Building Diagnostic Tests as Assessment Tools 診 斷 樓 宇 狀 況 的 測 試 : 樓 宇 檢 驗 的 評 估 工 具

Transcription

1 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

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

3 Building Collapse at Ma Tau Wai Road on 29 January 2010 (Source from Yahoo website)

4 Building Collapse at Ma Tau Wai Road on 29 January 2010 (Source from Yahoo website)

5 Common Building Defects Concrete Spalling Reinforcement corrosion Concrete crack

6 Common Building Defects Concrete Spalling Concrete Honey Combing

7 Common Building Defects Spalling and Cracks

8 Risks to the Structure

9 Risks to the Public

10 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

11 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

12

13 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

14 Building Diagnostic Tests on Concrete Carbonation test carbonation depth Covermeter survey concrete cover Half-cell potential measurement rebar corrosion Infrared thermography debond on external wall

15 Building Diagnostic Tests on Concrete 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

16 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.

17 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.

18 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.

19 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.

20 Resistivity measurement Principle: Measurement of electrical resistivity to assess the corrosion risk of reinforced concrete structures.

21 Surface hardness measurement Principle: This test method involves applying a rebound hammer to the concrete surface. The hammer measures the rebound of a springloaded 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.

22 Surface hardness measurement There are different types of rebound hammers design for different situations. For example: Concrete with compressive strengths<25 N/mm 2, the P type rebound hammer is more preferable

23 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.

24 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.

25 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

26 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

27 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

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

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

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

31 Details of HOKLAS Supplementary Criteria on Diagnostic Tests on Concrete (cont d) Calibration/verification interval of the equipment (shown on the appendix of the HOKLAS SC-19)

32 Details of HOKLAS Supplementary Criteria on Diagnostic Tests on Concrete (cont d) Test methods for IR and radar Published by Hong Kong Concrete Institute (HKCI) Tel:

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

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

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

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

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

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

39 Which one is real thermogram? Visual photo Photo A Photo B

40 The End & Thank you!