| Nowadays, the concrete has become the biggest amount and the most widely used materials because of its superior plasticity, good permeability, excellent fire resistance, and the most competitive economy. But with the large-scale construction in developing countries, the use of concrete and concrete structure is increasing year after year, and the engineering accidents related to the shrinkage cracking of concrete cracks is also growing rapidly. Eventually, the durability of concrete structures and the service life will decline result from increasing permeability which was cause by cracked concrete in the realistic use under the condition of the long-term external environment (season or day and night temperature and humidity changes). The changing of temperature and humidity by day and night or seasonal can be described by the changing of cyclical temperature and humidity. Consideration should be given to the function of hygro-thermal and the "equivalent to effects of fatigue" when make a study of the volume deformation in concrete. The paper focuses on the experimental research on the hygro-thermal deformation in concrete and the study of "Equivalent to effects of fatigue" under cyclical temperature and humidity.First of all, experiment was carried out on the distribution of temperature and humidity and volume deformation inside the concrete under the condition of the natural environment and the constant and cyclical temperature and humidity. The results show that, under the condition of constant temperature and humidity, the concrete shrinkage rate in early age about 1 d to 10d of different water-cement ratio have the same change trend, and the early age concrete of water-cement ratio of 0.4 has the largest shrinkage strain. Under the condition of natural environment, the early age concrete shrinkage deformation of 0.5 water-cement ratio are greatly influenced by the environment, and appears the alternate changing along with the growth of the age. The temperature in the boundary location of concrete is lower than the middle in the same depth, and the temperature in the bottom of concrete is lower than the surface in different depth. Under the conditions of cyclical temperature and humidity, The concrete of different water-cement ratio after curing 28d, which volume deformation has alternative change as the cyclical temperature and humidity change, and the change is gradually narrowed as the growth of the age, and gradually stabilized. In general, the concrete of low water cement ratio has expansion deformation under the condition of cyclical temperature and humidity, while other groups exist shrinkage deformation.The high temperature and low humidity has great influence on the shrinkage deformation in concrete of low water-cement ratio, and the swelling of deformation of low water cement ratio of concrete is bigger at high temperature and low humidity.According to the characteristics of porous media, the wet and heat transfer mechanism and fatigue damage mechanism, and combined with the experimental results, the volume change and the "Equivalent to effects of fatigue" of concrete material under the action of cyclic temperature and humidity was analyzed. The results show that the temperature and humidity inside the concrete is interaction and mutual influenced, embodying in the hygro-thermal effect of concrete, and it determines the development of concrete volume deformation. By the size of the stress level can indirectly reflect the damage degree of concrete under the action of cyclic temperature and humidity, and cyclical temperature and humidity can be equivalent to the fatigue load, and the concrete structure produced damage strain in its internal under the conditions of cyclical temperature and humidity. When the damage accumulate to a certain degree, the crack growth is changing from stable stage gradually transition to the unstable crack extension stage, and then quickly achieve the ultimate strain of concrete and crack to failure. |
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