| Lightweight aggregate concrete has the characteristics of light weight,high strength,heat preservation,fire resistance,good seismic resistance,and good deformation performance.It is widely used in industrial and civil buildings and other projects.It can reduce the weight of structure,save material consumption,improve the efficiency of component transportation and hoisting,reduce foundation load and improve building functions.It is suitable for high-rise and long-span buildings.On the other hand,because of the porous nature of the lightweight aggregate concrete,the micro-cracks caused by external loads or temperature penetrate quickly,which are easy to form macro-cracks and fracture.Therefore,in order to avoid this kind of accident and further understand the basic performance and failure mechanism of lightweight aggregate concrete,it is necessary to study the fracture performance of lightweight aggregate concrete.However,due to the complexity of concrete materials,the damage mechanism and crack propagation law of lightweight aggregate concrete cannot be well obtained only by experiments,which has been effectively solved by the development of numerical simulation experiments in recent years.In this paper,the fracture tests of lightweight aggregate concrete with different aggregate volume fraction and different aggregate strength are carried out by using three-point bending beam test,and the mechanical properties of the material are measured.On the other hand,through the joint of random aggregate delivery model and finite fracture model based on coupling criterion(CC),a finite damage fracture mesomechanics model is established,and the mechanical parameters of mortar and aggregate measured by the experiment are substituted into the model.The whole fracture process of concrete beams with different aggregate strength and different volume fraction of light aggregate(LA700)is calculated by numerical model.The damage-fracture process of beams under bending state is reproduced and the damagefailure mechanism of different materials is analyzed.The following conclusions are drawn:1.The finite damage and fracture model based on Coupled Criterion is applied to the numerical simulation of lightweight aggregate concrete for the first time.The tensile fracture process of lightweight aggregate concrete three-point bending beams with different aggregate volume ratio and different aggregate strength is analyzed.The simulation results correspond well with the test results,which shows that the finite element damage and fracture program can accurately reflect the whole damage-fracture process of lightweight aggregate concrete.2.When the mechanical properties of aggregate are worse than that of mortar,the crack propagation begins in the weak area with lighter aggregate.However,with the improvement of mechanical properties of aggregate,cracks will propagate around aggregate into mortar,crack path length will increase,energy consumption will increase,and bearing capacity of beams will also increase.Mechanical properties of 700-grade shale ceramsite are weaker than mortar,no matter how the volume ratio of aggregate changes,cracks will pass through aggregate.With the decrease of aggregate volume fraction,crack development needs to overcome more areas of mortar,the energy consumption increases,and the bearing capacity of beams increases.3.In the process of lightweight concrete fracture,most energy is consumed by damage and fracture,and the energy consumed by damage decreases with the increase of volume fraction of lightweight aggregate.The energy consumed by fracture increases first and then decreases with the increase of the volume fraction of lightweight aggregate.Adding lightweight aggregate with a certain volume fraction(about 15%)in mortar can increase the energy consumed by fracture.On the premise that the volume fraction of aggregate is 40%,the improvement of mechanical properties of lightweight aggregate will increase the damage energy and fracture energy,but the total crack length will decrease. |
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