Condition assessment of structures

CONDITION ASSESSMENT OF STRUCTURES
(Visual inspection & non-destructive testing of structures)
Mohammad Alhusein, PhD
Managing Partner
M: +971 552592001
E: malhusein@superarc.net
W: www.superarc.net
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WEBINAR OUTLINE
Deterioration
Process
Chemical
Physical
Biological
Initiating
Factors Causing
Deterioration
Intrinsic
Extrinsic Leads to
Cracking
Scaling Spalling
Popouts Delamination
etc.
Visible
Damage
Assessed
Principles for
repair and protection
Repair
Visual inspection
Non-Destructive Testing
Destructive Testing
Condition
evaluation
Condition
survey
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OUTLINES
➢Introduction
➢Main objective of condition assessment
➢Deterioration / Building materials
➢Condition assessment
▪Condition Survey Planning
▪Visual inspection
▪Non-Destructive testing (NDT)
✓detection of cracks/ voids/ delamination…etc
✓corrosion assessment, location and diameter of reinforcement
and cover thickness

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Introduction
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https://www.nachi.org/visual-inspection-concrete.htm

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Deterioration of Concrete Structures
Why concrete structures fail?
❖ Concrete has long been known as a reliable
construction material, but deficiencies in material
selection, detailing, and design can affect the service
life of Concrete.
❖ Deterioration of concrete structures can become a
challenge for the owners of these structures. It is
important to identify these defects on time, and plan
appropriate repair strategies.
❑ Defect: An identifiable, unwanted condition that was not part of
the original intent of design.
❑ Deterioration: A Defect that has occurred over a period of time

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What Are the Different defects involved in the deterioration of concrete?
1- SCALING
What is it?
Scaling is referred to the loss of the surface portion of concrete
(or mortar) as a result of the freezing and thawing. It is a
physical action that usually leaves the aggregates clearly
exposed.
How it happens?
Scaling happens when the hydraulic pressure from water
freezing within concrete exceeds the tensile strength of
concrete. Scaling is more common in non-air-entrained
concrete, but can also occur in air-entrained concrete in the fully
saturated condition.
Severity (Ontario Structure Inspection Manual (OSIM)
Light - Loss of surface mortar to a depth of up to 5 mm without exposure of coarse aggregate;
Medium - Loss of surface mortar to a depth of 6 to 10 mm with exposure of some coarse aggregates;
Severe - Loss of surface mortar to a depth of 11 mm to 20 mm with aggregate particles standing out from the concrete
and a few completely lost.
Very Severe - Loss of surface mortar and aggregate particles to a depth greater than 20 mm.

2- DISINTEGRATION
What is it?
Disintegration is the physical deterioration (such as scaling) or
breaking down of the concrete into small fragments or
particles.
How it happens?
It usually starts in the form of scaling. It may be also caused by
de-icing chemicals, sulphates, chlorides or by frost action.
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Light - Loss of section up to 25 mm in depth with some loss of coarse aggregate;
Medium - Loss of section between 25 mm and 50 mm deep with considerable loss of coarse aggregate and exposure of
reinforcement;
Severe - Loss of section between 50 mm and 100 mm deep with substantial loss of coarse aggregate and exposure of
reinforcement over a large area.
Very Severe - Loss of section in excess of 100 mm deep and extending over a large area.

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3- EROSION
What is it?
Erosion is the deterioration of concrete surface as a result of
particles in moving water scrubbing the surface.
How it happens?
When concrete surface is exposed to the water-borne sand and
gravel, the surface gets deteriorated by particles scrubbing
against the surfaces. Flowing ice particles can also cause the
problem. It is an indicator of poor durability of concrete for that
specific exposure.
Light - Loss of section up to 25 mm in depth with some loss of coarse aggregate;
Medium - Loss of section between 25 mm and 50 mm deep with considerable loss of coarse aggregate and exposure of
reinforcement;
Severe - Loss of section between 50 mm and 100 mm deep with substantial loss of coarse aggregate and exposure of
reinforcement over a large area.
Very Severe - Loss of section is in excess of 100 mm deep and extending over a large area.

