✅ Core Cutting Test of Concrete
๐ Introduction
Core cutting test (also called Concrete Core Test) is a non-destructive cum minor-destructive method used to determine the compressive strength, quality, homogeneity and integrity of hardened concrete in existing structures.
It is widely used in:
Old buildings & bridges
Quality doubtful structures
Structural audit & rehabilitation works
Govt. quality checks (RCC buildings, roads, retaining walls)
Post-construction strength verification
> IS Code Reference: IS 516 (Part-5/Sec-1): 2018
ASTM Standard: ASTM C42/C42M
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๐ฏ Purpose of Core Test
To determine actual compressive strength of concrete
To check durability & density
To verify grade of concrete used (e.g., M20, M25, M30)
To evaluate structural safety
For dispute resolution between contractor & client
Locate honeycombs / segregation zones
> Field Note: Core test is typically suggested when UPV test, rebound hammer and visual inspection show doubtful results.
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๐งฐ Equipment Required
Equipment Purpose
Concrete Core Cutting Machine To cut cylindrical concrete core
Water supply Cooling cutter
Core Barrel (Diamond bit) Cutting tool 50mm–150mm
Compressive Testing Machine To test core cube strength
Vernier caliper / steel scale Measure core dimensions
Digital weighing scale Density calculation
Capping material / grinding machine Level surface preparation
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๐ Standard Sample Criteria
Parameter Requirement
Minimum Diameter ≥ 100mm preferred (or 3x max aggregate size)
Height/Diameter Ratio 1.0 to 2.0 (standard = 2.0)
Min. No. of Cores At least 3 cores/location
Curing before test 48 hours in water
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๐ ️ Core Cutting Test – Step-by-Step Procedure
1️⃣ Site Preparation
Identify sampling locations (critical beams, slabs, columns)
Check drawings, load conditions & reinforcement positions
Mark drilling points avoiding rebars
> Tip: Rebar scanner use เคเคฐ्เคฏो เคญเคจे best results เคเคँเค।
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2️⃣ Core Extraction
Fix the drilling machine firmly
Water supply continuously เคฆें to avoid overheating
Drill slowly to avoid cracking
Extract cylindrical concrete core sample
> Professional note: Sudden force may crack the core—patience is key in field!
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3️⃣ Core Labeling & Storage
Place core carefully
Tag with date, location, element, core ID
Moist curing for 48 hours (as per IS)
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4️⃣ Surface Preparation
Trim core ends
Grind / cap both ends for smooth loading surface
Measure length, diameter & weight accurately
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5️⃣ Compression Testing
Place core in CTM
Apply load gradually
Record ultimate load
Calculate compressive strength:
f = \frac{P}{A}
Where:
P = Load at failure (kN)
A = Cross-sectional area (mm²)
> Correction factor applied based on L/D ratio (IS 516 Table)
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๐ Example – Sample Core Test Calculation
Parameter Value
Core Diameter 100 mm
Core Length 200 mm
Load at Failure 500 kN
Step 1: Area of core
A = \pi r^2 = 3.14 \times 50^2 = 7850 mm^2
Step 2: Strength
f = \frac{500,000}{7850} = 63.69 MPa
Step 3: Apply correction factor (L/D = 2.0 → CF = 1.00)
f_{corrected} = 63.69 \times 1.00 = 63.69 MPa
✅ Final Result: 63.7 MPa
(This indicates excellent concrete strength)
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๐ Acceptance Criteria (IS Codes)
Concrete Grade Acceptable Core Strength (Average of 3)
M20 ≥ 75% of design strength
M25 ≥ 80% of design strength
M30 & above ≥ 85% of design strength
If below limit → structural review required
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๐ Common Observations
Problem Reason
Low strength Poor compaction, over-water, weak mix
Voids/Honeycomb Improper vibration
Uneven core ends Improper cutting or capping
Cracks during drilling Excess pressure / poor technique
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๐ Field Experience Notes
Slab cores often weaker than column cores due to curing difference
Use rebound hammer + UPV + core for best evaluation
Do not core structural members excessively – affects integrity
Typical core size used onsite: 100mm × 200mm
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๐ค Practical Example
A G+3 building slab suspected low quality concrete.
Core test results:
Core No Strength (MPa)
1 22.5
2 24.8
3 23.9
Average 23.7 MPa
Designed grade = M25 (25 MPa)
Required = ≥ 80% = 20 MPa
✅ Passed — Structure safe
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๐งพ Conclusion
Core cutting test is the most reliable method to determine actual compressive strength of hardened concrete in existing RCC structures. It ensures safety, quality control, and long-term durability.
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๐ Short Note (Nepali Summary)
Concrete core cutting test เคฒे old เคตा doubtful concrete structure เคो actual strength check เคเคฐ्เค। Machine เคฒे cylindrical sample เคाเคिเคจ्เค, lab เคฎा pressure เคฆिเค strength measure เคเคฐिเคจ्เค। Typical core size 100×200 mm। IS code เค
เคจुเคธाเคฐ strength acceptable threshold เคญเคจ्เคฆा เคฎाเคฅि เคญเค structure safe เคฎाเคจिเคจ्เค।
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✨ Final Tip
Always combine Visual check + Hammer test + UPV + Core test for professional assessment.