# Energy-Efficient Mixtures Suitable for 3D Technologies
## 2 Materials and Methods  
To obtain materials investigated as mineral additives, we used Portland cement (CEM I 42.5 R (EN 197-1)), blast furnace granulated slag (GBFS), fly ash (FA), limestone powder (LP), and granite aspiration dust (GD). The mineralogical composition of the climker of used cement was as follows: C\({}_{3}\)S-57.10%; C\({}_{2}\)S-21.27%; C\({}_{3}\)A-6.87%; C\({}_{4}\)AF-12.19% (EN 196-2). The specific surface area of Portland cement was S = 330-350 m\({}^{2}\)/kg (EN 196-6). The chemical composition of Portland cement and mineral additives is given in Table 2.  
\begin{table} \begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Name Material**} & \multirow{2}{*}{**L.O.I.**} & \multicolumn{6}{c}{**Oxide Content, \%**} \\ \cline{3-8}  & & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **CaO** & **MgO** & **SO\({}_{3}\)** \\ \hline \hline \multicolumn{1}{c}{Clinker *} & - & 21.80 & 5.32 & 4.11 & 66.80 & 0.95 & 0.63 \\ \multicolumn{1}{c}{Blast-furnace slag} & 0.59 & 39.51 & 6.47 & 0.14 & 47.19 & 3.12 & 1.76 \\ \multicolumn{1}{c}{Fly ash} & 5.1 & 46.1 & 18.1 & 22.1 & 2.1 & 2.0 & 2.3 \\ \multicolumn{1}{c}{Granite dust} & - & 64.8 & 15.6 & 6.31 & 2.59 & 0.33 & 0.11 \\ \multicolumn{1}{c}{Limestone} & 43.8 & 0.29 & 0.40 & 0.11 & 54.40 & 0.40 & 0.08 \\ \hline \hline \end{tabular}   
*Blast furnace granulated slag had a glass phase content of 75-80%, its specific surface S = 320-350 m\({}^{2}\)/kg, density--2.9 g/cm\({}^{3}\), bulk density--1340 kg/m\({}^{3}\). Granite aspiration dust used with a specific surface S = 230-250 m\({}^{2}\)/kg, density--2.79 g/cm\({}^{3}\), bulk density--980 kg/m\({}^{3}\). Fly ash of type II category B with the size of particles passing through a sieve of 45 um no more than 25% (class 2) (EN 450-1:2012) was used. The specific surface of ash is 250-280 m\({}^{2}\)/kg. Limestone powder had a specific surface S = 450-480 m\({}^{2}\)/kg;  
In addition, the effectiveness of activated slag in the composition of concretes based on slag-alkaline binders was studied, the composition of which was adopted based on the studies of a number of authors [27] and included GBFS, CEM I 42.5 R, and NaOH (85%, 10%, and 5% of the mixture, respectively). Superplasticizer of the polycarboxyl type, with a water-reducing effect of 30% (EN 934-2), was used. Sodium hydroxide (NaOH) was used as a hardening activator. Quartz sand with a fineness modulus of 2.1, and a content of dusty and clay particles up to 1.0% (EN 12620) was used as an aggregate. In order to study the properties of extruded mixtures, a laboratory printer was designed and constructed, as shown in Figure 2. The head of the nozzle was a rectangle with dimensions of 20 \(\times\) 40 mm. The main task in the study of concrete mixtures suitable for a 3D printer is to ensure their necessary shape during extrusion from the printer head with the achievement of the specified strength of the layers (structural strength), as well as the adhesive strength between the layers of extruded concrete without the formation of cracks and other defects [4; 37]. To determine the structural strength, a method is proposed that allows measuring the ultimate load on a sample of an extruded layer of concrete, at which it begins to deform (Figures 3 and 4). Figure 2: Photograph showing the laboratory 3D printer: 1—electric motor of the extruder; 2—hopper of building mixture; 3—auger; 4—replaceable nozzle; 5—control panel; 6—frequency converter of electricity; 7—reverse motor moving the extruder in the horizontal direction; 8—manual drive moving the extruder in the vertical direction; 9—frame; 10—power cable of electric motors. The workability of concrete mixtures was determined by cone spreading. The bending, tensile strength at splitting, and compression were determined according to EN 196-1 at 1, 3, and 28 days. The adhesion strength of layers on samples formed by a laboratory 3D printer was determined by measuring the corresponding splitting stress.