4- CORROSION OF REINFORCEMENT
What is it?
Corrosion is the deterioration of steel reinforcement in concrete.
Corrosion can be induced by chloride or carbonation. The corrosion can
result in cracking in the concrete cover, delamination in concrete decks,
etc.
How it happens?
When the concentration of chloride ions above the surface of
reinforcement reaches the threshold limit (which is the amount required
to break down the passive film) corrosion begins. The volume of
resulting material (rust) is 6-7 times, which increases the stress around
the rebar, and causes fracture and cracking. The cracks extend to the
surface of concrete over time; that is when we can visually see the sign
of rust over the surface of concrete.
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Light - Light rust stain on the concrete surface;
Medium - Exposed reinforcement with uniform light rust. Loss of reinforcing steel
section less than 10%;
Severe - Exposed reinforcement with heavy rusting and localized pitting. Loss of
reinforcing steel section between 10% and 20%;
Very Severe - Exposed reinforcement with very heavy rusting and pitting. Loss of
reinforcing steel section over 20%.

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Light Stains on Concrete Surface Indicating Corrosion
of Reinforcement

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5- DELAMINATION
What is it?
“Delamination is defined as a discontinuity of the surface
concrete which is substantially separated but not completely
detached from concrete below or above it.” Delamination is
often identified by the hollow sound by tapping or chain
dragging of concrete surface.
How it happens?
The corrosion of reinforcement and subsequent cracking of the
cover can cause delamination. When the rebar have small
spacing, the cracking extends in the plane of the reinforcement
parallel to the exterior surface of the concrete.
Intercoat Delaminations
Light - Delaminated area measuring less than 150 mm in any direction.
Medium - Delaminated area measuring 150 mm to 300 mm in any direction.
Severe - Delaminated area measuring 300 mm to 600 mm in any direction.
Very Severe - Delaminated area measuring more than 600 mm in any direction.

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6- SPALLING
What is it?
Spalling can be considered an extended delamination. In fact,
when the delamination continues, the concrete fragments
detach from a larger concrete mass.
How it happens?
If delamination is not repaired on time, the progress of damages
as a result of external loads, corrosion, and freezing and thawing
can break off the delaminated pieces.
Very Severe Spalling and
Delamination in
Concrete Beams
Light - Spalled area measuring less than 150 mm in any direction or less than 25 mm in depth.
Medium - Spalled area measuring between 150 mm to 300 mm in any direction or between 25 mm and 50 mm in depth.
Severe - Spalled area measuring between 300 mm to 600 mm in any direction or between 50 mm and 100 mm in depth.
Very Severe - Spalled area measuring more than 600 mm in any direction or greater than 100 mm in depth.

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Very Severe Spalling in a Concrete
Pier Cap Due to Corrosion of
Reinforcement
Severe Local Spalling

7- ALKALI-AGGREGATE REACTIONS
What is it?
It is the internal cracking of concrete mass as a result of a chemical
reaction between alkalis in the cement and silica in the aggregates.
The AAR/ASR (Alkali Silica reaction ) cracking are very famous for
their crack patterns.
How it happens?
The alkalis in the cement can react with the active silica in the
aggregates to form a swelling gel. When this gel absorbs water, it
expands, and applies pressure to surrounding environment which
makes the concrete crack.
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Severity
Light - Hairline pattern cracks, widely spaced, with no visible expansion of the concrete mass.
Medium - Narrow pattern cracks, closely spaced, with visible expansion of the concrete mass.
Severe - Medium to wide pattern cracks, closely spaced, with visible expansion and deterioration of concrete.
Very Severe - Wide pattern cracks, closely spaced, with extensive expansion and deterioration of concrete.

8- CRACKING OF CONCRETE
What is it?
A crack is a linear fracture in concrete which extends partly or
completely through the member.
How it happens?
Some people believe that concrete is born with cracks; that its
ingredients, and how it is produced - from the batching plant
to pouring, setting, and curing - is influenced by so many
factors that cracking of concrete does not come as a big
surprise; and to a great extent, that might be true. Cracking of
concrete can happen in different stages: It can happen before
hardening of concrete, and it can happen in an old concrete
structure:
Before Hardening
+ Settlement within concrete mass
+ Plastic shrinkage
After Hardening
+ Drying shrinkage
+ Thermal contraction
+ Sub-grade settlement
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Severity
Hairline cracks - less than 0.1 mm wide.
Narrow cracks - 0.1 mm to 0.3 mm wide.
Medium cracks - 0.3 mm to 1.0 mm wide.
Wide cracks - greater than 1.0 mm wide.

