Overhaul of testing policy vital after fiasco at Hong Kong-Zhuhai-Macau bridge
Since the arrest of 21 employees of a government contractor by the Independent Commission Against Corruption, further faked concrete test results by the same contractor in the Hong Kong-Zhuhai-Macau bridge have been revealed by the Civil Engineering and Development Department.
While most people are worried about the safety of the bridge because of these test results, it would be useful to put things in perspective regarding the purpose and use of these tests.
Firstly, the purpose of these tests is to verify that the concrete strength is up to the specified standard. Secondly, these results enable the engineer to decide what to do if this specified standard cannot be met.
In theory, the concrete for testing should have the same quality as that pouring into the structure. Provided the same compaction effort has been applied, the concrete strength should be similar. However, no one can guarantee this in practice.
Accordingly, passing the test does not necessarily imply that the concrete in the structure has satisfied the standard required. On the other hand, failing the test also does not mean the structure must be condemned.
In both cases, non-destructive testing on the concrete structure must be first carried out. Passing this test implies that the structure is safe. To be absolutely sure, coring of concrete for testing can be done.
A very vital step to be taken by the engineer in case of such failure is to investigate its cause. This can either be due to the testing laboratory or a design fault or both. Under both conditions, the engineer must take timely corrective measures.
At present, the public’s concerns can only be alleviated if the civil engineering department can inform people the reasons why the bridge is safe. Only the testing time was faked, not the concrete strength. Moreover, non-destructive testing and further coring in the structure have proved the bridge is safe. Some people might question the use of all these test results. Also, they might ask if is too late to do anything if any faked results are only discovered one year later. And why should the government squander millions of dollars to do these tests?
A complete overhaul of the government’s testing policy is certainly required, as I pointed out in my letter (“Flawed tests for concrete need rethink”, May 31).
Dr Wong Hong-yau, Happy Valley