APC Revision Course

8 July 20131

Building Condition Survey

and

Diagnosis

APC Revision Course

8 July 20132

Condition Survey

Common Practice in Hong Kong

� Fixed fee for a report and hourly rate for presentation at Court

if required

� Testing fees that require the use of special equipment and

participation of specialist personnel will be separately

reimbursed

APC Revision Course

8 July 20133

Condition Survey

Surveyors Responsibilities

� Duty of care (reasonable care to avoid acts or omissions)

� Reasonable level of competence and knowledge associated with a member of the surveying profession

� Guidelines as set down by professional bodies are used as a reference

Professional Negligence (Point of Law)

� Duty of care exists

� Breach of duty of care

� Financial/non-financial loss of client

� Reasonable test

APC Revision Course

8 July 20134

Condition Survey

Inspection Procedures

� Digest client’s instructions. What does he/she want?

� Establish type and extent of survey

� Undertake survey preparations (access & equipment)

� Undertake desktop study (third party documentation)

� Undertake preliminary survey

� Undertake detail survey (external & internal, destructive/non-

destructive)

� Assimilate findings and analyse results

� Prepare report and conclusions

APC Revision Course

8 July 20135

Condition Survey

Tools & Equipment Required

Plans Tapping Rod Marble Ball

Torch Screw Driver Compass

Laser Pointer Electricity Test Driver Brush

Pocket Mirror Mallet/Hammer Tape rule

Magnifying Glass Stripping Knife/Scrapper Recorder/ iPad

Binoculars Spirit Level/Plumb Rule Marker/Pen

Camera Filler Gauge/Crack Gauge PPE

APC Revision Course

8 July 20136

Condition Survey

Testing Techniques

Type of tests:

� Destructive test

� Non-destructive test

Field/ In-situ tests

� More accurate and representative of performance

APC Revision Course

8 July 2013

7

Condition Survey

Laboratory tests

� Removal of sample of material and subsequent testing at test

laboratory

� Take sample at various locations

� Large amount of samples allow comparison and the result

would be more justifiable

8

Defects in Concrete

APC Revision Course

8 July 2013

APC Revision Course

8 July 2013

3 Main Types of Defects

1. Design and Workmanship

� Wrong mix

� Wrong design

� Misplacement of reinforcement

� Inadequate cover to reinforcement

� Poor construction joints

� Not enough compaction—honey comb

� Too much water

� Poor curing

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APC Revision Course

8 July 2013

2. Chemical

� Chlorides

� Carbonation

� Sulphates

� Alkali-aggregate reaction

� Acids

� Electrolysis

� Grease, oil & waste water

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3. Physical

� Overloading

� Fire damage

� Mechanical Impact

� Adverse temperature or

inclement weather

APC Revision Course

8 July 2013

Chlorides (Calcium Chloride)

� High concentrations of chloride ion in concrete (above 0.4%

by weight) will have a corrosive effect on steel bars

� Only soluble chlorides are involved in the corrosion process,

therefore the concrete must be porous and moist for this to

happen

� Symptoms: Efflorescence on surface or deterioration of paint

finishes, rust stains tend to be very dark, often in patches, and

show deep pitting

� Degree of chloride content: Low (0.4% content), Medium (0.4

– 1.0% content), High (over 1.0% content)

� Sources: admixtures (hardening), salt water, marine sand,

course aggregate, cement, airborne, leaking flushing pipes,

toilets

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• Collect samples for selected building at wall, beam, column at

different locations

• Obtain drilling powder samples.

Engineering Assessment –

Chemical Composition Analysis (Chloride Content) Test) Field Work

• Cement content determined according to BS1881: Part 124: 1988

• Chloride content determined according to CS1: 1990, section 21

• Chloride content by weight of cement (%) is determined.

• The presence of chloride ions can depassivate the steel and promote

corrosion.

• The most widely accepted reinforcement corrosion threshold is concrete

that contains more than 0.4% chloride by weight of cement (i.e.

approximately 0.06% by weight of concrete sample).

Engineering Assessment –Chemical Composition Analysis (Chloride Content Test)

Assessment Criteria

Source: The Concrete Society – Technical Report No. 54,

Diagnosis of Deterioration in Concrete Structures

APC Revision Course

8 July 2013

Carbonation

� Normally start at surface and penetrate into concrete;

� No harm to concrete itself and may slightly increase concrete

strength;

� Caused by carbon dioxide in the atmosphere slowly and steadily

transform calcium hydroxide into calcium carbonate (limestone);

� pH value will then drop thus causing corrosion of reinforcement bars;

� pH value ranges from 1.0 to 14.0. When pH value over 12,

reinforcement is protected from corrosion (Passivation);

� Rate of carbonation depends on: time, concrete cover, concrete

density, cement ratio, cracks, alkalinity of original concrete.

