Multicomponent concretes with local raw materials and organic mineral additives

. The paper presents the results of studying dense structure concrete containing highly dispersed aleuropelite rocks; amorphous silica-containing, plasticizing and water-repelling additives. The use of natural raw materials and modifying additives in rather low dosage ranges has been proved rational for mass construction concentrated on the use of B30-50 class concretes. It has been established that concrete structure forming, its physical and technical characteristics and durability are ensured by the compositions without involving additional grinding operations and activating the mineral component in the technological process. The proposed technical solutions serve as the basis for the production of a whole class of micro-concrete that is efficient in terms of technical and economic indicators.


Introduction
The contemporary concrete science contains a number of provisions to control the structure and properties of concrete mixture and hardened concrete [1][2][3][4][5][6].
One of the common techniques is to use various modifying components capable of changing the rheological and technical characteristics, as well as the durability of concrete.
Scientific and experimental data prove that the effectiveness of the modifying component is determined by a number of factors including the chemical nature and composition, the average grain size and particle size distribution [7][8][9], the mineral base of the component.At present, from 2 to 5 components are added into the traditional composition when manufacturing concretes.The increase in the competence of concrete mixtures mainly comes to the addition of natural, man-made materials characterized by grains of a fine, ultradispersed and nanoscale range in dosages up to 20-25%.This complicates the concrete production technology since a number of complex organizational and technical problems arise in the acceptance, storage, processing of materials with a high degree of dust generation.
The widely used microsilica is introduced into modern concrete mixtures in a sufficiently large amount; scientific data [10] indicate its introduction in dosages up to 20% thus increasing the cost of concrete significantly.
Metakaolin is well-known among the modifiers of concrete mixtures [11,12].Its dosage should also be limited since the pozzolanic activity required to bind portlandite is much lower than the amount of introduced additive.Therefore, part of the added kaolin operates as fine filler in the cement stone.
The strategy for the production of reinforced concrete structures should be based, first of all, on scientific and practical grounds for obtaining concretes required for mass construction (B30-50) with a high degree of durability.When choosing mineral raw materials and additives, it is necessary to pay attention to technical and economic indicators, i.e. improvement of the technical characteristics of concretes should handle a full range of issues in the design, construction and operation of facilities.
The most difficult issue in the study of a cement stone structure formation is the hydration processes and interactions of the obtained products with active and low-reactive mineral additives of the ultradispersed and nanometric range.A variety of inorganic materials and substances from the category of numerous varieties of secondary mineral raw materials are used as mineral additives.To identify common patterns, leading researchers [13,14] argue that the effect of modifying components should be examined at various scale levels.
The technique of the multicomponent concrete allows each component to exhibit its characteristic effect (figure 1), It is necessary to analyze a number of combinations of modifying components in order to obtain a synergistic effect.The research was focused on the effect of natural mineral materials in combination with superplasticizing, hydrophobizing and pozzolanic additives.

Materials and methods
The research was carried out with Portland cement CEM 1 42.5 of JSC "Sukholozhsky Cement Plant".We made use of HeroCrete C as an effective superplasticizer, as a water repellent -triethanolamine (TEA), a pozzolanic component -amorphous silica (AS), a mineral component -natural aleuropelite rock (ANR) of the Ishim Formation in the south of Tyumen region.The rock deposits are diagnosed in large volumes [15], they are considered geologically integral and represent a single suite with a thickness of up to 20 m.
A system of physical and chemical methods was applied in the research at various scale levels.The chemical composition of the main hydrate formations was distinguished by Xray analysis.The rheological properties of cement pastes were maintained at a constant level while studying.The influence of the components was assessed by water requirement change.
Standard techniques were employed to characterize density and strength at different curing periods.

Results
The chemical analysis of aleuropelitic rocks reveals its main components.They are SiO2 (71.4-81.0%)and Al2O3 (11.3-14.8%).The content of Na2O, K2O, Fe2O3, MgO is from 1 to 3%, Cl is below the definition limit.The results of X-ray phase analysis indicate quartz, sodium-potassium feldspars as the predominant minerals in the rock.The bulk of the rock is made up of particles up to 50 microns, the content of grains up to 15 microns is 40.0%, up to 30 microns -88.0%.The grains are mostly rounded (figure 2).In natural occurrence, the moisture content of the rock does not exceed 3-5% [15].Amorphous silica is a chemical synthesis product, tested in dosages of 0.5-1.5% in accordance with the established index of pozzolanic activity.
Mineral components were added into the cement paste composition in accordance with the recipe (table 1), the strength characteristics of the cement stone are shown in figure 3.

days
The combined introduction of aleuropelitic rock (20%) and amorphous silica (0.5%) provides the possibility to replace part of the Portland cement without reducing the cement stone strength characteristics.
The results of X-ray phase analysis state that the main structure-forming hydrates are hydrosilicates of the xonotlite-bermorite series.
The established ratio of finely dispersed mineral components was tested in concrete mix compositions (table 2).To optimize the concrete structure and concrete mixture rheotechnological properties, granite crushed stone with a grain size of 5-7.5-10 mm was used.The proportion of sand (concrete filler) in the total amount of fillers in the studied compositions was 0.33-0.35.
The compression strength of concrete samples was determined at the age of 28 days (figure 4).Sample cylinders were made in order to determine the water resistance and strength.They were tested at the age of 180 days.The concrete water resistance grade was defined by the air permeability method on the Agama device.The tensile strength of the specimens was determined by the splitting method, and the concrete tensile class Bt14 was obtained.
The bulk of the hydrosilicate phases contains lamellar, needle-like and fibrous forms, which present radial-fibrous, parallel-fibrous concretions.Intraphase recrystallization of these phases proceeds slowly due to the relatively low dispersion of the initially formed crystals in low-basic hydrosilicates.The structure of the concrete and the morphological features of the hydrated phases contributed to an increase in the tensile strength of the concrete composite.The change in the pore structure transforming into a conditionally closed one is associated with the completeness of pozzolanic and hydration processes, and provides increased water resistance to the W18 grade values.

Conclusion
Finely dispersed mineral additives of quartz-feldspar nature can be made use of.They occur in the form of aleuropelites.Combined with a superplasticizer, a pozzolanic additive and a hydrophobizing agent, they produce a synergistic effect.It can be achieved through physical and chemical interaction processes and obtaining fractal structures of composites with increased strength, both during compression and bend.
The combination of plasticizing, hydrophobic and sealing effects has made it possible to increase the water resistance up to high threshold values W18.The use of natural raw materials is quite rational since no special technology is required for the preparation and production of ultradispersed materials.

Table 2 .
Concrete compositions.The concrete mix contains HeroCrete C plasticizing additives and TEA.