Tension Strength Research Articles

Some Technological Parameters of Construction Joints Formation Using the Self-Compacting Concrete Mixtures

Introduction. The important condition ensuring the monolithicity of the erected massive monolithic reinforced concrete structures, divided in compliance with the standards into the heat-shrinkable blocks, is the quality of construction joints in terms of the new-to-old concrete bonding. The research on the bonding strength dependence on the technological parameters of the construction joints formation using the widely spread in recent years self-compacting concretes is a relevant task, because the number of publications on the respective topic is insufficient. The aim of the present paper is to develop a scientific concept regarding the influence of the certain technological parameters on the new-to-old concrete bonding strength during the construction joints formation.Materials and Methods. The research was carried out using the self-compacting and ordinary heavy vibratory-compacted concretes with the compressive strength ranged from 34.5 to 69.2 MPa. The object of the study was the dependence of the new-to-old concrete bonding strength on the method of standardised surface pre-treatment of the “old” concrete in a joint and the compressive strength of the grade of the “new” self-compacting concrete. The composite Mörsch specimens in which the “old” concrete was cured for up to 3 days were used as the main samples. The construction joint relative strength was considered to be the joint quality evaluation criterion equalling to the ratio of the shear strength of concrete in a composite Mörsch specimen to the minimum axial tension strength values of the “new” and “old” concrete. The quality indicators of the concrete were determined by applying the standard methodology. The specimens were cured under conditions simulating the production of works in the spring-summer season.Results. During the research, the construction joint quality criteria in terms of the “old” to “new” concrete bonding were analysed along with the changes they undergo depending on the studied recipe (concrete grade) and technological (length of the technological break, surface treatment method) factors. The dependences of the proposed construction joint quality criterion on the “new” concrete compressive strength (grade) were obtained and the inefficiency of the surface treatment with a metal brush was shown, especially if accompanied with the technological break extension. The required bonding strength values for B25 ... B35 grade concretes can be for sure provided by the surface pre-milling, whereas the extension of the technological break has negative affect on the bonding strength.Discussion and Conclusions. Due to the revealed low bonding strength of the “old” to “new” concretes, regardless the technological factors, it is expedient to look into the ways of ensuring the construction joint quality by implementing structural solutions such as keyed joints and (or) additional reinforcement.

Application of Mangrove Timber in Reinforcing Concrete

Use of mangrove timber beams for supporting floor slabs in historic buildings in Zanzibar Stone Town is still applied although the available structural data on mangrove timber is inadequate. This concern has called for an investigation on the structural properties of mangrove timber, so that the information obtained could help to establish the structural strength of the existing floor slabs in historic buildings. Hence, mangrove timber specimens were sampled from Zanzibar, and tested in the laboratory for their strengths in tension, compression and shear. The test results showed that mangrove is a hardwood timber of strength class D70, the highest rank of timber classification. Also, concrete beam specimens reinforced with mangrove timber rods, and others reinforced with structural steel were studied. The obtained test results showed that beams reinforced with mangrove timber rods with enlarged ends performed better than those reinforced with uniform mangrove rods. The strength of the beams reinforced with mangrove timber was found to be 50% of the beams reinforced with steel bars, implying that mangrove timber can be used to reinforce concrete beams.

Optimizing natural rubber blends for examination gloves: Vacuum radiation for mechanical strength and solvent barrier

AbstractNatural rubber (NR) is emblematic of sustainability compared to synthetic rubber. However, the tradition of adding sulfur as a vulcanization ingredient results in the release of toxic substances and the potential for health issues. In this study, a feasible strategy was proposed to replace sulfur and discover a safe bulk modification process for NR films. The results have shown that the NR particle size was disintegrated to below 10 nm by gamma irradiation. High tension strength up to 24.45 MPa was observed in the vulcanized NR blend film, which could be elongated up to 800% strain after exposure to an optimum dose of 14 kGy. In comparison to commercial NR latex and nitrile gloves, the vulcanized NR/ SIS films exhibited better chemical resistance ability against hexane, methanol, toluene, and acetone, as revealed by the permeation test. The appearance of amorphous regions and highly oriented NR crystallites was observed through transmission electron microscopy. Findings from this study propose the vacuum radiation strategy that can replace conventional vulcanization methods, resulting in NR films with high mechanical and barrier performance. Furthermore, the emission of toxic substances is reduced by this green process, making it practically useful for potential chemical‐resistant examination glove applications.

