ASSESSMENT OF CRACKING RESISTANCE OF CELLULAR CONCRETE PRODUCTS UNDER MOISTURE AND CARBONISATION DEFORMATIONS WITH STRESS RELAXATION

Objectives. On the basis of the experimental, theoretical and field studies, an engineering calculation method was developed for assessing the cracking resistance of external enclosing constructions made of cellular concrete, with the maximum gradient development of moisture and carbonisation forced deformations along their thickness, taking into account the relaxation of the shrinkage stresses. In this regard, the aim of the work is to provide technological measures at the manufacturing stage in order to increase the operational cracking resistance of the construction's outer surface layers by reducing the moisture and carbonation shrinkage of cellular concrete by introducing a large or fine porous aggregate in calculated amounts.Methods. A number of analytical equations were applied to establish the dependence of the shrinkage of heavy concrete of conventional hardness on the amount of aggregate introduced and its elasticity modulus, water-cement ratio and cement consumption, as well as the concrete's moisture content.Results. Knowing the volumes of the structural aggregate and the cellular concrete mass, as well as their modulus of elasticity, the shrinkage reduction factor of the cellular concrete was calculated with the addition of a lightweight porous aggregate. Subsequently, the shrinkage deformations of concrete in the surface layer of the outer enclosing construction, maximising crack resistance due to moisture exchange and carbonation influences under operating conditions, were defined, taking into account the relaxation of tensile stresses due to creep of concrete.Conclusion. Theoretical calculations, based on the recommended method of assessing the cracking resistance of cellular concrete enclosing constructions under moisture exchange and carbonisation processes, taking into account the relaxation of shrinkage stresses, showed that in order to exclude the appearance of cracks in wall panels 280 mm thick made of 700 kg/m3 gas ash concrete with elasticity modulus of 2500 MPa, it is necessary to have 70-80% of keramzite or granulated slag, and 50-60% of stone crumb (granite or marble crushed stone) of the volume of cellular concrete in the surface layer of 30-50 mm

REGULATION OF SEISMIC LOAD ON BUILDINGS SEISMIC DEVICES

The issues of regulation of seismic loads on structures using kinematic supports of highstrength concrete on the impregnated coarse aggregate and seismic isolation bearings Belleville. The results of experimental studies related to the obtaining of a new coarse aggregate and construction of seismic isolation bearings. Addresses the issues of interaction forces in thehemispherical supports vibration process

A novel operando approach to analyze the structural evolution of metallic materials during friction with application of synchrotron radiation

In this study, we describe an experimental setup and a new approach for operando investigation of structural evolution of materials during wear and friction. The setup is particularly suited for testing various friction pairs, including those in which both rubbing bodies are made of metals. The developed device allows circumventing the problems related to significant scattering of X-rays produced by metals and makes it possible using “real samples” in synchrotron beamlines operating in reflection mode. To demonstrate the capabilities of the device and the proposed new approach, an iron-based massive sample was subjected to thousands of friction cycles using a cemented carbide pin. The material was probed with synchrotron X-ray radiation within a few milliseconds after leaving the friction zone. The results of the microstructural and structural analysis, as well as results obtained from diverse mathematical models, allowed us to evaluate several features, including gradual accumulation of defects, microstructural refinement, dislocation density changes, surface layer oxidation, as well as several other phenomena caused by the dry sliding friction process. Mainly, it was possible to conclude that the process of wear occurred due to the cooperative action of oxidation and plastic deformation, which began during the first cycle of frictional interaction and was manifested in increasing the dislocation density, whose type was changed gradually during testing. The number of defects quickly reached a threshold value and subsequently fluctuated around it due to periodically repeated processes of defect accumulation and stress relaxation resulting from material wear. It was also observed that friction led to the quick formation of a mechanically mixed layer, consisting of the sample material and a mixture of two types of iron oxide – hematite and magnetite. The delamination of this layer was probably the primary wear mechanism

CHOICE THEORY OF CREEP DEFORMATION FOR EVALUATION OF LONG FINE-GRAINED AUTOCLAVED AERATED CONCRETE IN VIEW OF FACTORS CARBONIZATION

Experimental data on the effect of the age of autoclaved aerated concrete with and without carbonation factor to change its physical and mechanical characteristics, as well as by the amount of creep deformation and degree of reversibility. It was found that the solution of applied problems creep theory for structures of autoclaved aerated concrete, in accordance with their carbonation from the effects of atmospheric carbon dioxide, it is necessary to use the theory of elastic-creeping body on the basis of function creep measures in the form proposed by prof. S.V. Alexandrovsky

