The need to cut construction cost of residential and public buildings and provide them with a free and transformable planning structure during their operation cause interest in building wall systems with a large step of bearing walls. In order to reduce labor inputs and increase rate of construction in such building load-bearing system it is also necessary to maximize the use of large-sized prefabricated products and minimize consumption of in-situ concrete. In this case prefabricated products should be substituted according to the conditions of local (regional) construction industry base and volume of in-situ concrete must be sufficient to ensure a complete redistribution of internal forces between elements of the bearing system under load. As for the described bearing wall system of a multi-storey building the paper presents a flat precast solid floor formed by hollow-core slabs and monolithic crossbars supported by load-bearing walls. The hollow-core slabs supported at the ends on cast-in-place crossbars in the planes of bearing walls are arranged in dense groups between cast-in-place braced cross-beams. Dense contacts between overlapping elements are fixed by internal bonds. New data on distribution of forces in floor elements under the action of a vertical load have been obtained on the basis of full-scale tests and existing theoretical assumptions. It has been established that due to this load reactive thrust forces ensuring an operation of every hollow-core slab group in the floor as an effective solid plate supported along the contour have been originated in the floor plane along two main axes. Calculation of the reactive thrust forces makes it possible more accurately to assess a load-bearing capacity and rigidity of the precast solid floor and to increase a step of bearing walls up to 8 m and more while having hollow-core slabs with a thickness of 220 mm.

The paper presents an analytical review of materials recycling for pavement dressing. Recycling or repeated usage of pavement dressing materials while making reconstruction and repair of road pavements is not considered as a new conception and it has been realized in various countries of the world since 20th century. Recycling (hot, cold) is based on methods of its execution, properties of pavement dressing materials which are subjected to processing and which influence on the quality of final material, technical and operational indices, specific economic efficiency. Investigations on the processes of structure formation, thermo-physical properties in components based on granulates of transformed pavement dressings during recycling demonstrate that regeneration makes it possible to attain 100 % recovery of material properties for road pavement base. The paper describes other factors which represent a complex of challenges concerning exterior and internal problems. These problems have arisen due to actual processes of heat and mass transfer in one layer, multi-layer systems of pavement dressings. At known coefficients of heat conductivity, steam- and mass permeability, diffusion, filtration, temperature conductivity, density of material layers etc. initial and boundary conditions it is possible to carry out optimization of heat- and mass transfer problems from bottom surface of road layer to its base (sand, bulk materials, ground). In addition to it, while taking into account development of scientific prospective direction that concerns nano-technology and creation of nano-materials for higher reliability of road dressings it is necessary to consider nanomaterial science in road-construction industry as the most actual one because when we study problems pertaining to fractional composition of all road dressing components including transfer to nanomaterials, for example, application of modified water-reducing agent based on nanostructured carbon it is possible significantly to increase physical and technological properties of asphalt concrete and concrete road dressings. The paper reveals that it is necessary to continue and expand study of physical and technical and thermophysical properties of new materials on the basis of nano-technologies with application of modified, nanostructured carbon-based plasticizer for construction-road industry because especially these additives significantly increase cement activity that leads to improvement of strength, reliability and longevity for the obtained materials.

Critical comments on the European standards for designing steel structures including welded and bolted joints have been given on the basis of application experience and executed analysis. Comments are presented in comparison with similar regulatory documents which are in effect in Belarus. European standards concerning loads (determination of calculated load values and drawing up of design load combination) have been also analyzed. Particular attention has been paid to the analysis of European standard requirements to steel and welding materials and their comparison with mechanical characteristics of similar materials used for manufacture of steel structures in Belarus. The paper gives notice to the rules which are accepted in the European norms and the rules being compared with the similar rules used in Construction rules and regulations (SNiP) lead to a significant increase in material consumption of steel structures. First of all, it concerns assignment of partial load factors and classification of sections for ensuring local stability of compressed and partially compressed elements. The paper pays a special notice to the rules of Eurocodes that do not meet requirements of State standards and technical specifications operating in the Republic of Belarus. Significant limitations of some European rules regarding calculation of centrally and eccentrically compressed elements, absence of rules for testing overall stability of through and step columns which are widely used while implementing projects Belarus have been described in the paper. Conclusions have been made on the basis of the analysis results and according to them application of European standards for designing steel structures has significant limitations on the territory of the Republic of Belarus.