Mechanical, durability and microstructural characterization of various types of outflows in the production of glass fiber-reinforced sustainable concrete

This experimental program strives to explore the mechanical, durability, and microstructural characterization of glass fiber-reinforced geopolymeric recycled aggregate concrete (GRAC) developed by using five discrete types of outflows. The freshwater was fully swapped with each type of outflow for the GRAC fabrication to assess its influence on the efficacy of GRAC at different testing ages. The microstructural characterization and the mineralogy of fabricated mixes were determined by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The results depict that considering textile factory outflow in the development of GRAC offers the highest strength in tension and compression, which were 19% and 16% improved than that of the GRAC fabricated using fresh water. The application of fertilizer factory outflow in the manufacturing of GRAC presented the highest mass loss due to an attack of H2SO4 solution and the highest chloride attack penetration. The SEM and XRD results indicated that in GRAC made with fertilizer factory and domestic sewage effluents, the lower portlandite, dolomite, and labradorite intensities encourage the formation of calcium phosphate and CaZn2(OH)6H2O, which lowers the geopolymerization and strength of concrete mixes. The mixes with textile and service station outflow included much more hatrurite implying that these mixes contained more C−S−H hydrate. Consequently, the mix produced using textile factory effluent outperformed in terms of mechanical and durability performance. The addition of fly ash to all concrete mixes produced the maximum quantities of silica and labradorites so that the fly ash and Ca(OH)2 the pozzolanic reaction might produce more C−S−H gel and densify the internal structure.

Behavior of Nanoparticles in Service Transformer Oils and their Performance on Laboratory Ageing

The transformer is the most critical apparatus in the electric power network. Reliable operation of it is of foremost concern for a proficient power supply. Therefore, it is vital to safeguard the transformer so that it functions at its highest capacity. In order to achieve it, an improvement in the insulation system is necessary, as the majority of faults in transformers are due to the malfunctioning of the insulation system. Petroleum-based oils are extensively used as insulating liquids in transformers. The latterly evolved field of nanotechnology has encouraged studies on Nanofluids (NFs), which are suitable as liquid insulators. In spite of the advantages of NFs in electrical and thermal behavior compared to their base fluids, further studies are needed to establish their long-standing performances as liquid insulators. In this study, three mineral oil samples, new, mid-aged, and extensively aged, were taken. Nanofluids of 0.02% Al2O3 and 0.02% SiO2 of these oils were prepared. The base fluids and nanofluids were characterized by interfacial tension, acidity, dielectric dissipation factor, resistivity, and electric strength. The nanofluids prepared were subjected to laboratory thermal ageing in the presence of copper and kraft paper for 64 hours at 150 °C. The unaged and laboratory-aged nanofluids were characterized for acidity, Interfacial Tension (IFT), Specific Resistance (SR), Tan Delta (TD), and Dielectric Strength (BDV). It was found through this work that the addition of nanoparticles upgraded the properties of oil samples. The long-term applicability and permanence of nanofluids might depend on catalytic effects. These catalytic effects are derived from the internal assembly materials of the transformer.

3D-printed strong and ductile high-entropy alloys with orientation arranged nanostructure complex

The rapid development of 3D printing technologies demands new materials with novel properties, as many high-strength metallic materials (up to over 1000 MPa) suffer from a significant weakness in ductility despite their enhanced mechanical properties, particularly in tension strength. To address this issue, we fabricated precipitation-hardened high-entropy alloy (Fe28Co29.5Ni27.5Al8.5Ti6.5) and employed aging post-treatment to obtain a duplex multicomponent intermetallic nanoprecipitate arrangement while retaining the in-situ dislocation network features. This approach resulted in the formation of a novel orientation arranged nanostructure complex (NSC) in the alloy. The NSC structure is composed of duplex multicomponent intermetallic nanoprecipitates (L12 and L21 phases), disordered multicomponent FCC matrix, and in-situ dislocation network. This resulted in ultra-high tensile strengths of 1430 MPa and an excellent tensile elongation close to 16%, surpassing the performance of other advanced commercial steels and alloys. These findings offer an effective approach to facilitate the design of high-strength and high-ductility structural materials for industrial applications. This is achieved by tailoring the microstructure through a combination of in-situ generation of high-density dislocations structure and multicomponent intermetallic nanoprecipitates in additive manufacturing. As such, this study represents an important step forward in the development of advanced materials for 3D printing technologies.

