Determination of physico-mechanical characteristics of concrete for 3D printing building designs

Abstract

Problem statement. Currently, methods of manufacturing building structures and products using a 3D printer are becoming increasingly popular. In 3D printing technology one of the main factors that affects the quality of the final product is the composition of the concrete mix used. Moreover, for each type of product, it is important to develop a separate composition of the mixture, which has certain physical and mechanical properties. Analysis of the current state of development and research of concrete for 3D printing of structures showed that the choice of materials for printing depends on the functional purpose of the created object and its scope. At the same time, a distinctive feature of concrete used in the practice of modern construction is that each developer of a 3D printer presents its mixture without revealing its composition. Analysis of publications. The main material used in 3D-construction is concrete-an artificial stone building material obtained as a result of the formation and solidification of a rationally selected and compacted mixture. Such a mixture consists of a binder-cement, large and small aggregates, water, and in some cases with the addition of various modifying additives. One of the main directions of modification of concrete mix is the use of special additives, which significantly affect the characteristics of concrete. Examples of such additives are kaolin clay, silica fume, air lime, fly ash, superplasticizers, hardening accelerators, and mixture strength set. In world practice, for 3D printing of structures for concrete reinforcement, a variety of fibers, fiberglass and other fillers are introduced into the mixture, which can significantly increase the strength of concrete. Currently, in Dnipropetrovsk region in Bratskoe village there is a production room, where the production of small piece concrete products with the help of 3D printing has been established. Department of Reinforced Concrete and Masonry Structures, State Higher Education Institution “Pridniprovska State Academy of Civil Engineering and Architecture” established cooperation with this production facility, engaged in the improvement of manufacturing technology and the application of mixtures, as well as the development of optimal concrete compositions. The first step of such cooperation is the development of mixtures with various binders and hardening accelerators, which significantly affect the reduction of the setting time of mixtures. Purpose of the work was to identify physico-mechanical characteristics of concrete,which is used to manufacture the structures at the production plant in Bratskoe. At the same time the goal was also to compare the characteristics of concrete made using 3D printing by extruding the mixture through a nozzle and molded by manually sealing the mixture. Conclusions. It is found out that in modern construction it is quite efficient and technologically simple to implement the advantages of 3D printing technology for the manufacture of individual structural elements of buildings and structures. As a result of tests of concrete compositions for 3D printing of structures, it was found that the closest concrete grade in terms of strength of basic samples-cubes that were made in molds is M300, and samples-cubes that were selected from structures is M250. Scale factors were established for the samples-cubes with ribs of 100, 70, and 50 mm, which were determined with respect to the strength of standard specimens with a 150-mm rib size.