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External Restraint Induced Cracks
(due to temperature increase in top surface
of beam)

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9-SURFACE DEFECTS
- Stratification;
- Segregation;
- Cold Joints;
- Deposits - efflorescence, exudation, incrustation, stalactite;
- Honeycombing;
- Pop-outs;
- Abrasion and Wear;
- Slippery Surface.
Surface defects are not necessarily serious in themselves; however, they are indicative of a potential weakness in
the concrete, and their presence should be noted but not classified as to severity, except for honeycombing and
pop-outs.

STRATIFICATION is the separation of the concrete components into horizontal layers in over-wetted or overvibrated
concrete. Water, laitance, mortar and coarse aggregates occupy successively lower positions. A layered
structure in concrete will also result from the placing of successive batches that differ in appearance.
SEGREGATION is the differential concentration of the components of mixed concrete resulting in non uniform
proportions in the mass. Segregation is caused by concrete falling from a height, with the coarse aggregates settling
to the bottom and the fines on top. Another form of segregation occurs where reinforcing bars prevent the uniform
flow of concrete between them.
COLD JOINTS are produced if there is a delay between the placement of successive pours of concrete, and if an
incomplete bond develops at the joint due to the partial setting of the concrete in the first pour.
DEPOSITS are often left behind where water percolates through the concrete and dissolves or leaches chemicals
from it and deposits them on the surface. Deposits may appear as the following:
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Efflorescence - a deposit of salts, usually white and powdery.
Exudation - a liquid or gel-like discharge through pores or cracks in the surface.
Incrustation - a hard crust or coating formed on the concrete surface.
Stalactite - a downward pointing formation hanging from the concrete surface, usually shaped like an icicle.

HONEYCOMBING is produced due to the improper or incomplete
vibration of the concrete which results in voids being left in the
concrete where the mortar failed to completely fill the spaces
between the coarse aggregate particles.
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Severity
Light - Honeycombing to a depth less than 25mm and 50mm.
Medium- Honeycombing to a depth between to a depth between
25mm and 50mm
Severe - Honeycombing to a depth between 50mm and 100mm.
Very Severe - Honeycombing to a depth greater than 100mm.
Efflorescence Incrustation
Stalactite
HONEYCOMBING Exudation

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Pop-outs Severity
Light - Pop-outs leaving holes up to 25 mm in depth.
Medium- Pop-outs leaving holes between 25 mm and 50 mm in depth.
Severe - Pop-outs leaving holes between 50 mm and 100 mm in depth.
Very Severe - Pop-outs leaving holes greater than 100 mm in depth.
POP-OUTS are shallow, typically conical depressions, resulting from the breaking away of small portions of the
concrete surface, due to the expansion of some aggregates or due to frost action. The shattered aggregate
particle may be found at the bottom of the depression, with a part of the aggregate still adhering to the pop-out
cone.
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ABRASION is the deterioration of concrete brought about by vehicles or snow-plough blades scraping
against concrete surfaces, such as, decks, curbs, barrier walls or piers.
WEAR is usually the result of dynamic and/or frictional forces generated by vehicular traffic, coupled with
the abrasive influx of sand, dirt and debris. It can also result from the friction of ice or water-borne particles
against partly or completely submerged members. The surface of the concrete appears polished.
SLIPPERY CONCRETE SURFACES may result from the polishing of the concrete deck surface by the
action of repetitive vehicular traffic.
Severity
There are no severity descriptions given for slippery concrete surfaces as this is a serious and potentially
hazardous situation.
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➢ Main Objective of Condition Assessment
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➢ Deterioration / Building materials (1/2)
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➢ Deterioration / Building materials (2/2)
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➢ Condition assessment planning
Preliminary investigation: Detailed investigation:
YES
1. Review of relevant
documents
Visual inspection, with
documentation of defects
Field and laboratory testing
Preliminary analysis and
evaluation
1. Review of additional
documents and data source
Additional field
observations, and field and
laboratory testing
Detailed analysis and
evaluation
Is further
investigation
required?
2. 2.
3.
4. 3.
NO
Is
repairing
required?
Identify and analysis repair
options
YES
Final
report
Identify special conditions
to further considered (e.g.
maintenance, planning
NO
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Review of plans and relevant documents
• To review documents from design
and construction process as well as
inspection and maintenance reports
is in general the easiest way of
gathering data about the structure to
be assessed.
It has to be assured that the reviewed
documents are correct.
Loads can be usually determined from
current loading codes and
environmental conditions may be
obtained from inspection reports.
• Resistance properties like material
and structural properties and
dimension can be obtained from:
– Construction specifications -
Codes
As-built drawings--architectural,
structural, mechanical, and
foundation plans
Construction documents (e.g.
material delivery documentation)
Documentation of performance,
defects, maintenance, and
changes (Alterations)
Reports of earlier inspection and
maintenance.
–
•
• –
–
–
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VISUAL INSPECTION
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Scope of Visual Inspection
• Prior to the starting of visual inspection,
the structural engineer is to obtain a set
of the building’s structural layout plans
from the building owner.
• The availability of the structural layout
plan will help the structural engineer to:
a understand the structural system and
layout of the building;
b) identify critical areas for inspection;
c identify the allowable imposed loads,
in order to assess the usage and
possibility of overloading; and
d verify if unauthorised addition or
alteration works that affect the
structure of the building have been
carried out.

