Experimental Study On Mechanical Properties Of Recycled Coarse Aggregate Concrete Strengthened With Sodium Silicate

At present,the country is vigorously developing urbanization,driving the vigorous development of the construction industry,but meanwhile brought a large amount of construction waste.In the face of the problem of disposal of a large amount of construction waste and the consumption and shortage of resources in the world,the application of recycled concrete in practical engineering has become the trend of the times.In this paper,the recycled concrete is studied by means of experiment and relevant theoretical knowledge.Silica gel will precipitate when sodium silicate is reacted under carbon dioxide.Silica gel can block the pore of recycled aggregate,and glue the micro-crack inside the recycled aggregate,so as to improve the pore structure of recycled aggregate.A large amount of Ca?OH?₂ is formed by cement hydration.Sodium silicate can react with Ca?OH?₂ to form hydrous calcium silicate colloid,which fills the pore of recycled aggregate,thus improving the compactness and strength of aggregate.Recycled aggregate can remove dust and impurities on its surface during soaking in water glass solution,reduce the weak interface between such low active dust and newly formed cement paste,and thus improve the strength of recycled concrete.The basic physical properties of recycled coarse aggregate are improved by using sodium silicate,and the mechanical properties of recycled concrete are tested.In this paper,the common recycled coarse aggregate is strengthened by sodium silicate,and the physical properties of natural coarse aggregate,common recycled coarse aggregate and recycled coarse aggregate strengthened by sodium silicate are studied.Such as particle size,apparent density,bulk density,water absorption rate,crushing index and so on.It is found that sodium silicate has a significant reduction effect on crushing index and water absorption of recycled coarse aggregate.The performance differences of natural concrete,ordinary recycled coarse aggregate concrete and sodium silicate reinforced recycled coarse aggregate concrete were studied with two water binder ratios of 0.5 and 0.35 and four kinds of substitution rates of 30%,50%,70%and 100%as variables.It is found that the compressive strength of 0.45 water-binder ratio concrete is higher than that of 0.55 water-binder ratio under the same substitution ratio.The order of compressive strength of three kinds of concrete is natural concrete>sodium silicate reinforced recycled coarse aggregate concrete>recycled coarse aggregate concrete.Under the same water-binder ratio,the cube compressive strength of the three kinds of concrete decreases gradually with the increase of the replacement rate of recycled coarse aggregate.The uniaxial compression test of concrete is carried out by using electro-hydraulic servo pressure testing machine and rigid auxiliary frame.The whole process of stress and deformation of the test block is observed.The failure phenomena of different concrete test blocks are mainly divided into vertical cracks.Vertical oblique crack,diagonal crack and middle oblique crack.The constitutive curves of different concrete samples were obtained by origin software.The effects of water-binder ratio and the replacement ratio of recycled coarse aggregate on the peak stress,peak strain,Poisson's ratio and elastic modulus of the constitutive curve were analyzed.In order to obtain the descending section of the stress-strain curve of recycled concrete,the uniaxial compression test of recycled concrete was carried out by consulting a large number of literatures and the actual conditions in the laboratory,and selecting the rigid auxiliary frame as a tool to enhance the stiffness of recycled concrete.Through the test,it is found that the crack failure types of various concrete blocks are vertical,vertical oblique,angle oblique crack,diagonal crack and middle crack.The constitutive curves of different concrete samples were obtained by origin software.The effects of water-binder ratio and the replacement ratio of recycled coarse aggregate on the peak stress,peak strain,Poisson's ratio and elastic modulus of the constitutive curve were analyzed.Finally,various constitutive curves of concrete are fitted,and the advantages and disadvantages of the existing constitutive curve equations are compared and analyzed.By using the piecewise function proposed by Guozhenhai to fit the constitutive curves of concrete,it is found that the degree of fitting is high.