# Energy-Efficient Mixtures Suitable for 3D Technologies
## 1 Introduction  
The development of new technologies in the construction industry in the near future will make it possible to fundamentally change the views and approaches to the traditional methods of erecting buildings and structures, as well as solve a number of environmental and economic problems. The most urgent problems include reducing the cost and impact on the environment and increasing the speed of construction without losing quality. A rational solution to these problems is using the additive method of erecting buildings and structures. This technology involves using a special 3D printer to apply a plastic concrete mixture layer by layer and building the walls by extrusion. The accuracy, speed, and ability of the 3D printer to build three-dimensional shapes of considerable complexity make this technology increasingly popular [1; 2; 3]. Fine-grained concretes based on Portland cement have become the most widely used for 3D printing in construction [4; 5; 6]. They can be attributed to the so-called digital concretes, which mean materials obtained using machines with numerical software control. As a rule, for extrusion molding, mixtures should contain more binder than ordinary concrete mixtures with similar mechanical characteristics [7; 8; 9; 10]. Composites with lower cement consumption, high mechanical characteristics, and good durability can be obtained using active mineral additives [11; 12]. In these composites, additives can play the role of cementing, pozzolanic, or filling materials [13; 14]. Usually, such active mineral additives include blast furnace slag, fly ash, and microsilica, which are often used in energy-efficient and digital concretes [15; 16; 17; 18; 19; 20; 21]. Limestone as a filler in concrete, consisting mainly of calcium carbonate, causes the formation of monohydrocarboaluminates and hexagonal calcium hydroaluminates [22]. This effect makes it possible to stabilize ettrin96 by increasing the volume of hydrates and reducing porosity. Inert materials, such as powders of granite, basalt, and other rocks [23; 24], act as nuclei of crystallization that fill the voids in the microstructure of the cement dough and physically stimulate the hydration of cement in the first few days of hardening [14; 25]. Cementless or low-cement materials (geopolymers) are promising synthesized compounds based on crystalline aluminosilicate materials and alkaline-activated binders. Hardened geopolymers have a different chemical composition than Portland cement stone and fundamentally differ in structure [26; 27]. According to [28], Table 1 shows the corresponding characteristics of typical \"standard\" concretes compared to some digital concretes, divided into one-component (1K) and two-component (2K) systems. The cement content is much higher for digital concretes, unless they contain significant cement replacement materials. The development of digital concrete involves increased early strength, including the strength achieved by the previous layer of the concrete mix, before laying the next layer (structural strength). An essential factor to consider when designing the composition of digital concrete is its durability. In this regard, it should be considered that the dominant technology of extrusion printing can lead to uneven application of layers, the formation of defects, and, as a result, a decrease in adhesion between them (Figure 1). The time interval contour length and printing speed also affect the quality of the layers [37]. The reduction of adhesion between the layers is no less substantial than the strength under compression and bending from the standpoint of durability, while the formed defects create ways for the accelerated penetration of water and aggressive agents, which in turn affects the waterproofness and frost resistance of the multilayer structure. It should be noted that with an increased content of cement paste, there is a greater risk of cracking and shrinkage.