The composition of dry mix on the basis of two-component cementing agent (aluminous cement and clay of the “Kustikha” field), mineral additives (a metakaolin, the RSAM sulfoaluminate modifier, waste of basalt fiber), Ufapore foamer and the accelerating and plasticizing “Citrate-T” additive is developed. When mixing “Citrate-T” additive with water at Water/Solid = 0.45–0.70, the subsequent mechanical binder and hardening of a foam mass heat-resistant foam concretes with a density of 300–650 kg/m³ are formed (depending on Water/Solid value). Foam concretes have strength on compression of 0.2–2.5 MPa before warming up when their initial strength depends on processes of hydration curing of aluminous cement that provides fixation of their porous structure. After annealing at 1000 °C foam concretes have final strength of 0.3–3.2 MPa due to processes of solid-phase agglomeration of clay with other components of dry mix at their heating. Foam concretes after annealing unlike foam concretes on the basis of a Portland cement and aluminous cement have big strength. Introduction of the accelerating and plasticizing “Citrate-T” additive into composition of the dry mix leads to an increase of rheological properties in expanded foam mass and time reduction of its drying and curing. It has been established that an essential role is played by the relation Water/Solid: at increase in the relation Water/Solid (with 0.45 to 0.70) occurs increase in volume of foam mass after a mechanical binder, and also heterogeneity of pores and their sizes increases that leads to reduction of density of foam concretes and strength on compression.

Reliable calculation of concrete carbonization development is considered as a basis of forecasting corrosion of steel reinforcement and longevity of reinforced construction structures. Investigation results for stochastic specific features of carbonization in a protective concrete layer or its residual thickness in reinforced structures operating in airspace have been obtained for the last 20 years. In this case it is recommended for simulation of a protective concrete layer to use a normal law of distribution and a histogram which looks like distribution of extreme values is recommended for its residual thickness. Stochastic estimation for multiple measurements (1211 results excluding obviously unsuccessful ones) has made it possible to determine rather large values of variation coefficient (maximum values up to 0.34 with average index about 0.19) for indices of initial carbonization for С12/15−С20/25 concrete grades. At the same time these variation coefficients for С25/30 and С30/37 concrete grades have decreased up to 0.15 and 0.11, respectively. It has been established that density of distribution for random carbonization values of С12/15−С18/22.5 concrete grades being operated under conditions of agricultural premises with high aggressive environment corresponds, as a rule, to a normal law after excluding evidently unwanted values. In this connection use of maximum and minimum values of concrete carbonization in selections for estimation of variation coefficients differs from determination for the whole selection and it requires a corresponding correction. While operating С12/15−С18/22.5 concrete grades under conditions of agricultural premises in the period of 10−40 years average values of variation coefficients remain approximately constant with fluctuation up to ±0.01 with average value of 0.11−0.12. Spread in some variation coefficient values for concrete carbonization is decreasing from two to 1.25-fold within this period of time and later on it likely becomes stabilized. As a whole while determining duration of concrete protective layer carbonization it is necessary to take into account not only stochasticity of concrete protective layer and carbonization rate but also random values of concrete carbonization at specific carbonization rate and depth.

Thermo-technical installations consuming significant amounts of thermal energy are used in order to intensify precast and reinforced concrete production processes under industrial conditions. Despite significant progress in the study of concrete hardening in accelerated hydration devices, a prominent lack of reliable and cost-effective research and optimization methods of their operation is observed. The methods used in real production processes are mainly based on empirical dependences obtained for specific technological conditions. These methods can not always be applied for other modes and technologies. The present paper develops calculation methods based on fundamental laws that make it possible to obtain functions for evolution of concrete product hydration process. Methods of mathematical modeling permit to develop new ways directed on improvement of modes for heat treatment of concrete products and accelerated hydration technologies. The paper describes a mathematical model for calculating a hardening process of a concrete product that includes a transient three-dimensional heat conductivity equation, a function of internal heat release due to behavior of exothermic reactions of cement hydration and also a system of initial and boundary conditions. A numerical simulation for temperature and hydration coefficient of a concrete product having shape of a 0.1´0.1´0.1 m cube has been performed in the paper. Verification of the non-stationary mathematical model for calculating temperature fields and hydration degree while using experimental data on concrete product strength obtained under industrial conditions. Investigations on hydration degree function of time have shown that experimentally obtained values of compressive strength correlate with hydration coefficient and hydration rate functions of heat treatment time which are calculated on the basis of the proposed non-stationary mathematical model of concrete product hardening. Satisfactory agreement of experimental and calculated data confirms adequacy of the proposed non-stationary mathematical model for calculating temperature fields and hydration degree with accelerated heat treatment of concrete products.

For the last decades in the Republic of Belarus, there is a tendency of decreasing river flow, but at the same time the probability of flood is increasing. Majority of all hydraulic engineering structures on the territory of the Republic of Belarus is projected for a pressure up to 15 m. Risk of an accident at the hydraulic unit appears due to insufficiently substantiated methodology for calculation of hydraulic engineering structures at the stage of design, unsatisfactory level of their maintenance, absence or understaffing of operational personnel. A danger increases significantly when reservoirs are located in cascades. A hydraulic system in Merkulovichi, Chechersk district, Gomel region can serve as an example of such water reservoir and uncoordinated activity of the operating personnel. While operating the hydraulic unit an overflow occurred through a crest of an earth dam during a rain flood and due to this there was a partial destruction of the dam body. The paper considers problems concerning prediction of such situations. The paper proposes a simplified methodology for calculating changes in water level for two reservoirs during flood discharge and this methodology is based on a joint solution of differential equations of water balances in reservoirs without taking into account unsteady movement along their length. It has been assumed that at the entrance to an upper reservoir discharge change in time corresponds to flood hydrograph, and the change in time at the entrance of a lower reservoir and at its exit corresponds to discharge hydrographs in accordance with such schedules for control of spillway water gates for the first and second reservoirs in order to prevent overflow through dams (dam) of the reservoirs. While using this methodology an example for prediction calculation of levels in Merkulovichi channel reservoir and a lower pond has been considered with their cascading location and in the case of flood discharge.

