Study On Distribution Of Transverse Cracks And Punchout Prediction Of Continuously Reinforced Concrete Pavement

Punchout is the main distress of continuously reinforced concrete pavement, and often occurs at cluster cracks. It is not relative to average crack spacing and average crack width. In the dissertation, the distribution of transverse cracks along pavement longitudinal direction because of temperature drop and shrinkage is studied, then punchout is predicted on this basis. That study has important theoretical significance and practical value.Field investigations are carried out on the CRC pavements along several highways which include Leiyi Expressway,210 second class highway, Sunwu second class highway and Yuegan Expressway. Results show that the punchout is up to 90% of the distress which affect riding safety and comfort and the number of punchouts in cluster cracks regions in each of these four highways is 100,44,50 and 63 percent of the total number of punchout in each highway, respectively. So punchout should become one design index of CRCP and punchout prediction should be based on the longitudal direction of transverse cracks.According to the bond-slip constitutive relation between the reinforced bar and concrete and the linear calculation model between the subgrade and concrete, the equilibrium differential equations are established for the analysis of the stress caused by temperature drop and shrinkage in CRCP. The analytic solution is derived and the formula is provided to calculate the CRCP stress and displacement under the temperature drop and shrinkage. The creep of concrete is accounted for by effective modulus method. The finite element model is established. The concrete slab is discretized by CPS4; reinforcing steels are modeled by B21; and the bond slip between concrete and the steel bar is modeled by horizontal springs, the underlying layers are modeled by vertical springs, and the frictional resistance at the interface between concrete and base is modeled by horizontal springs. Analysis on the stress and displacement of CRCP under temperature drop is carried out and the contours of the stress and displacement are given. Sentivity study show that, elasticity modulus of concrete, bond-slip coefficient between concrete and base and expansion coefficient of concrete are key parameters. Their variation should be accounted for when the longitudal distribution of transverse cracks is predicted.Using Monte-Carlo method, considering the variation of the concrete strength and bond-slip coefficient between concrete and base, the longitudal distribution of transverse cracks is predicted, in which, the average air temperature is changed monthly, and the temperature load is also changed monthly relative to setting temperature. Analysis show that the growth rate of transverse cracks will become very small in approximately 100 days. Crack spacing is counted, and crack width is analyzed accordingly.The formulas used to get the equivalent linear temperature from the nonlinear temperature distribution are established and the method of transforming moisture gradient to temperature gradient is proposed. Considering the effects of load transfer efficiency (LTE) at the transverse cracks and the friction coefficient between banes course and concrete slab, the mechanical response analysis is carried out on the CPCP under temperature gradient, moisture gradient and vehicle load, in which the equivalent slab thickness and equivalent steel concept are used.Considering the changes of load transfer coefficients of the cracks, crack spacing, temperature gradient and slab thickness, the stress nomograms of CRCP under vehicle load and temperature gradient are given. The procedure of punchout prediction is given. When the critical transverse stress on the top of CRCP is calculated out in cluster cracking region, it can be determined whether the punchout will occur. Then the number of punchout can be predicted according to the longitudal distribution of transverse cracks.Eleven test sections were designed and constructed, in which concrete material, base, the erosion prevention of steel, the angle between transverse steel and longitudinal steel, the depth of longitudinal reinforcement, and the distance of cracks active controlled varied. The compressive strength, tensile strength, flexural strength, compressive modulus and flexural modulus of concrete were tested. The cracks in early age were surveyed and Falling Weight Deflectometer tests were carried out. Results show that, concrete material, the angle between transverse steel and longitudinal steel and base have more effects on cluster cracking than the separating layer between concrete slab and base does, and active crack with the spacing of 1 m to 5 m can prevent the occurrence of natural cracks between active cracks. For CRCP systems under environmental loads, the strains and stresses in CRCP in early age due to environmental loads were measured. Results show that, when analysis on the early age behavior of CRCP under environmental loads, the steel is not completely bonded with concrete, the perfectly free or restrained boundary condition across cracking is not true, and the longitudinal steel strains across cracking will help develop proper boundary condition across cracking. On the other hand, for the CRCP under vehicle loads and environmentalloads, the test results of concrete strains and steel strains are much closer to the theoretical analysis results which illustrate that the theory analysis models are reasonable.