Visual Inspection Tools and Instruments
• Simple tools and Instruments like:
–
–
–
–
Camera
Magnifying glass
Binocular
Gauge for crack width
measurement
Chisel and hammer are usually
needed.
Pocket knife, screwdriver
Occasionally, a ladder or light
platform/scaffold tower can be
used for access to advantage.
–
–
–
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Scope of Visual Inspection
overloading or adverse effects on
deterioration or defects, the visual
the structural engineer otherwise
be taken
c any addition or alteration works
affecting the structure of the
building
• to identify any addition or alteration
works which can result in
the structure
If there are no signs of any structural
inspection should suffice and unless
advises, no further action needs to
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A visual inspection is generally carried
out of:
a the condition of the structure of
the building
• to identify the types of structural
defects
• to identify any signs of structural
distress and deformation
• to identify any signs of material
deterioration
b the loading on the structure of the
building
• to identify any deviation from
intended use, misuse and abuse
which can result in overloading

Visual inspection report (example)
1. General Information of the Building
• address, usage of the building,
maintenance history etc.
2. Structural System of the Building
• reinforced concrete, prestressed
concrete, steel, etc
3.
4.
Date and Scope of the Inspection
Survey of addition or alteration works
to building structure
Survey of signs of structural defects,
damages, distress, etc.
Survey of exposure to aggressive
environment
Conclusions on the structural
condition
Sketches, plans and photographs
5.
6.
7.
8.
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Examples of typical defects found by visual inspection
Erosion of Brick Face Efflorescence Brick Spalling/Delaminating
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Reference: ACI 201.1R-08 (Guide for Conducting a Visual Inspection of Concrete in Service

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Examples of typical defects found by visual inspection
Crack and Spall of
Concrete Around Steel
Member
Delaminating
Concrete
Over Reinforcement
Concrete Crack

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What is Detailed visual inspection?
A detailed visual inspection is Element-by-element “close-up” visual assessment of:
a) Material defects,
b) Performance deficiencies
c) Maintenance needs
Answer: a or b or c all of them
Who can perform it?
a) professional engineer
b) or a technician with structures inspection experience working under the direction of a
professional engineer.
Answer: a or b all of them

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Non-Destructive testing (NDT)
on
reinforced concrete structure
Concrete Testing
Testing
Concrete
Non-Destructive
Destructive

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Deliverables of NDT
Density
Elastic
Modulus
Cracks and Voids
Determination
Reinforcement
Location
strength
Surface
Hardness
Quality of
Workmanship
Surface
Absorption

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NDT Objectives
NDT methods are extremely valuable in
assessing the condition of structures,
such as bridges, buildings, elevated
service reservoirs and highways etc.
– Position and condition of steel
reinforcement
Concrete cover over the
reinforcement.
Reliable assessment of the
integrity or detection of defects of
concrete members even when they
are accessible only from a single
surface.
–
• The principal objectives of the NDT /
PDT of concrete in situ is to assess one
or more of the following properties:
–
–
–
–
–
–
–
–
In situ strength properties
Durability
Density
Moisture content
Elastic properties
Extent of visible cracks
Thickness of structural members
having only one face exposed

