[Poor Construction 'Out'] ② The Temptation of 'Diluted Concrete' and Threatened Safety

No Legal Binding for Standard Specifications
Differences in Structural Concrete Quality Also Occur

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 a disconnect between the regulations set by the state and what actually happens on-site. Over three installments, we will examine the current issues and suggest alternatives to what must be improved to ensure the safety of construction structures.

"If you add water, less material is used, and if it's too stiff, it's hard to mix, but if it's less stiff, it's easier to mix and more convenient to work with, so there is a strong temptation to do so."

An industry insider in construction spoke about the so-called ‘watered-down concrete’ issue in this way. Construction companies generally order ready-mixed concrete (Remicon) with a slump of 150 mm, which is a measure of workability. Slump measures the consistency of unset concrete to check its workability. The problem is that a 150 mm slump is difficult to work with, so construction companies demand a slump of 180 mm or more. However, since the increased cost is not reflected, water is often added beyond the standard to meet the slump requirement.

The concrete unit water content inspection checks whether the amount of water used per 1㎥ of concrete exceeds the set standard during manufacturing. The problem arises when low-quality aggregates absorb water, making it impossible to achieve the required workability with the set standard, leading to additional water being added at the production plant or on-site.

‘Watered-down concrete’ causes cracks and strength reduction in concrete, seriously affecting the durability of structures. In January last year, one of the causes of the collapse accident at Gwangju Hwajeong I-Park apartment was identified as quality deficiencies, including reduced concrete strength.

Last July, workers were carrying out demolition work on the rooftop of Building 101 at Hwajeong I-Park in Seo-gu, Gwangju.
[Photo by Yonhap News]

The standard specifications that set the standards and regulations for concrete work are ineffective. The government established unit water content inspection standards and announced the revised standard specifications on September 1 last year, which came into effect on December 1 of the same year. However, since construction companies are not legally bound to follow the standard specifications, voices are emerging that it is insufficient to prevent the distribution of low-quality concrete.

Another problem revealed at some construction sites is the difference in quality between the ready-mixed concrete brought to the site and the structural concrete. To ensure the stability of structures, the compressive strength of structural concrete must meet or exceed the quality standard strength, but it is known that on-site, only the compressive strength of Remicon test specimens under laboratory conditions has been evaluated. Considering the quality of domestic raw materials, environmental conditions, and deviations occurring during construction, the compressive strength of structural concrete inevitably differs from the quality inspection results conducted when Remicon is delivered to the site.

Once the ‘Development of On-site Curing Test Specimen Evaluation Standards for Securing Quality at Concrete Construction Sites’ research conducted by the National Construction Standards Center is completed, the related standard specifications are expected to be revised. However, the industry argues that since the standard specifications are not mandatory provisions, it is necessary to enforce compliance through related laws such as the Construction Technology Promotion Act’s subordinate regulations, the Construction Work Quality Management Guidelines, and the Building Act.

This content was produced with the assistance of AI translation services.