The paper presents results of the study for samples of concrete beams reinforced with fiberglass rebar produced by LLC “KomAR”. The aim of the study is to determine strength, stiffness and crack resistance of beams with fiberglass rebar, various reinforcement schemes and their comparison with calculated data. Tests have been carried out in accordance with the regulatory requirements for a design scheme with two points of load application P1 = P2. The adopted scheme of pure bending is used in the laboratory for informativeness of the obtained results and getting maximum efforts in a stretched zone of bent elements. A comparison has been made of the data obtained as a result of tests with the ones which have been calculated according to the document SP (Construction Rules) 295.1325800.2017 “Concrete structures reinforced with polymer composite reinforcement. Design rules”, this document is based on the design principle of concrete structures reinforced with metal reinforcement. Due to the fact that composite fittings significantly differ from metal fittings in a number of indicators, comparative tests of concrete beams reinforced with metal and composite fittings have been carried out earlier. Data of the investigations are necessary for understanding behavior of structures and possibility of their application in the objects of capital construction. An excess of inclined section strength on the action of transverse forces over an actual one has been revealed when calculating concrete beams according to the I group of limiting states. While making calculations for the II group of limiting states, the need has been revealed to make changes in the procedure for calculating width of crack opening in order to approximate the calculated data to the data obtained as a result of tests and a procedure for calculating deflections.

Combination of hydrodynamic impact on the formation with acid treatment may be seen as a promising direction in the field of well development and repair in complex geological conditions. With multiple repetition of hydraulic shocks in conjunction with the injection of acid solution, the depth and opening of cracks gradually increases, which contributes to a deeper penetration of the acid solution into the reservoir. The article presents analytical studies, which are aimed at determining the effectiveness of applying the technology of hydrodynamic impact on the bottomhole zone of an oil reservoir when using two fluids with different viscoelastic characteristics as a working fluid. They are devoted to determining the pressure drop at the borehole bottom depending on the initial applied pressure at the wellhead, the velocity of the shock wave, the viscosity of the working and well fluid, and their quantity. These studies were based on the well-known models of Thomson – Tаt and Maxwell, considering viscous liquid flow. The dependence obtained proves that with an increase in the pressure pulse generated at the wellhead, the development of pressure pulses at the borehole bottom is a power-law dependence, and with significant volumes of fluid in contact with the bottomhole formation zone, the pressure drop generated at the borehole bottom does not depend only on pressure pulses generated at the wellhead, but also on the dynamic viscosity of this fluid. Conducted studies have shown the effectiveness of hydrodynamic impact technology application when using two liquids with different viscoelastic characteristics and obtaining a synergistic effect during the development and repair of wells in low-permeable reservoirs. Analytical studies were based on data from previously conducted experimental industrial tests on the operating injection well.

The paper considers a mathematical model which is used to study a composite material similar in structure to asphalt concrete and it takes into account presence of solid particles of different sizes and a soft and plastic binder. The twodimensional method of discrete elements has been applied to investigate destruction of asphalt-concrete samples under uniaxial compression, tension during splitting and compression by the Marshall method. The numerical model takes into account presence of large particles of rubble, asphalt mastic filling rubble pores and sticky (capable of recovering after rupture) communication between rubble particles. The force interaction between various components of the asphalt concrete has been described with the help of elastic repulsion between rubble particles, friction force and force responsible for sticking of particles due to presence of a binder. This model gives a correct fracture pattern for uniaxial compression, stretching during splitting and compression according to the Marshall method and this pattern coincides with the real experiment. It is the correct picture of destruction for three different schemes of material loading which makes it possible to assess the adequacy of the mathematical model which has been used. Basic physico mechanical characteristics of the binder which determine strength and deformability of asphalt concrete have been established in the paper. It has been shown that for an adequate description of physico mechanical characteristics for asphalt concrete it is necessary to study and measure properties of an asphalt binder that is a mixture of bitumen and fine mineral filler which determines parameters of interaction between rubble particles. The numerical experiments serve as a basis and make it possible to propose new laboratory methods for testing a mixture of stone materials and organic binders which are much simpler and, therefore, cheaper than standard tests on asphalt concrete. In addition these tests will more accurately predict behavior of asphalt concrete in real conditions.