2. Causes and detection of damages

 

2.1 Causes of Damages

Structures can suffer damage due to natural, environmental, or human-induced factors. The most common causes include:

1. Distress

• General term for structural discomfort or weakness.

• Causes: Overloading, poor workmanship, design flaws.

• Example: Cracks in beams due to undersized reinforcement.

2. Earthquake

• Earthquakes induce lateral forces.

• Effects: Cracking, tilting, collapse due to seismic loads.

• Example: Shear cracks in columns after seismic activity.

3. Wind

• High-speed wind exerts pressure, especially on tall structures.

• Damage: Displacement of roofing sheets, failure of cladding.

• Example: Flying debris damaging windows in cyclone-prone areas.

4. Flood

• Floodwaters can erode foundations or soak walls.

• Damage: Weakening of soil, rusting of steel, fungal growth.

• Example: Settlement of buildings after prolonged submersion.

5. Dampness

• Entry of moisture through walls or roofs.

• Damage: Peeling paint, efflorescence, weakening of plaster.

• Example: Moisture rising from ground due to poor DPC (Damp Proof Course).

6. Corrosion

• Steel corrodes in presence of water, oxygen, and chlorides.

• Result: Expansion and cracking of concrete.

• Example: Rusted reinforcement causing spalling in columns.

7. Fire

• High temperatures weaken materials.

• Damage: Loss of strength in steel, spalling of concrete.

• Example: Blackened walls and melted electrical conduits.

8. Deterioration

• Ageing, lack of maintenance, or use of low-quality materials.

• Example: Crumbling of mortar joints in a 50-year-old building.

9. Termites

• Attack wooden components.

• Damage: Hollow doors, weak furniture, loss of load-carrying capacity.

• Example: Roof beams eaten from inside.

10. Pollution

• Chemicals in air or water degrade building materials.

• Example: Acid rain eroding stone facades of old buildings.

11. Foundation Settlement

• Uneven soil movement or poor compaction leads to sinking.

• Damage: Cracks in walls, misaligned doors/windows.

• Example: Stair-step cracks in masonry walls.

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2.2 Visual Observations for Detection of Damages

Visual inspection is the first and most cost-effective method to assess damage.

What to observe:

• Cracks: Location, width, direction.

• Discoloration: Suggests dampness or chemical attack.

• Spalling: Falling off concrete due to corrosion.

• Unevenness: Signs of settlement or movement.

• Leakages: From pipes or ceilings.

• Rust Stains: Indicators of internal corrosion.

Example: A diagonal crack in a wall at a door corner often indicates settlement.

Tools Used: Flashlight, binoculars, camera, crack width gauge.

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2.3 Load Test and Non-Destructive Tests (NDT)

Load Test:

• A direct method where loads are applied to test the structure's strength.

• Usually applied on slabs, beams, or bridges.

• Purpose: To assess safety and serviceability under actual loads.

Example: Applying sandbags or water tanks over a slab and measuring deflection.

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2.3.1 Non-Destructive Tests (NDT) on Damaged Structures

NDT methods help assess internal conditions without damaging the structure.

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2.3.1.1 Rebound Hammer Test

• Measures surface hardness of concrete.

• Procedure: A spring-loaded hammer hits the concrete; rebound value gives strength estimate.

• Use: Quick field assessment of concrete quality.

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2.3.1.2 Ultrasonic Pulse Velocity (UPV)

• Sends sound waves through concrete.

• Measures: Wave speed; slower speed = cracks or voids.

• Use: Detects internal cracks, honeycombing.

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2.3.1.3 Rebar Locator

• Locates steel reinforcement within concrete.

• Uses magnetic fields to detect bars and estimate cover depth.

• Use: Ensures safe drilling, checks corrosion potential.

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2.3.1.4 Crack Detection Microscope

• Small handheld microscope for magnified viewing of cracks.

• Use: Accurately measures hairline cracks and crack width.

• Helpful in monitoring crack progression over time.

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2.3.1.5 Digital Crack Measuring Gauge

• Electronic tool to measure crack width with high precision.

• Displays real-time readings, often with data logging.

• Useful for structural health monitoring.

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2.4 Chemical Tests

These tests analyze the chemical properties of concrete or building materials to detect deterioration and durability risks.

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2.4.1 Chloride Test

• Detects chloride content in concrete (from sea water or de-icing salts).

• High chloride levels cause steel corrosion.

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2.4.2 Sulphate Attack

• Sulphates in soil/water react with cement, leading to expansion and cracking.

• Test: Sample analyzed to measure sulphate concentration.

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2.4.3 Carbonation Test

• Measures depth to which CO₂ has penetrated concrete and reduced pH.

• Method: Spray phenolphthalein; no color change = carbonation.

• Carbonation leads to steel corrosion.

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2.4.4 pH Measurement

• Determines alkalinity of concrete.

• Healthy concrete pH ≈ 12–13.

• Low pH (<9) indicates carbonation or chemical attack.

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2.4.5 Resistivity Method

• Measures concrete’s electrical resistance.

• Low resistivity = higher moisture and corrosion risk.

• Used for durability evaluation.

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2.4.6 Half-Cell Potential Meter (Intro & Demo)

• Measures electrical potential of embedded steel.

• Indicates probability of corrosion.

• Demo Use: Place electrode on concrete surface connected to reinforcement.

• Results:

  • <-350 mV = high chance of corrosion

  • -200 mV = low risk