| With the rapid development of the construction industry,many old buildings have been demolished and rebuilt with low utilization ratio,a large amount of construction waste has been produced,and a large amount of natural materials have been consumed.Therefore,the reuse of construction waste can not only reasonably dispose of construction waste,but also save resources,and ease the shortage of resources and other issues to achieve sustainable development.At the same time,most of the waste and waste fiber products produced by textile are non-degradable polyester,polypropylene,etc.Incineration or landfill will damage the ecological environment,but mixed with recycled concrete can be used as reinforcing fiber.To make up for the low tensile strength of recycled concrete and other deficiencies.However,there are many researches on the influence of natural organic fiber on recycled concrete at home and abroad,and there are few researches on recycled concrete mixed with waste fiber and organic fiber.In this paper,fly ash is used to partly replace cement and recycled concrete coarse aggregate to replace natural coarse aggregate to prepare recycled concrete.The ratio of waste polypropylene fiber and polyacrylonitrile fiber is changed according to different proportion and total content.The basic properties of recycled concrete test blocks and the crack resistance of test beams are studied experimentally.The results show that:First of all,through the experimental study on the basic properties of recycled concrete and the crack resistance of recycled concrete beams with different ratio of waste polypropylene fiber and polyacrylonitrile fiber,it can be seen that the different combinations of fiber have effect on the strength of recycled concrete and the bearing capacity of beams.The number and width of cracks,the mid-span deflection of the specimen beam and the strain of the steel bar in the beam have different effects,among which the anti-crack effect of the A75B25 group test beam is the most obvious.This paper is based on this,the ratio of waste polypropylene fiber and polyacrylonitrile fiber 3:1 is mixed.Through the experimental study on the basic properties of recycled concrete and the crack resistance of concrete beams by changing the total mixing ratio,it is concluded that the mixed fiber has a positive effect on the performance of recycled concrete.The comprehensive analysis of the bearing capacity,the crack width and the mid span deflection of the cracks of the slanted cracks shows that the anti cracking performance of the mixed fiber is the most significant when the mixed fiber admixture ratio is 0.1%?0.15%.In this paper,the formula of crack resistance of recycled concrete beams with waste polypropylene fiber is deduced by theoretical analysis according to the original codes and regulations.According to the maximum crack width of hybrid fiber regenerated concrete beam under the limit state of normal use,through fitting and analyzing the test value,the influence coefficient ?1,P2 of fiber on crack width of reinforced fiber reinforced concrete member,?B,is determined.Through fitting analysis,the influence coefficient of fiber on the short-term stiffness of reinforced fiber reinforced concrete flexural members is determined by fitting analysis for the maximum deflection under the limit state of normal use.The failure process of all the specimens is divided into four stages:elasticity,crack,yield and limit,and cracks appear in the middle part of the span first.With the increase of load,the cracks gradually develop to both sides and the upper part,and the oblique cracks connecting the bearing and the loading surface are formed.Finally,the vertical cracks are destroyed because of the rapid growth of the vertical cracks.The development and variation of cracks in the test process are similar to those obtained by finite element simulation.The simulated bearing capacity and deformation performance of the finite element method are in good agreement with the experimental results. |
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