Utilization of recycled construction powder in 3D concrete printable materials through particle packing optimization

With the enhancement of awareness of environmental protection and sustainable development, reuse of industrial solid waste has gradually attracted people's attention. The utilization of recycled construction powder (RCP) and recycled construction aggregate(RCA)in the production of 3D concrete printable material(3DPM) can not only reduce carbon emissions, but also promote the application of 3D printing technology by reducing material costs. Considering the defect of low-reactivity and inferior property of RCP, the appropriate RCP is screened out according to the modified Andreasen and Andersen model to optimize the gradation of printable materials. Influence of RCP on the fresh property is investigated by rheological experiment and the incipient failure height test. The results show that the addition of 10%RCP would increase the yield stress from 1423Pa to 1573Pa and maintain the viscosity of the material. Moreover, unconfined compressive strength test, isothermal calorimetry and mercury intrusion porosimetry test are also used to characterize the properties of 3DPM. The results show that although the addition of RCP reduces the total heat release of 3DPM, it also reduces the macropore(>1000 nm) of 3DPM from 10.7% to 7.1%, and keep the compressive strength within an acceptable range through the gradation optimization. Finally, the results of laboratory printing or industrial printing also confirm the printing performance of 3DPM.