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Objectives. The aim of this study was to identify variation patterns of the in-series variation coefficient of adhesive strength to base and the dependency of the frost resistance coefficient on the criterion of adhesion on prescription factors of fine-grained concrete obtained from dry building mixtures based on various Portland cements containing various low-modulus inclusions and redispersible polymer powders from 0 to 3%. According to GOST 31357, the main quality indicators of the hardened mixture or fine-grained concrete, in addition to frost resistance, include the indicator of “frost resistance of the contact zone”, which characterises the ability of the hardened concrete to maintain adhesion to the base during normal separation following a certain number of freeze-thaw cycles.Method. The tests of the main samples were carried out after 75 freeze-thaw cycles in accordance with GOST 31356. The marks of the frost resistance of the contact zone are set from FKZ25 to FKZ100. The number of freeze-thaw cycles is taken as a mark, after which the adhesion strength to the base, determined according to GOST 31356, is at least 80% of the strength of the control samples. The arithmetical average is taken at between at least 5 values, while the variation coefficient measured across a series of adhesion strength values is not considered.Results. The average values of the variation coefficient of adhesion strength were: following 75 cycles of freezing-thawing – 0.224 (in a range from 0.058 to 0.616); following 25 cycles of freezing-thawing – an average of 0.129 (in a range from 0.016 to 0.352). The variation coefficient of adhesion strength can exceed the variation coefficient of compression strength by approximately 2.5 to 3 times. When introducing the redispersible powders into the structure of fine-grained concrete, there is no unambiguous pattern of change in the values of the variation coefficient of adhesion to base and it is possible to increase or decrease this value, while the values of the variation coefficient of adhesion can vary by an order of magnitude.Conclusion. For all concretes, there is a tendency of increase of the coefficient of frost resistance with a decrease in the adhesion variation coefficient both after hardening under normal conditions as well as during cyclic freezing and thawing. When conditions VF/V28A<1 are met, the coefficient of frost resistance of adhesion, determined when considering the variation coefficient, will satisfy the requirements of GOST 31356.

This paper shows the results of experiments to study the effect of the auxiliary voltage with frequency fi= 40000Hz on the stability of arc discharge at the limit mode of the welding process with single, coated electrodes. This effective method of connecting rolled and prefabricated elements of metal structures has found widespread use in their installation, manufacture and repair in the construction of various facilities: industrial and civil purposes, thermal and nuclear power facilities for responsible purposes. In this regard, the increase in the quality and technological, strength parameters of welds, the productivity of the manufacturing metal structure process, is largely associated with welding modes and an increase in the stability of arc discharge as an important element of the system: "power source-arc-welding tub-product." Improving the performance of the welding process under consideration is particularly important under mounting conditions in conjunction with its stability is an important task on the agenda. When performing the study, the following criteria and their values   regarding the stability of the welding arc were taken into account, such as: lexpl - rupture length in mm, coefficients of variation: KV(Iwd) - welding current, KV(Uwd) - voltage, qt - constant time, as well as their numerical values were obtained. The obtained numerical values of the above criteria were obtained based on the analysis of graphs (oscillograms) of the dependence of the electric current (Iwd, A) and the voltage (Uwd, V) of the arc on the time of the process duration (t, sec). The obtained results of the analysis indicate an increase in stability, a decrease in inertia of the deviation of the resistance (conductivity) of the welding arc when the auxiliary voltage is applied with a frequency of fi = 40000Hz at the limit mode of welding with coated electrodes.