building diagnostic tests as assessment tools · 2014-01-06 · electromagnetic field caused by...

Building Diagnostic Tests as Assessment Tools

診斷樓宇狀況的測試 : 樓宇檢驗的評估工具

presented by Ir Samson K.Y. WONG

Senior Accreditation Officer, Hong Kong Accreditation Service, Innovation and Technology Commission

The Government of HKSAR

&

Ir. Kenneth Pak, Senior Project Officer,

Engineering Discipline In-service Training Office, VTC

17 April 2013

Case Study on the Collapse of a 55-year-old building

Building Collapse at Ma Tau Wai Road on 29 January 2010

(Source from Yahoo website)

Common Building Defects Concrete Spalling

Reinforcement corrosion

Concrete crack

Common Building Defects

Concrete Honey Combing

Concrete Spalling

Common Building Defects – Spalling and Cracks

Risks to the Structure

Risks to the Public

Mandatory Building Inspection Scheme (“MBIS”)

Require building owners to carry out regular building inspections and repair works in respect of their buildings Cover private buildings aged 30 years or above, except domestic buildings not exceeding three storeys in height

Building owners will be required to carry out an inspection once every 10 years Areas to be inspected:

common parts, external walls, certain projections and signboards of a building

Our Discussion

1. Mainly concentrated on reinforced concrete structures

2. Sharing non-destructive test methods to support MBIS:

- estimate concrete strength - identify possible defects - locate reinforcement and estimate their

sizes - estimate corrosion activities

Please refer to Buildings Department’s Web Site for the most updated Registered Personnel under MBIS

Building Diagnostic Tests on Concrete

Carbonation test Covermeter survey Half-cell potential measurement Infrared thermography Resistivity measurement

Surface hardness measurement Surface penetration radar survey Ultrasonic pulse velocity measurement


Carbonation test carbonation depth

Covermeter survey concrete cover

Half-cell potential measurement rebar corrosion

Infrared thermography debond on external wall


Resistivity measurement

corrosion risk of reinforced concrete

Surface hardness

measurement

concrete strength

Surface penetration

radar survey

rebar layout,

concrete cover

Ultrasonic pulse

velocity measurement concrete strength

Carbonation test

Principle:

Carbonation of concrete occurs when the carbon dioxide, in the atmosphere in the presence of moisture, reacts with hydrated cement minerals to produce carbonates, e.g. calcium carbonate. The extent of carbonation is determined by spraying a freshly exposed

surface of the concrete with a 1% phenolphthalein solution. The calcium hydroxide is coloured pink while the carbonated portion is uncoloured.

Covermeter Survey

Principle:

This method is mainly used for locating reinforcing steel within a concrete member by measurement of the change of an electromagnetic field caused by steel embedded in the concrete.

Half-cell potential measurement

Principle:

The risk of corrosion of the reinforcement in the immediate region of the test location may be related empirically to the measured potential difference by the Half cell equipment. The test involves measurement of the potential difference between the metal in reference electrode and the steel in concrete.

Infrared thermography

Principle:

IR involves the recording of surface temperature differentials

on a concrete member undergoing heating or cooling. Hidden features, including voids or cracks, will influence the local rate of heating or cooling and may be detected by examination of temperature contour plots.

Resistivity measurement

Principle:

Measurement of electrical resistivity to assess the corrosion

risk of reinforced concrete structures.

Surface hardness measurement

Principle:

This test method involves applying a rebound hammer to the concrete surface. The hammer measures the rebound of a spring- loaded mass impacting against the concrete surface. Its rebound is dependent on the hardness of the concrete and is measured by the test equipment. By reference to the conversion chart, the rebound value can be used to determine the compressive strength of concrete surface.

Surface hardness measurement

There are different types of rebound hammers design for

different situations. For example: Concrete with compressive strengths<25 N/mm2, the P type rebound hammer is more preferable

Surface penetration radar survey

Principle:

A surface penetration radar system is used to examine the

reflections of short duration pulses from interfaces between materials with different dielectric constants lying below the surface. Reinforcing bars, voids and ducts may be identified and thickness of slabs may also be determined.

Ultrasonic pulse velocity measurement Principle:

The method is based on the study of sound

wave propagation through concrete materials and more particularly o the measurement of their velocity of transmission. Measurement of pulse velocity can be used to determine the integrity of concrete specimen such as homogeneity, presence of voids, cracks or other imperfections.