Methods for Uniform Wet Etching in Narrow Trenches and Vias

Abstract. Advanced semiconductor technology features complicated three-dimensional nanostructures and nanoconfined spaces such as nanosheets, supervias, deep contact holes and nanocavities. Uniform wet etching of such nanoconfined spaces across different feature sizes or critical dimensions (CD) is extremely challenging. Typically, etch rate decreases with decrease in CD size. In this paper we report methods to achieve uniform wet etch rate (ER) of SiO2 across different CD sizes by mixing organic solvents in the etching solution. We also report a reversal of etch rate trend where SiO2 structure of smaller CD etches faster than a larger CD, by tuning the ratio of organic to water solvents in the etching solution. We also investigate the impact of parameters such as solvent type, wall material, surface tension and ionic strength on ER. Our data suggests, while surface tension and ionic strength show no impact, the type of wall material, surface potential and organic solvent amount in the etching solution show a strong influence on SiO2 ER. Also, zeta potential could explain most of our results but not all, suggesting that surface potential is not the only factor impacting CD dependent ER in a nanoconfined spaces.

Determination of Physical and Mechanical Properties of Toona Ciliata and Acrocarpus Fraxinifolius Woods from São Paulo State

The use of wood in construction has many advantages, such as and the use of as speed of construction, high mechanical resistance, greater thermo-acoustic comfort, and sustainability with the use of reforestation wood. In Brazil, the main wood from planted forests are pine and eucalyptus, but other species are being planted in national soil such as Toona ciliata and Acrocarpus fraxinifolius. However, to use wood for structural purposes without compromising the safety of users, it is necessary to know the properties of wood. The aim of this work was to evaluate the physical-mechanical properties of Toona ciliata and Acrocarpus fraxinifolius. The properties evaluated were basic density, apparent density, shrinkage, strength, and modulus of elasticity in compression parallel to the fibers and tension strength perpendicular to the fibers, according to the test methods of the Brazilian standard ABNT NBR 7190:2022. Statistical analyses were performed using the t test at the 5% level of significance. Both woods have potential for structural use, with high mechanical properties and good dimensional stability, being like other woods already applied for this purpose. Acrocarpus fraxinifolius wood showed better mechanical properties than Toona ciliata due to its higher basic density. Australian cedar wood has been classified as D35 and Indian cedar wood has been classified as D70, due to its resistance to compression parallel to the fibers.

Magnetic string matter collapse in rainbow gravity

This work investigates the dynamics of a collapsing magnetic string dust and string fluid in the Plank Era via spherically symmetric rainbow geometry. The field equations are modified and solved to obtain the dynamical quantities, including mass density, pressure, string tension, and magnetic field strength. These quantities are presented graphically. The energy conditions are computed showing that all the dynamical quantities are associated with physical matter. The distance and moment of apparent horizon formation are computed. The magnetic field is found to affect the distance and moment of the apparent horizon’s formation. It accelerates the collapsing process. Further, the dynamical variables are maximum in the collapsing configuration’s center leading to compact object (black hole) formation. The probing particle’s energy affects all the dynamical variables of the fluid in a direct proportion. This resolves the information paradox as a particle with greater energy grasps the information from a particle with lesser energy and takes it out in the real world.

Exploring the potential of Mg-Zn-Mn-Ca/ZnO composites as a biodegradable alternative for fracture fixation: microstructural, mechanical, and in-vitro biocompatibility analysis

The current research investigates the microstructural, mechanical, in vitro degradation, biocompatibility, and in silico biomechanical behaviour of highly alloyed Mg-Zn-Mn-Ca quaternary system reinforced with ZnO nanopowder as candidate material for resorbable fixation devices. The as-cast composite materials showed dendritic microstructure comprising of α-Mg as major constituent and Mg7Zn3 and Ca2Mg6Zn3 phases distributed in interdendritic zones, as revealed by X-ray diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy. The addition of ZnO led to a 17% and 22% increase in ultimate and yield strengths in tension and a 24% and 27% enhancement in ultimate compressive and compressive yield strengths, respectively. The mechanical strengthening and observed tension–compression reversed yield asymmetry strongly correlated with the lattice distortion (c/a ratio) resulting from the macroalloying. The amplitude-dependent internal friction confirmed the presence of immobile obstacles to dislocations and their role through their hysteretic-type anelastic response. The in vitro degradation results revealed corrosion barrier effect of secondary phases. The cell adhesion, viability, and cytoskeleton observations favoured their biocompatibility except for hemolysis rate. The finite element results showed reduced stress-shielded zone for developed materials indicating the favourable mechanical environment for peri-implant tissues at fracture interface required for faster fracture healing.