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NDT Advantages and Disadvantages
Disadvantages
Advantages
• More than one test method may be
required
Environmental conditions may
effect or distort results
Construction details & building
components may effect results
Some conditions cannot be
determined with a reasonable
degree of accuracy without
destructive testing
• Access to hidden items – “see
through walls”
Better investigations with NDT
Rapid accumulation of data
Generally less expensive than
destructive testing
Minimize interruption of building
services
Evaluation and quality assurance
•
•
•
• •
•
•
•

Typical situations where non-destructive testing is needed
representative of the quality to be
deterioration of concrete resulting from
external or internal chemical attack or
effects
concrete
change of use of a structure for
• Quality control of pre-cast units or
construction in situ
• Monitoring of strength development in
relation to load application or similar
purpose
• Location and determination of the
extent of cracks, voids, honeycombing
and similar defects within a concrete
structure
• Determining the concrete uniformity,
possibly preliminary to core cutting,
load testing or other more expensive or
disruptive tests
• Determining the position, quantity or
condition of reinforcement
• Increasing the confidence level of a
• Determining the extent of concrete
variability in order to help in the
selection of sample locations
assessed
• Confirming or locating suspected such
factors as overloading, fatigue,
change, fire, explosion, environmental
• Assessing the potential durability of the
• Providing information for any proposed
insurance or for change of ownership.
smaller number of destructive tests
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NDT Methods for Specific Distresses
Distresses Condition Assessment Methods
Air Pockets and
Honeycombing
Chain Dragging, Ground Penetrating Radar, Hammer
Sounding, Impact-Echo, Ultrasonic, Visual Inspection
Alkali-Silica Reaction Visual Inspection
Chloride-Induced
Corrosion
Half-Cell Potential, Rapid Chloride Permeability, Resistivity
Cracking Impact-Echo, Ultrasonics, Visual Inspection
Delamination
Chain Dragging, Coring, Ground Penetrating Radar,
Hammer Sounding, Impact-Echo, Infrared Thermography,
Ultrasonics
Popouts Visual Inspection
Potholing (Caving) Visual Inspection
Scaling Visual Inspection
Spalling Visual Inspection
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NDT for detection of cracks/
delamination etc.
voids/
❑ Hammer sounding
❑ Chain dragging
❑ Ground penetrating radar
❑ Impact-echo
❑ Ultrasonic pulse velocity
❑ Radiographic testing
❑ Crack width measurement

NDT - Sounding
• A qualitative evaluation of concrete can
be easily obtained by just sounding it
(i.e. tapping it) with a hammer.
When the hammer is struck on good
concrete, a ringing sound is created.
On areas where delaminations or
cracks occur, the striking of the
hammer produces a drum-like sound.
The limitation of this method is that it
cannot detect defects that exist deep in
the member.
Also, defects lying under overlays are
also difficult to find.
•
•
•
•
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NDT - Chain Dragging
• The objective is to detect regions where
the sound from dragging the chain
changes from a clear ringing sound
(sound deck) to a somewhat mute and
hollow sound (delaminated deck).
Chain drag is a relatively fast method
for determining the location of a
delamination
Chain Dragging is normally used on
large concrete surface areas, such as
bridge decks
The method typically rely on the
experience of the inspector to
differentiate the relative sounds of
similar materials
•
•
•

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REBOUND HAMMER TEST

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Limitation
a) Smoothness of surface under test
b) Size , shape and rigidity of the specimen
c) Age of specimen
d) Surface and internal moisture condition of the
concrete
e) Type of coarse aggregate
f) Type of cement
g) Type of mould
h) Carbonation of concrete surface

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Rebound Hammer & strength of
Concrete
WET
Horizontal
hammer
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A test point is described as intact if the dominant return frequency corresponds to the bottom of the deck.
A delaminated point in the deck will theoretically demonstrate a shift in the return frequency toward higher values because
the wave reflections occur at shallower depths.
Depending on the extent and continuity of the delamination, the partitioning of the wave energy reflected
from the bottom of the deck and the delamination may vary.

