Experimental Research And Computational Analysis Of Recycled Aggregate Concrete Performance

China is in the progress of industrialization, Urbanization and modernization. In this special development stage, and because of large population, the situation that great deals of various resources material are consumed and great quantities of various garbage or wastes are produced is coexistence. With the resources and the environment problem are continuously worsen, the sustainable development strategy is urged to implement. The civil engineering should be the major field to bring into effect because it is the biggest resources waste industry. Recycling and resource recovery of C&D waste are an effective way to the implementation of this strategy.The C&D waste are used to concrete production in two way:one way that the decompounded concrete pieces are produced into the recycled concrete aggregate and another way that C&D waste is directly produced into the recycled combined aggregate.The recycled aggregate behaviour was found that apparent density and stacking density are between 2.31-2.62 (kg/m3) and 1.29-1.47 (kg/m3), water absorption is 4%-10%, crush index is 14.2%-23.1%. The compressive strength of recycled concrete reduces with the increase of recycled aggregate substituting ratio and water/cement ratio. Its tensile strength was less affected by substituting ratio. With the increase of recycled aggregate substituting ratio, the slump of recycled concrete rapidly reduce, its elastic model reduce, its shrinkage markedly increase, its frost resistance is less infected, its permeability increase, its carbonization speed slightly increase, its sulphate resistance slightly reduce.The effects of different materials in the recycled combined aggregate on the properties of concrete were summarized, including the effects of tile,crashed concrete,glass,wood sawdust,asphalt,oyster shell and recycled plastic on the properties of concrete which include compressive strength,tensile strength,elastic modulus,shrinkage quantity. The activity of tile and glass which were crashed into some degree of fineness increased, and it could minish the effect on the properties of concrete. The crashed concrete had bad effect on the properties of concrete. The recycled plastic could enhance the toughness of concrete. The oyster shell would reduce the elastic modulus of concrete, but had not affect on its early-strength.Through different components of the recycled aggregate concrete performance test it is found that, the density of recycled combined aggregate broken from C&D wastes in the Xiamen area is less than the traditional density of recycled aggregate and natural aggregate, and because of broken brick and other ingredients exist, the water absorption of recycled combined aggregate is high than the recycled concrete aggregate and natural aggregate, the strength is lower than the recycled concrete aggregate and natural aggregate. The average strength of recycled combined aggregate concrete is the maximum when the water quantity is 300kg, water-cement ratio is 0.6, and the recycled combined aggregate replacement rate is 50%. Orthogonal tests results showed that water-cement ratio on the compressive strength has of the greatest impact, the recycled combined aggregate replacement rate is next, and water quantity is the minimum. Recycled fine aggregate has of high-impact on concrete strength than the recycled coarse aggregate. Compressive strength and tensile strength has a difference of 17.7% and 18.5%. The content of the recycled combined coarse aggregate have no clear impact on the strength of the concrete when it is not more than 50%. The increase of the red-brick component in the recycled combined coarse aggregate would make the compressive strength and tensile strength decreased by 11.3% and 7.4%. the broken tile component will make the compressive strength and tensile strength fell by about 8.1%. Beforehand wetted the recycled fine aggregate and recycled aggregate would seriously reduce the strength of recycled concrete. The replacement rate of the recycled combined fine aggregate increases, the tensile strength of concrete will fall. With the increase in the rate of sand, recycled concrete tensile strength increase. Adding a certain amount of polycarboxylate superplasticizer, the recycled concrete workability and fluidity are improved, and the slump will increase, can increase 10% to 15% of compressive strength, tensile strength can be increased by 10%~14%. When the fly ash amount are 25% and 35%, its strength declined by about 32.1% and 36.8%. The recycled combined aggregate can be used in the manufacture of concrete blocks and meet the general requirements of the block strength. Admixture of fly ash, its reasonable dosage is less than 15%Through the experiment results of the recycled concrete aggregate gradation on concrete strength and working properties, it is found that if using recycled aggregate natural gradation, concrete work performance is poor, compressive strength is low. Preparing the recycled concrete aggregate gradation on requirements of "Technical Specification for Construction of Concrete Pumping, " the recycled concrete work performance is poor, compressive strength is relatively low. The compressive strength of recycled aggregate concrete has a close relationship with coarse aggregate gradation. When the recycled coarse aggregate gradation is weaker the strength of recycled aggregate concrete is very low,28 days compressive strength is less than 15Mpa. When the recycled coarse aggregate gradation is in the reason state, its compressive strength will be greatly improved; 28-day compressive strength will be able to reach 40Mpa. Increasing the size range 19-26.5mm and 26.5-31.5mm in aggregate content concrete workability is good, compressive strength is high. Increasing the size range 4.75-9.5mm aggregate content, performance of concrete is poor, compressive strength is low. When coarse and fine recycled aggregate content is not more than 60% the workability of recycled concrete can meet the construction requirements and the strength can reach 40Mpa around. Recycled aggregate replacement rates were 50%, 60%, adjusting the content of 9.5-26.5mm size of the aggregate to make gradation close; recycled concrete strength can be higher than the natural aggregate concrete strength.Aggregate itself as a complex non-rule body, using traditional geometry to describe the aggregate is very difficult. The use of fractal analysis to the characteristics of the aggregate shows that:aggregate gradation of particle size requires a certain width in order to meet the particle size aggregate gradation fractal conditions; aggregate porosity with the aggregate maximum size, minimum size, aggregate gradation and fractal dimension of packing density of aggregate has relationship; the total surface area of aggregate gradation depends on the largest and the smallest particle size, of aggregate, the fractal of aggregate gradation, surface area fractal and aggregate quality; also depends on the measurement scales; the aggregate surface mainly react with cement, so the measurement scales can take the particle size of cement.The product of aggregate total surface area with the thickness of aggregates combination layer is the volume of mortar required for wrapping aggregate. The mortar volume required for wrapping aggregate divided by the total volume of available mortar is called wrapped ratio. Wrapped ratio is a direct reflection of the inter-relationship between the aggregate combination layer and mortar. Wrapped ratio reflects the change of the aggregate surface changes due to the different aggregate gradation. The greater wrapped ratio the larger the aggregate surface area, more needed mortar to wrap aggregate. When the water-cement ratio was 0.55, the wrapped ratio was greater than 0.085, the concrete workability is poor, with low compressive strength. When wrapped ratio is less than 0.085, the concrete workability is better, compression strength is high. When the wrapped ratio is smaller, the difference of aggregate gradation in central particle size range 9.5-26.5mm is small, concrete workability is better, compressive strength is high; the difference of aggregate gradation in the middle size range 9.5-26.5mm is large, concrete workablity is poor, with low compressive strength.Determining the aggregate particles size distribution by aggregate gradation and randomly distributing aggregate particles in concrete space, through the particles-spring model to simulate aggregate particles and mortar the meso-mechanics calculation model can be established. The calculation results show that this method not only can be used to analysis of ordinary concrete, and can also be used to recycled concrete analysis through the spring adjustment.