See a video on Non-Destructive Evaluation Tests Acknowledgments Ir Prof. C.S. POON, Dr Wallace W.L. LAI, Dr S.C. KOU, Mr. K.H. WONG, Mr. Kenneth K.K. LEE and Mr. B.J. ZHAN Department of Civil and Structural Engineering, The Hong Kong Polytechnic University

Surface Penetration Radar Survey

Infrared Thermography Survey

Ground penetration radar and covemeter test.wmv

Infrared thermography.wmv

Video/Infrared thermography.wmv

Accreditation of Building Diagnostic Tests on Concrete

Some of the testing laboratories have been granted accreditation for some of the tests already Recently issued - HOKLAS Supplementary Criteria No.19

Strengthen accreditation requirements to tighten control of test laboratories providing building diagnostic tests on concrete Facilitate the implementation of MBIS

Increase the confidence of users of HOKLAS-accredited testing laboratories

Details of HOKLAS Supplementary Criteria on Diagnostic Tests on Concrete (cont’d)

Laboratories for diagnostic tests on concrete shall operate under a

management system complying with the relevant HKAS and HOKLAS requirements.

HOKLAS 003 specifies the management system and technical

competence requirements

Management requirements:

Organisation

Management system

Document control

Review of requests, tenders and contracts

Subcontracting of tests and calibrations

Purchasing services and supplies

Service to the customer

Complaints

Control of nonconforming testing

……

Technical requirements:

Personnel

Equipment

Handling of test items

Test methods

Accommodation conditions

Sampling

Measurement traceability

Assuring the quality of test results

Reporting the test results


HOKLAS SC-19 gives specific requirements with respect to the followings: Personnel Equipment & calibration Test methods Handling of test items & records Strengthening of supervision Measurement uncertainty Proficiency testing


Requirements on personnel Approved signatory (Infared Thermography & Surface Penetration Radar)

Approved test operators (Infared Thermography & Surface Penetration Radar)

International qualification or completion of specified

training course


Requirements on equipment and calibration

Equipment shall be properly stored, maintained and

calibrated.

Equipment records shall be maintained up-to-date.

General requirements on equipment calibrations are

given in the HOKLAS Supplementary Criteria No.2.

Specific requirements on equipment calibration/ verification intervals for various diagnostic tests are given in HOKLAS Supplementary Criteria No.19.


Calibration/verification interval of the equipment

(shown on the appendix of the HOKLAS SC-19)


Test methods for IR and radar

Published by Hong Kong Concrete Institute (HKCI)

Email: [email protected] Tel: 2789 2389

mailto: [email protected]


HKCI : TM1 Detection of Building Surface Defect by Infrared Thermography

Measuring apparatus – Infrared camera (with a

thermal resolution of 0.1°C or better and a spatial

resolution of at least 1.3 mrad) equipped with zoom lens

Testing procedures – carry out the IR survey at low

wind speed (i.e. not higher than 6.5 m/s)

Thermogram – not more than four to five storeys of a building on each thermogram


HKCI : TM2 Determination of Concrete Cover and Distribution of Steel Rebar by Surface Penetration RADAR

Measuring apparatus – The centre frequency of

antennas should normally range from 500 MHz to 2 GHz, RADAR control unit, suitable data storage and display device.

Testing procedures – on-site calibration

Calculation and expression of results – equation for determination of the cover/element thickness


Requirements on handling of test items and records

Items shall be traceable and identified against test results

high resolution digital photograph records

For Infrared Thermography,

For Surface Penetration Radar,


Requirements on strengthening of supervision

HOKLAS Supplementary Criteria No. 36

Construction Materials Test Category – Additional Accreditation Requirements

ensure effective supervision. undue pressure frequent unannounced on-site visits


Requirements on measurement uncertainty

The organisation shall have procedures for estimating

uncertainty of measurement.

All the significant components of uncertainty for each

test shall be identified.

If requested by the client, the organisation needs to report the uncertainty of measurement in HOKLAS endorsed reports.


Requirements on proficiency testing

The aim of proficiency testing schemes is to give a way for an organisation to monitor its performance against both its own requirements and the performance of other organisations.

Which one is real thermogram?

Visual photo

Photo A Photo B

The End &

Thank you!

www.hkas.gov.hk

www.hkas.gov.hk

building diagnostic tests as assessment tools · 2014-01-06 · electromagnetic field caused by...

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