The Effect Of Freezing Thawing Cycles On Humidity And Deformation Of Concrete

With the improvement of attention on concrete durability, people realize that humidity had a great influence on the durability of concrete. There are a lot of researches on the effect of humidity on plastic shrinkage, drying shrinkage and autogenous shrinkage of concrete at room temperature, but study on the influences of humidity at freeze-thaw cycle is less. This paper studies the distribution and change of humidity of concrete on the freeze-thaw cycle process, and the influence of humidity on the internal icing, volume, and analyzes the influence mechanism.It is shown that the relationship between temperature and humidity can be divided into four stages, that is freezing-humidifying stage,freezing-dehumidifying stage, thawing-humidifying stage and thawing-dehumidifying stage during freezing and thawing cycle. The internal relative humidity values of conceret cannot return to its initial humidity value in each end of the freeze-thaw cycle, and with the increasing of freeze-thaw cycle times, both the phase change range and figure line of slope also showed a trend of increase.The same regularity can be find in different depth of the specimen, also the different cycles.In the freezing or melting time,we find that the humidity value stay the same while the temperature decline. For same water-cement ratio of concrete specimen, the humidity increases with the distance further from the surface of the specimen, freezes the corresponding humidity value and melting humidity value also increased. For different water-cement ratio of concrete specimen, with the increase of water cement ratio, the humidity value has he same trend like depth increased, freezes the corresponding humidity value and melting humidity also showed a trend of increase.With the action of cycle of freezing and thawing, the freezing temperature of samples is below0℃but about-10℃found in the trials.With the increase of water-cement ratio, the temperature regards the freezing increase also. After join the cement dosage1%cholesterol and silver iodide(AgI), the "degree of under cooling" phenomenon can be partly eliminated by5℃or something like that.The result of mortar sample shows that, with the action of cycle of freezing and thawing, the mortar sample have the regular volume change. Mortar specimens in each volume change curve of the freeze-thaw cycle basic presents the shape of the hysteresis loop back. Its cooling stage computs more closer to the linear change.In the period of temperature increasing,different slope of the volume change curve can be found in the trials. By fitting the deformation curve function of freeze-thaw cycle, we found that in the process of freezing process and the initial melting process it conforms to the linear relationship apparently. But a three times function in the melting process within the temperature range-5～10℃in conformity, resistance has a mutation also, what reveals that in this phase mortar or concrete internal change process is more complicated. Under the action of freeze-thaw cycle, a volume change which is cumulative damage exist in the specimen. With the increase of freeze-thaw cycles times, the irreversible damage cumulative increase and never gets a recover. It is shown that, after25times cycle of freezing and thawing, the average aperture of concrete sample interior, aperture median and the porosity present increasing trend in the mercury injection test. The specimen which has a high relative humidity initialy (namely the higher water-cement ratio specimens), also has a pore structure change more severely under this condition.In this paper, it is concluded that, with the action of cycle of freezing and thawing, the mass of ice forming of the concrete interior, volume change and the change of relative humidity have a certain relevance, the relative humidity is the important factor that affects the durability of concrete.In the different conditions of multi-factor coupling research has its certain necessity, this respect is worth in a follow-up study to dig deeper. The freeze and volume stability inside the conceret caused by the humidity factor can influence the durability of concrete.Further research of that can certainly provide more reference and theoretical basis to improve the durability of conceret.