Evaluation of the frost resistance of concrete under a sign-alternate temperature load

One of the most important characteristics of building materials is their frost resistance. At the same time, the standard method for determining it, based on fixing the number of cycles of alternate freezing and thawing, does not always meet the requirements for the production of building materials, in particular those for the durability of buildings and structures, and has a number of significant drawbacks. A detailed comparison of the results of laboratory tests of concrete frost resistance and service life in real structures does not allow, in the general case, to establish a direct correspondence between them. In this regard, studies devoted to the development of accelerated methods for determining frost resistance are becoming extremely relevant. New methods should eliminate the main difficulty of this problem, which is the discrepancy between the conditions of laboratory studies and the real conditions in which this material is located in the constructions and buildings in operation. To obtain information about the frost resistance of concrete under real operating conditions, a combined conductometric method for independent measurement of the kinetics of moisture diffusion and ice formation in the process of one-sided freezing of samples is proposed. It is shown that in concrete samples that are subjected to one-sided freezing, that is, they are in conditions as close as possible to the actual operating conditions in building structures, intense mass transfer processes take place. The rates of propagation of the front of ice formation and diffusion of moisture and the corresponding depth of freezing of concrete samples depending on the capillary-porous structure and initial storage conditions are established. In general, the conducted studies made it possible to obtain a more reliable picture of the behaviour of concrete under sign-alternating temperature loads and conditions of different initial moisture content (including in hydraulic structures) than is provided for by the current regulatory documents. The rapidity of measurements makes it possible to use the proposed method for assessing the frost resistance of materials with one-sided freezing under real operating conditions and to effectively control the technology for manufacturing building materials with desired properties.