Experimental Study On Flexureal Behavior Of Lightweight Aggregate Concrete Composite Slabs

The progress of modern construction engineering technology is indissociable from the research of new materials and new structures.This paper starts with a high quality shale ceramsite produced in Yiyang,Hunan Province.First of all,the lightweight aggregate concrete made with the shale ceramsite is studied.Studing the physical and mechanical properties of lightweight aggregate concrete improved by adding silica fume and fly ash.The premium mix proportion of the shale ceramsite concrete is obtained.This can provide a basis for its popularization and application in Hunan Province.And the lightweight aggregate concrete is applied to prefabricated construction.Proposing a lightweight aggregate concrete composite slab of precast slab made of lightweight aggregate concrete and cast-in-place part made of normal concrete.Producing precast slab of composite slab with lightweight aggregate concrete.So that the slab has self-insulation performance and reducing the slab weight.The cast-in-place part of composite slab is still made of normal concrete to facilitate site construction and ensure the stiffness of composite slab.Carrying out bending tests and ABAQUS finite element simulations on the improved composite slab.The main work and achievements are as follows:（1）After summarizing relevant references and data,the characteristics and research status of lightweight aggregate concrete and composite slab are described.And the research significance and application prospect of lightweight aggregate concrete and composite slab with precast lightweight aggregate concrete panel are pointed out.（2）Basing on the method of loose volume,making silica fume and fly ash compound admixtures lightweight aggregate concrete.By orthogonal experiment design,casting lightweight aggregate concrete blocks with different mix proportion by changing net water-cement ratio,fly ash replacement,sand ratio,silica fume replacement.Then measuring their dry apparent density,28 d compressive strength,specific strength（ratio of compressive strength to dry apparent density）and analyzing the influence of various influencing factors on lightweight aggregate concrete by means of variance and range analysis.The results prove that the silica fume has the most significant effect on the compressive strength and specific strength of lightweight aggregate concrete and silica fume replacement is reasonable between3%-6%.（3）A single variable test was designed by controling the net water-cement ratio of 0.40 and 0.33 and only changing the silica fume replacement of 4%,5%,6%.The material property tests of 6 groups of lightweight aggregate concrete blocks were completed.The consequences show that as the silica fume replacement increasing,the compressive strength of lightweight aggregate concrete first increases and then decreases.There is an optimal silica fume replacement and it increases with the decrease of the net water-cement ratio.When lightweight aggregate concrete net water-cement ratio is 0.40 and 0.33,the optimal silica fume replacement is 5% and6%,respectively.（4）7 composite slabs with different forms were designed.And carrying out bending tests on lightweight aggregate concrete composite slabs with different reinforcement ratios,different precast layer thicknesses and different construction conditions.The failure characteristics,crack development and distribution rules,flexural stiffness,bearing capacity and so on were analyzed.Meanwhile,they were compared with the common concrete composite slab.The results show that the failure characteristics of the lightweight aggregate concrete composite slab are similar to the common concrete composite slab,and the composite surface with truss steel bars and natural rough surface has sufficient shear strength.The number of cracks is more and the width is smaller than that of the common concrete composite slab.The measured ultimate bearing capacity is about 5% lower than that of the common concrete composite slab.（5）ABAQUS was used to set up the model of the lightweight aggregate concrete composite slab.The test specimens were simulated and analyzed.Then the simulation consequences of the tensile damage neogram,bending moment-deflection curves and bearing capacity of the specimens were obtained.And the simulation consequences were compared with the test consequences.The consequences show that the concrete constitutive relation of code for design of concrete strutures is converted to CDP model in ABAQUS.And the concrete damage factor is calculated by the formula proposed by Sidoroff F.The model parameters of the lightweight aggregate concrete composite slab are effective and reliable.They can be used in the damage and bearing capacity simulation calculating of lightweight aggregate concrete composite slabs.