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

Why Concrete?

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

Building Stock

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

Common Problems

Factors Affecting Performance Design Materials Workmanship Exposure Usage and maintenance

Design Strength Serviceability Fire resistance Durability Ductility

Exposure conditions

Materials

Workmanship

Usage and Maintenance 2-storey UBW overloading change in use

Lack of Maintenance

Unauthorized Building Works

Consequences

Consequences

Accident

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

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

Investigation & Assessment visual inspection detailed investigation

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

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

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

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

Concrete Repair patch repair resin injection injection grout recasting spray concrete

Strengthening and Retrofitting plate bonding fiber wrapping column encasement strengthening

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

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

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

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)

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

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

Operation Building Bright One-off operation launched in 2009 by DEVB, HKHS and URA Financial and technical assistance to owners About 1 500 Category 2 composite and domestic buildings aged 30 or above will benefit

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 4 000 buildings Inspection of cantilevered slab canopies - about 3 700 buildings

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

MBIS

MWIS

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

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

Publicity and public education Promotion via media Leaflets and website Seminars

Thank You