Investigation of the Factors Influencing the Effectiveness of Fine-Grained Self-Compacting Concrete with Crushed Concrete Sand

Introduction. The justified use of mineral raw materials from construction waste for the preparation of vibro-compacted concrete mixtures is economically beneficial and environmentally efficient, however, the effect of aggregates from scrap concrete on the rheological characteristics of fine-grained self-compacting mixtures and the structure of hardened concrete has not been sufficiently studied. The aim of this work is to study the factors influencing the effectiveness of fine–grained self-compacting concrete with crushed concrete sand. Materials and Methods. To determine the effectiveness of the compositions of fine-grained self-compacting concretes, mixtures of equal workability of the PK1 grade were prepared on Portland cement CEM0 52.5N. Sand from crushed concrete was introduced into the fine natural sand of local quarries as a reinforcing component. Polyplast PC, a polycarboxylate superplasticizer, was used to give the mixtures the required fluidity and self–compacting properties. The evaluation of the grain composition of the fine aggregate was carried out by changing the grain size modulus in accordance with the standard methodology. Rheological and technological characteristics of self-sealing concrete mixtures were established according to the methods of GOST R 59715-2022. Crack resistance of fine-grained self-compacting concrete was assessed by a coefficient reflecting the ratio of strength characteristics of concrete. Results. Throughout the course of the research, it was found that, provided a highly stable concrete mixture is obtained, the optimal structure of fine-grained concrete is achieved with a content of 30% crushed concrete grains in the fine aggregate and a dosage of polycarboxylate superplasticizer Polyplast PC – 1%. Discussion and Conclusion. The technical efficiency of fine-grained self-compacting concrete using coarsening sand grains from crushed concrete is substantiated. By optimizing the formulation factors of fine-grained concrete with aggregate from construction waste and using vibration-free technology of monolithic reinforced concrete structures made of self-compacting mixtures, an economic effect is ensured.