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15
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(c)
(d)
Answer:
Mr President,
the number of housing blocks built with sub-standard concrete and the proportion of such blocks to the total number of public housing blocks; the names of those housing estates having this problem, and the dates of completion of these housing estates; and
the number of contractors involved in building housing blocks which are found to be of sub-standard concrete strength, the number and names of these contractors who are still taking part in the public housing building programme, and the reasons why their continued participation is permitted by the authority concerned?
Before 1980, the standard of concrete for public housing blocks was 20 MPa (Megapascal), which was then the common international standard. Since 1980, the standard has been progressively raised to 30-35 MPa, again in compliance with common international standards.
Normally, a building is designed to a much stronger strength than it actually needs to take the loading upon it. This strength reserve is added at the design stage to cater for uncertain situations, such as variations in workmanship and future usage. Non-compliance with the design specifications does not necessarily imply danger for the building. Causes of non-compliance of strength include mainly the varying standards of workmanship and material. In order to make a realistic assessment of the structural safety of an existing building, it is necessary to look at the actual load carrying capacity of various parts of the building.
During the period from 1981 to 1985, the Housing Department investigated the structural safety of all public housing blocks built before 1981. Concrete samples were taken from 836 blocks for testing. All the blocks were found to be structurally safe. 411 of them were found to have average concrete strength which did not fully comply with the originally designed specifications. Of these, 201 have already been demolished under the Housing
the Housing Authority's Comprehensive Redevelopment Programme. The remaining 210 blocks (information just tabled Annex 1) represent 17% of the existing stock of public rental housing. Of these, 76 do not require strengthening work. Work on strengthening 125 was completed by mid-1996, and one more block will be completed in the near future. We are conducting a detailed appraisal of the remaining 8 blocks to see whether strengthening work is required.
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Twenty-five contractors were involved in the construction of the 411 above- mentioned blocks. Three (Annex 2) are still on the Housing Authority's approved list of contractors for new works as they fulfill the criteria set by the Housing Authority. As a general practice, the Housing Authority closely monitors the performance of contractors, and will remove from the list any contractor who fails to perform satisfactorily.