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1 An Unified Approach of Non Destructive Testing and Evaluation on Building, Civil Engineering and Underground Utility Structures and Materials at HKIE (Buildings) Division (5 Sep 2013) Ir. Dr. Wallace W.L. Lai Assistant Professor, Department of Land Surveying and Geo informatics, HK PolyU Visiting Scientist, Federal Institute of Materials Res. and Testing (BAM), Berlin, Germany HOKLAS Technical Assessor Who are we? Surveyor? Engineer? Scientist? What are we doing? Surveying? Testing? Measurement? Presentation outline Introduction Ordinance and Code of Practice Technology: Ground penetrating radar Technology: Infrared thermography Conclusion Coming events 1

2 Nondestructive inspection of building, civil engineering structure and underground utilities First Q: People working on these structures are used to be very distinct in different disciplines, building surveyors, structural engineers, civil engineers, materials engineers, land surveyors (utility). What is in common? Concl. Milestone of building diagnostic and survey/nde CE in HK 2

3 Because the technologies are all about INSTRUMENTAL applications of WAVE and its properties in MATERIALS So without exception amongst nondestructive evaluation on building, civil engineering structures, U/G utilities, there are common terms like: Reynolds, J.M. An Introduction to Applied and Environmental Geophysics. England, John Wiley & Sons Ltd, Absorption (material) 2.Attenuation (material) 3.Scattering (material) 4.Interface (material) 5.Frequency (instrumentation) 6.Resolution (instrumentation) 7.Dynamic range (instrumentation) 8...and others How? What is common? What happens overseas? Covermeter Ultrasonic S-wave Pile integrity test Infrared thermography Ground penetrating radar test on U/G utility Photo snapshots in Nondestructive Testing Civil Engineering and surveying in Federal Institute for Materials Research and Testing (BAM), Berlin (June 2013) 3

4 Why nondestructive? Visual inspection: does not tell what happens inside, relies on surface defects to predict internal conditions of structures. Random open up/take core/trial pit: WHERE? HOW MANY? REPRESENTATIVE? NDE methods are non destructive, effective and cover a large area. It serves as a screening tool before rational open up/taking core/trial pit s scheme are decided. Visual inspection NDE inspection Presentation outline Introduction Ordinance and Code of Practice Technology: Ground penetrating radar Technology: Infrared thermography Conclusion Coming events 4

5 Mandatory Building Inspection Scheme (MBIS) which is an Ordinance The Buildings (Amendment) Ordinance 2011 The Hong Kong Laboratory Accreditation Scheme (HOKLAS) which is a practice 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 Local standards on concrete and buildings Test methods for IR and radar 5

6 Three most important Ordinances and codes of practice on Utility management in HK COP on Monitoring i and Structural Maintenance of Water Carrying Health Services Affecting Slopes by ETWB (enacted 1996, revised 2006) monitoring Gas Safety Ordinance CAP 51B (1997) Mapping Electricity Supply Lines (Protection) Regulation CAP406H (enacted 2002, revised 2005) Mapping Presentation outline Introduction Ordinance and Code of Practice Technology: Ground penetrating radar Technology: Infrared thermography Conclusion Coming events 6

7 1. Ground penetrating radar (GPR) Ground Penetrating Radar Time/ depth Ground zero Ground zero Time/ depth 1. GPR is a device which emits and receives high frequency ( MHz) EM wave penetrating into materials like concrete, soil, asphalt, etc. 2. Image reconstruction of the reflected wave amplitude by signal processing and imaging techniques. 2D radargram 1D waveform 7

8 The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. 9/9/2013 Data acquisition and Imaging 2-dimensional measurements on the surface of elements B-Scan C-Scan Surface Imaging A-scan: 1D stationary collection of GPR waveforms B-Scan: 2D radargrams in x-z plane (compilation of A-scans) C-Scan: 2D slice view in x-y plane (signal re-construction in a particular depth z ) Cube view: 3D spatial re-construction in x-y-z plane GPR centre frequency MHz Planetary science Snow and ice thickness Geology, geophysics, archaeology and forensic Environmental Infrastructures (bridge, highway, tunnel, airport runway, buried utilites) Building 8

9 The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. 9/9/2013 GPR example 1: slice C scan in a reinforced concrete wall Salt water concrete Fresh water concrete B-Scan Plastic pipe C- Scan Surface 2 nd layer steel bar 1 st layer steel bar Slice C-scan Useful GPR parameters in B scan radargram Ground surface or time zero (4) (1) (2) (5) A B C D E (3) z x Information contained in GPR data 1. Concrete cover 2. Estimation of surface dielectric which may indicate locations with high moisture content 3. Thickness of concrete wall 4. Positions and spacing of embedded objects (steel bars, plastic pipes) 5. Amplitude of the steel bar reflections C-Scan Surface B-Scan 9

10 The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. 9/9/2013 GPR example 2: slice C scan and radargram B scan of a reinforced concrete footbridge B-Scan C- Scan Surface Any possible reasons for higher intensity in GPR slice scan? There can be several reasons, but one of those is chlorideinduced corrosion. Source: Prof. C.S. Poon, CEE Dept, HKPU 10

