The ICAC has arrested 21 people suspected of involvement in faking test results for concrete supplied to the Hong Kong-Zhuhai-Macau bridge project.

The anti-graft agency said today it had detained two senior executives, 14 lab technicians and five lab assistants of a contractor to the Civil Engineering and Development Department (CEDD).

It said  had launched operation Greenfield last Tuesday to investigate a corruption complaint from the CEDD.

It was revealed that when some of the tests were not conducted within the set time frame in compliance with the contract requirements, the site laboratory technicians and laboratory assistants might have adjusted the times on the testing machines to cover up the irregularities.

During the ICAC operation, it was further revealed that some of the laboratory staff might have replaced the concrete samples by using a metal calibration cylinder and/or high strength concrete cubes to falsify the tests, so that the tests would appear to have been conducted properly. It was suspected that the above malpractice might have started in early 2015.

Two senior site laboratory technicians had certified the false test reports, and “might have corruptly connived at the submission of the false reports to the CEDD,” the ICAC said.

It said the contractor had been carrying out tests for the CEDD since 2013. The 21 staff have all been released on bail pending further inquiries.

Raymond KS Chan, a former head of Geotechnical Engineering Office, has said that if use of the fake concrete was widespread, affected sections of the bridge would have to be rebuilt.

Development Secretary Eric Ma said today officials would review the bridge construction to see if any improvements were needed, SCMP.com reports.

“If the situation is not that serious, reviewing the existing construction is already enough. Otherwise we will take serious measures and follow up actions. But I do not have any information in hands now,” Ma said.