Problems of operational reliability of monolithic buildings and structures in case of non-compliance with the requirements of sequential concreting

Abstract

Operational and structural reliability is the most important criterion for the life cycle of monolithic buildings and structures.

One of the most important processes in the construction of a building is the sequential concreting of structures. In fact, the construction of a building is carried out gradually; therefore, at the joints of structures, there are zones where, during the technological process, breaks in concreting are performed, which leads to the appearance of a thin layer of cement film, which does not meet the technical characteristics of concrete and must be removed before laying the concrete mixture of the next layer. Unfortunately, as practice shows, builders do not always comply with these requirements, which can lead to accidents.

The article presents real cases of such situations in construction.

At one of the construction sites, an inspection was conducted of the structures prepared for closing the formwork and subsequent concreting. It was noted that the previous cement surface of the floor slab was not cleaned properly, and grease, which is used to lubricate the formwork, had leaked onto the surface of the slab. In another case, the technical engineer recorded a situation where the previous cement surface was not cleaned off the objects, and construction dirt and spots remained. For another example, the concreting of columns at one of the sites was suspended, and the formwork was opened. Many welding residues were found on the concrete surface in the column area and other defects. In all other cases, after placing the concrete mix in the structure and its hardening, we cannot speak about the integrity of the concrete. Therefore, design and calculation models do not work.

What are the consequences of such deviations from the design? As practice has shown, over time, this can lead to an accident or become part of the reason why an accident occurred. As an example, we can consider the situation that happened in the year 2023 at one of the boiler houses in the city of Odessa.  After examining the destroyed parts and the corresponding reports, it was noted that the destruction occurred clearly along the concreting seams. The destroyed part of the chimney was divided into blocks, each of which is limited by these seams. As the examination showed, the accident occurred for several reasons, but one of them was the lack of a competent organization of the concreting seam.

Therefore, when carrying out concrete work, it is important to ensure that there are no interruptions during concrete pouring and to ensure that the control over the breakdown of the work is carefully explained to engineers and workers, as well as the importance of surface preparation during concrete pouring.