11 Concrete floor slab with embedded corroded steel reinforcement Area with corroded steel reinforcement Comparison of GPR slice map (left) and halfcell potential (right) 11

12 Accelerated corrosion of steel bar in concrete 1. Stationary measurement at fixed positions 2. Direct current applied across the anode and cathode bars 3. Specimens were submerged into NaCl water for 7 days, dewater below the bars and surface dried for 2 days Accelerated corrosion of steel bar in concrete (cont d) Snapshot photos on top of the specimen during corrosion Specimen after corrosion 12

13 Mechanisms Mechanisms between the interaction of corrosion and GPR wave are not yet well understood. Probable mechanisms are: 1. Positions of contrasting dielectric properties move upward from original steel concrete to steel corrosion product concrete interface, where reflectors in shallower depth are less attenuated. 2. Generation of multi interfaces (steel concrete corrosion product air cracks) which may change the local conductivity i distribution ib i around the steel bar and increases the reflectivity. Non-corroded state Corroded state ASCE Journal of Infrastructure Systems (2013) Vol. 19(2) pp GPR example 3: Underground utility s slice C scan Surface manhole U/G pipe at 55cm deep Storm drain at 89cm deep 13

14 GPR example 4: Ground penetrating radar mapping prior to excavation in an archaeological site in Tung Chung One of the GPR slices (x, y plane) at particular z white reflections indicate strong reflections indicative to archaeological remains One of the GPR sections (x, z plane) at particular y hyperbolic reflections indicate strong reflections indicative to archaeological remains Presentation outline Introduction Ordinance and Code of Practice Technology: Ground penetrating radar Technology: Infrared thermography Conclusion Coming events 14

15 Infared thermography: external wall debond and internal wall s water leak The debond, insulated by air void, stores heat energy more rapidly than intact area. So look for a HOT spot!!! On the surface of the finishes, the sign of water heats up slower because its heat capacity is 4 times than that of air. So look for a COLD spot!!! Qualifying debond and quantifying debond size Step 1: adjust an optimum color scale according to the principle (1) professional judgment (2) environment consideration (3) weather, etc degc degc degc Step 2: Highlight the white/yellow area in iron palette (or other palette in different color) which seems to represent the extent of debond Estimated debond = 3.6 m 2 Estimated debond = 1.2 m 2 Estimated debond =??? m 2 15

16 Do it quantitatively in 7 steps? Step 1: ROI extraction 1. When a debond is identified d on-site, recognize the region of interest (ROI) example as follows 2 Measure the azimuth 2. Measure the azimuth angle, elevation angle and SD (or other parameters if necessary) from the camera to the debond 16

17 Step 2: image filter of exclude tile joints Step 3: x cut and y cut of the temperature profile 17

18 Step 4: Binary transformation Step 5: Fusion of x cut and y cut images 18

19 Step 6: image resolution (IFOV) and Step 7: boundary and size measurement of the defect Limitations patch of defect is not measurable because only isolated defect yields Gaussian distribution (low high low temperature) over both the defective and defect free areas. low thermal contrast between the defective and defect free area, that it is not adequate to define a Gaussian distribution, Limitations in HKCI: TM1 apply also, such as curved surface of the building. wet building surface. building surface is obscured by contaminants (bird droppings, mud, oil) in rain 19

20 Refl. to DW TTT DW amplitude DW peak freq /9/2013 Presentation outline Introduction Ordinance and Code of Practice Technology: Ground penetrating radar Technology: Infrared thermography Conclusion Coming events The concept NDE structural health monitoring (SHM) in building diagnostic and utility survey Yr 30 Yr 1 Yr 5 GPR, ultrasonics, IRT and other NDEs Material properties by destructive tests according to rational coring 20

21 Challenges of NDE survey Object identifications and location mapping are very mature. But NDE interpretation on material properties is still not straightforward because of different sensor types, multi-dimensional signal processing and variation of material properties. Signal inversion in this context is still a big subject of research. The property it measures is not directly related to what engineers are interested, e.g. higher ultrasonic pulse velocity (UPV) is related to but not always implies high concrete strength. Conclusion Nondestructive technologies are originated from areas like geophysics, medical imaging, aerospace engineering, remote sensing. Swopping wavelength allows survey, inspection and assessment of buildings, civil engineering structure and underground utilities. Missile-guidance Medical For existing buildings, these technologies allow material/structural evaluation in large scale. Two relatively new NDE-CE technologies are introduced, which are ground penetrating radar, and infrared thermography. Its advantages are the ability to see through the unseen, offer very fine spatial resolution, provide traceable record and rapid data collection compared to open-up, other NDE-CE survey methods. 21

22 Presentation outline Introduction Ordinance and Code of Practice Technology: Ground penetrating radar Technology: Infrared thermography Conclusion Coming events Coming events (join us!) Local training at PolyU leading to company s accreditation purpose (to be confirmed) Contact: wllai@polyu.edu.hk 22

23 NDT&E CES workshop June