Optimization of Mix Designs and Experimental Study of the Properties of Concrete Mix for 3D Printing

Currently, much attention is paid to sustainable development issues, including the search for new environmentally friendly materials and technologies. Such a material is geopolymer, the result of mixing aluminosilicates with an alkaline solution. It has many advantages over conventional concrete, including quick strength gaining. This quality is one of the key ones for the additive manufacturing technology, since the construction mixture for 3D printing must meet certain requirements. The purpose of this article is to determine the effect of fiber on the mechanical properties of geopolymer concrete in terms of 3D printing. In this study the composition of the working mixture with fiber for use in a construction 3D printer was selected and the cone flow diameter for mix and the compressive strength and bending strength of the concrete samples was studied in the age of 1, 3 and 7 days. The highest values of both bending and compressive strength were achieved by samples with 0.5% polypropylene fiber. On the 7th day, the flexural strength was 5.811 MPa, and the compressive strength was 44.035 MPa. The addition of fiber slightly improves the strength of concrete, however, it affects the overall integrity of the mixture and concrete, the technological properties of the mixture improve, the mix becomes more viscous. In the context of 3D printing, the resulting strength values satisfy the need of fast strength gain.