Study On Of Waste Concrete Preparation Of Concrete For CFG Pile

Building facilities will produce a large amount of waste concrete after demolition and transformation,and its recycling rate is very low at this stage,if it is simply stored,it will cause serious waste of resources and environmental pollution;Fly ash is the main product after coal combustion,and its stock and output are large.The reuse of waste concrete is of great significance to the sustainable development of resources,and if it can be specifically applied in engineering practice,it will greatly alleviate environmental pressure and save resources.In this thesis,waste concrete is broken into recycled fine aggregate and recycled coarse aggregate,replacing natural fine and coarse aggregate,and fly ash is replaced with part of the cement to prepare recycled concrete.The mechanics,carbonization resistance and frost resistance tests of recycled concrete were carried out,the optimal replacement rate of each construction waste was selected,and the engineering and economic properties of concrete for CFG pile pile were analyzed in combination with the indoor CFG pile composite foundation test.The detailed results of the study are as follows:(1)Cube compression test of recycled concrete for piles.The main and secondary factors affecting the cubic compressive strength of recycled concrete at 3D,7D and 28 D were as follows: recycled coarse aggregate,recycled fine aggregate and fly ash,all of which showed negative effects on the compressive strength of recycled concrete.Due to the low strength,large porosity and large hole diameter of recycled coarse aggregate,the impact on the strength of recycled concrete is much greater than that of recycled fine aggregate and fly ash.The 28 d compressive strength of each group of recycled concrete is greater than 30 MPa,which meets the strength requirements of CFG piles.(2)Carbonization resistance and frost resistance test of recycled concrete for piles.The carbonization depth of recycled concrete at 3D,7D,14 D and 28 D was studied,and it was found that the carbonization depth difference between 50% and 0% of recycled coarse aggregate was small,and the carbonization depth increased significantly at 100%.After300 freeze-thaw cycles,the strength of the partially recycled concrete specimens still meets the strength requirements of CFG piles.Based on the utilization rate of waste concrete,the relative optimal replacement rate was determined to be 20% fly ash,50%recycled fine aggregate and 50% recycled brick aggregate.(3)CFG pile composite foundation test and economic analysis.When the settlement value reaches 18 mm,the calculated load is 22.5k N,that is,the ultimate bearing capacity characteristic value of the composite foundation is about 358 k Pa,which meets the requirements of the specification.,the upper part of the pile body is greater than the lower deformation under the action of stress,the stress distribution is larger at the top of the pile body,the overall compression deformation occurs,and the compression deformation decreases sequentially from the top of the pile body.The cost per square meter of recycled concrete CFG piles is about 13.5% lower than that of ordinary concrete,and it has the advantages of saving land resources,reducing pollution to farmland,reducing the loss of ecological resources and other environmental protection advantages.