Structural Assessment and NDT Procedures

Transcription

1 Structural Assessment and NDT Procedures Mohd. Saleh Jaafar Seminar on Concrete Repair and Rehabilitation of Concrete Structures Pusat Kecemerlangan Kejuruteraan & Teknologi JKR (CREaTE), Alor Gajah, Melaka 16 May

2 Content 1. Background 2. Concrete Deterioration 3. Physical Cracks 4. Cracks due to Chemical Actions 5. Thermal Cracks 6. Structural Assessment 7. Classification of Damage 8. NDT for Different Types of Distress 2

3 1 History BC 300 BC 1824 mud and straw for bricks gypsum and lime for mortar use of volcanic ash by the romans Portland cement was invented & patented by Joseph Aspdin of England The Ingalls Building, Ohio - 16 story Concrete Sports Dome University of Illinois Tallest Concrete Building 65 story 3 Gorges dam China worlds largest concrete structure, 35 million cubic yards of concrete 3

4 1 Durability of Concrete

5 1 Chemical Composition of Portland Cement Oxide and Compound Compositions of Typical Portland Cement Typical average values of compound composition of Portland Cements of Different Types Typical Oxide % Calculated Compound CaO 63 C 3 S 10.8 SiO 2 20 C 2 S 54.1 Al 2 O 3 6 C 3 A 16.6 Fe 2 O 3 3 C 4 AF 9.1 MgO 1.5 Alkali (Na 2 O, K 2 O) 1 SO 3 2 % Cement Compound composition, % Type I Modified Type II Ordinary Type III Rapid H Type IV Low H C 3 S C 2 S C 3 A C 4 AF CaSO 4 CaO MgO Type V Sulphate Resistance

6 1 Main Chemical Reactions 6

7 2 Concrete Deterioration Causes of Deterioration Physical Chemical Thermal 7

8 2 Concrete Deterioration 8

9 2 Concrete Deterioration 9

10 3 Physical Cracks Plastic Shrinkage 10

11 3 Physical Cracks Plastic Settlement 11

12 3 Physical Cracks Drying Shrinkage 12

13 4 Cracks due to Chemical Actions Mechanism of Corrosion 13

14 4 Cracks due to Chemical Actions Spalling Delamination 14

15 4 Cracks due to Chemical Actions Carbonation 15

16 4 Cracks due to Chemical Actions Alkali Silica Reaction (ASR) 16

17 4 Cracks due to Chemical Actions 17

18 4 Cracks due to Chemical Actions Sulfate Attacks 18

19 4 Cracks due to Chemical Actions Sulfate Attacks 19

20 4 Cracks due to Chemical Actions Minimizing Risks for Sulfate Attacks 20

21 5 Thermal Cracks 21

22 5 Thermal Cracks 22

23 6 Structural Assessment PROCEDURAL STEPS FOR DAMAGE ASSESSMENT AND REPAIR OF CONCRETE 1 Initial Inspection Check List 6 Cost of Repair 2 Classification of Damage and intensity 7 Prepare Tender Document 3 Condition Survey 8 Carry out Repair/ Replacement 4 Strength Evaluation 9 Investigation of Repair Structures 5 Recommendation on Remedial & Preventive Measures, Materials for Concrete Repairs 23

24 6 Structural Assessment 6.1 Initial Inspection: Objectives 6.2 Initial Inspection: Checklist Identify the causes of damage and source of the problem Determine the extent of damage Type and age of construction Visual defects due to poor workmanship or material deterioration Classify the type of damage Determine material properties Assess safety and serviceability of the structure Inspect the site with special attention to potential hazards Determine the background information about the structure Lack of structural adeuacy excessive deflection or structural cracks Foundation movement distortion of door or cracks around doors/windows Material deterioration and surface defects e.g. spalling, rusting Examinations of cracks and defects Actions in case of safety hazard 24

25 6 6.3 Condition Surveys Structural Assessment Good checklist can unfold overall damaged state of structures and allows specialist to identify scope of work to carry out condition survey. Dimensional surveys Survey of cracks, spalling, steel pitting and potential mapping of corrosion of steel Carbonation depth Chloride content Sulfate content Concrete cover Cores for concrete strength Depth of discoloration of fire damage Ultrasonic for honeycombing Schmidt hammer test for delamination Deflection of beams and slabs Verticality of columns/ walls Alkali reactivitiy Electro potential and resistivity survey Permeability Structural load test 25

26 6 6.3 Condition Surveys Structural Assessment Good checklist can unfold overall damaged state of structures and allows specialist to identify scope of work to carry out condition survey. Phase I: Visual Inspection Phase II: Crack Classifications Phase III: Detailed Inspection First task is to establish information about the structure Walk around for visual signs Design drawing can be useful Make initial assessments of the structural forms Note locations of deterioration Note for potential difficulty of access to important locations Visual inspections enable classification of various types of cracks Describe symptoms and main factors causing them (chemical, physical or thermal) Note possible inadeuacy of design, materials or construction deficiency Determine mechanism of cracks Assessment of the conditions based on crack depth, areas and volume involved. Use findings from Phase I and II to plan for detailed inspection Extent and scope depends on structural forms, degree of change in use, and extent of deterioration Determine suitable test methods Determine number of specimens or locations of test points Samples from unaffected areas to serve as baseline Identify relevant standards 26

