Several major property projects in Shenzhen - including what will be the city's highest building - have been ordered to suspend construction after CCTV reported that concrete used by some local developers was made from cheap, untreated sea sand.
More projects are likely to be affected as the Shenzhen government ordered a citywide inspection into the practice, which they said was common throughout the Pearl River Delta. Untreated sea sand contains high levels of salt and chloride that could corrode steel reinforcements, causing buildings to collapse.
The Shenzhen Housing and Construction Bureau called an emergency news conference yesterday and said it was conducting a blanket investigation into the city's concrete-mixing plants. So far they had found 15 of the 92 plants in Shenzhen using low-quality sea sand as the raw material. The concrete was sold to local real estate developers.
The official refused to disclose how many residential and commercial buildings were erected with problematic concrete. But it ordered three high-profile projects - including the 660-metre-tall Pingan Financial Centre, scheduled to be completed in 2016 - to suspend construction pending further notice. Pingan Financial Centre will be the tallest structure in Guangdong. Construction workers were still busy on the site after the Shenzhen government's press conference.
China Central Television reported on Thursday that many Shenzhen developers replaced expensive river sand with much cheaper sea sand as a building material. It named and shamed four concrete-mixing plants - including one owned by Hong Kong-listed China Resources Cement Holdings.
The report also accused the two largest sandpits in Shenzhen, which supply concrete-mixing plants, of using seawater instead of much more expensive fresh water to wash sand. It said sea sand was used in several government-funded projects, including subways. Shenzhen Metro insisted all its projects were safe and met national standards.
China Resources Cement Holdings said it had launched an investigation and no substandard products had been found.
Experts in Hong Kong said sea sand was never used in the city even though it is not banned.
"Treating the sea sand is very costly and it requires a large area to soak it in [fresh] water," said Chan Chi-ming, who is head of the department of construction at the Institute of Vocational Education. He said the soaking process was intended to remove all traces of the salt.
A professional at a Hong Kong construction company said no developer here would risk using sea sand. "If it is not treated well, the concrete will peel off the building after 10 years or so."
A spokesman for the Housing Authority said the sand used in its buildings came from crushed rocks at a quarry in the Pearl River region.
Zu Lihong, an official at the Shenzhen housing and construction bureau, admitted that the use of sea sand in construction was widespread because of a lack of river sand.
The central government - to protect the rivers that supply fresh water to Hong Kong and Macau - banned local authorities from mining river sand.
Zhu tried to play down the danger and said sea sand can be used after washing and desalting, in line with a regulation issued by the construction ministry.
The owner of a luxury flat developed by China Resources said he was worried. "These units are so expensive. How could you imagine they are using substandard material?" he said.
Kou Zuomin, a retired architect in Shenzhen, said the use of sea sand was an open secret.
"Both developers and supervisors know it but they just turn a blind eye."