Some thoughts on concrete

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Some thoughts on concrete

The author is the political news editor of the JoongAng Ilbo.

The essence of concrete is mixing. It is made by properly mixing aggregates such as sand and pebbles as well as concrete and admixture that enhances strength with water. Generally, aggregates such as sand and pebbles make up 70 percent and cement makes up about 30 percent. As sand and pebbles, which can be easily washed away by rain, are mixed with other materials, the mixture magically hardens and becomes as solid as rock.

Concrete has been used since ancient Roman times. In the form of mortar made by mixing lime and sand with water, it was used as an adhesive to keep stones and bricks together. As bricks basically are stacked and bonded with concrete between, it was hard to build structures higher than four or five stories.

A revolution started in the 19th Century. Concrete’s shortcoming is that it cannot withstand pulling or twisting. But after research showed that wire mesh or rebar with tensile strength can reinforce the material, the “reinforced concrete” method was invented. Though rebar also has a weakness to high temperatures and can be easily oxidized, the concrete exterior supplements these features. It was the golden combination of supplementing weaknesses and enhancing strength.

Thanks to the reinforced concrete revolution, landmark structures popped up around the world in the early 20th Century. The most notable is the Empire State Building in New York, built in 1931. Around that time, never-before-seen reinforced concrete buildings were built in Korea, including the Bank of Korea Headquarters in 1912, Seoul Station in 1925 and Seoul City Hall in 1926. They have stood for nearly 100 years now.

Apartment buildings are the typical residential form for Koreans, and they are also built using reinforced concrete. However, rather than lasting 100 years, a building collapsed during construction in Gwangju in January. The accident investigation committee of the Ministry of Land, Infrastructure and Transport announced on Feb. 14 that there had been overall quality issue, such as using substandard concrete mixture by adding water. While it was not mentioned regarding this particular accident, we often saw on the news that some apartments use less rebar than required.

Providing 2.5 million housing units is a core campaign promise of President-elect Yoon Suk-yeol. While post-accident measures such as punishing those responsible for accidents are important, prevention is far more crucial. If structural causes are not addressed, there is no guarantee that “poor concrete” won’t be an issue while building those 2.5 million apartments Yoon promised.

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