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The initial or incipient delamination, described as occasional separation within the depth of the slab, can be identified
through the presence of return frequencies associated with the reflections from both the bottom of the deck and the
delamination.
Progressed delamination is characterized by a single peak at a frequency corresponding to the depth of the
delamination.
Finally, in cases of wide or shallow delaminations, the dominant response of the deck to an impact is characterized by a
low frequency response of flexural-mode oscillations of the upper delaminated portion of the deck.
This response is almost always in the audible frequency range, unlike responses from the deck with incipient
delamination that may exist only in the higher frequency ranges (Gucunski et al. 2006; Cheng and Sansalone
1995; Lin and Sansalone 1996).
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Ultrasonic Pulse Velocity
• Ultrasonic waves are very
similar to light waves in that
they can be reflected,
refracted, and focused.
Reflection and refraction
occurs when sound waves
interact with interfaces of
differing acoustic properties.
Ultrasonic reflections from the
presence of discontinuities or
geometric features enables
detection and location.
•
•
(USPV Test)

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 This test is used for determination of the uniformity
of concrete in and between members.
 Reference code: “Standard Test Method for Pulse
Velocity through Concrete” (ASTM C 597, 2016).
 Principle:the velocity of an ultrasonic pulse through
any material depends upon the density, modulus of
elasticity and Poisson’s ratio of the material.
 Higher is the velocity, better is the quality of concrete
USPV Test

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1- Pulse Velocity Determination
2- Concrete Quality Assessment
3- Establishing Homogeneity and Uniformity of Concrete
4- Measurement of Surface Crack Depth
5- Prediction of Compressive Strength of Concrete
Applications of UPV Testing for Concrete

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 (a) Electrical pulse
generator
 (b) Pair of transducers
 (c) Amplifier
 (d) Electronic timing
machine
UPSV Equipment
•Equipment should be capable of measuring transit time over path
lengths ranging from about 100 mm to the maximum thickness to be
inspected to an accuracy of ±1%
UPSV Contd…Equipment:

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UPSV Contd…. Methodology
 Calibration: done by measuring transit time on
standard calibration rod.
 Transducers arrangement: 3 methods

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Ultrasonic pulse velocity in concrete (UPV) ASTM C597

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Experimental Evaluation of Cracks in Concrete by Ultrasonic Pulse Velocity

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In order to conduct a reliable ultrasonic testing of concrete, the surface of concrete should
be clean, and free of dust. A suitable couplant is needed to establish an ideal connection
between concrete and UPV transducers. Special attention should be given to rebar in
concrete, since the wave travel speed in metal is much higher than in concrete. The
interpretation of test results in heavily reinforced concrete is somewhat difficult. The direct
configuration is the most ideal for getting reliable readings; however, the use of this
configuration is mainly limited to laboratory. In summary, the following issues should be
addressed before, during, and after performing the test:
1- Concrete Properties (aggregate size, type, and content)
2- Transducer Contact/ couplant material
3- Presence of Rebar
4- Sensor Configuration
UPV - Influencing Parameters

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3 Methods for Crack Depth Measurement in Concrete
What is Crack | Why Does Concrete Crack?
A crack is a linear fracture in concrete which extends partly or completely
through the member. In a concrete element, tensile stresses are initially carried by
the concrete and reinforcement. When the tensile stresses in the beam exceeds the
tensile capacity, the concrete cracks. After this point the tensile force is transferred
completely to the steel reinforcement.
Several issues can result in cracks in concrete, including:
❑ excessive external loads
❑ external restraint forces
❑ internal restraint forces
❑ differential movements
❑ settlements
In a concrete element, the crack (shrinkage, thermal, and service loads) width and
distribution is mainly controlled by steel reinforcement.

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Severity
Hairline cracks - less than 0.1 mm wide.
Narrow cracks - 0.1 mm to 0.3 mm wide.
Medium cracks - 0.3 mm to 1.0 mm wide.
Wide cracks - greater than 1.0 mm wide.

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How To Evaluate Concrete Cracks ?
Visual inspection and monitoring is the first step towards understanding the nature of
existing cracks, and the underlying causes.

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1. Crack Width
Crack severity on the surface of concrete is normally measured using a crack width
ruler (crack gauge). Depending on the opening of the cracks on the surface, cracks
can be described (as tiny as hairline, or severe (few millimeters opening).
2. Crack Depth
There are cases where structural engineers are interested in the crack depth
measurement. Crack depth is used to evaluate structural integrity, and verify
durability performance. Crack depth measurement can help repair contractor in
evaluating the repair costs.
Depending on the nature of the project, engineers rely on different intrusive and
non-intrusive techniques to estimate the crack depth.

