Experimental Study On Behavior Of Concrete Subjected To Freezing-thawing Action Under Given Cryogenic Temperature Range

Concrete is extremely important as the structural material of LNG tanks. Its mechanical properties and deformation characteristics are very critical to engineering safety. In practice, the concrete tank walls can be exposed to cryogenic temperatures. To solve this problem, many scholars started to research the properties of concrete under extremely low temperatures from the 1970 s on. Due to the stock changes in tanks, the heat exchanging between inside and outside, the maintenance needs and the existence of idle period, the concrete walls have to experience the freezing-thawing process between cryogenic temperature and normal temperature or between different cryogenic temperatures. Previous studies mostly focus on the freezing-thawing process in natural environment, which leads to the little research in the freezing-thawing process under cryogenic temperature.To improve the previous studies on the properties of concrete subjected to the freezing-thawing action under cryogenic temperatures, our cryogenic concrete research group starts to conduct a series of experiments to explore the mentioned properties, and this article is just a part of the series.This article focuses on the experiments of concrete specimens which are subjected to the freezing-thawing action between 10 ℃ and-190℃ after wetting and drying.Factors examined include the water content, the number of freezing-thawing cycles, the warmed rate and so on. These experiments also discuss the mechanical properties and deformation characteristics after freezing-thawing process, such as the compressive strength, the elastic modulus, the stress-strain curve and so on. This article particularly includes the thermal expansion of concrete under cryogenic freezing-thawing actions, which is a blank area in previous research.According to above experiments and their results, the water content affects the properties of concrete after cryogenic freezing-thawing process significantly, especially the compressive strength and elastic modulus, which is obvious in the regression formula. The number of freezing-thawing cycles come with the cumulative damage of concrete mesostructure, but it does not alwasys lead to the recession of concrete mechanical behaviors, especially the compressive under cryogenic temperature which often changes reversely. The warmed rate influences the properties of concrete less than the water content and number of cycles, but it can affect the temperature distribution uniformity in concrete specimens and the moisture migration in the pores of concrete. The thermal expansion caused by cryogenic temperature is discrete, because it’s influenced by many different factors. But the most important factor is the number of cycles. The thermal expansion will converge with the increase of cycles.This article introduces the finite element method to simulate the changes of concrete microstructure after cryogenic freezing-thawing process. The key point is the life and death cell technology, which can reflect the cumulation of damage around the pores after some simplifications and assumptions and relate the macro performance degration to the micro structure changes.These experiments and results provide data support for the further research into properties of concrete under cryogenic freezing-thawing process, and make up for the lack of research in related fields to some extent. The conclusions can be used in some practical engineering projects.