News: concrete made with unprocessed sea sand has been found in at least 15 buildings under construction in Shenzhen – including what will be China's tallest building when completed – putting them at risk of collapse.

An industry-wide investigation made public last week discovered that 15 buildings in the city were partly constructed from concrete made with sea sand instead of river sand, including the 660-metre-high Ping’an International Finance Center, expected to be the second tallest building in the world.

While cheap sea sand offers cost-saving opportunities for contractors, the salt and chloride present in it can corrode steel reinforcements over time and ultimately cause a building to collapse.

The Shenzhen Housing and Construction Bureau found that 31 companies had violated industry rules and ordered eight of them to suspend business for one year in the city, Bloomberg reported.

Construction has now been halted on Ping'an International Finance Center, which was designed by US firm Kohn Pedersen Fox and has been under construction since 2009.

Like many Chinese cities, Shenzhen is undergoing a frenzy of construction activity, with architects including OMA and Mecanoo working in the city.

OMA recently won a competition to design a financial office tower, the firm's second building in the city after the Shenzhen Stock Exchange. Mecanoo are woking on a cultural complex in the Longgang district, while the Futian District - an area that's larger than Manhattan - is being redesigned by SWA Group to create pedestrian areas and green spaces.

See all our stories about architecture and design in China.

Image is by Kohn Pedersen Fox.