Nº 12 (2024)

Concrete and reinforced concrete structures are susceptible to the negative effects of bacteria, mycelial fungi, and actinomycetes. The purpose of this research is development of compositions of cement binders with active mineral additives for biocidal concretes creation. For biocidal cements with an active additive manufacture following components were used: Portland cement clinker produced by JSC Mordovcement, two-water gypsum of the Poretsky deposit, fly ash of the Krasnoyarsk CHP-3 and biocidal ingredients: sodium sulfate, sodium fluoride. Biocidal cements were obtained by joint grinding of mineral components and biocidal additives, then an active mineral additive was added. The physico-chemical, physico-mechanical and technological properties of the cements with an active mineral additive and composites based on them were determined in accordance with current regulatory documents. X-ray phase analysis, thermogravimetric analysis, differential thermogravimetry, calorimetry and other methods were used in this work. The features of phase transformations in cement stone are revealed depending on the type and content of biocidal ingredients, active mineral additives and hydration time. The absence of ettringite formation during hydration of cements modified with sodium fluoride and the presence of a new hydroaluminate phase have been established. The curves of TG, DTG and DTA for hydrated biocidal cement with the addition of fly ash modified with sodium sulfate are almost identical to the curves of hydrated ordinary cement. The largest amount of C-S-H gel (40 wt. %) was recorded in formulations with an active mineral additive. Based on the results of the study of normal density and setting time of the cement dough, the strength of samples of biocidal cement stone during compression and bending, regression equations were obtained, graphical dependencies were built and optimal compositions of biocidal cements were determined. Compositions of biocidal cements superior in physical and mechanical properties to ordinary Portland cements, which are recommended for the manufacture of biostable building products, have been obtained.

Research related to the development of the criteria for optimizing the composition of building mixtures based on mineral powders is currently still relevant and is one of the priority issues in the industry. Based on the fact that the processes of disintegration of raw material of rocks are predominantly used in preparation for its further technological processing, this paper proposes to use the parameter of the surface activity of the resulting powder system to assess the process of mechanical activation during material crushing, and to use the analog value of the Hamaker constant to optimize the composition of the mixture based on the principles of maximum dispersion interaction of powder particles. Using the example of rocks of various genetic groups of natural and technogenic origin (basalt, quartz and polymineral silica-containing sands, saponite-containing waste from the enrichment process of kimberlite ores), the algorithm for calculating the above-mentioned characteristics is shown. It has been established that with the same duration of grinding (and comparable values of the dimensional characteristics of the resulting powders), the surface activity increases in the following series: polymineral sand, quartz sand, saponite-containing material. The dispersion obtained by mechanical grinding of serpentine is characterized by the maximum dispersion interaction of the particles of the studied mineral powders (basalt, saponite-containing waste, serpentine), estimated by the values of the analog Hamaker constant.

The multicomponent composition of the raw material mixture and the heterogeneity of the structure of highly functional concretes at various scale levels make it possible to effectively control the formation of indicators of its damping properties due to prescription and technological factors. Experimental compositions included Portland cement, quartz sand, granite screening, silica, metacaolin, quartz flour, microcalcite, shrinkage compensators, hyperplasticizer and reinforcing microfiber. The hydrodynamic properties were investigated by methods of free and forced oscillations.Experimental compositions included Portland cement, quartz sand, granite screening, silica, metacaolin, quartz flour, microcalcite, shrinkage compensators, hyperplasticizer and reinforcing microfiber. The hydrodynamic properties were investigated by methods of free and forced oscillations.Experimental compositions included Portland cement, quartz sand, granite screening, silica, metacaolin, quartz flour, microcalcite, shrinkage compensators, hyperplasticizer and reinforcing microfiber. The hydrodynamic properties were investigated by methods of free and forced oscillations.A laboratory complex of vibrodynamic tests has been developed that provides automated processing of the amplitudes of bending damping vibrations of the first mode of concrete samples to calculate the dynamic modulus of elasticity and the logarithmic decrement of attenuation. The high accuracy of the results obtained made it possible to identify the nature of the influence of various prescription factors (consumption of cement, pozzolan additives, microfiber, shrinkage compensators) on the dynamic modulus of elasticity and damping of concrete. An increase in the value of concrete damping (by 1.22 times) was established with an increase in cement consumption from 300 to 734 kg/m³. The introduction of shrinkage compensators, differing in the mechanism of action, made it possible to obtain non-shrinkable injection molding compositions and favorably affects the vibrodynamic parameters correlating with the magnitude of the overall heterogeneity of the microstructure of concrete.The results of the research have been tested in the manufacture of prototypes of concrete and reinforced concrete cutting machines (small-sized milling machine), as well as laboratory testing equipment.

The paper provides the results of studying the dependence of elastic-strength properties of unfilled epoxy polymers on moisture content by example of 18 different compounds. It includes the analysis of possible effects associated with changes in free moisture content in the polymer matrix structure, including a change in nature of behavior under load from brittle to viscous with a multiple increase in relative deformations at rupture, as well as quasi-embrittlement, manifested in the elimination or reduction of forced highly elastic deformations on the deformation curve. In addition to the shape corresponding to the one close to linear dependence of the change in tensile strength and modulus of elasticity on moisture content with a maximum around W~0%, the study revealed other forms of interrelation of parameters under consideration: with a local maximum of values in the “optimal moisture content” area differing from W~0%; with “plateau” sections around both extreme humidity conditions. The similarity of the effects occurring around moisture content of W~0% for epoxy polymer samples both in the control state and after prolonged climatic aging is shown. A hypothesis was formulated regarding the existence of a pattern common to epoxy polymers of change in the nature of the dependence of mechanical strength on moisture content during field climatic aging. Based on a joint analysis of the dependence curves of elastic-strength parameters on moisture content, the most representative epoxy polymer compounds for field studies were selected to compile training datasets for a machine learning model predicting changes in the elastic-strength properties of polymer materials exposed to environmental factors.

A standard assessment of clayey raw materials from the Neftegorsk field in the Samara region was carried out. It has been established that clay, in all respects except CaO content, meets the GOST requirements for raw materials for the production of expanded clay gravel. The group of clay raw materials is defined as slightly intumescent clay. The influence of firing temperature, content of organic and iron-containing additives on the degree of swelling was studied. A non-standard assessment of clay was carried out using a calculation method based on chemical composition. The types of necessary additives and their percentage content for targeted adjustment of the composition in order to obtain maximum swelling are theoretically justified. A complex additive composition has been developed to increase the swelling properties of clayey raw materials from the Neftegorsk field, including flask, pyrite cinders, alkaline aluminum etching sludge and solar oil.