THEORETICAL BASIS OF COMPATIBILITY OF COMPLETELY-FILLED MULTICOMPONENT BINDING SYSTEMS

Abstract. Aim. An important direction in contemporary concrete science is aimed at the development of multicomponent systems using mineral powder fillers in a finely dispersed state to create strong and durable building composites. One of the most significant factors affecting the properties of multicomponent systems is the compatibility of its components. Efforts on the part of leading scientific institutes are aimed at replacing expensive and energy-intensive Portland cement with composite concrete products produced using mixed binders. In this context, the development of modern effective composites based on clinkerless alkaline binders becomes an urgent problem. Methods. Studies into the compatibility of multicomponent cementing systems are based on a contemporary technological approach that contributes to the production of strong and durable cement stone, without the use of traditional Portland cement. Results. Electron probe studies and X-ray phase analysis of concrete produced using a clinker-free alkaline activation binder showed that the studied multicomponent system contains a hydro-aluminosilicate zeolite phase of variable composition, as well as indicating the presence of calcite, quartz, albite feldspar, mica, zeolites and potassium feldspar. Conclusion. The results of the studies confirm the compatibility of all components of the multicomponent system comprised of mineral powder, alkaline coater and surfactant. The proposed technological method can be used to produce strong and durable building composites with clinker-free technology avoiding the use of expensive and energy-intensive Portland cement. Acknowledgments. The work was performed as part of research on the implementation of scientific project No. 05.607.21.0320. “Development of technology for new building composites on clinker-free alkaline binders using substandard natural and secondary raw materials” which received support from the federal target program “Research and Development in Priority Directions for the Development of the Russian Science and Technology Complex for 2014-2020.” Unique identifier for the agreement RFMTFI60719X0320

CRACK RESISTANCE AND DURABILITY OF PRESTRESSED WALL PANELS CONSTRUCTED FROM CELLULAR CONCRETE

Objectives The aim of the studyis to develop ways to increase the crack resistance and durability of prestressed wall panels made of cellular concrete.Method A complex study was carried out at the stage of factory manufacturing of two-module, aerated concrete wall panels with prestressed rods of class A-III reinforcing steel, 10 mm in diameter, located in the middle of the panel in the longitudinal and transverse directions.Results It was found that the total stress losses in straining rods prior to casting of the aerated concrete mix, connected with stress relaxation in the reinforce and with deformations of the headings of the straining rods in the gripping jaws, the steel mould deformations, as well as the losses after the panel exit from the autoclave during the transfer of force to the concrete, are 15-20% of the initial level. At the same time, depending on the dimensions of the straining rods, the length of the strain transfer zone was in the range of 150 to 250 mm. A study of the effect of pre-compression on the closure of possible technological cracks in concrete test panels showed that, due to biaxial compression of concrete, new cracks do not appear when they work on bending and stretching (during the decking and transportation). Moreover, initial cracks that sometimes can appear during the autoclave processing become closed.Conclusion Comparative tests of prestressed and typical panels for short-term load in accordance with GOST 8829-94 requirements indicate a significant increase in their rigidity and crack resistance, as well as the shear strength of their bridge part. The design of straining reinforcing rods with the end transverse anchor in the form of a horseshoe, together with attached flat welded frameworks made of Vr-I wire with a diameter of 5 mm, which are installed along the contour of the window openings of the test panels, ensure its reliable adhesion to cellular concrete and effective anchoring in the panel's body until the end of its useful life. Biaxial prestressed reinforcement by single rods in combination with conventional frame reinforcement opens up possibilities for the production of external wall panels from non-autoclaved cellular concrete with ordinary heat treatment, instead of ceramsite concrete panels

Effects of severe plastic deformation on the magnetic properties of terbium

We report on the magnetic and magnetocaloric properties of Terbium ribbons subjected by cold rolling. The magnetic entropy change ΔS = 8.66 J/(kg·K) and adiabatic temperature change ΔT = 4.38 K for a bulk sample of Terbium in an external magnetic field change of 1.9 T are larger by about 12% and 26% respectively, than those values of cold rolled Terbium. The changes are fully reversible and can be fully restored by an additional annealing

Effects of severe plastic deformation on the magnetic properties of terbium

We report on the magnetic and magnetocaloric properties of Terbium ribbons subjected by cold rolling. The magnetic entropy change ΔS = 8.66 J/(kg·K) and adiabatic temperature change ΔT = 4.38 K for a bulk sample of Terbium in an external magnetic field change of 1.9 T are larger by about 12% and 26% respectively, than those values of cold rolled Terbium. The changes are fully reversible and can be fully restored by an additional annealing

Magnetocaloric Properties of Severe Plastic Deformed Gd100−xYxGd_{100-x}Y_x Alloys

In this work we report on the results of investigation of the magnetocaloric effect in $Gd_{100-x}Y_x$ (x = 0, 5, 10, 15) cold rolled ribbons. It is shown that the magnetocaloric effect exists within a wide temperature interval 258-295 K and is comparable with magnetocaloric effect observed in bulk samples of pure gadolinium. The value of the magnetocaloric effect in the rolled samples is reduced as compared with the bulk samples and strongly depends on the degree of the plastic deformation. Heat treatment procedures can restore the values of the magnetocaloric effect in the cold rolled ribbons up to initial ones. Thus, cold rolling is proposed to be a promising technique for producing thin forms of magnetocaloric materials for heat exchangers of magnetic cooling devices, modifying microstructure of the materials and related magnetic properties