Experimental study of the interfacial micromechanics of multifunctional unidirectional carbon fiber reinforced polymer composite laminates with copper mesh

The mechanical properties of a unidirectional carbon-fiber reinforced polymer (CFRP) laminate with Cu mesh layers were investigated for use in aerospace applications as a multifunctional structural and electromagnetic interference shielding component. Nanoindentation was used to study the fiber/PEEK and Cu/PEEK interfaces. A data analysis methodology is presented to assess the interfacial strength from plots of hardness and modulus versus distance from fiber/Cu edge. The results indicated that annealing resulted in enhanced adhesion at the fiber/PEEK interface. Additionally, indents near the Cu/PEEK interface indicated poor interfacial adhesion. Bulk mechanical testing was performed to determine the effect of adding Cu mesh layers on the mechanical properties of the laminate. Additional Cu mesh layers decreased the tension, shear, and bending strength/modulus, while the open hole compression strength increased. This indicates that the Cu/PEEK interfaces weaken the laminate and lower the tension, shear, and bending strength by delamination.

Nomex Material and Nomex Honeycomb Structure Honey Comb Structure in Electre Method

This paper presents detailed experimental results. Paper A primer on honeycomb mechanical modelling architectures Studies always focus on stable conditions paying; Some random innovative honeycomb Based paper assembly structures their They have excellent mechanical performance and are specific Significant in recent years due to operations have received attention. The geometrically varying feature of honeycomb structures is the hollow cells that form between the thin vertical walls. The hexagonal shape of the actual honeycomb is usually the strongest shape. Advantages of Honeycomb Mixtures Exceptional strength to weight ratio. High hardness fire and fungus resistant honeycomb structures: It is found in soils ranging from 0.02 mm to 0.002 mm. ELECTRE (Elimination and Choux Traduisant La Reality - Elimination and Choice expresses reality) methods from recruitment to many real-world decision-making there are problems widely used. Transportation and more. Theoretical research on the fundamentals of electret methods is also active at this time. Alternative: Length of structure, Width of structure, Total thickness of structure, Hexagonal core height, Upper and lower sheet, longitudinal tension strength. Evaluation Preference: Population size, Number of generation, Crossover probability, Crossover distribution index. From the result it is seen that data flow testing is got the first rank where as is the Crossover distribution index is having the lowest rank.

Low-resistance joints for YBCO-coated conductors with Ag nanoparticle paste

Due to the limited available piece length of YBCO-coated conductors (i.e. tapes or wires) and the different requirements for magnetic field, joints are inevitable for manufacturing high-temperature superconducting magnets. In this study, a sintering nano-silver (Ag) process was developed and used to connect YBCO tapes stabilized by anAg layer with low-temperature and short-time sintering of Ag nanoparticle (NP) paste. The thermodynamic characteristics of Ag NP paste were explored using a TG/DSC setup. The effects of sintering temperature, mechanical pressure and lapped length on microstructures and electrical properties of joints were comprehensively investigated. It is found that the pre-volatilization of low-boiling-point solvent in the paste is beneficial to improve the densification of sintered structure, thus contributing to increasing the critical current I c of the joint. With increasing sintering temperature, the I c of the joint will be close to that of the virgin tape, and the joint resistance experiences small fluctuations, but joint connectivity is enhanced. As the temperature reaches 205 °C, I c decreases to 84% of the virgin tape, and joint resistance increases obviously. In addition, the axial tension strength at room temperature is improved with the increase in mechanical pressure, while the resistance does not demonstrate distinct variation. Considering the electromechanical properties, the optimal joining process is determined as sintering at 180 °C and 30 MPa for 10 min. The joint with this technology possesses a closely connected interface and a well-sintered nano-Ag microstructure with pores. By further extending the lapped length, a YBCO joint resistivity as low as ∼10.56 nΩ cm2 is obtained, which is around a quarter of that of the soldering joint, and the process is much easier than that of the Ag diffusion joint.

