Shenzhen's "Sand Dangerous Building" Tracking Rules

Recently, the media reported that excessive chloride ions in sea sand will seriously corrode the steel bars in the building and even collapse. This kind of “sea sand dangerous building” abounds in Shenzhen.

The reporter’s investigation found that building buildings with sea sand was no longer a secret, but a “hidden rule.” The relevant regulations were introduced as early as 2004, and substandard sea sands flowed into construction sites and were repeatedly exposed by the media. Related supervision has not kept up with the delay.

According to Han Ningxu, general academic consultant of the Key Laboratory of Durability of Coastal Civil Engineering in Guangdong Province who has regulations, cases, and non-mandatory tests, the degree of steel corrosion depends on the chloride ion content of the concrete, and the sea-sand exceeding the standard of chloride is mixed into the concrete. Corrosion promotes and reduces the service life of buildings.

In fact, the inflow of substandard sea sand into the construction site is not a single case. In 2007, Jintan Garden in Pingtan County, Fujian Province used sea sand illegally; in 2011, the construction of the Shenzhen Blue Sea Resort in Shatoujiao turned into a dangerous building due to the use of sea sand for only 20 years; in December 2012, Foshan’s Expo Garden Four other real estate projects under construction were found to be suspected of illegal use of excessive sea sand...

As early as in 2004, the “Opinions of the Ministry of Construction on the Management of Strict Architectural Sea Sand Management” clearly stated that some coastal cities used sea sand to mix concrete and mortar in the construction activities, which led to the appearance of chloride ions in construction projects. The corrosion situation reduces the durability of the project and brings hidden dangers to the project quality.

The opinion clearly stated: "The sea sand used in the construction project must be specially treated desalinated sea sand. Public buildings or high-rise buildings should not use sea sand." "For reinforced concrete, the chloride ion content in sea sand should not exceed 0.06%. For the prestressed concrete, sea sand should not be used. If it is necessary to use sea sand, it should be rinsed with fresh water and its chloride ion content should not exceed 0.02%."

It is understood that the use of sea sand in construction projects is becoming increasingly common due to the reduction in river sand resources. Hu Jianwen, deputy director of the Shenzhen Municipal Housing and Construction Bureau, said: “The use of sea sand is an objective reality.” Zu Lihong, deputy director of the Department of Energy Conservation Technology and Building Materials of the Shenzhen Municipal Housing and Construction Bureau, said that at present, the Shenzhen market is on river sand. The proportion is indeed small.

The reporter found that at present, it is a consensus within the industry that construction projects cannot use desalinated sea sand. However, why is there still nearly 10% of excessive chloride ions in the market?

The reporter visited the construction site and found that when ready-mixed concrete enters the construction site, although the quality of the test block is also tested, only the intensity is detected, and the indicator of chlorine ion is not included.

A person in charge of a construction site in Shenzhen told the reporter that because the concrete is made of various materials such as sand, some concrete mixing stations will use the other materials with low chloride content to mix the unsweetened sea sand, thereby reducing the purchase. Sand cost. According to regulations, it is forbidden to mix concrete and mortar on the construction site, and ready-mixed concrete must be used. “The inspection should not be detected when entering the mixing station. It means that the construction party’s control over the material quality has been weakened, and the government’s monitoring has not been strengthened accordingly. So a Worrying regulatory weaknesses."

Some people checked to enter the qualified sand, no one checks to enter the unqualified date, while notifying the construction of the sand ion content of surprise sampling failure rate of 9.7% at the same time, Shenzhen City Housing and Construction Bureau also announced another set of data: For the whole year of 2012, the sampling failure rate of routine construction sand was 3.9%.

Why is the gap so great? Liu Nanyuan, director of the Shenzhen City Construction Engineering Quality Inspection Center, explained: “In the event of a surprise inspection, the general proportion of inspections is higher. When routine inspections are conducted, they may do a better job.”

Liu Nanyuan also said that the current chlorine ion is not a mandatory test item. He said that in accordance with national standards, there is no provision for the use of the unit must be tested for chloride ions. Therefore, the monitoring department only inspects the mixing station and the construction site when there is doubt. "Now we will conduct routine inspections once every quarter. We will conduct spot checks once again for those who have questions or suspicions."

Originally, the time and routines of routine inspections have long been solved by concrete mixing stations: When the relevant departments come to inspect, they enter the qualified sand; when no one checks them, they enter unqualified sand.

The industry believes that in the increasingly common situation of the use of sea sand, the relevant departments urgently need to strengthen the supervision of the sea sand desalination process and circulation process, and must not allow the failure rate to remain at a high level, increasing the safety risk of the building.