = compressive strength (N/mm²)
• (P) = maximum load at failure (N)
• (A) = cross-sectional area of specimen (mm²)

Summary Table for Specimen Sizes (IS 516:1959)

flowchart TD
    A[Sampling (IS 1199)] --> B[Specimen Preparation (IS 516)]
    B --> C[Compaction & Capping]
    C --> D[Specimen Curing]
    D --> E[Testing (Compression)]
    E --> F[Report Generation (Clause 8.1)]

This ensures standardized testing and reliable strength correlation between normal and accelerated curing methods.

IS 9013: Calculation of Compressive Strength of Accelerated-Cured Concrete

Key References:

• Clause 7.1: Follow IS 516-1959 for compressive strength calculation.
• Clause 3.1: Specimen preparation per IS 516-1959.
• Clause 10.3 & Appendix A: Correlation between accelerated and normal curing strength.

Important Points:

• Accelerated curing accelerates hydration; strength after accelerated curing ≈ 50% of 28-day normal curing strength.
• Correlation depends on:
  • Cement chemical composition
  • Water-cement ratio
  • Mix proportions
  • Curing temperature regime

Typical Correlation Formula (Regression Equation):

[ f_{a} = k \times f_{28} ]

Where:

• ( f_{a} ) = compressive strength after accelerated curing (N/mm²)
• ( f_{28} ) = compressive strength after 28 days normal curing (N/mm²)
• ( k \approx 0.5 ) (approximate factor from Appendix A)

Specimen Preparation & Testing (IS 516-1959):

• Sampling, mixing, compacting, curing, and capping per IS 516.
• Size of specimen: usually 150 mm cubes or 150 mm diameter × 300 mm cylinders.
• Test age for accelerated curing: as per standard accelerated curing regime (e.g., boiling water or warm water method).

flowchart LR
    A[Material Sampling] --> B[Mixing & Proportioning]
    B --> C[Specimen Preparation]
    C --> D[Accelerated Curing]
    D --> E[Compressive Strength Test]
    E --> F[Calculate \(f_a\)]
    F --> G[Use Correlation \(f_a = 0.5 f_{28}\)]

Summary: Use IS 516 for test procedures. Calculate accelerated curing strength and correlate with 28-day strength using factor ~0.5 as per IS 9013 Appendix A. Adjust based on local materials and experience.

IS 9013 - Reporting of Results: Key Points & Correlations

Reporting Requirements (Clause 8.1)

Each test report must include:

• Identification: Specimen mark, size, type, date of casting
• Testing details: Date/time, age of specimen
• Concrete particulars: Mix details, compaction method
• Specimen details: Size, mass, defects
• Timings: Water addition, specimen making, curing & cooling immersion/removal times
• Temperature: Thermographic record of curing water
• Results: Maximum load at crushing, compressive strength, fractured face description

Use of Results (Clause 10.2 & 10.3)

• Results help in rapid variability assessment and process control.
• Strength values depend on materials, mix, and curing; correlations with local experience are essential.

Correlation of Accelerated and Normal Curing (Appendix A)

• Accelerated curing achieves ~50% of 28-day normal curing strength.
• Correlation depends on cement chemistry, w/c ratio, mix proportions.
• Standardized curing regimes reduce variability.

Typical Regression for Strength Correlation:

[ R_a = k \times R_{28} ] Where:

• (R_a) = Accelerated curing strength (N/mm²)
• (R_{28}) = 28-day normal curing strength (N/mm²)
• (k \approx 0.5) (approximate factor for boiling/warm water methods)

Summary Table for Reporting

flowchart TD
    A[Test Specimen] --> B{Report Includes}
    B --> C[Identification]
    B --> D[Test Timing]
    B --> E[Concrete Mix]
    B --> F[Specimen Details]
    B --> G[Process Timings]
    B --> H[Temperature Record]

IS 9013: Key Precautions for Accelerated Curing

Clause 9.1 Precautions:

• Curing tank maintenance:

  • Clean tank and renew water periodically to avoid detritus buildup.
  • Prevent impairment of heating/circulating system.

