1. Tackling Concrete Problems in Old Buildings and their Controlby
Ir Prof Paul PANG
Assistant Director/Existing Buildings 1
Buildings Department

2. Why Concrete?

3. Advantages Durable Economical Environmentally friendly Fire resistant
Easy maintenance
Versatile
Customized design

4. Building Stock

5. Building Stock Profile
Total number of private buildings around 42,000

6. Common Problems

7. Factors Affecting Performance
Design
Materials
Workmanship
Exposure
Usage and maintenance

8. Design
Strength
Serviceability
Fire resistance
Durability
Ductility

9. Exposure conditions

10. Materials

11. Workmanship

12. Usage and Maintenance
2-storey UBW
overloading
change in use

13. Lack of Maintenance

14. Unauthorized Building Works

15. Consequences

16. Consequences

17. Accident

18. Investigation and Assessment
To assess the overall condition
To ascertain the extent and cause of problems
To determine structural performance and integrity

19. Investigation & Assessment
Visual Inspection
Physical Appearance intact, loose, stained, cracked, deformed
Concrete Colour below 300℃ normal
300 – 600 ℃ pink to red
600 – 950 ℃ gray to buff
above 950 ℃ buff
Detailed Investigation
In-situ Tests destructive, non-destructive
Structural Assessment upon inspection/investigation results

20. Investigation & Assessment
visual inspection
detailed investigation

21. Diagnostic Tests infrared thermography half-cell potential mapping
carbonation depth
tell-tale
resistivity measurement
infrared thermography
half-cell potential mapping
cover-meter

22. ground penetration radar
Diagnostic Tests
ground penetration radar
impact echo test
Schmidt hammer test
rebar tensile test
concrete coring
ultrasonic test

23. Investigation & Assessment
The Worst Credible Strength (WCS) is used for assessment
WCS = 1/n . Σfi (1-0.2/√n)
where n = no. of samples (n ≥3)
fi = sample strength

24. Mitigation Measures Determine overall repair regime Stop at source
Provide protection
Replace defective concrete and re-bars
Provide structural strengthening

25. Concrete Repair patch repair resin injection injection grout
recasting
spray concrete

26. Strengthening and Retrofitting
plate bonding
fiber wrapping
column encasement
strengthening

27. Proof Tests for Repair Works
Schmidt hammer test
pull off test
cube test

28. Control Legislation Enforcement
Support and assistance to building owners
Publicity and public education

29. Legislation Buildings Ordinance (B.O. s24, s26, s26A, s28)
Minor Works Control System (MWCS)
Mandatory Building Inspection Scheme (MBIS)
Mandatory Window Inspection Scheme (MWIS)

30. Enforcement on Dilapidated Buildings
Respond to reports from public & other parties
Issue advisory letters and repair orders
Prosecution
Government contractor action
Planned programmes (large scale operations)

31. Enforcement on Dilapidated Buildings
Statutory orders issued in the past 3 years
Repair orders (building) – about 2 300
Repair orders (drainage) – about 1 500
Investigation orders – about 450
Demolition orders – about 10
Government contractor action on repair – about 1 350

32. Planned Programmes Operation Building Bright (OBB)
Large Scale Operation on repair and investigation
Mandatory Building Inspection Scheme (MBIS)
Mandatory Window Inspection Scheme (MWIS)

33. Operation Building Bright
One-off operation launched in 2009 by DEVB, HKHS and URA
Financial and technical assistance to owners
About Category 2 composite and domestic buildings aged 30 or above will benefit

34. Large Scale Operation
Repair or Investigation of Buildings, for Enhancement, with Age Under Thirty Years (REIN-BEAUTY)
- 500 target buildings per year, aged below 30
Inspection of buildings aged 50 or above
- about buildings
Inspection of cantilevered slab canopies
- about buildings

35. MBIS and MWIS Preventive Measures
Owners of target buildings are required to inspect and repair their buildings and windows regularly
2 000 MBIS target buildings per year
5 800 MWIS target buildings per year

36. MBIS

37. MWIS

38. Minor Works Control System (MWCS)
Simplified System for the carrying out of
minor building works
Class 1: 44 items
Class 2: 40 items
Class 3: 42 items

39. Support and Assistance to Owners
OBB
MBIS
Building Safety Loan Scheme
Integrated Building Maintenance Assistance Scheme

40. Publicity and public education
Promotion via media
Leaflets and website
Seminars

41. Thank You