Structure and properties of mortar printed on a 3D printer

The influence of the molding process of sand-cement mortar printed on a 3D printer on its structure and properties is investigated. The mortar mix was characterized by a mobility P_k = 2, which corresponds to an immersion depth of the etalon cone of 5 cm. Determination of compressive strength was carried out on standard samples of beams with dimensions of 40×40×160 mm by loading them on a press in pure compression mode. Water absorption was defined as the ratio of the difference between the mass of a water-saturated sample and the mass of a dried sample to the mass of a dried sample. The porosity of the hardened mortar samples was determined by the results of determining their density, water absorption and sorption moisture. Defects of the sand-cement mortar mix and hardened composites, formed by the extrusion (3D printing), were determined by the visual and instrumental methods using a measuring metal rule. It is shown that the raw mixes currently used (similar to accepted in experimental studies) are not adapted for their extrusion (3D printing), as reflected in the appearance of various defects – different layer thicknesses, crushing of the underlying layers, cracks, skew of the mixture, inhomogeneous structure of the hardened composite, mix spreadability, high porosity. It was found that the molding of the studied sand-cement mortar by the extrusion (3D printing) leads to increased total pore volume by 10 %, open capillary pore volume by 22 %, conditionally closed pore volume by 9 %, microporosity by 8 %, reduction in open non-capillary volume by 65 % compared to the traditional injection molding samples of a similar composition with further compaction. This leads to a decrease in compressive strength by half compared with the injection molding method with further compaction, and an increase in water absorption by 22 %. Based on the results, the directions of improving the raw mixes for 3D printing are determined.