Key Engineering Materials Vol. 864

Abstract: Fiber-reinforced concretes are varieties of composite materials. Such materials are commonly used nowadays. Concrete is fiber-reinforced using various fibrous materials, or fibers, which are evenly distributed over the volume of the concrete matrix and simultaneously provide its 3D reinforcement. Fiber-reinforced concrete has better stress-related strength characteristics than ordinary concrete. Since building structures must meet both the strength, rigidity and stability requirements, and the fire safety requirements, then for the extensive use of fiber-reinforced concrete structures, not only the external load design, but also temperature effect design should be conducted in the design phase. The strength and strain characteristics of fiber concrete exposed to high temperatures must be known for this purpose. In view of this, three series of prisms were manufactured and tested: the first series contained no fiber at all (control prisms), the second series contained basalt fiber, and the third series contained steel fiber. The test results showed that adding fibers improves the mechanical characteristics of fiber-reinforced concrete samples under specified conditions.

Abstract: Two models of hollow core slabs were tested: reinforced concrete and steel fiber concrete. When designing slab models, the proportions of full-sized structures were preserved for the further possibility of correct data comparison. As a result of testing models of hollow core slabs, it was found that the bearing capacity of a slab with combined reinforcement is 24% higher than that of reinforced concrete, the deflection is 36% less, and the crack resistance is 18% higher. The use of steel fiber made it possible to avoid the brittle fracture of a steel fiber reinforced concrete slab, which was observed in the model of a conventional reinforced concrete slab.

Abstract: The results of concrete testing on sulphate-resistant slag Portland cement for rigid coating of agricultural roads and aerodromes are presented in the paper. The results of experimental investigations of samples in the form of cubes on compressive strength and samples in the form of prisms on bending strength under different hardening conditions and at different water-cement ratios are presented. Selection of hardening conditions of concrete on sulphate-resistant slag Portland cement was made based on achievement of quality indicators no worse than in concrete on Portland cement. The expediency of introducing into the concrete organic surface-active additives - lignosulfonates in order to achieve the required strength is grounded. It is proved experimentally that the proposed concrete has sufficient frost resistance.

Abstract: One of the main components of urban design and landscape architecture that shapes and emphasizes the urban environment are small architectural forms. These elements of landscape architecture are used outdoors, so the material is influenced by a variety of atmospheric phenomena (temperature fluctuations, insolation, etc.). The results of the experiments showed that increased water resistance rates reduce the degree of exposure of the aggressive liquid medium, in particular sulfate and magnesium surface and groundwater, and frost resistance create conditions for the operation of these samples outdoors. The whiteness of the obtained results indicates that the obtained composition of concrete can be used as decorative with the addition of colored pigments.

Abstract: The article considers issues relating to the decorative concrete stability to frost impact. The study of the influence of prescription factors on the frost resistance value of composite compositions, manufactured of high-mobility mixtures, was carried out according to a symmetrical 5-factor plan with 27 experiments. Depending on the nature of the effect on the decorative composite, the variable raw materials are grouped into two groups of factors - modifications of cement-sand system, parameters of dispersed reinforcement. Kinetic curves, correlation, experimental-statistical model were constructed based on the results of the field experiments. The results of the research demonstrated – the use of zeolite instead of part of cement, glass fibres and fillers of optimal granulometric composition in combination with a plasticiser contributes to reducing integral porosity and provides the preservation of composite strength, and accordingly, resistance to climate impacts, saving the decorative properties during the operation of the decorative composite.

Abstract: The characteristics of the macrostructure of expanded clay concretes are compared using the topological and fractal approaches. The sensitivity of concrete strength to the fractal dimensions of a cement-sand matrix, expanded clay gravel, feldspar grains, large fractions of quartz and pores is verified. The trend of the influence of the expanded clay concrete macrostructure on its strength is determined using the fractal approach. Fractal modeling of the macrostructure of expanded clay concrete made it possible to reduce the forecast error in the indices of their strength by 1.18...2.03 times in comparison with the topological approach.

