In a recent report, it was revealed that the excessive presence of chloride ions in sea sand poses a serious threat to the structural integrity of buildings. The use of such "dangerous sea sand" has become widespread in Shenzhen, raising concerns about the safety and durability of construction projects.
According to investigations, the use of sea sand in construction is no longer a secret but rather an unspoken rule within the industry. Despite regulations introduced as early as 2004, substandard sea sand continues to find its way onto construction sites, often going undetected until media exposure brings attention to the issue. This indicates a gap between policy and enforcement.
Han Ningxu, an academic consultant at the Guangdong Provincial Key Laboratory for Coastal Civil Engineering Durability, explained that the corrosion of steel reinforcement in concrete is directly related to the level of chloride ions present. When sea sand with high chloride content is used, it accelerates the degradation of structures, significantly reducing their lifespan.
The problem is not isolated. In 2007, Jintan Garden in Fujian used illegal sea sand; by 2011, the Shenzhen Blue Sea Resort had already become a dangerous building after just 20 years of use. In 2012, multiple real estate projects in Foshan were found to be using sea sand illegally. These incidents highlight a growing trend that has yet to be effectively addressed.
The Ministry of Construction issued guidelines in 2004, clearly stating that sea sand must be desalinated before use in construction. It also emphasized that public or high-rise buildings should avoid using sea sand altogether. For reinforced concrete, the chloride ion content must not exceed 0.06%, while prestressed concrete should not use sea sand at all—unless it is thoroughly rinsed and meets a stricter limit of 0.02%.
Despite these rules, the use of sea sand has increased due to the declining availability of river sand. Hu Jianwen, deputy director of the Shenzhen Housing and Construction Bureau, acknowledged that the use of sea sand is now an "objective reality." However, the challenge lies in ensuring that it is properly treated and monitored.
Industry insiders agree that desalinated sea sand is the only safe option, yet nearly 10% of sand samples on the market still contain excessive chloride ions. One construction site manager revealed that some mixing stations blend unsalted sea sand with low-chloride materials to cut costs, despite strict regulations against on-site mixing of concrete.
Currently, inspections focus mainly on compressive strength, not chloride content. Liu Nanyuan, director of the Shenzhen Engineering Quality Inspection Center, noted that chloride ion testing is not a mandatory requirement under national standards. As a result, monitoring efforts are reactive rather than proactive.
This has led to a troubling situation where sand suppliers manipulate inspections, using qualified sand during checks and substandard sand otherwise. While surprise inspections have a higher failure rate (9.7%), routine checks show a lower rate (3.9%).
Experts argue that the lack of consistent and comprehensive oversight puts public safety at risk. With sea sand becoming more common, stronger regulatory measures are urgently needed to ensure that desalination and quality control processes are strictly followed. Only then can the risks associated with "dangerous buildings" be truly minimized.
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