[Poor Construction 'Out'] ① The Vicious Cycle of Inferior Aggregate - Poor Construction - Safety Threats

Issues such as Selected Crushed Aggregate and Opaque Distribution Structure
Calls for Transparency in Distribution and Strengthened Quality Inspection Emerge

Editor's NoteBehind the repeated issues of structural safety and quality problems at recent construction sites lies the problem of concrete quality. Concrete must adhere strictly to specified standards, but there is currently a mismatch between the regulations set by the government and what actually happens on-site. Over three installments, we will examine the current problems and suggest alternatives to what must be improved to ensure the safety of construction structures.

GS Construction's apartment construction site in Geomdan New Town, photographed on July 6. The area where the accident occurred in April is covered.
[Photo by Yonhap News]

The common factors in recent collapse accidents at construction sites are the omission of rebar during design and construction processes and insufficient concrete strength compared to standards. Concrete, made by mixing cement with aggregates such as sand or gravel and water, is one of the most significant building materials in modern architecture. Quality control is crucial as it directly affects the safety of citizens' lives and property.

If inappropriate materials are chosen or errors occur in design and construction, the strength and durability of concrete deteriorate. It is essential to comply with established laws, design standards, standard specifications, and codes (specifications). However, every time an accident occurs, patchwork solutions and stopgap measures are applied, leading to negligence in quality control at construction sites. Urgent measures are needed to eradicate poor construction practices at construction sites.

According to the report "Suggestions for Improving the Quality of Construction Structures for Public Safety" prepared by the Korea Aggregates Industry Research Institute on the 12th, domestic construction sites face complex issues such as △selected crushed aggregates △opaque distribution structures △poor domestic aggregate supply conditions △watered-down concrete △inadequate strength evaluation. First, selected crushed aggregates, which are by-products generated during rock excavation, account for a high proportion. According to the "2023 Aggregate Supply Plan" announced by the Ministry of Land, Infrastructure and Transport last year, the supply of selected crushed aggregates has been steadily increasing due to the reduction in sea sand extraction. In the metropolitan area, the supply proportion exceeds about 80%.

Selected crushed aggregates have the problem of containing a high amount of soil components (clay) included in the aggregates. On-site, they are scooped up without removing the soil. This is known to cause about a 30-40% reduction in strength compared to concrete made with high-quality aggregates. The continuous influx of low-quality aggregates into the market is also problematic. Aggregates that have passed quality inspections under the Aggregate Mining Act have no separate regulations regarding delivery documents, making it difficult to know where the aggregates were produced, who sells or transports them, and related information if falsified. Although the Korean Industrial Standards (KS) certification provides a standardized delivery document format, the industry explains that obtaining and maintaining KS certification is difficult. Among more than 1,400 companies, only 14 had KS certification as of June.

Low-quality recycled aggregates also undermine construction quality. Recycled aggregates are made by physically and chemically reprocessing construction waste for reuse. Due to a shortage of aggregate sources and difficulties in extracting marine aggregates, the use of recycled aggregates is increasing amid poor aggregate supply conditions. Low-quality recycled aggregates are distributed at about half the price of general aggregates. In fact, according to data received by Assemblyman Kim Byung-gi of the Democratic Party from the Ministry of Land, Infrastructure and Transport and the Korea Land and Housing Corporation (LH), poor aggregates such as brick fragments and weathered rock were used in the concrete of the apartment in Geomdan, Incheon, where a collapse accident occurred in April, causing concrete defects. Assemblyman Kim's office explained, "The detailed safety inspection report commissioned by LH to the Architectural Institute of Korea cited poor concrete compaction and the use of poor aggregates as the main causes of insufficient concrete strength," adding, "Poor aggregates are the cause of the lack of concrete strength."

Concrete at the apartment in Geomdan, Incheon, where a collapse accident occurred last April
[Photo by Kim Byung-gi, Office of the Democratic Party of Korea]

The industry's solution is to make the aggregate distribution structure transparent. When supplying or selling aggregates, it should be mandatory to submit a delivery document to users as stipulated by the Ministry of Land, Infrastructure and Transport. The standard delivery document format clearly indicates the origin of the aggregate source, quality markings, producer, and seller to transparently disclose the entire distribution process. This is expected to prevent the distribution of poor aggregates.

Strengthening aggregate quality inspection and management is also necessary. Aggregate quality inspections are divided into regular inspections conducted once a year and irregular inspections conducted unexpectedly. However, since regular inspections require prior notice of the date, reason, and content at least seven days in advance, there is concern about misuse by preparing in advance, so increasing irregular inspections is recommended. Considering that irregular inspections cost about 1 to 1.5 million KRW, government support should also be expanded. There is also a claim that recycled aggregates should be subject to regular and irregular quality inspections by specialized aggregate quality management institutions, just like general aggregates. An industry official said, "There are no irregular inspections for recycled aggregates," adding, "Applying the same standards to recycled aggregates as general aggregates would enable systematic quality management."