The control of rheological behaviour for 3D-printable building mixtures: experimental evaluation of «nano» tools prospects

The extrudability and firm stability are the criteria rheological characteristics of building 3D printable mixtures. This paper presents the results of experimental studies of the rheological behaviour of fresh cement pastes as matrices for 3D printable mixtures. The squeezing test, with constant plate speed, has been used for determination plasticity of cement pastes as criteria of their extrudability. As a result, the typical rheological models of the fresh cement pastes have been identified. In addition, the value of plastic yield stress was evaluated as criteria for the extrusion process. The squeezing test, with constant strain rate, has been used for determination structural and plastic strength, plastic deformations as criteria for the ability of a 3D printable mixture to hold shape during multi-layer casting. It is shown that these properties are significantly controlled by the plasticizer and viscosity modifying additives as factors of changes of disperse system «cement + water» properties. It is established that electrolytes, nanodispersed adsorption-active inorganic modifying additives increase the plasticity of the fresh cement pastes. At the same time, the nanodispersed adsorption-active inorganic modifying additives develop plastic strength as criteria of firm stability. The introduction of inorganic polymers, inert to cement, improves the structural strength of fresh cement pastes but significantly reduces their plasticity. It is shown that the management of rheological behaviour of 3D printable mixtures should be based only by the complex using of chemical addi-tives such as electrolytes, plasticizers and nanodispersed inorganic viscosity modifying additives.