Investigation Of Moisture Vapor Transfer Behavior In Asphalt Mortar

The durability of asphalt pavement is susceptible to ambient humidity.Clarifying moisture vapor movement in asphalt pavement is of importance for revealing durability failure mechanism.Transfer behavior of moisture in pavement includes adsorption/desorption and diffusion.However,most researches focus on analyzing diffusion rate and its influencial factor by applying Fickian model,which is unable to consider transfer behaviorm of moisture vapor comprehensively.Investigations in other porous materials have obtained plenty of findings so that they could provide reliable theorical and technical support.Therefor,this study investigage transport behavior from aspects of adsorption/desorption and diffusion of moisture vapor in asphalt motar.The characteristics of adsorption/desorption process is and its hysteresis are analyzed.Dominating diffusion mode and influencial of diffusion characteristics are illuminated.The main study contents and results are as below.In the first place,moisture adsorption/desorption experiments in asphalt mortar under fixed temperature and humidity condition were conducted.The variation of adsorption content,adsorption rate,desorption content and desorption rate of moisture vapor process was evaluated.The effects of asphalt species,temperature and humidity on the adsorption and desorption process were analyzed.The thermodynamic properties of adsorption and desorption processes were analyzed based on thermodynamic parameters.The results shows that physical adsorption is main adsorption mode in adsorption and desorption processes.These two processes cannot occur spontaneously.At the same time,they are entropy reduction process and requires heat from external environment.Besides,the desorption process is less endothermic than the adsorption process and is more likely to happen.Secondly,cyclic adsorption/desorption experiments were conducted for in full humidity range under fixed temperature.Based on Guggenheim-Andersen-de-Bore(GAB)model,the characteristics of monolayer adsorption and multilayer adsorption in the process of adsorption and desorption in each cycle were analyzed.Hysteretic characteristics of each adsorption and desorption process were analyzed based on hysteresis area.Thus,it was realised that the water vapor retention increase increases due to repeated increases or decreases of humidity.Besides,condensation is common in adsorption-desorption cycle.However,the main existing phase of moisture is still vapor phase.Next,the penetrate type diffusion experiments were carried out.Arrhenius theory and Fickian theory were used to clarify the main diffusion mode.The results suggest that raw materials and environmental factors have certain influence on the transformation of diffusion mode,but they could not chage the main diffusion mode.At last,different diffusion characteristics were investigated by applying Fickian model and non-Fickian models.The types of aggregates,asphalt,ambient temperature and relative humidity affect the diffusion rate,the interconversion of free water and bound water,and the time-variable characteristics of diffusion.Temperature has a significant effect on different diffusion characteristics.At the same time,the effects of environmental factors are more important than the properties of the material itself.