The city of Shenzhen has vowed to prevent apartment blocks from being built with substandard sand from the sea by setting up a city-wide monitoring system to supervise the production of concrete, the city's construction agency said on Thursday.

The move is in response to a China Central Television (CCTV) report exposing dangerous concrete buildings made with substandard sand.

The Shenzhen housing and construction bureau told reporters at a news conference that the agency dispatched two teams of investigators Thursday morning to inspect the two concrete plants highlighted in the CCTV exposé, which showed them using low-quality sea sand in the concrete they sold to real estate developers.

The sea sand used in several of the city's residential blocks, CCTV said, contains higher levels of chloride ion than are permitted by the Ministry of Housing and Urban-Rural Development. Chloride ion can corrode steel reinforcing bars and lessen the sturdiness of buildings, the report said.

Han Ningxu, a professor with the College of Civil Engineering at Shenzhen University, compared the corrosive properties of chloride ion to cancer cells, adding that buildings built with substandard sea sand will not last as long.

"The life of such a building is less than half of others built with proper construction sand," Han said.

According to sznews.com, a Shenzhen-based news portal, the construction bureau will release the results of its investigation as soon as it is finalized. The bureau said it has also formed a team of 60 experts, who will conduct "a blanket investigation" of the city's 120 concrete mixing plants, the news website said.

Shenzhen housing and construction bureau said that any cement plant caught using substandard sea sand illegally will be immediately closed and operators punished according to regulations.

The CCTV report, which was broadcast Thursday morning, said that walls and floors of buildings at Shezhen's Ludan village residential block began to crack, allowing rainwater to seep in, when they were just over 10 years old.

"We refurnished the apartment twice, otherwise it would not be livable," a resident told CCTV.

The CCTV report sparked a public outcry with some Sina Weibo users criticizing Shenzhen's housing and construction bureau.

"A few years ago, the media reported that some construction sites in Shenzhen used improper aggregate in their concrete mix. There was no inspection of the plants, the housing and construction bureau just let it go," wrote Weibo user Aijiade Yidao.

According to guidelines published by the Ministry of Housing and Urban-Rural Development in 2004, sea sand must be processed before it is used to make reinforced concrete to ensure it contains less than 0.06 percent chloride ion.

Global Times