EXPERIMENTAL SUBSTANTIATION OF CONSTANTS IN THE MATHEMATICAL MODEL OF CONCRETE IN STRUCTURES MADE BY 3D PRINTING TECHNOLOGY

The paper presents the results of the study of concrete fracture mechanisms in structures made by 3D printing technology using the layer-by-layer extrusion method. It is established that concrete fractures in such structures occur by fundamentally different mechanisms - cohesion and adhesion fracture mechanisms. The type of fracture mechanism is determined by the load direction relative to the direction of concrete extrusion layers. The compressive strength of concrete and the corresponding basic constant (compressive strength of concrete - Rb) is determined, in general, by the cohesive fracture mechanism. But when loaded parallel to the extrusion layers, the influence of the adhesion mechanism of fracture on the overall value of the key constant of the concrete model has been established. Fracture of concrete in structures made by 3D-printing technology by layer-by-layer extrusion is determined by the direction of loading relative to the direction of concrete extrusion layers. Under loading perpendicular to the extrusion layers (direction of tensile stresses is parallel to the extrusion layers), failure occurs by cohesive mechanism. The value of concrete tensile strength (Rbt) corresponding to the cohesive fracture mechanism can be used as a key constant of the mathematical model of concrete. When loading parallel to the extrusion layers (direction of tensile stresses is perpendicular to the extrusion layers), the failure occurs by the adhesion mechanism. As a key constant of the mathematical model of concrete can be used the value of adhesive strength of interaction of layers (Radh), corresponding to the adhesive mechanism of fracture. The presented experimentally substantiated key constants of the mathematical model of concrete provide adaptation of such a model for concrete in structures made by layer-by-layer extrusion.