Effects of build orientation and strain rate on the tensile-shear behaviour of polyamide-12 manufactured via laser powder bed fusion

Laser powder bed fusion (L-PBF) of engineering thermoplastics is a well-established additive manufacturing technique. In this work, an experimental investigation of the tensile-shear behaviour of L-PBF processed polyamide-12 (PA12) is presented, with a particular focus on the concurrent effect of build orientation and rate dependency at strain rates ranging from 10−3 to 103s−1. Results show that the deformation behaviour features significant anisotropy at both low and high strain rates, while quasi-static ultimate strength in either tension or shear shows no dependence on the build direction. As the strain rate increases, the tensile strength is characterised by apparent positive rate dependence but remains insensitive to the build orientation; however the shear strength displays significant build orientation-dependent anisotropy, highlighted by the decreasing shear strength of specimens printed in the loading direction. Post-mortem scanning electron microscopy (SEM) demonstrates torn dimples with stretched filaments in quasi-static fractography, while cleavage facets with flake structures retrieved from high-rate loading. A fibrillar structure is observed from high-rate torsional loading indicating adiabatic decohesion during rapid crack propagation. These findings draw attention to the significant anisotropy of L-PBF PA12 parts in a high-rate loading regime and provide directions to improve the current L-PBF techniques.

ГРАНИЧНИЙ СТАН ДВУТАВРОВОГО АРМОВАНОГО ПЕРЕРІЗУ З ВИКОРИСТАННЯМ ПРУЖНОПЛАСТИЧНИХ ДІАГРАМ ДЕФОРМУВАННЯ МАТЕРІАЛІВ

The paper considers a technique for constructing the strength area of a I-reinforced section. The concept of "section strength area" is used in structural calculations based on ultimate equilibrium. The strength area is a closed area in the coordinates "moment - longitudinal force". A specific feature of the section strength region is that inside the strength region the section operates in the elastic stage, and at its boundary it passes into the limiting state with the possibility of unlimited plastic deformation. The equations describing the boundary of the section strength region are often called yield conditions. The complexity of obtaining dependencies describing the boundary of the section strength region largely depends on what mathematical dependencies describe the physical properties of the materials from which the section is made. In this work, it is assumed that the material from which the section is made and the reinforcing material are deformed according to the law of an ideal elastoplastic body. Thus, the deformation diagrams of materials are described by the Prandtl diagram. Moreover, the material from which the section is made has different yield strengths in tension and compression. The reinforcing material has the same tensile and compressive yield strengths. When deriving the equations describing the strength region of the section, it was assumed that a bending moment and a longitudinal force applied in the center of the I-beam wall. Taking into account that the section of an I-beam can be asymmetrical and have asymmetric reinforcement, different equations are used to describe the upper and lower boundaries of the strength region. To construct the strength area, in the general case, it is necessary to solve the optimization problem - for a given value of the longitudinal force, find the extreme value of the moment, taking into account the constraints (equalities and inequalities). Analysis of the results obtained in this way for a symmetrically reinforced section made it possible to propose a simpler technique for constructing the strength area of a I-reinforced section without solving the optimization problem. Keywords: elastoplastic body, reinforced I-section, strength area, calculation by limit equilibrium

Masonry Arch Bridges with Finite Compression Strength Subject to Horizontal Longitudinal Seismic Actions

The great diffusion of masonry arch bridges, sometimes of historical interest, requires the development of simple but effective methodologies for a preliminary but reliable evaluation of their static and seismic capacity. In this paper, the behaviour under longitudinal seismic actions is analysed by using the mechanism method. The masonry is supposed to have no tension strength but a rigid–perfect plastic behaviour with finite strength in compression. The arch is subject to permanent loads and to a horizontal acceleration acting in the longitudinal direction, which causes a horizontal inertial loading acting on the arch. Three hypotheses about the effects of the inertial actions of the backfill are considered, which correspond to three different real behaviours. A comprehensive numerical investigation is performed, which allows us to point out the influence of the geometrical and mechanical parameters on the seismic capacity of a masonry arch bridge. The results are given by means of diagrams that can be easily used for a preliminary seismic check of a masonry arch bridge.