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Test for Carbonation- by coring and application of phenolphthalein

Carbonation Front

Carbon Dioxide Penetration from Atmosphere

High pH >12

protects the reinforcement

Carbonation Front

• Reinforcement steel does not corrode when embedded in highly alkaline concrete

despite high moisture levels.

Source: Currie R.J. , Robery P.C. ; (1994) Repair and Maintenance of Reinforced Concrete;

Building Research Establishment, Garston, Watford, WD2 7JR; chapter 2.

Carbonation Process

• Carbonation process: hydrated cement is neutralised, and a carbonation front

progresses from outer concrete surface inward.

• Once concrete cover is carbonated, protection to steel reinforcement is lost.

Building Age > 30

yrs

• Universal indicator (colourless) – phenolphthalein, is used to determine the

carbonation front. Colour change is a direct measure of carbonation depth.

• Colour change from colourless to purple-red indicates alkaline, hence NO

occurrence of carbonation in concrete.

• Colourless reaction indicates carbonated cement.

Engineering Assessment –Carbonation Depth Test

Assessment Criteria

Carbonation Depth Test

Scoring

SystemCriteria

(Best) 1 0mm to 5mm, < reinforcement depth

2 6mm to 25mm, < reinforcement depth

3 At reinforcement depth

(Worst) 4 Beyond reinforcement depth

APC Revision Course

8 July 2013

Electrolysis

� There are differences in electrical potential between different

parts of reinforcement steel due to the differences in soluble

salt concentration.

� If these anodic (+ve) and cathodic (-ve) areas are

connected by an electrolyte such as salt solutions in the

hydrated cement, an electro-chemical corrosion process is

set up and a corrosion cell is formed.

� Positively charged metal ions at the anode pass into solution

as Fe++ and the free electrons pass along the steel to the

cathode. They are absorbed by the electrolyte and on

combining with oxygen and water form hydroxyl ions.

� These in turn combine with ferrous ions to form ferric hydroxide

and are converted to rust.

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Engineering Assessment –Half-Cell Electrochemical Potential Survey

• Select test locations

• Measures the potential of an embedded reinforcing

bar relative to a reference half-cell placed on the

concrete surface

Source: ASTM International Standards Worldwide, http://www.astm.org/Standards/C876.htm

Measures

the Potential

Difference

Reference

Electrode on

Concrete

Surface

On

Reinforceme

ntBar

Engineering Assessment –Half-Cell Electrochemical Potential Survey

Assessment Criteria

• Survey conducted according to ASTM C876.

• Investigate the probabilities of occurrence of

corrosion activities in reinforcement bars.

• In the vicinity of corrosion within a structure, the

value of free corrosion potential becomes increasing

negative.

• Select test locations

Engineering Assessment –Concrete Resistivity Measurement

Field Work

• A four probe device is connected to a high impedance resistivity meter.

• An electrical current is passed through the outer electrodes while the voltage

drop between the inner electrodes is measured.

Engineering Assessment –Concrete Resistivity Measurement

Assessment Criteria

• Resistivity measurement is according to BS 1881 – 201 : 1986

• The apparent resistivity of concrete is calculated from the current, voltage

drop and electrode spacing.

• The moisture content primarily affects the electrical resistivity of the cement

paste medium surrounding the steel bar which provides the electrolyte in the

electrochemical corrosion process, supporting the transport of ions from the

cathode to the anode.

• The higher the resistivity the lower rate of corrosion supported by the concrete,

if the reinforcement is corrosively active (note the resistivity does not indicate

if the reinforcement is actually corroding).

• 75mm/100mm dia. concrete core samples per

selected building at different locations

• Rebound hammer test at different locations.

Engineering Assessment –Concrete Core Compression Test, Schmidt Rebound Hammer Test

Field Work

Engineering Assessment –Concrete Core Compression Test, Schmidt Rebound Hammer Test

Assessment Criteria

• Concrete coring method and compression test according to CS1: 1990

• Rebound hammer test according to BS EN 12504 – 2 : 2001

(superseded BS 1881 – 202 : 1986)

• Expected concrete strength is:

12.5 MPa (Pre-1959 age band) ;

20 MPa (1959-1980 age band)

Source: B.D. Surveys -

B.D. Consultancy Agreement CAO C55, Dec 1995; B.D. Consultancy Agreement CAO E25, Sep 1999

Typical Building Condition Change with Short Term Repair(For Typical HK Pre-1980 Buildings)

0 10 20 30 40 50 60 70Year(s)

Good

Satisfactory

Varied

Poor

Beyond Economic Repair>$200

k

$15k