Abstract: The paper describes the methodology of processing of the experimental data from the study of the hardening process of the binder paste, which allows to reveale information hidden in the results and objectively divide the period of structure formation into steps that differ in mechanisms and conditions. The proposed method has a universal character, is designed to study compositions of a heterogeneous structure and is implemented using experimental data on the plastic strength of gypsum binder paste as a simplified model of such a composition. It consists of two stages - the transition to normalized values and coordinate transformation to adequately display the observed processes of structure formation. To determine the type of the corresponding coordinate transformation, Erofeev and Kolmogorov equations were considered, which describe, in particular, crystallization processes. Based on the proposed equations, a physically reasonable choice of coordinate transformations of the re-logarithmic type was carried out. Processing the data on the plastic strength of the hardening gypsum binder paste as a model of the composition of an inhomogeneous structure allows us to identify the main stages of structure formation characterized by linear dependencies and transition stages in which qualitative transformations of the regime of change in plastic strength during hardening are observed. The separation of the total time of structure formation at the step is fixed on the graphs of changes in the corresponding properties, and the transition stages correspond to the points of change in the angular coefficients of the obtained dependencies. It is shown that the stationary step of structure formation corresponding to the stable maintenance of supersaturation is reflected in the general linear section on the graphs. It is shown that the time of occurrence of transition stages recorded during the measurement of plastic strength approximately corresponds to the setting time obtained by regulatory methods. A geometric interpretation of the angular coefficients of the obtained dependences which allows one to determine the structure of growing nuclei of a new phase was considered. The proposed technique can be applied to control the processes of structure formation of heterogeneous composition compositions.

Abstract: To this day, there is a large volume collected of the results of experimental studies on structure changes in various dispersions serving as base for production of most construction materials. The analysis of collected information revealed that there is an entire category of stick-slip phenomena, the case history of which is represented by N-and S-type inflections on rheological, kinetic and other curves. We should emphasis that the view of such non-trivial charts is alike with geometry of standard curves of standard conditions. And this alikeness predetermines the possibility of applying topological models of «fold» and «ruffle» types for studying various abnormal effects. We must also note that besides N- and S-types there is a range of other characteristics («flags») pointing to applicability of the methods of catastrophe theory to studying certain processes initiating the apparition of interruptions in system development. Recognition of above-mentioned particularities allows determining the fact and type of catastrophe, the standardised structure of which facilitates finding strict patterns and thus defines directions of optimisation of various situations of research and practical nature. This work shows that pieces of evidence and consistent patters are reliably interpreted within the framework of the proposed concept.

Abstract: This study examines the thermal insulation properties of panels made from recycled rubber. The reasons, in addition to the use in construction, are environmental protection, sustainable development, energy conservation. The thermal conductivity coefficient λ is the main characteristic, on the basis of which a decision is made on the choice of material as a heat insulator. Materials with λ <0.2 W / (m · K) are heat-insulating. Tested 3 composition of the material of different particle size distribution. It is shown that the key parameters that determine the heat-shielding properties of a material are its density and particle size distribution. It has been confirmed that with decreasing density the insulating properties of materials are improved. Compositions consisting of small grains have the best heat-insulating properties. After samples with grains of small size, in order of deterioration, samples of grains of large size and, finally, samples of mixed particle size distribution follow. The results also showed that the amount of binder in this case is negligible (4.2-7.5%) and practically does not affect the insulating properties of the material. Abstract: This study discusses the thermal insulation properties of panels made from recycled rubber. The reasons, in addition to the use in construction, are environmental protection, sustainable development, energy conservation. The thermal conductivity coefficient λ is the main characteristic, on the basis of which a decision is made on the choice of material as a heat insulator. Materials with λ <0.2 W / (m · K) are heat-insulating. Tested 3 composition of the material of different particle size distribution. It is shown that the key parameters that determine the heat-shielding properties of a material are its density and particle size distribution. It has been confirmed that with decreasing density the insulating properties of materials are improved. Compositions consisting of small grains have the best heat-insulating properties. After samples with grains of small size, in order of deterioration, samples of grains of large size and, finally, samples of mixed particle size distribution follow. The results also showed that the amount of binder in this case is negligible (4.2-7.5%) and practically does not affect the insulating properties of the material.