27 6 Structural Assessment 6.4 Strength Evaluation To determine of the structure is safe for use under the design load, actual service load or reduced load, taking into consideration of damage. Two methods for strength evaluation: Analytical Method In-situ Load Testing It is often more economical and less disturbing. It can be conclusive if sufficient information on dimensions and details of members are available. It is always difficult to ascertain the actual properties of materials and intensity of damage It is practical only if the members are primarily flexural (slabs and beams) Decide test under existing conditions of after rehabilitations are made 27

28 6 Phases in inspection, assessment and repairs Structural Assessment Analysis of Condition Survey Results Condition Survey Visual and Site Observation NDT Results LAB Test Results Design Records Loading Records Filter Expert Knowledge Experience Expert Knowledge Experience 28

29 6 Steps for Diagnosis Structural Assessment Important Notes 29

30 6 Steps for Diagnosis Structural Assessment Important Notes 30

31 6 Steps for Diagnosis Structural Assessment Cracks after loading 31

32 6 Cracks between 2-10 Hours Structural Assessment Cracks at 2 20 Days 32

33 6 Structural Assessment Cracks between few months to a year Cracks during or after winter season 33

34 6 Cracks along reinforcement Structural Assessment Random Cracks after few years 34

35 7 Classification of Damage and Damage Intensity Structural Damage Grade Intensity Visual Damage Residual Deformation 1 Light Fine cracks (<1mm); light spalling at isolated spots Not apparent 2 Moderate Medium cracks (1-2mm); light spalling; doors/ windows slightly stuck Slight 3 Severe Wide cracks (>2mm); medium spalling; doors/ windows stuck Medium 4 Very Severe Wide cracks everywhere; doors/ windows distorted, utility pipes and glass broken Slope of floor exceeding l/125 35

36 7 Classification of Corrosion Damage Grade Intensity Cracking Spalling Cover Carbonation 1 Light Hairline cracks (<0.1mm); without rust stain Not apparent Partial 2 Moderate Fine cracks (<0.2mm);without rust stain Isolated spot Slight 3 Severe Extensive with rust stain Extensive; corroded Complete steel visible 4 Very Severe Extensive and wide with rust stain Extensive; substantial steel pitting visible complete 36

37 7 Classification of Fire Damage Grade Intensity Plaster/ finish Surface color Crazing Spalling Reinforcing exposure 1 Light Some peeling Normal Slight Slight None 2 Moderate Substantial loss Pink Noticeable Localized 10-25%; non buckled 3 Severe Total loss Buff Extensive; Extensive; 25-50%, not more than one buckled 4 Very Severe Total loss Buff Extensive Extensive; Over 50%; > 1 bar buckled 37

38 8 Visible Distress and Related Concern 38

39 8 Concrete Parameters and Related NDT Parameter Concrete strength Flexural strength Tensile strength Homogeneity Permeability Concrete Lamination Chemical composition Cracks Related NDT Rebound Hammer, Windsor Probe, Core TestLok Test, Capo Test, Pull-out test Break-off test Pull-off Test UPV, Acoustic Emission, Impact-echo, Gamma Ray Radiography, Endoscopy, Integrity tests Initial Surface Absorption Test, Figg s air and water permeability tests, Visual inspection for water leakages, accumulation Radar Techniue, Infrared Thermography Chloride content, carbonation test, XRD, XRF, DTA UPV, Impact echo, crack measuring microscope, visual inspection 39

40 8 Concrete Parameters and Related NDT Tell-tale Installed over a Crack to Evaluate Movement Ultrasonic pulse velocity meter is used for uality of concrete after construction Windsor probe test for strength of concrete Rebound hammer is used for testing surface strength of concrete 40

41 8 Concrete Parameters and Related NDT Coring of concrete for in-situ strength test Ratio of length of cylinder to diameter (L/D) Strength correction factor

42 8 Visible Distress and Related Concern Diagnosis of Deteriorations and Defects of In-Situ Concrete 42

43 8 Visible Distress and Related Concern Concrete In-Situ Durability Tests 43

44 8 Visible Distress and Related Concern Concrete In-Situ StrengthTests 44

45 8 Visible Distress and Related Concern Relative Number of Readings Recommended for Various Test Methods Test Methods Recommended Number of Readings at a Location Standard cores 3 Small cores 9 Schmidt hammer 12 Ultrasonic pulse velocity 1 Internal fracture 6 Windsor probe 3 Pull-out 4 Pull-off 6 Break-off 5 45

46 8 Visible Distress and Related Concern General Guidelines for Concrete Quality based on UPV PULSE VELOCITY CONCRETE QUALITY >4.0 km/s Very good to excellent km/s Good to very good, slight porosity may exist km/s Satisfactory but loss of integrity is suspected <3.0 km/s Poor and los of integrity exist. 46

47 8 Visible Distress and Related Concern Identification of Corrosion Prone Location based on Pulse Velocity and Hammer Readings Sl. No. Test Results Interpretations 1 High UPV values, high rebound number Not corrosion prone 2 Medium range UPV values, low rebound numbers Surface delamination, low uality of surface concrete, corrosion prone 3 Low UPV, high rebound numbers Not corrosion prone, however to be confirmed by chemical tests, carbonation, ph 4 Low UPV, low rebound numbers Corrosion prone, reuires chemical and electrochemical tests. 47

48 Acknowledgement Thank you to all who have been involved in the preparation of the slide. Materials were retrieved from various sources. The slides are to highlight key points only. 48