Study On The Influence Of Ultrafine Powder Of Construction Waste On Concrete Performance

Concrete is widely used in urban construction,which leads to the shortage of cement,coal ash,slag powder and other materials,and the rising price of cement.On the other hand,a large amount of construction waste will be produced in urban construction.Therefore,the shortage of building materials and the disposal of construction waste become urgent problems to be solved.The waste concrete and bricks are broken and ground into a kind of ultrafine powder as mineral admixture.It can replace a certain proportion of cement,coal ash and slag powder,which can effectively alleviate the problem of material shortage and construction waste treatment,in line with the concept of sustainable development and green development.The test mainly used the ultrafine waste concrete powder to replace the cement,the substitution rate is 0%,2.5%,5%,7.5%,10%,12.5%,the ultrafine waste concrete powder to replace the fly ash and the slag powder respectively,the ultrafine waste brick powder to replace the fly ash and the slag powder respectively,the substitution rate of fly ash and the slag powder is 0%,10%,20%,30%,40%,50%.The work performance and mechanical properties of concrete were analyzed,including slumps,cohesion and water retention,compressive strength(7d,28d,90d),splitting tensile strength(28d,90d),and flexural strength(28d,90d).A total of 234 cubic compressive strength test blocks,156 split tensile strength test blocks and 156 flexural strength test blocks were made for the experiment.The main conclusions are as follows:1.Ultrafine waste concrete powder and ultrafine waste brick powder will reduce the slump of concrete mixture,and ultrafine waste brick powder has a greater impact on the slump,and less influence on the cohesion and water retention.2.Mechanical properties analysis of concrete:(1)when superfine waste concrete powder replaces cement,the optimal replacement rates of compressive strength,splitting tensile strength and flexural strength are 5%,5%and 7.5%and the maximum content is 12.5%,10%and 10%.(2)when ultra-fine waste concrete powder replaces fly ash,the optimal replacement rate of compressive strength,splitting tensile strength and flexural strength is 20%,and the maximum content is 40%,40%and 30%.(3)when the superfine waste concrete powder replaces the slag powder,the optimal replacement rate of compressive strength,splitting tensile strength and flexural strength is 20%,20%and 10%,and the maximum content is 40%,40%and 30%.(4)when ultra-fine waste brick powder replaces fly ash,the optimal replacement rate of compressive strength,splitting tensile strength and flexural strength is 10%,and the maximum content is 30%,20%and 30%.(5)when slag powder is replaced by ultra-fine waste brick powder,the optimal replacement rate of compressive strength,splitting tensile strength and flexural strength is 10%,and the maximum content is 30%,20%and 20%.3.The strength of concrete mixed with ultrafine waste concrete powder is basically higher than that of concrete mixed with ultrafine waste brick powder,and the effect of superfine waste concrete powder is better than that of superfine waste brick powder.4.By analyzing the concrete strength data of the superfine waste concrete powder and the superfine waste brick powder,the fitting curves and formulas of the cube compressive strength and the splitting tensile strength,the cube compressive strength and the flexural strength of the concrete were obtained,and the regression formulas of the content and strength of the superfine powder were obtained.