Fundamental Study on Development of Methods for Evaluating Frost Damage Performance of Concrete

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The main purpose of the present study is to make a model for describing the mechanism to cause the frost damage of concrete. In this study, a theoretical model was developed on the basis of thermodynamics by taking into consideration the microstructure of hardened cement paste. The predicted results were proved by a series of experimental study in which the deformation was measured for mortar specimens with different levels of water content. It was shown that the deformation behavior of mortar under low temperatures was influenced very much not only by the temperatures but by the water content and the microstructure.In the meanwhile, the temperature and moisture conditions in concrete was also experimentally studied as a fuction of the climatic environmental conditions. Three sets of a group of concrete specimens were exposed in the air on the roof of a first story building and one of them was covered with a plastic roof for avoiding rain and snow. Each set of concrete specimens of the … More same mix proportions (w/c=0.45 or 0.65) was composed of nine prisms of 10Ox10Ox40O(mm). Temperatures were measured at two points on each surface of four prisms facing to north, south, east and west directions. Temperatures in concrete were also measured at three points in the prism located in the central position among nine prisms. The depths of measuring points in the central position were 10, 100 and 200 mm from the top surface. Then the temperature in concrete was analyzed as a funtion of the climatic environmental conditions to formulate empirical formulae. As a result, the highest temperature was described as a linear fuction of the highest air temperature, the mean wind speed during daytime and the total solar radiation while the lowest temperature was given as a fuction of the lowest air temperature, the mean wind speed during night and the fine-weather index. The highest and lowest tempeeratures were also varied by the direction, the mixproportion and the existence of the roof.On the basis of the empirical formulae, the number of freeze and thawing cycles in representative cities in Japan was calculated and the risk of the frost damage of concrete structures was analysed. Less