The Aggregate Distribution Effect On The Compressive Strength Of Recycled Concrete

In our country recycled concrete as a kind of green building material is in the initial stage of application.At present,the research of recycled concrete in China is still in the stage of the traditional test chamber.The study period is long,and a lot of manpower and material resources are consumed.And can only show the mechanical characteristics of the macro mechanical properties of recycled concrete,at the meso level the development of damage and the mutual influence of the interior of the recycled concrete under the external load,it is very difficult to observe and study with test method.The application of finite element simulation software is very good for this limitation.In this paper,we use the Ansys finite element software to simulate the compressive test of recycled concrete specimens in the meso level.In the numerical simulation,the recycled concrete can be calculated from the macro,meso and micro levels,The micro level is the most ideal,the most useful level.In this paper,the recycled concrete is considered as the five phase composite material:Aggregate,new hardened cement paste,old hardened cement paste,new interfacial transition zone,old interfacial transition zone.With MonteCarlo method and Fuller curve,Use the APDL parametric programming in Ansys to establish a random aggregate model of two-dimensional and three-dimensional spherical.And establish the cubes and the prism numerical simulation in the two dimensional and three dimensional of recycled concrete.Conducted these specimens under uniaxial compression.Analysis the mechanical changes of the aggregate,mortar,new and old interface zone with the loading,and the influence of the compressive strength of the whole specimen.Get stress strain curve of recycled concrete,then compared with the real test results.Simulation results show,when the old hardened cement paste strength is bigger,the thickness of the new and old interface is smaller,the more the replacement rate of recycled aggregate,the greater the compressive strength of recycled concrete.The crack of recycled concrete specimen is always first appeared in the grain size of the recycled aggregate,and then to the surrounding extension.Finally,the influence of the distribution of the aggregate on the compressive strength of recycled concrete is analyzed.When the aggregate in specimen in a higher degree of regional agglomeration is conducive to the development of crack,And when the degree of aggregation of recycled aggregate is high,it will speed up the development of the crack,and reduce the bearing capacity of the specimen.Stress cloud images show that the internal stress of the specimen is larger in the vertical direction from the edge of the specimen to the middle area.When the recycled aggregate is mostly distributed in the edge of the specimen,it is not conducive to the enhancement of the carrying capacity.The relative strength of the weak layer will occur when the load is applied in the direction of the load,which leads to the decrease of the bearing capacity of the specimen.