Effect of a gap on the open hole tension strength of carbon fiber reinforced plastic laminates

Tensile tests of quasi-isotropic laminates with a circular open hole, which include a gap in the hole area, were conducted to demonstrate the effect of the gap on the strength. The test showed that the reduction in the open-hole strength owing to the gap was less significant than that in the no-hole tensile strength. A two-dimensional mechanical model of quasi-isotropic laminates with an arbitrary inclined gap was proposed and analytically solved to obtain a closed-form expression for the stress concentration. An approximate expression was provided as the sum of the global uniform stress field and the local stress field near the open hole, which was solved based on a complex variable method. The present analytical solution agrees well with the corresponding two-dimensional finite element solutions. The solution indicated that the stress increase owing to the gap is limited at the stress concentration area. The analytical results were consistent with the experimental results.

Mechanical and acoustic properties of deformable alloys

The paper is devoted to correlation dependences of ultrasound velocity with characteristics of strength and plasticity in uniaxial tension of Fe18Cr10Ni austenitic stainless steel with a unique set of physical and mechanical properties. Such a successful set of mechanical properties is provided by dislocation slip and twinning, the formation of stacking faults, and martensitic transformation. It should be noted that the assessment of changes in the mechanical characteristics of metals (especially at low temperatures) is a very laborious task and requires the use of non-destructive control methods. Experimental data was obtained using a bench designed to synchronize with recording of the “stress – strain” diagram for determining the values of ultrasound velocity propagation and the attenuation coefficient of the ultrasonic wave as a function of deformation. Measurement of ultrasound velocity propagation was reduced to determining the time of passage of an ultrasonic Rayleigh pulse between transmitting and receiving transducers. Attenuation was determined from the change in pulse shape. The pulses were excited by a piezoelectric transducer at a frequency of 5 MHz. The authors experimentally studied static loading effect on acoustic characteristics and calculated the destruction parameters. The propagation ultrasound velocity in deformable material is an informative feature for analyzing the nature of the processes that control plasticity. The effect of test temperature in the range 180 K ≤ T ≤ 320 K on acoustic and mechanical characteristics of the steel was studied to ensure control of its structural state and mechanical properties by means of non-destructive testing. The temperature range was chosen taking into account the possibility of direct γ → α′ martensitic transformation.

Synthesis and characterization of bulk mechanical properties of a bio-based resin filled by graphene nanoplatelets and cellulose nanocrystals

In the present paper, a novel bio-based resin derived from epichlorohydrin was reinforced by Graphene NanoPlatelets (GNPs) and Cellulose NanoCrystals (CNCs) in different weight ratios and characterized experimentally through tension tests and fracture toughness tests on bulk specimens. The nanofillers were applied separately. The experimental results showed that the neat resin has a Young’s modulus of 3.29 GPa, a tensile strength of 45.15 MPa, a stress intensity factor of 0.61 MPa m1/2 and a critical strain energy release rate of 0.091 kJ/m2. The level of the properties reveal that the bio-based adhesive can be used for cosmetic and for some structural applications. The addition of cellulose nanocrystals in the epoxy resin didn’t improve the mechanical properties of the neat resin mainly due to the development of intense aggregation of cellulose nanocrystals. On the other hand, the addition of graphene has led to the increase of the Young’s modulus and the fracture toughness and to the decrease of the tension strength of the resin. Development of agglomerations of graphene were also present in this case. The contradictory findings on the mechanical properties of the reinforced resin gives a clear message about the need for optimizing the manufacturing process. Both nanocomposites have undergone a complete life-cycle analysis which has shown that they are far more environmentally friendly than a conventional epoxy resin.

Refractory foam concrete for nuclear power

The composition of refractory foam concrete for long-term use at high temperatures in the nuclear power industry has been developed. Foam concrete based on Portland cement has an average density class of D700 and a maximum permissible application temperature class of I5 (500 °C). It is shown that Refractory foam concrete has improved deformation characteristics in terms of axial tension and flexural tensile strength. Changes in the strength of refractory foam concrete with an increase in the heating temperature of samples up to 400 °C, as well as its strength during prolonged exposure (up to 2000 h) at 200 and 400 °C. are presented. A thermodynamic calculation is given with the possible formation of low-base hydrosilicates (gyrolite and afwellite) up to 400 °C, which is confirmed by the results of studies of the phase composition of samples of refractory foam concrete. Ill. 8. Ref. 23. Tab. 5.