Corrosion-resistant concretes for coastal underground structures

Introduction. The underground structures of the coastal zone in Vietnam are periodically flooded with seawater, which causes corrosion of concrete. Therefore, the aim of the study is to increase the corrosion resistance of coastal underground concrete structures by modifying the structure of concrete with a complex of mineral additives obtained mainly from local raw materials, including micro- and nanosilicon, fly ash from thermal power plants and finely ground white quartz sand. In addition, it requires development of a mathematical model describing the processes of mass transfer in conditions of liquid corrosion of concrete underground structures in coastal zone, to assess their durability. Methods. The development of concrete mixtures, the study of their properties and properties of concrete, were carried out in accordance with the requirements of current Russian and Vietnamese standards. Results and Discussion. The results of experimental studies confirmed the possibility of using local raw materials to create modifying additives and obtain corrosion-resistant concretes with high performance. It was found that with an increase in the content of white quartz sand in the concrete mixture, the compressive strength of concrete increased rapidly at an early age of hardening up to 7 days, after which its growth rate gradually decreased. Replacing 60 % of river sand with white quartz sand provided the highest compressive strength, axial tension and flexural tension of concrete, which can be explained by the fact that white quartz sand is finer than river sand, and this increases the density of the concrete structure. In addition, an increase in the density of concrete can be explained by a decrease in water absorption and an increase in resistance to sulfate corrosion with an increase in the content of white quartz sand in the concrete mixture instead of river sand, as well as with the introduction of 1–1.5 % nanosilicon. Conclusions. For the construction of underground structures in the coastal zone of Vietnam, we developed corrosion-resistant concrete compositions based on local raw materials with high strength characteristics and low water absorption. A mathematical model is proposed to solve the problem of determining the mass transfer of Ca²⁺ ions in the system "concrete structure – moist soil – coastal area" to control the processes of mass transfer during the corrosive destruction of concrete underground structures in coastal zones periodically flooded with seawater, in order to predict their operational durability.