| China has a vast territory,complex climate distribution and a wide range of temperature and humidity changes.The average annual temperature in the western region is about 14°C,while the average atmospheric relative humidity is below 40%,so it is in a low-temperature and low-humidity environment.The annual average temperature in the southern coastal areas is above 24℃,while the average atmospheric relative humidity is above 80%,so it is in a high-temperature and high-humidity environment.There are significant differences in climate environment among different areas.There are temperature and humidity gradients inside and outside concrete buildings serving in different atmospheric temperature and humidity environments.Under the combined action of temperature gradient and humidity gradient,concrete will absorb water vapor in the atmospheric environment.The evolution of micro-pore structure and moisture content of concrete caused in the process of heat transfer and humidity transfer will have a comprehensive impact on the macro-mechanical properties of concrete,resulting in differences in physical and mechanical properties of concrete in different atmospheric temperature and humidity environments.Moisture transfer and heat transfer of concrete is a complicated and slow process,which often takes months or even longer to reach equilibrium.When concrete has not reached equilibrium under certain atmospheric temperature and humidity conditions,atmospheric temperature and humidity conditions have changed,and concrete is in a continuous process of temperature and humidity diffusion,and will not be in a stable state for a long time,that is,the evolution of physical and mechanical properties of concrete under different atmospheric temperature and humidity conditions is the cumulative effect of the continuous diffusion of temperature and humidity.Therefore,systematic research on the influence law of different atmospheric temperature and humidity conditions on the physical and mechanical properties of concrete before moisture absorption equilibrium has a certain supporting significance for the catastrophic evolution and safety evaluation of concrete structures serving in atmospheric environment.The following conclusions were obtained in this paper:(1)The water vapor adsorption experiments of C30 concrete under different constant temperature and humidity conditions of four atmospheric temperatures of 20,40,50,60°C and four atmospheric relative humidities of 30,60,90,98% were carried out,the results showed that the moisture content of concrete increased rapidly within 5 hours in the early stage of adsorption,and became gentle with the extension of adsorption time.The higher the temperature,the greater the relative humidity,the greater the increase of moisture content of concrete and the higher the moisture content of concrete.The higher the temperature,the greater the relative humidity,and the shorter the time it took for concrete to reach the same moisture content.Under different coupling effects of temperature and humidity,the maximum moisture content of concrete was 1.53%,and the occurrence conditions were that the temperature was 60°C and the relative humidity was 98%.The minimum moisture content of concrete was 0.09%,and the occurrence conditions were that the temperature was 20°C and the relative humidity was 30%.Under different constant temperature and humidity environment,the temperature has the most significant effect on the moisture content of concrete,followed by the relative humidity.(2)The mechanical properties experiments of C30 concrete under different constant temperature and humidity conditions of four atmospheric temperature 20,40,50,60°C and four atmospheric relative humidity 30,60,90,98% were carried out,the results showed that when the temperature was lower than 40°C,the higher the temperature and the greater the relative humidity,the lower the compressive strength and splitting and tensile strength of concrete.When the temperature was higher than 40°C,the higher the temperature and the lower the relative humidity,the greater the compressive strength and splitting tensile strength of concrete.The maximum loss rates of compressive strength and splitting tensile strength of concrete under different temperature and humidity conditions were 32.19% and 31.63%,respectively.The occurrence conditions were that the temperature was 40°C and the relative humidity was 98%.The high temperature and low humidity environment is the most favorable for compressive strength and splitting tensile strength of concrete.Under different constant temperature and humidity environments,the relative humidity has the most significant influence on the compressive strength and splitting tensile strength of concrete,followed by the temperature.With the increase of relative humidity,the peak compressive strain of concrete increases and the peak tensile strain decreases.With the increase of temperature,the peak compressive strain of concrete increases first and then decreases,while the peak tensile strain decreases first and then increases,and the temperature of 40°C is the turning point.(3)The experiments on the evolution law of moisture content of C30 concrete under two constant atmospheric relative humidity of 60% and 90% and three cyclic temperature difference of 20,30,40°C were carried out,the results showed that when the relative humidity was constant,the moisture content of concrete increased with the increase of cycle times,and gradually tended to be flat,with a large increase in 100 cycles.Under the condition of relative humidity of 60%,the moisture content of concrete increases with the increase of temperature difference,and the increase rate decreases.Under the condition of relative humidity of 90%,the moisture content of concrete decreases with the increase of temperature difference,and the decrease rate increases.The relative humidity has the most significant effect on moisture content of concrete under different temperature difference cycles,followed by cycle times,and the effect of temperature difference is the weakest.(4)The mechanical properties experiments of C30 concrete under the conditions of two constant atmospheric relative humidity of 60% and 90% and three cyclic temperature difference of 20,30,40°C were carried out,the results showed that when the relative humidity was constant,the compressive strength and splitting tensile strengths of concrete all decreased with the increase of cyclic times,and the decrease was significant in 100 cycles.The compressive strength and splitting tensile strength of concrete decrease with the increase of temperature difference.The maximum loss rate of compressive strength of concrete under different temperature difference cycles was43.14%,which occurred when the temperature difference was 40°C,the cyclic times were 400 times and the relative humidity was 60%.The maximum loss rate of splitting tensile strength of concrete was 32.90%,which occurred when the temperature difference was 40°C,the cycle times were 400 times and the relative humidity was 90%.Under the action of different temperature difference cycles,the temperature difference has the most significant effect on the compressive strength of concrete,and the relative humidity has the most significant effect on the splitting tensile strength of concrete.The peak compressive strains and peak tensile strains of concrete increase with the increase of cycle times. |
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