• Safety measures with boiling water:

  • Avoid scalding/eye burns from steam when opening cover.
  • Careful immersion to prevent splashing.

• Specimen protection:

  • Protect and store specimens carefully during initial curing.

• Safety devices:

  • Provide thermograph and heating control panel.
  • Use separate switchboards for safety.

Tank Dimensions (Fig. 1):

• Length (a): 1.60 m
• Width (b): 0.50 m
• Height (c): 0.65 m
  (Suitable for 12 cubes of 150 mm size)

Important Notes:

• Specimens should stand undisturbed in molds at 27 ± 2°C for at least 1 hour before immersion.
• Time between mixing and immersion: 1 to 3.5 hours.
• Accelerated curing strength is roughly 50% of 28-day normal curing strength.

Summary Diagram of Precautions & Setup

flowchart TD
    A[Curing Tank] --> B[Clean & Renew Water]
    A --> C[Heating & Circulating System]
    C --> D[Safety Devices & Thermograph]
    E[Specimens] --> F[Initial Storage & Protection]
    E --> G[Immersion in Tank (27±2°C)]
    H[Boiling Water] --> I[Safety Measures]
    I --> J[Prevent Scalding & Splashing]

For detailed correlation of accelerated and normal curing strengths, refer to Appendix A of IS 9013.

IS 9013: Interpretation of Results – Key Points & Formulas

1. Use of Results (Clauses 10.2 & 10.3)

• Results help in rapid assessment of variability for process control.
• Strength values depend on material combinations and curing methods.
• Use results with experience or site-specific correlations (Appendix A).

2. Correlation Between Accelerated & Normal Curing (Appendix A)

• Accelerated curing (e.g., Boiling Water Method) achieves ~50% of 28-day normal strength.
• Correlation depends on cement chemistry, water-cement ratio, mix proportions.
• Regression equation (typical) relating 28-day strength ( R_{28} ) and accelerated strength ( R_a ):

[ R_{28} = 12.65 + 1.30 \times R_a ]

• Site-specific calibration recommended for accuracy.

3. Test Report Requirements (Clause 8.1)

Include:

• Specimen ID, size, type, and casting date
• Test date, time, and specimen age
• Concrete particulars & compaction method
• Specimen size, mass, defects
• Times of mixing, casting, curing, cooling
• Temperature records during curing
• Maximum load & compressive strength
• Fracture face description

Summary Diagram: Correlation of Strength Results

graph LR
A[Accelerated Curing Strength (Ra)] --> B[Apply Regression]
B --> C[Estimate 28-day Normal Strength (R28)]
C --> D[Use for Quality Control & Adjustments]

This ensures reliable interpretation of accelerated test results aligned with site conditions and material specifics.

IS 9013 - Correlation of Compressive Strength: Normal vs Accelerated Curing

Key Points from Clause 10.3 & Appendix A:

• Accelerated curing (e.g., boiling water or warm water methods) speeds hydration, achieving ~50% of 28-day normal curing strength in shorter time.
• Strength correlation depends on cement composition, water-cement ratio, mix proportions.
• Standardized curing regimes reduce variability.
• Site-specific correlations are recommended for accuracy.

Typical Correlation (Boiling Water Method):

Regression Equation (from Fig. 2):

[ R_{28} = 12.65 + 1.28 \times R_a ]

• This means the 28-day strength can be estimated from accelerated strength.
• Accelerated strength is roughly 50% of 28-day strength.

Testing Requirements (Clause 3.1):

• Specimen preparation per IS 516-1959.
• Sampling, mixing, curing, compacting, and capping as per IS 516.
• Use standardized accelerated curing methods.

graph LR
A[Normal Curing (28 days)] -->|Strength R28| B[Strength Measurement]
C[Accelerated Curing (Boiling Water)] -->|Strength Ra| B
B --> D[Correlation Equation]
D --> E[Estimate R28 from Ra]

Summary: Use the regression (R_{28} = 12.65 + 1.28 R_a) to estimate 28-day strength from accelerated curing tests, ensuring materials and procedures align with IS 9013 and IS 516 standards.