The possibility of obtaining effective highly dispersed additives from natural wollastonite is substantiated and their influence on the properties of fine-grained concrete is investigated. On the basis of wollastonite, a complex micro-filler with particle sizes up to 100 microns was developed, obtained by joint grinding with quartz sand in a 3:1 ratio in a ball mill in the presence of an anionic surfactant naphthalene-formaldehyde type C-3 and a calcium stearate hydrophobizer technical C-17. A suspension of wollastonite with a modal particle diameter of 405 nm was obtained by pre-grinding wollastonite and anionic surfactant in a ball mill, with their further ultrasonic treatment in a bath-type activator. Mathematical models of the dependence of compression and bending strength on the content of the initial components are developed. It is established that the complex microfill leads to an increase in the strength of fine-grained concrete in bending by 2 times, in compression by 1.7 times with its content in the composition of fine-grained concrete in the amount of 10% by weight of cement. Wollastonite suspension increases the bending strength of fine-grained concrete to 3.1 MPa, compression to 57.8 MPa. The results of qualitative x-ray phase analysis showed that the total intensity of diffraction maxima of not fully hydrated alite C3S, belite C2S grains and their aggregates in cement stone with wollastonite decreases by 1.5-2 times compared to the control composition. This is most likely due to the amorphous nature of the wollastonite surface after grinding in a ball mill and ultrasonic dispersion in a bath-type activator. In addition, such particles are the centers of crystallization. Their needle-like shape contributes to the reinforcement of the structure by crystallizing new formations of cement stone.
The research results of the effect of active mineral additive tripoli of the deposits of Grishina Sloboda of the Bryansk region on the strength of heavy concrete are presented in the article. The chemical composition and structure of the sedimentary rock tripoli are studied. It is found that the tripoli grinding to the specific surface area of 340 m2/kg leads to the production of concrete class B35 with its content of 5% and class B30 with its content of 10%. The extreme dependence of the concrete strength on the tripoli content after 7 and 28 days of hardening is established. It is shown that the diminution in the sand fineness modulus from 2.87 to 1.14 reduces the concrete strength with 5%-tripoli addition from 38.9 MPa to 21.8 MPa, and with its content of 10% from 36.3 MPa to 20.4 MPa. The dependence of heavy concrete strength after 7 and 28 days of hardening on the content of its components was determined by the method of mathematical planning of the experiment, it allows predicting the values of this indicator when varying the composition of the concrete mixture.
The composition of disperse-reinforced polystyrene concrete for the manufacture of small-pieces load-bearing structural insulating wall products is developed. Its properties and microstructure are studied. It is composed of Portland cement, granular foamed polystyrene, basalt fibre, water and silica-containing modifier obtained by mixing condensed silica, superplasticizer S-3 and an aqueous solution of sodium water glass. The developed disperse-reinforced polystyrene concrete modified by silica-containing additive is characterized by higher values of adhesive strength (0.231 MPa), class by bending tension strength (Btb4), class by compressive strength (B5), cracking resistance coefficient (0.77), grade by frost-resistance (F1150) with a slight increase in the average density and thermal conductivity coefficient. The increase of physical and mechanical properties and frost resistance of polystyrene concrete of the developed composition is achieved by compaction and hardening of cement stone, improving its adhesion to granular foamed polystyrene due to the synergistic effect of a silica-containing modifier acting as an adhesive and structure-forming additive, and basalt fibre as a disperse-reinforcing component.
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