### Core Test of Hardened Concrete as per Indian Standard

#### Key Points and Concepts

Purpose of Core Testing:

- Assess the compressive strength and quality of hardened concrete.
- Verify the integrity of concrete in existing structures.

Standards and Guidelines:

- Follow guidelines provided in IS 516 (1959): "Method of Tests for Strength of Concrete."
- Refer to IS 456: "Code of Practice for Plain and Reinforced Concrete."

Core Sampling:

- Cores are extracted using diamond-studded core drilling machines.
- Standard core diameter: At least three times the nominal maximum size of the aggregate.
- Length-to-diameter ratio of the core: Preferably between 1.0 and 2.0.

Testing Procedure:

- Preparation:
- Ensure the core ends are smooth and perpendicular to the axis.

- Measurement:
- Measure diameter and length of the core to calculate the aspect ratio.

- Loading:
- Apply load continuously and without shock.
- Note the failure load.

- Preparation:
Formula for Compressive Strength:

$$\text{CompressiveStrength}(MPa)=\frac{\text{FailureLoad}(N)}{\text{Cross-sectionalArea}(m{m}^{2})}$$Calculations:

- Adjust for the length-to-diameter ratio if it deviates from the standard.
- Apply correction factors for cores taken from in-place concrete.

Assessment:

- Compare the test results with specified concrete strength requirements.
- Analyze any discrepancies to determine the cause (e.g., poor compaction, inadequate curing).

Factors Affecting Results:

- Moisture condition of the core.
- Age of the concrete.
- Method of drilling and core extraction.

Reporting:

- Include details: Core identification, location, depth, dimensions, moisture condition, and failure load.
- Provide calculated compressive strength values and any applied correction factors.

#### Important Formulas

- Compressive Strength Calculation:$${f}_{core}=\frac{P}{A}$$Where:
- ${f}_{core}$ = Compressive strength of the core (MPa)
- $P$ = Failure load (N)
- $A$ = Cross-sectional area of the core (mm²)

Remember to ensure that all core tests and calculations are aligned with the relevant Indian Standards to maintain accuracy and reliability in the assessment of hardened concrete.

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