| When concrete with early strength and high fluidity is used in the cement concrete pavement slab replacement and maintenance project,the high strength and high fluidity of the repairing material concrete in the early stage leads to a slow growth and shrinkage in the later stage,and then leads to a decrease in fatigue performance.Therefore,this paper studies super early strength and super plastic concrete from the aspects of mix ratio design,mechanical properties,fatigue properties,fine microstructure and simulation.Firstly,the mix ratio of the super early strength and super plastic concrete was designed by orthogonal test method,and the optimal mix ratio of concrete was determined as follows:water-binder ratio 0.32,silica fume content 0.05(5%),sand ratio 0.38 by means of flexural tensile strength and other indicators;The ratio of the measured values of the axial compressive strength and the cubed compressive strength at the curing age of 12h,3d,7d,and 28d are 0.72,0.77,0.77,and 0.76.Secondly,the fatigue performance of super early strength and super plastic concrete cured under different environmental conditions(standard curing,freeze-thaw cycle,temperature alternations,dry-wet action)was tested,and the relationship between the stress of concrete subjected to different environmental conditions and its fatigue life was analyzed.The double logarithmic fatigue equation under different environments with failure probability of 0.05,0.1,0.2,0.3,0.4,0.5 was established,and the fatigue life attenuation rule of super early strength super plastic concrete in different environments and different stress levels was obtained.Then,the four different pairs of coupling effect of super early strength and super plastic concrete porosity and crack evolution by electron microscope(SEM)and the industrial CT.the fatigue damage degree of the concrete is:alternate freeze-thaw cycle and fatigue load coupling>effect of temperature alternation and Fatigue Load>dry wet effect and fatigue load and fatigue load coupling>standard curing and fatigue load coupling.With the increase of stress level,the crack propagation speed increases rapidly,which leads to the crack and even fracture behavior at the macroscopic level.The relationship between fatigue properties and microstructure of super early strength and super plastic concrete was preliminarily obtained.Finally,in order to further study the fatigue performance of the super early strength and super plastic concrete,the particle Flow(Partical Flow Code)software is used to imitate the true process simulated fatigue tests.The fatigue crack is mainly in the loading line area at the lower part of the trabecular model and the middle part of the span,cracks along the contact model of cimc and mortar interface area extending from the bottom.The verification and correction of discrete element simulation results combined with laboratory test results. |
