Abstract: Test results of concrete under the conditions of simultaneous action of multiply repeated loads of axial compression and cyclic freezing at different temperatures are given. It is established that such variable stress state of concrete under the condition σmax<R0T (where σmax is the maximum stress of the loading cycle and R0T is the stress level determining the lower boundary of the microcrack formation region of concrete) can increase its frost resistance. This is only true if the degree of water saturation of gel pores and pore capillaries of concrete does not exceed a critical value – more than 90% by volume. The results of the investigations of the structural and technological characteristics of concrete (water-cement ratio, moisture content, differential porosity, ice content, determined by calorimetric and ultrasonic methods), frozen to temperatures down to minus 70 °C, confirm the validity of the conclusions about the effect of the variable stressed state of concrete on its frost resistance.
Abstract: The article deals with the mechanism of interaction of super-plasticizers and hyper-plasticizers additives with mixing water, the formation of micelles and organized water. The interaction of mixing water and additives with Portland cement particles, surface tension, specific surface of bindings and their significance in setting and hardening processes are considered. It is shown that a local effect plays a decisive role in micro-heterogeneous organized media associated with the dissolution of hydrophilic and hydrophobic molecules in the volume of the micellar system or the receptor molecule cavity. In this case, the change of dissolved substances properties is due to the change of the medium state only in the microenvironment, and not in the whole solvent - water. The surface energy of the dispersed material and the degree of dispersion are very important for the concrete technology. All dispersed materials of the system are unstable. The aggregation of powder particles of building materials spontaneously takes place in highly dispersed powders and if such powders get pressure, it is possible to get a hard and strong material without water and additives.
Abstract: This work presents the results of investigations of the topological characteristics of quartz raw materials of various mineral compositions crushed to the critical state of the dispersed layer under which the shape of the particles and the action of the electrostatic repulsion forces change.
Abstract: The physical and mechanical properties of lightweight constructional heat-insulating concrete (sawdust gypsum concrete) with high-strength gypsum binder, modified by food cotton microcrystalline cellulose and organic fillers of plant origin from the waste wood of coniferous and deciduous species in the form of cavitationly processed pine and birch sawdust have been studied. The dependence of the cavitation extraction time of water-soluble reducing substances (sugars) from sawdust on the strength of sawdust gypsum concrete is established. The changes in microstructure of the gypsum matrix, the mean density, bending tension strength and compression strength, the thermal conductivity coefficient of sawdust gypsum concrete on the basis of the cavitationly processed sawdust with the introduction of microcrystalline cellulose are analyzed. It is proven that microcrystalline cellulose compacts the space between the crystalline hydrates of calcium sulfate dihydrate in the gypsum matrix microstructure and improves the physical and mechanical properties of sawdust gypsum concrete.
Abstract: Current trends in the field of construction material is focused on enhancement of sustainability of building materials and constructions urging on development of new types of inorganic binders and composites in order to meet the modern requirements of service performance and special properties. This research studied and demonstrated the opportunity to develop zero-cement heat-resisting granite-based nanostructured binder (GNB) using «green» technology production. XRD and DTA analyses demonstrated that the thermal exposure of GNB to wide range of temperatures of 20–1000 °C leads to such phase transformations in the binder as α-quartz to β-quartz transformation; amorphous alkali-aluminosilicate (gel) to crystal phase of Са-albite. The calculation of cell volumes characteristics for low-temperature (before thermal exposure) and high-temperature (after thermal exposure) phases was performed using following equation: where is concentration (by wt. %) of mineral phases; Vi is unit cell volume of mineral phases, Å. The calculated ratios of unit cell volumes were close to 1 which ensures a structural stability of the GNB under thermal exposure and confirms its heat-resistant performance.
Abstract: A multi-level optimization of size-consist of foam concrete is considered with the aim of significantly increasing its construction and mechanical properties. The results of theoretical and experimental studies confirming the expediency of using this process technology are given. In the course of the studies, theoretical and experimental conditions for creating balanced size-consist of non-autoclaved modified foam concrete with an increased solids concentration per volume unit and performance properties with complex organo-mineral admixture of sustained action on the basis of balanced ratio of chemical and finely-dispersed mineral ingredients optimizing its size-consist and structure were developed. The use of microsilicasuspension in foam composition is theoretically justified, and in the composition of foam-concrete mix of finely-dispersed slag and complex chemical modifier with an accelerating agent, that provide an increase in the strength of non-autoclaved foam concrete by more than 2 times, a decrease in thermal conductivity by 25%, shrinkage – by more than 4 times.
Abstract: Non-autoclaved aerated concrete certain advantages are significantly lower production organization costs and technology energy intensity due to the lack of autoclave curing, the possibility of different scales industries foundation as well as monolithic construction applications. All of this allows to solve complex problems of various purposes buildings erection, heat and noise insulation. Portland cement consumption significant reduction and material properties management can be achieved through use of composite binders containing local natural and technogenic components selected on the basis of their genesis and properties. The applicability of heavy concrete and ceramic bricks processing wastes as well as such large-tonnage extraction of iron ore as sandstones granulation selection as mineral additive for non-autoclaved aerated concrete production as well as a number of accompanying issues of the of a high-quality pore space structures formation control are considered in the present article.
Abstract: The paper overviews the process of thermolysis of fire-retardants based on melamine, ammonium polyphosphate and pentaerythtritol and containing titanium dioxide of different trademarks. The role of titanium dioxide as a component of fire-retardants is revised. Titanium dioxide was perceived only as white pigment, but this paper states that the properties of a charred layer forming from an intumescent coating depend on the properties of titanium dioxide's species, such as surface treatment and crystalline structure. This statement is proven by using thermal analysis of intumescents with different titanium dioxide's trademarks; it shows that rutile titanium dioxide helps forming a charred layer with the highest thermal stability thus fire retardant efficiency grows up. It means that the knowledge of processes which occur in intumescents based on primary products with different qualities helps to create fire-protective compositions which will perform more reliable in case of fire.
Abstract: Due to its novelty, futuristic appearance of created forms, a vivid contrast with a conventional image of a construction site, construction 3D printing attracts attention of a wide audience. Specialists see it as affording significant possibilities for saving all kinds of resources, reducing construction time, giving possibility to implement progressive design solutions, but they also see serious problems, such as: an immature general concept of development of additive technologies, a limited range and high cost of consumables, lack of methods for development of new compositions and lack of experience in application of such methods as a result. The paper analyzes links between the process factors and properties of molding components; principles of their practical implementation are proposed. Special attention is given to the issues in assessment of construction printability of newly-developed compositions.
Abstract: Researches by definition of optimum temperatures at hashing asphaltic concrete mixes on bitumens of different structural types with application of a method of mathematical designing of experiments are presented. Varied factors at manufacturing asphaltic concrete mixes were an index of a penetration of bitumen as the characteristic of a structural type of bitumen, the maintenance of bitumen and temperature of hashing of mixes. Processing of results of experiment is executed with application of computer technologies by means of a package of applied programs Maple. Mathematical models of physicomechanical properties of asphaltic concretes in the form of the equations the regressions reflective link between investigated properties of asphaltic concretes and varied factors are received. It is determined that at reduction of an index of a penetration and a rise of temperature of mixing strength of an asphaltic concrete increases. At a rise of temperature of hashing and increas asphalt content in mixes the water-resistance of an asphaltic concrete increases. On extreme dependences of indicators of durability at a tensioning and a tension in bending from hashing temperature optimum temperatures of hashing asphaltic concrete mixes are defined. It is established that optimum temperatures of hashing depends on an index of a penetration of bitumen and raise at its reduction.