COMPREHENSIVE SOLUTIONS FOR REDUCING SHRINKAGE DEFORMATIONS AND CRACKINGIN CONCRETE SEWER STRUCTURES

The article substantiates the importance of considering shrinkage deformations of concrete as one of the key factors determining the corrosion resistance and durability of sewer structures. It is shown that even when modern polymer and composite protective coatings are used, their effectiveness strongly depends on the condition of the concrete substrate, particularly on the presence of cracks caused by shrinkage processes. Cracks serve as “transit channels” for aggressive media to reach the reinforcement, which leads to accelerated material degradation. Therefore, the control and minimization of concrete shrinkage is a critical task in the design and operation of sewer networks and wastewater treatment facilities. The paper presents the results of experimental studies of concrete specimens of various compositions, produced using local raw materials and modern complex organo-mineral admixtures. A simplified methodology was applied to evaluate shrinkage deformations, developed based on current DSTU, EN, and ASTM standards, which accounts for the conditions of sealed curing, controlled drying, and water saturation. This approach can be adapted to yield data representative of real construction and service conditions by determining the specific curing and environmental parameters of sewer structures. The study results confirmed the significant influence of the water-cement ratio and cement content on the magnitude of shrinkage. For the control mix with higher cement and water consumption, the shrinkage values were the greatest, while optimized mixes with complex admixtures demonstrated a marked reduction in shrinkage deformations. The use of polycarboxylate superplasticizers and air-entraining agents allowed for a reduction in water and cement content by up to 40%, while the inclusion of finely dispersed inert fillers ensured the mixes' homogeneity and stable rheological properties. Polypropylene microfibers were included with the aim of enhancing crack resistance in real structures. An important outcome of the study was the confirmation of the critical role of curing conditions. Shrinkage deformations in specimens cured under sealed, moisture-retaining conditions were several times lower than in those exposed to air-dry environments. Repeated water saturation of concrete samples for 30 days led to a significant reduction in shrinkage deformations. This indicates that prolonged moisture curing at early stages and prevention of premature drying are essential for ensuring the long-term durability of sewer structures. In conclusion, it is demonstrated that the combination of mix design solutions (reduction of cement and water content, application of organo-mineral admixtures and microfibers) with proper curing regimes provides an effective strategy for minimizing shrinkage deformations and preventing crack formation. The outcomes can guide ready-mix producers and designers in improving the reliability and service life of sewer infrastructure.