hankyoreh

Rebar and other rubble hang from the side of the partially collapsed outer wall of an apartment building under construction in western Gwangju’s Seo District on Wednesday. (Shin So-young/The Hankyoreh)

After 14 stories of an apartment building under construction in the Hwajeong neighborhood of Gwangju partially collapsed, experts say pushing ahead with concrete placement despite freezing winter temperatures may have caused the facade to crumble. Though cranes halted operations on the day of the accident due to strong winds, concrete placement was confirmed to have continued despite sub-zero temperatures.

According to a guideline on the quality control of concrete structures built during winter released Wednesday by the Ministry of Land, Infrastructure and Transport, insulation and heating should precede concrete placement during weather conditions in which the day’s average temperature is 4 degrees Celsius or below. The guideline ensures that the poured concrete reaches a compressive strength of 4 MPa or more, after which it should be hardened and cured for two days at a temperature of 0 degrees Celsius or above so that it doesn’t freeze over. At the time of the accident, the temperature in the area was 2.2 degrees Celsius below zero.

HDC Hyundai Development Co., the company in charge of the construction, said had it submitted a written plan detailing its quality control scheme for the winter construction of concrete structures to Gwangju’s Seo District Office, which has jurisdiction over the Hwajeong neighborhood. In practice, however, many construction sites operating over the winter months of December through February are known to not properly ensure insulation and heating during concrete placement.

Park Jeong-gyu, a 48-year-old construction worker who operated a crane at the construction site until five hours before the accident, said during a phone call with the Hankyoreh, “I started working at 8 am and at 10:30 am told HDC Hyundai Development that strong winds prevented me from working and stopped the crane.”

“[But then,] I heard that ready-mixed concrete would be arriving at the site at 10 am and that concrete placement for the flooring at the 39th level was 90% complete right before the accident,” he continued. “I’ve been in this line of work for 20 years but have never heard of nor seen this kind of accident, so I don’t understand why it happened.”

Ahn Hong-seob, a professor of architectural engineering at Kunsan National University, explained, “In order for concrete to set at a normal strength level, it has to spend a certain amount of time at room temperature. In low temperatures, concrete fails to attain sufficient strength even after a lot of time has passed. In terms of the recent accident, it’s possible that the underlying layer of concrete supporting the newly poured layer of concrete was not strong enough, buckling under the weight of the upper layer due to reasons such as strong winds.”

Choe Myeong-ki, a professor of civil engineering at Dongshin University, said, “The accident may have happened because the formwork being used on the 38th floor collapsed under the weight of the new concrete placement above or because the construction was pushed ahead in order to save time despite the concrete not having hardened enough due to winter weather conditions.”

However, HDC denied these possibilities, saying, “The construction was moving ahead of schedule, so there was no need to forcibly push for further time-saving.” It also said, “The concrete placement [for the building that collapsed] was cured for 12 to 18 days, achieving the necessary strength level.”

Ultimately, finding out whether HDC in fact abided by its quality control plan for the winter construction of concrete structures it submitted to the local district office may be the key to solving the puzzle of the tragedy in Gwangju. Moreover, the fact that wall structures that act as pillars of the building also collapsed may suggest poor connection and consolidation between floorings and walls, which may point to additional faulty construction that compounded to cause the exterior wall to crumble.

Meanwhile, investigators with the Gwangju Metropolitan Police obtained search and seizure warrants on Wednesday to investigate the on-site offices of HDC as well as some of its subcontractors.

By Jung Dae-ha, Ahn Kwan-ok, Kim Yong-hee and Shin Da-eun; staff reporters

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