Mix Design And Performance Research Of 3D Printing Recycled Fine Aggregate Concrete

Recycled concrete technology is an important way to realize the sustainable development of the construction industry,and 3D printing concrete technology is an advanced construction technology.If the recycled concrete technology and 3D printing concrete technology can be combined,Can realize the integration development of green building and automatic building,with a broad prospect.3D printed concrete has strict requirements for the fluidity,constructability,cohesiveness,suitable setting time and early strength of materials,and materials are very important for 3D printed concrete technology.In order to prepare recycled fine aggregate concrete meeting the requirements of existing 3D printing equipment,the performance of recycled fine aggregate concrete with 3D printing is studied in this paper.First,the optimal mix proportion test of recycled fine aggregate concrete for 3D printing is completed according to the orthogonal test.The results show that the optimal replacement rate of recycled fine aggregate to replace natural sand is 33%.Secondly,the influences of the replacement rate of recycled fine aggregate,water cement ratio,water reducing agent,early strength agent and retarder on the fluidity time loss and mechanical properties of printing materials are analyzed.Thirdly,the recycled fine aggregate is used to replace all the natural sand,and the composite mineral admixture(single optimization)composed of fly ash,slag powder and silica powder and the combination of composite mineral admixture and polypropylene fiber(double optimization)are used to optimize the printing material of the recycled fine aggregate concrete.It is concluded that the optimal replacement rate of the admixture for cement is 20%,and the optimal mixing rate of polypropylene fiber is 0.2%.Finally,based on the above ratio,the 3D printing concrete equipment designed by the research group is used to print out the test wall.It is found that the recycled fine aggregate concrete with mineral admixture and fiber modification(double optimization)has better workability,pumping performance and longer initial setting time.The strength of cube and prism specimens cut from the test wall is measured,and the results show that the recycled fine aggregate concrete with mineral admixture and fiber modification(double optimization)has better workability and longer initial setting time The compressive strength,flexural strength and splitting strength of recycled fine aggregate concrete printing materials are significantly improved.