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I. Visual Examination of Concrete Cores
Extracting core samples from the defects is considered a popular method among
inspectors and engineers. Core samples can provide information about the extent,
depth, and severity of cracks.
Crack Depth Measurement in Concrete

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II. Impact-Echo Method
In Impact-Echo test, a stress pulse is generated at the surface of the element. The
pulse spreads into the test object and is reflected by cracks, flaws or interfaces, and
boundaries. The surface response caused by the arrival of reflected waves, is
monitored using a high precision receiving transducer (Malhotra and Carino, 2004).
When stress waves travel within the concrete element, a part of emitted acoustic
waves by the stress pulse on the surface is reflected over the boundary layers, where
different the material stiffness changes. The data received by the transducer is
normally analyzed in the frequency domain to measure the wave speed and the
thickness. This procedure has been standardized as the ASTM C1383, “Standard Test
Method for Measuring the P-Wave Speed and the Thickness of Concrete Plates Using
the Impact-Echo Method”.
Impact-Echo can be used to assess the depth of surface cracks. To do so, an impact-
echo test setup with two transducers is needed.

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where L1 is the distance between the horizontal impact point and the crack; L2 denotes the
distance between the second sensor and the surface-opening crack; L3 represents the distance
between the impact point and the first sensor; VP is the P-wave velocity; and Δt denotes the
travel time for the P-wave from the start of the impact to its arrival to the transducer 2.
II. Impact-Echo Method

III. Ultrasonic Pulse Velocity (UPV)
Ultrasonic Pulse Velocity (UPV) is an effective
non-destructive testing (NDT) method for
quality control of concrete materials, and
detecting damages in structural components.
The UPV methods have traditionally been used
for the quality control of materials, mostly
homogeneous materials such as metals and
welded connections. With the recent
advancement in transducer technology, the test
has been widely accepted in testing concrete
materials. Ultrasonic testing of concrete is an
effective way for quality assessment and
uniformity, and crack depth estimation. The test
procedure has been standardized as “Standard
Test Method for Pulse Velocity through
Concrete” (ASTM C 597, 2016).
III. Ultrasonic Pulse Velocity (UPV)
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BS 1881 Part 203 1986 Recommendations for Measurement of Ultrasonic Pulse Velocity Through Concrete (London: British Standars Inst)

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Measuring Magnifier Crack Width Gauge
• Crack widths are normally limited to 0.2
mm or 0.3 mm in concrete structures.
Measuring Magnifier device enables
accurate determination of whether
cracks exceed this limit.
• Align the Crack Width Gauge where the
calibration and the crack are the same
width.
Record the width, length and location of
the crack.
•
•
–
–
–
Magnification 10x
Measuring range 20 mm x 0.1 mm
Field of View 32mm
Crack width measurement

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Crack width measurement
CRACK DETECTION MICROSCOPE • Specification:
–
–
–
Magnification x 40
Measuring Range 4 mm
Divisions 0.02mm
•
•
Measure crack widths in concrete.
Consisting of a high definition
Microscope connected to an adjustable
light source which provides a well-
illuminated image under all working
conditions.
The image is focused by turning the
knob on the side of the microscope and
the eyepiece can be rotated through
360 degrees to align with the direction
of the crack being examined.
The 4mm measurement has a lower
scale divided into 0.2mm divisions.
the maximum crack widths should not
exceed 0.3mm which is 15 divisions on
the scale for most types of
environment.
•
•
•

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NDT for corrosion assessment, location and
diameter of reinforcement
thickness
and cover
•
•
•
Cover meter
Half Cell Potential test
Concrete Resistivity test

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Cover meter test
• Cover meter test is used to assess the
location and estimate the diameter of
reinforcement bars and concrete cover.
Principle:
•
– based measurement of change of
an elctromagnetic field caused by
steel embedded in the concrete.
• Equipment:
– profometer comprise a search
head, meter and interconnecting
cable.
• The concrete surface is scanned, with
the search head kept in contact with it
while the meter indicates, by analogue
or digital means, the proximity of
reinforcement

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Cover meter test
• The cover meter applies a current
pulse
The instrument measures the
amplitude of the induced current, which
depends on the orientation, depth, and
size of the bar.
The search head is directional and
maximum signal is obtained when the
bar is aligned with the long axis of the
search head.
The pulse-induction technique is
uniquely stable, is not affected by
moisture in concrete or magnetic
aggregates, and is immune to
temperature variations and electrical
interference.
•
•
•

