Study On The Joint Change Of Cement Concrete Pavement Under Temperture

Joints are important structures of cement concrete pavement, but also are the weak positon of cement concrete pavement. There are some main diseases caused by joints, such as pumping, cavity, slab corner crack. One reasean of joint damage is the change of open and close of joints under environment. Therefore, the change of joints under environment is deeply studied, which has the important practical significance.After diseases of cement concrete pavement are investigated and factors of joint chang, such as temperature gradient, humidity, slab size, are analyzed, and then the conclusions are that the open and close of joints are increased as the temperature gradient increases. The influence of humidty is the same as the temperature. The width of contraction joint and the day change of joints are significantly decreased by the the increase of expansion joint spacing and the decrease of contraction joint spacing.Through the day change of surface temperature, surface temperature of different depth at different times, the maximum temperature gradient and humidity of surface temperature are analyzed, the open and close of joints under warping deformation, expansion deformation, and dry and wet concitions are studied, and then the prediction formula of joints is derived when the pavement is in the pure bending condition under positive and negative temperature gradient.The three-dimensional joint model is established by finite element software, many factors of open and close of joints are quantitatively analyzed, the results have shown that temperature gradient, base modulus, slab length and slab thickness has the significant effect. The relationship between open and close of joints and temperature gradient is the logarithmic, the base modulus is the power, slab length and slab thickness is the exponential. And that the influence of temperature gradient is greater than slab length and base modulus, and the slab length and slab thickness has a considerable impact, they are greater than the slab thickness. The influence of base thickness and interlayer state is not significant. Based on the above analysis, the formula of open and close of joints with temperature gradient, base modulus, slab length, and slab thickness has established.According to theoretical results, there different base types about lean concrete, cement stabilized crushed stone, gravel graded, have on-site observation of open and close of joints for one year in Guangxi, and then the theoretical analysis is verified, the numerical fitting formula is updated based on measured data.Through the application investigation of joint filler, the selection criteria of joint filler is proposed based on natural divisions, and then the dowel bar size, bar size, spacing and width of conctract joint and expansion joint are designed.