Experimental Study On Crack Performance Of Waste Fiber Recycled Concrete

With the continuous expanding of urban city space and the rapid development of construction industry,for a long time,the development of the traditional construction industry is largely built on the excessive consumption of the energy and resources,but also on the basis of the serious pollution of the environment.Recycling and deal with the construction waste effectively and processed into recycled aggregate,and making it replacing natural aggregates.This approach will not only alleviating the status quo which the shortage of natural aggregate resources,protect the ecological environment,making the effect of protecting the aggregate of habitat ecological environment,but also helping solve the phenomenon which urban construction waste and other stack disorderly,occupying public land and pollution of the environment and other issues.Therefore,recycling construction waste effectively has significant social,ecological and social benefits.In this Paper,on the basis of previous research results,using waste fiber to improve the shrinkage performance of recycled concrete,and draw the following conclusion:(1)The incorporation of the waste fiber has greatly improved the anti-cracking performance of recycled concrete,embodied in the following aspects:delay the initial cracking time,the addition of waste concrete which made the recycled concrete initial cracking time has been delayed by 3.8?1.4d;then Inhibit the production and development of recycled concrete's initial cracks,when length waste fiber is 19 mm at the time of initial crack,the maximum crack width was reduced by 17.6%?35.5%;reduce the total number of cracks and through crack number,postponed the appearing time of through cracks.When the waste fiber length is 19 mm,volume fraction is 0.12%of waste fiber recycled concrete is the most optimal crack resistance and refinement effect of the crack.(2)The addition of the waste fiber in the recycled concrete has very good performance in reduction the contraction in both the early-term and long-term,in the ages of 3d,compared with the not adding waste fiber recycled concrete,shrinkage value of adding waste fiber was reduced by 16.07%-0.41%,;in the ages of 150d,shrinkage rate of adding waste fiber recycled concrete has reduced by 1.7%?19.2%.Among them,the addition which the length is 19mm,the volume content is 0.08%,the waste fiber recycled concrete has the most significant reduction effect.(3)Effect of volume fraction on fracture properties.Under the condition of recycled aggregate replacement rate of 50%,waste fiber length of different circumstances,displays for the most significant of enhancing the effect,the volume content which added 0.12%volume content of waste fiber on fracture properties,followed by the volume of content waste fiber is 0.08%,when add 0.16%,development of recycled concrete ability for resisting crack instability is weak.(4)Effect of fiber length on fracture properties.In the recycled aggregate rate was 50%,the fiber content is 0.08%,0.08%and 0.16%of cases,specimen which waste fiber length is 19 mm has show optimal fracture performance,compared with the length 12 mm and 30 mm in all kinds of fracture criterion,critical crack-mouth opening displacement increased 2.5%?47.8%,and the critical crack-tip opening displacement increased 2.3%?96.9%,instability of fracture toughness is increased by 2.6%?2.6%,and the stress intensity factor increased 18.8%?145.1%.(5)The influence of recycled aggregate replacement rate on fracture properties.In the case of the same fiber length and fiber content of waste concrete,which under the condition of different substitution rate,by comparing cracking load and fracture toughness of equivalence,it found that,followed by recycled aggregate replacement ratio is greater,specimen fracture index is smaller,when replace rate of 100%,waste fiber fracture properties of recycled concrete is decreased obviously.(6)Effect of initial crack depth on performance.By comparing the same replacement rate,under conditions of fiber length and fiber content,cracking load decreases with the increasing initial fracture height ratio,it indicating that the initial macroscopic defects in more hours,the fracture properties of waste fiber recycled concrete stronger.