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Integrity Assessment Techniques
MAB1033 Structural Assessment & Repair
Prof. Dr. Azlan Abdul Rahman
Universiti Teknologi Malaysia (UTM)
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Introduction
Integrity assessment involves either,
·Determination of localised integrity of a
particular element, or
·General assessment of behaviour of entire
structure.
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Reasons for Integrity Assessment
·Assessment of fire damage or other accidental
damage.
·Assessment of effects of overloads.
·Detection of delaminations.
·Detection of construction defects.
·Identification of hidden construction details.
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Range of Testing Methods
·Rebound Hammer (surface hardness)
·Ultrasonic Pulse Velocity (UPV)
·Dynamic Response
·Radiography
·Radiometry
·Thermography
·Radar
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Surface Hardness Test
·A Rebound (or Schmidt) Hammer consists of a mass impacting the concrete surface with a standardized energy and causing localized crushing. ·The amount of rebound of the mass is measured & expressed as a ‘rebound number’. ·A quick & simple test but not recommended for
absolute strength assessment. ·Strength correlations provided with the equipment should only be used when confirmed by calibration trials for the condition of use.
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The Rebound Hammer
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The Rebound Hammer
Conventional Calibration Anvil Digital Rebound Rebound Hammer Hammer in Use
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Use of the Rebound Hammer
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Rebound Hammer Test
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The Rebound Hammer (contd.)
·Results of rebound hammer are affected by conditions within 30mm of the surface & may be greatly influenced by localized carbonation hardening in concrete > 3 months old & member rigidity.
·Use is most reliable in determination of uniformity of
young concrete with CoV of 4% on good concrete.
·Details of test described in BS1881 Part 202.
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Rough Guide on Rebound Hammer
Rebound Hammer Nos.
Probable Concrete Strength (N/mm2)
Concrete
Quality Assessment
< 25 20 Poor
25 – 35 20 – 30 Intermediate
> 35 > 30 Sound
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Factors Affecting Rebound
Hammer Test ·Mix characteristics ·Concrete maturity ·Moisture conditions ·Nature of surface finish ·Instrument orientation (horizontal, vertical etc.) ·Surface carbonation hardening ·Inadequate member rigidity ·Test located on aggregate particle at the surface. ·Reinforcement close to the surface.
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Ultrasonic Pulse Velocity
·Measurements are made of the transit time of a high-frequency pulse (typically 54kHz) over a measured path length between transducers placed on the concrete surface
·Well established method, quick & reflects the characteristics of the interior of a concrete member.
·UPV test method is well documented in BS 1881 Part
203.
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The UPV Equipment
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Modern Version of PUNDIT
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Principle of Pulse Measurement
The UPV Measurement
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Pulse Path
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The Pulse Velocity
Path Length(m)
Transit Time (microsec)
= Pulse
Velocity (km/sec)
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Rough Guide UPV
Pulse Velocity
(km/sec)
Probable Concrete Quality
> 4.5 Excellent
3.5 – 4.5 Good
3.0 – 3.5 Fair (Doubtful)
2.0 – 3.0 Poor
< 2.0 Very Poor
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Direct UPV Measurements
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Indirect
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UPV Measurement (contd.) ·Most reliable applications are for determination of
concrete uniformity & the location of internal defects. ·Strength estimation may be possible with the aid of correlation charts. ·Access is required to opposite faces of the concrete
member for the most reliable results & surface staining may result from use of couplants. ·Erroneous results may be caused by : poor surface
coupling, internal air-filled cracks or voids, reinforcement bars, small path length or small lateral dimensions. ·Corrections may be made for the presence of reinforcing bars close to the pulse path if unavoidable. ·A 2% change in UPV if often regarded as indicative of a significant difference in concrete properties.
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Dynamic Response : Pulse Echo Tests
·Involves the measurement at a concrete surface of the internally reflected shock waves from a single hammer blow or similar impact on the surface. ·An accelerometer placed on the concrete surface is used
to monitor stress waves resulting from the impact & the output is displayed visually as a digital reading of the amplitude using simple hand-held equipment or oscilloscope. ·Pulse-echo technique using instrumented hammer is
well-established in the field of pile testing and are widely used to assess length & uniformity.
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Principle of Pulse Echo
Receiver & Display
Hammer blow
Concrete surface or
major delamination
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Pulse Echo / Impact Echo
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Impact Echo
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Instrumented Hammer
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Pile Integrity Assessment
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Delamination or Flaw Detection
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Other Flaw-Detection Methods
Acoustic Emission
Ultrasonic Flaw Detection Method
Boroscope for Internal Examination
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Radiography
·This provides a ‘photograph’ of the interior of a concrete member indicating variations in density.
·A beam of gamma ray is directed through the concrete towards a film held against the opposite face (max. thickness 500mm)
·Voids, poor compaction & reinforcement can be located.
·Details of technique in BS1881 Part 205.
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X-ray sensitive
film
X-ray or Y-ray
source
Principle of Radiography
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High Energy Radiography
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Radiometry
·A beam of gamma rays is directed at the concrete & the intensity of radiation emerging is measured by means of a Geiger counter to indicate concrete density.
·Direct measurement may be made of radiation passing through a concrete body up to 600mm thick.
·In backscatter method, radiation is reflected back to
the same surface. Easier to perform.
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Radiometry : Backscatter Method
Detector Radioactive source
Neutron paths
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Thermography
·Based on measurement of surface temperature differentials on concrete member while heating or cooling. ·Infra-red measurement techniques are necessary to detect
& record small temperature differentials. ·The method does not require contact with the concrete surface & can be used with measurement equipment some distance away provided that effects of extraneous heat sources can be avoided. ·Applications : detection of delamination in bridge decks; location of moisture or major ducts or voids within walls or slabs; evaluation of pavements.
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Infrared Thermography for Building Inspection
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Radar Method
·Specialized surface-penetrating radar scanning equipment may be used to identify reinforcing bars, voids, delaminations, ducts & similar features. ·Equipment consists of transmitting & receiving antennae together with a control unit & recorder. ·Resolution obtained depends on frequency used (1 GHz is typically used for investigating concrete up to 500mm thick). ·Results either provided in the form of graphic recorder
trace, or as colour display with facilities for signal processing to aid interpretation (based on pattern recognition).
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