Study On Cement Concrete Pavement Internal Humidity At Early Ages

Cement concrete pavement is prone to early-age damage in the particularclimatic condition.Reaserch has shown that the change of temperature and humidity atearly ages in cement concrete pavement is the most important factor that influence theearly-age performance of cement concrete pavement. Meanwhile, the change oftemperature and humidity at early ages in cement concrete pavement influences theearly-age performance of cement concrete pavement, then influences the long-termperformance of cement concrete pavement. But there has not been sufficient researchof this aspect at the present time, especially little research has been done on early-agehumidituy field of cement concrete pavement. Base on the above, the paper plans tostudy on the characteristics of early-age humidity field of cement concrete pavementand study on the influence of early-age humidity field on the early-age crack ofcement concrete pavement. The following is the contents of this work:First, based on the domestic and foreign research methods and models, the paperchooses parameters of the model, builds humidity diffusion equation on cementconcrete pavement, adopts finite difference method to solve the diffusion equation,and programs the computer to simulate early-age humidity field.For C30, C35and C80series of concrete, the paper carries out laboratoryexperiment to monitor their internal early-age humidity, based on the monitored testdata, the paper varifies the correctness of the program. Studies show that the valuecalculated by equation with variable diffusion coefficient could be well in line withexperiment results.Constructing cenment concrete pavements at morning and evening in summertemperature in site in Fujian province, and continuously monitoring their early-agehumidity as soon as the pavements constructed, based on the monitored data, thepaper verifies the correctness of the program, then in accordance with the verifiedprocedures the paper simulates the characteristics of the humidity field of the cementconcrete pavement. The results show that the early-age humidity of the surface ofcement concrete pavement changed with randomness, the largest reduce rate was74.28percentage points, relative humidity of the bottom of cement concrete pavementhad a significant change in the first25hours. the early-age humidity values which theprogram with variable-coefficient diffusion equation calculated could be well in linewith the test values in site.For C30, C35and C80series of concrete，the paper carries out laboratoryexperiment to monitor internal humidity and shrinkage at early ages, and gets thefitting relationship of early-age humidity and shrinkage of cement concrete pavementby regression analysis method. Meanwhile, based on the fitting relationship between the early-age humidity and shrinkage of cement concrete pavement, the paper predictsthe early-age shrinkage of site cement concrete pavement.Based on the fitted formulas for early-age humidity and drying shrinkage and onother related theory, turns the early-age humidity difference of cement concretepavement into effective temperature difference, adapts road three-dimensional finiteelement program to study the effect of early-age humidity field on the early-age crackof cement concrete pavement. Studies show that in sute test condition the early-agedrying shrinkage stress exceeded the tensile strength of concrete of the same ageperiod, and it caused the cracking of thepavement, which in line with the result in site.