Applying nanodispersed modifiers for producing shielding polyfunctional coatings

The first mineral based lacquer and paint coating have been developed based on Portland cement and soda glass, which does not require traditional silicators of zinc oxide and is also capable of absorbing man-made radiation. A significant change in the structure of silicate paint has been achieved by its modification with multi-layered carbon nanotubes. The developed composition has water resistance, good adhesion to the base, the improved durability, is capable of operating at high temperatures; the life of coating is 3 times longer in comparison with its analogues

Studying the stability of aqueous suspensions of multiwalled carbon nanotubes used for the modification of composite materials

In this paper, the stability of aqueous suspensions of multiwalled carbon nanotubes (MWCNTs) has been studied with physical and chemical methods. The optimum dispersion time of MWCNT suspension in a rotary homogenizer has been found. The dispersion time being increased, the quality of the suspension decreases. The data of the physical and chemical studies has also been confirmed experimentally on gypsum samples. The samples modified with MWCNT suspension of 2-hour dispersion show an increase in flexural strength and compressive strength by 40% and 48%, respectively, in comparison with the control sample, whereas the samples modified with MWCNT suspension of 10-hour dispersion show a decrease in flexural strength and compressive strength. The microstructure of the gypsum samples was studied with a scanning electron microscope

The influence of plasticising admixtures on drying shrinkage of cementitious composites

This article presents a research into the impact of plasticising admixtures on drying shrinkage of cementitious composites by evaluating the effectiveness of plasticising. Materials used in the study: Portland cement CEM I 42.5 R, plasticiser LS (modified lignosulphonates based), superplasticiser PCE (synthetic polycarboxylate esters based), superplasticiser MAP (modified acrylic polymers based), sand and water. The percentage change of plastic viscosity of cement paste indicates the effectiveness of plasticising of cementitious composites. The change of plastic viscosity has been tested by adding a specific amount of plasticising admixtures. The effectiveness of plasticising of pastes were tested using rotational viscometer. Chemical admixtures content in pastes varied from 0 to 1.2%. Drying shrinkage was tested based on length change of the specimens with fine aggregates. The method to minimise drying shrinkage of composites was established through use of plasticising admixtures. It has been found that by increasing plasticising admixture dosage from 0 to 1.2% the following changes occur: LS plasticising effectiveness increases by 35% while drying shrinkage decreases by 8%; MAP plasticising effectiveness increases by 70% while drying shrinkage decreases by 16%; PCE plasticising effectiveness increases by 80% while drying shrinkage decreases by 20%

Crack formation in vacuum concrete

The reasons of crack formation in vacuum concrete floors with reinforcing mineral wear-resistant coating were investigated. The main reasons of crack formation are connected with low concrete strength due to the lack of water for cement hydration, the absence of shrinkage seams in floor structure, wrong reinforcement and excess thickness of strengthening mineral coating of concrete floor which initiates the crack formation. At the concrete thickness 150 mm, the depth of crack spreading was 115 mm, the concrete strength in kerns—14.2–24.8 MPa instead of 30 MPa as planned, and the concrete macrostructure had the signs of lamination. Besides, an air clearance up to 4 mm in size was found between the foundation and concrete floor. The reinforcement skeleton structure in concrete floors did not envisage the possibility of horizontal displacement of concrete coating in the square limited by deformation seams, and the deformation seams did not penetrate into the depth planned eliminating their formation during concrete hardening. X-ray phase analysis of fresh hardening coating of concrete surface showed the presence of ettringite in it, and non- hydrated Portland cement minerals prevailed in the structure of concrete solution resulting in insufficient strength of the concrete hardened. Thus, due to the considerable heterogeneity of vacuum concrete structure and properties by thickness, the presence of the initiator of crack formation in the concrete upper layer (ettringite) and wrong reinforcing the formation of uneven shrinkage phenomena in hardening cement takes place resulting in crack net formation in the upper stretched concrete area. Frist Published Online: 30 Jul 201

A study on mechanical properties and structure of anhydrite binder modified by ultra-dispersed siltstone

This research is devoted to modification of physical and mechanical properties and structure of a binder based on natural anhydrite. A sedimentary rock siltstone was added into the composition as a mineral ultrafine additive. The presence of aluminosilicate minerals proves that finely ground siltstone can be used as a mineral additive in the composition of the anhydrite binder, accelerating crystallization of gypsum new formations and densifying the structure of gypsum stone. For the first time, the effectiveness of using sodium and ammonium phosphates as hardening activators of an anhydrite binder was shown. Siltstone, added to the composition in the amount from 0 to 5%, lead to up to 40% increase in strength, which is due to the action of siltstone particles as “crystallization centers” and formation of crystalline hydrates of calcium sulfate dihydrate on their surface. Combined action of calcined siltstone and lime leads to a 45% increase in strength due to the additional compaction by new hydration products formed in the course of metakaolin and lime interaction. Microstructural analysis showed that samples with calcined siltstone and lime have a more dense and uniform structure with a lower porosity, compared to those with only natural siltstone. First published online 03 February 202

Metallurgical hydrogen as an indicator and cause of damage of rolled steel

Fatigue tests and measurements of the volumetric distribution of metallurgical hydrogen in specimens cut from rolled I-beam 60Sh3 made of steel 10KhSND were carried out. Fatigue tests show a 20% reduction in fatigue limits compared to similar sheet material. On the fractures of the samples, there are flock-like defects in the areas of interface of the flanges of the I-beam or in the so-called zones of difficult deformation. The concentration of metallurgical hydrogen is unevenly distributed and varies from 0.17 ppm to 1.8 ppm. Large concentrations of hydrogen are observed in the zones of difficult deformation, which indicates the hydrogen nature of the metal defects observed at the fracture. The result of mechanical tests and hydrogen diagnostics is a manufacturing defect of rolled products that cannot be corrected. Hydrogen diagnostics using metallurgical hydrogen (without hydrogen charging samples) requires essentially less time than mechanical tests and yields the adequate result