Experimental Study On The Effect Of The Wrapped Slurry Recycled Coarse Aggregate On The Properties Of Self-Compacting Concrete

With the gradual acceleration of urbanization process,various buildings have been demolished,resulting in a large number of waste concrete,which has a huge impact on the ecological environment.The excessive exploitation of natural sand and stone also leads to the shortage of building materials.Under the pressure of double-layer pressure,the recycling of recycled concrete has become a hot research direction for many scholars at present Self compacting concrete has the characteristics of low water binder ratio,high fluidity,low engineering cost and high production efficiency.Combining the characteristics of recycled concrete and self compacting concrete,and a new type of green concrete,self compacting recycled concrete,is configured,which conforms to the sustainable development strategy of the country.Due to the defects of recycled coarse aggregate,such as many pores,low strength and high water absorption,which affect the properties of recycled concrete,the recycled coarse aggregate is modified by cement slurry of different strength grades to improve the overall compactness of recycled coarse aggregate,optimize the performance of recycled concrete,and open up a new way for the promotion and application of recycled concrete.The influence of the content of fly ash,the strength grade of the wrapped slurry cement,the replacement rate of recycled coarse aggregate and the content of water reducing agent on the mechanical properties of self compacting recycled concrete is studied firstly through experiments,and the concrete proportioning scheme with better mechanical properties is obtained by the comprehensive balance method.Then on this basis,the influence of the wrapped slurry recycled aggregate on the early self shrinkage,plastic cracking and frost resistance of self compacting recycled concrete is studied by taking the strength of cement as a single factor and controlling other factors unchanged.The main research contents are as follows:(1)Physical property test of recycled coarse aggregate.The results show that the void ratio and crushing index of recycled coarse aggregate are obviously reduced,but the water absorption is increased.In general,the properties of recycled coarse aggregate are improved by wrapping slurry.(2)Experiment on basic mechanical properties of self-compacting recycled concrete.The results show that the content of fly ash and the strength of the wrapped slurry cement have great influence on the mechanical properties of concrete,and the replacement rate of recycled coarse aggregate and the content of water reducer have relatively small influence;when the content of fly ash is 25%,the strength of the wrapped slurry cement is 42.5R,the replacement rate of recycled coarse aggregate is 20%and the content of water reducer is 0.9%,the basic mechanical properties of self compacting recycled concrete are relatively optimal.(3)Early self shrinkage and plastic cracking test of self compacting recycled concrete.The results show that the early self shrinkage trend of self compacting recycled concrete is similar to that of ordinary self compacting concrete,and the shrinkage is mainly concentrated 24 hours ago.The early self shrinkage value of recycled concrete with aggregate wrapping slurry is lower than that without wrapping slurry;The cracking area of the recycled concrete slab without wrapping slurry is about 1.5 times of that of the ordinary concrete.Though the cracking resistance of the recycled concrete slab with wrapping slurry is not as good as that of the ordinary concrete slab,compared with that without wrapping slurry,the cracking time of the concrete slab is delayed,the maximum width of the crack is reduced,the crack development area is reduced,and the cracking resistance of the recycled concrete slab is improved.(4)Freeze-thaw cycle test of self compacting recycled concrete.The results show that the recycled coarse aggregate by wrapping slurry can reduce the erosion of mortar on the surface of concrete after freezing and thawing,reduce the loss rate of compressive strength and improve the frost resistance of concrete.It can be seen from the microstructure that the improvement of frost resistance of aggregate slurry is mainly achieved by optimizing the physical properties of recycled coarse aggregate and strengthening the internal interface transition zone of concrete.