Experimental Study On Performance Of Reinforced Recycled Aggregate And Vibration Mixing Concrete

In recent years,the number of construction waste in China is increasing rapidly,and the consumption of natural sand and gravel is also increasing.In order to solve this problem,it is an efficient and convenient way to crush construction waste into recycled aggregate and reuse it in concrete.However,due to the weak compressive capacity and high water absorption of untreated recycled aggregate,the performance of concrete will be reduced,so it is necessary to strengthen the recycled aggregate.However,in the current strengthening methods,the physical strengthening energy consumption is high,and the chemical soaking strengthening reagent is seriously consumed and the strengthening time is long,which limits its practical application in engineering.At the same time,the emergence of vibration mixing technology provides a new method to improve the performance of concrete by changing the mixing method.Therefore,this paper intends to study the application of chemical slurry spraying strengthening and vibration mixing technology for recycled coarse aggregate.The main research work of this paper is as follows:Firstly,a total of 9 groups of cement-silica fume slurry and 3 groups of water glass solution were designed to spray and soak the recycled coarse aggregate.The results show that the crushing index and water absorption rate of recycled coarse aggregate are improved after the spraying of cement-silica fume slurry or water glass solution,but the apparent density decreases slightly after the strengthening of cement-silica fume slurry.And for cement-silica fume slurry and water glass solution,the two different strengthening methods of spraying strengthening and soaking strengthening have little effect on the performance of recycled coarse aggregate.At the same time,through the orthogonal test of four factors and three levels,nine groups of cement-silica fume-water glass double slurry were designed to spray the recycled coarse aggregate.It was found that the double slurry strengthening had a certain improvement on the crushing index of the recycled coarse aggregate,but had no significant improvement on the water absorption and apparent density.The effect of double slurry strengthening was not better than that of two single slurry strengthening.Secondly,the scanning electron microscope analysis of natural coarse aggregate,unreinforced recycled coarse aggregate and five kinds of recycled coarse aggregate after slurry strengthening was carried out.It was found that there were a large number of micro cracks and pores on the surface of recycled coarse aggregate,which caused its performance to be worse than natural coarse aggregate.After chemical slurry strengthening,these cracks will be filled with C-S-H gel,the hydration product of chemical slurry,so as to improve the performance.Then,natural coarse aggregate,unstrengthened recycled coarse aggregate and two kinds of recycled coarse aggregate after single slurry spraying strengthening and soaking strengthening were selected.The recycled concrete was prepared by vibration mixing and ordinary forced mixing respectively and its performance was tested.The results show that the recycled concrete made of recycled coarse aggregate has been improved in mechanical properties and durability after chemical slurry spraying.There is almost no difference in the effect of spraying strengthening and soaking strengthening on the performance of recycled concrete.After the apparent density of recycled coarse aggregate reaches the Class I standard,even if the strengthening will reduce the apparent density to a certain extent,it will not affect the improvement of the performance of recycled concrete,indicating that it may be inappropriate to evaluate the performance grade of recycled coarse aggregate based on the apparent density.At the same time,the performance of all kinds of concrete made by vibration mixing is stronger than that of ordinary forced mixing.When the recycled coarse aggregate is strengthened by slurry spraying,the recycled concrete made by vibration mixing has reached the level of natural concrete made by ordinary forced mixing in terms of mechanical properties.Finally,this paper analyzes the economic benefits of recycled coarse aggregate and recycled concrete after spraying strengthening and soaking strengthening.The results show that the slurry waste is serious and the cost is high during soaking strengthening.The price of recycled concrete after spraying strengthening is only about 85%of that of natural concrete,and the mechanical properties can reach more than 90%of that of natural concrete.