Introduction: Volumetric changes caused by shrinkage lead to cracking in concrete. The strength of concrete, especially in tension, largely depends on its ability to exhibit shrinkage deformations. Compensated shrinkage deformations increase resistance to crack formation. This also results in increased resistance in various environments. The aim of this work was to develop effective methods to minimize shrinkage cracking in concrete. This is achieved by creating a shrinkage-free structure and controlling the processes of formation of the structural framework during the initial period of hydration and hardening of the cement. Materials and methods. During the research, Portland cement CEM I-42.5 and a composite binder with sulfoaluminoferrite cement (CB) were used. Autogenous shrinkage was studied on prism samples measuring 40×40×160 mm during hardening under conditions that prevent moisture evaporation from the concrete. The total shrinkage deformation, e×10-6, was determined by summing the autogenous and moisture shrinkage. The deformation of the samples was determined according to GOST 18833. Electron microscopy was used to evaluate the structure of the hardened cement paste. X-ray diffraction analysis was used to determine the phase composition of the hardened cement paste. Identification of minerals was carried out using data from the ICDD (International Centre for Diffraction Data) database. Results. The types and mechanisms of shrinkage deformation in cement concrete and the most effective methods for combating shrinkage cracking are examined. Shrinkage compensation by using expanding additives is described as one of the effective measures. The kinetics and periods of structure formation in plastic cement paste in non-additive Portland cement and composite binder were determined. Experimental studies have shown that the total shrinkage deformation of Portland cement samples at the age of 90 days reaches 515×10-6. The autogenous shrinkage deformation is 60% (309×10-6). The total shrinkage deformation of the CB samples is 410×10-6, the share of autogenous shrinkage deformations is 22%. Conclusions. Effective method for minimizing shrinkage cracking in concrete can be achieved by creating a shrinkage-free structure. This structure is formed by a strong crystalline framework of newly formed crystal hydrates during the hardening of sulfoaluminoferrite cement. The use of composite binders in concrete can ensure the production of low-defect, reliable and durable building structures made of concrete and reinforced concrete.
Самченко et al. (Fri,) studied this question.