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Example of the cover meter test results

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Half-Cell Potential Method (ASTM C 876)
Principle:
• The electrical activity of the steel
reinforcement and the concrete leads
them to be considered as one half of
weak battery cell with the steel acting
as one electrode and the concrete as
the electrolyte.
• The electrical potential of a point on the
surface of steel reinforcing bar can be
measured comparing its potential with
that of copper - copper sulphate
reference electrode on the surface.
• Practically this achieved by connecting
a wire from one terminal of a voltmeter
to the reinforcement and another wire
to the copper sulphate reference
electrode.
• Then generally readings taken are
at grid of 1 x 1 m for slabs, walls
and at 0.5 m c/c for Column,
beams

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Half-Cell Potential Method (ASTM C876)
The results affected by: • Microcracks
– Localized corrosion can be
generated by microcracks, which
also modify the concrete resistivity,
consequently affecting the
corrosion potential measurement
• Degree of humidity in concrete
– More negative potentials result for
concrete with higher degree of
saturation.
• Stray currents
– The presence of stray currents will
significantly affect the
measurements of the half-cell
potential.
• Oxygen content near the
reinforcement
– The lack of oxygen near the
reinforcement results in more
negative potentials

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corrosion)
corrosion)
Measured
Potential
Ecorr values
Corrosion Condition
mV vs. SCE
<-426 <-500 Severe corrosion
<-276 <-350
High (>-90% risk of
-126
to
-275
-350
to
-200
Intermediate corrosion
risk
>-125 >-200
Low (10% risk of
CSE = Copper / Copper sulphate electrode,
i.e. the potential values are stated with the
respect to CSE

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Example of the Half Cell Potential test result

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Galvapulse - Surface Corrosion Rate System
typically been used in connection with:
Swimming pools
Bridges
Balconies
Parking houses
• The Galvanostatic Pulse
Measurements technique (GPM) was
first used in the field in 1988.
• It provides a solution to interpretation
problems found when the half cell
potential methods is used in some
environments, e.g. in wet concrete.
• estimation of corrosion rate as well,
which means how much reinforcement
steel is being dissolved per year.
• The GalvaPulse™ is a rapid, non-
destructive polarization technique for
the evaluation of reinforcement
corrosion rate as well as half-cell
potentials.
–
–
–
–

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Galvapulse - Surface Corrosion Rate System
Advantages • Measurements possible on uneven and
curved surfaces.
Measurement results in Excel-format
are easily transferred to PC for further
processing and presentation.
• Estimation of the corrosion rate in the
reinforcement can be made in less than
10 seconds.
Reliable evaluation of reinforcement
corrosion also in wet, carbonated or
inhibitor treated concrete.
Half cell potential and electrical
resistance of the cover layer are given.
Lightweight electrode / hand held
computer and easy to operate
software.
Durable Guard Ring system for
focusing the current field to the
reinforcement.
•
•
Threshold values
•
•
•

The Measurement Principle
Where
a is probe spacing [cm]
V is measured potential [V]
I is the current applied [A]
• measure the electrical resistivity of
concrete or rock in a non-destructive
test.
A current is applied to the two outer
probes, with the difference measured
by the two inner probes.
In concrete material with high electrical
resistivity the corrosion process will be
slow compared to concrete with low
resistivity in which the current can
easily pass between anode and
cathode areas
•
•

Concrete Resistivity test result
• The electrical resistivity of concrete was
proposed as an effective parameter to
evaluate the risk of reinforcing steel
corrosion, particularly when corrosion is
induced by chloride attack
• The resistivity measurement is a useful
additional measurement to aid in
identifying problem areas or confirming
concerns about poor quality concrete.
• Measurements can only be considered
along side other measurements.
• Reinforcing bars will interfere with
resistivity measurements.
Limitation
• It is difficult to measure resistivity in
very close reinforcement
Carbonation may affect the
resistivity
It cannot be used where ambient
change in temperature is there.
Experience operator is required to
handle this equipment.
•
•
•

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Dust Sampling for Sulphate and Chloride Test
Maximum chloride content according to CIRIA 2002
Sulphate
Chloride
accepted limit is max. 4.0% max

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What Is the is max accepted limit. Of Sulphate in the concrete?

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Thank YOU
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