Study On The Effect Of Coarse Aggregate Reinforced By Negative Pressure Grouting On The Performance Of Recycled Concrete

With the implementation of green building and sustainable development policies,the application of recycled concrete in the construction industry has received more and more attention.However,due to the inherent defects of recycled coarse aggregates,it is challenging to promote and apply in actual projects.In this paper,P-O42.5 normal silicate cement,silica fume and Class I fly ash are selected as the main reinforcing materials,and negative pressure grouting technology is used to strengthen the recycled coarse aggregate to enhance the infusion of reinforcing materials into the recycled coarse aggregate,which effectively improves the mechanical properties of the recycled coarse aggregate with high research significance and promotion value,and the macroscopic and microscopic experimental studies on the reinforced coarse aggregate are conducted.The following main conclusions were obtained:The cement slurry with different water-cement ratios was used to strengthen the recycled coarse aggregate,and the crushing value,apparent density and water absorption were used as indicators to characterize the performance of the strengthened recycled coarse aggregate with different water-cement ratios,and the range of the best strengthened water-cement ratio was determined to be around 1.1,which verified the implementability of the negative pressure grouting test and illustrated the superiority of the negative pressure grouting technology to strengthen the coarse aggregate,and also clarified the For the characteristics of raw materials such as high pressure crushing value and water absorption rate,low apparent density performance,this paper selects pure cement,cement with silica fume and cement with Class I fly ash to strengthen the recycled aggregates,and carries out quantitative analysis of pores in 2D level CT images,qualitative analysis of pores in3 D reconstruction mode and quantitative analysis of pores in 3D model by CT scan for different types of recycled coarse aggregates before and after strengthening,and obtains different The number of pores of recycled aggregates all showed an inverse function of decreasing trend as the pore diameter increased.Among them,brick blocks have the fastest decrease rate,concrete blocks the second and old mortar the slowest.In addition,the composition,production,source,age and external conditions of the aggregates affect the aggregate shape,pore volume size,and pore path length,which in turn affect the negative pressure grouting effect.Among them,the pore shape factor K of brick and concrete blocks is roughly in the same interval,much lower than that of old mortar blocks.On the basis of making different reinforced types of coarse aggregates to carry out the concrete ratio design;the basic mechanical properties of concrete specimens with different reinforcement types were tested,and the effects of reinforced coarse aggregate types on the damage morphology,cubic compressive strength,prismatic axial compressive strength,splitting tensile strength,flexural strength,modulus of elasticity and stress-strain of the recycled concrete were compared and analyzed to further illustrate the negative pressure The process of reinforced recycled concrete by grouting can be extended.The interfacial transition zone of recycled concrete was tested by microhardness tester and SEM scanning electron microscope,and it was found that there are various interfacial transition zones of recycled aggregate concrete;the hardness of mortar matrix is influenced by the quality of recycled aggregate,and the damage forms and paths of recycled concrete made by low quality recycled coarse aggregate casting are more complicated.Therefore,this paper suggests using treated recycled aggregates as much as possible to ensure the performance of recycled concrete.