Complex nanodispersed systems with multi-walled carbon nanotubes and nanodispersed silica have a significant impact on the processes of hydration, hardening and strength gain of construction composites predetermining their durability. While using a scanning electron microscope with an attachment for X-ray microanalysis and a device for infrared spectral analysis investigations have shown that the main effect of the cement matrix modification in the case of adding complex nanodispersed systems is provided by direct influence of hydration processes with subsequent crystallization of new formations. It has been noted that while adding carbon nanotube dispersion and nanosized silica a binding matrix is structured in the form of an extremely dense shell from crystalline hydrate new formations on the surface of solid phases that provides strong binding matrix in cement concrete. The addition effect of carbon nanotubes has been analyzed and quantitatively assessed through an investigation for every case of one sample with nanotubes and one sample without them with the help of a nanoindenter and scanning electron microscope. It is necessary to solve rather complicated challenging task in order to assess quantitatively the addition effect of CNT on material characteristics at a micromechanical level. At the same time it is possible to investigate surface of a concrete sample with one-micron resolution. In this case it is necessary to prepare samples for nanoindentation with exclusion of all CNT defectable effects that have been shown by a SEM. So in this case more adequate method for assessment must be a picoindenter , which combines a test method for nanoindentation with an optical SEM potential. Such equipment is in the stage of in-situ testing process at the Vienna University of Technology. The investigation is based on the fact that the main modification effect of mineral binding matrix while using incorporated complex nanodispersed systems and nanosilica is ensured by a direct influence of hydration processes and subsequent crystallization of new formations. Scanning electron microscopy and X-ray microanalysis with detection in IR spectra have revealed that adding of multi-walled carbon nanotubes dispersion together with nanodispersed silica provides structuring of rather dense shell of hydrated new formations along cement matrix on the surface of solid phase. The structured interfacial layers form separate cells in the modified cement matrix that ensures a formation of extremely filled system and predetermines structural strengthening of the modified cement matrix due to formation of spatial packaging. Consequently, the main factor increasing characteristics of cement concrete which is modified with carbon nanotubes and nanosilica is a structural modification of calcium hydrosilicates with relation to composition and morphology of new formations.

Modern visions on the role of high-dispersity additives in concrete mixtures reflect a positive effect of optimal amount of ash left after combustion of solid fuel on structure and physico-mechanical characteristics of cement compositions: hardening of contact zone between cement stone and aggregates with formation of “binder – aggregate” clusters due to high surface energy of aggregate particles; reduction of total cement stone porosity in concrete while increasing volumetric concentration and aggregate dispersion; binding of calcium hydroxide by amorphized silicon of pozzolanic aggregates; increase in pozzolanic aggregate activity with its fine grinding, etc. Experimental investigations have ascertained that usage of portland cement clinker ash samples left after brown coal burning at the Lelchitsky deposit contributed to an increase of cement working life and activity. Concrete samples have been obtained that have improved physico-mechanical properties owing to introduction the following components in their composition: 2–14 % (of cement mass) of ash left after brown coal burning and 1.6–2.1 % of sodium salt that is a condensation product of sulfur oxidate in aromatic hydrocarbons with formaldehyde. Efficiency of the executed work has been proved by solution of the problems pertaining to an increase of neat cement working life, cement activity, concrete strength. The paper also considers no less important problem concerning protection of the environment from contamination with ash left after burning of high-ash brown coal. 

A simplified method for calculation of standard coefficient for heat transfer in a residential building has been developed in the paper. Investigations have been carried out with the purpose to determine influence of building size, level of thermal insulation in external enclosures and share of heat regeneration in ventilation system on total heat losses. The paper considers buildings of a simple geometrical form (“matchbox”) with number of floors 1, 2, 4, 8, 16 and living area from 100 up to 25600 m² at the level of thermal resistance of walls 1; 3 and 5 m² ⋅°C/W and share of heat regeneration in ventilation air stream of 0; 0.5 and 0.66. The investigation results have shown that while increasing building size then there is a sudden transformation of dimensions and structure in external enclosures: share of overlapping area is reduced by 3-fold and share of wall area is increased by 2-fold. Surface area of building external envelope is reduced by 6-fold in comparison with its heated area. An average coefficient of building heat transfer assigned to heated area is decreased by 3-fold. It has been shown that the most efficient methods for further decrease of standard heat losses for residential buildings are the following: heat recovery in the ventilation system: it is deeper if heat protection rate is higher and climate of a building construction zone is colder; enlargement of building size through decrease of their number; limit-exceeding increase in heat protection of small apartment buildings and cottages; cubic form of 2–3-floor buildings for Far North.

It is recommended to have a vapor-proof barrier on the internal side of heat insulation system in multi-layer building enclosing parts in order to ensure protection of a heat-insulation layer against humidification because relative humidity of internal air is generally higher than external one and diffusion of water steam is directed from premises outside. While having a barrier with high vapor permeability a part of moisture can be accumulated in the structure and heat insulation core and difference of actual and maximum possible partial pressures leads to condensate formation. In order to improve thermal properties of enclosing parts the necessity arises to create a vapor-proof protection screen. It complies with the design of a panel with a vapor-proof screen in the form of non-perforated aluminium foil. The given screen located at internal panel layer prevents penetration of water vapor from premises into enclosing part and heat insulation layer. In such a case condensation zones and, consequently, their moistening can occur in some layers of enclosing parts according to their thermal and physical characteristics. The paper contains a calculation of thermal and moisture regime of the enclosing parts with vapor-proof layer (non-perforated aluminium foil) located in enclosing part core between various layers. An analysis of thermal and moisture regime diagrams for multi-layer external enclosing part demonstrates that the part of non-perforated screen (aluminium foil) located between internal concrete layer and perforated heat insulation layer is considered the most rational one. At the same time other screens between separate layers are perforated.

The paper considers reasons of internal air parameter mismatch in warm season of the year for public building premises having large area of translucent structures. The main reason of uncomfortable air environment is an underestimated value of air supply volume due to air exchange calculation according to multiplicity factor or air exchange rate per one person which are determinative values only for cold period and transient conditions. In other words multiplicity factor and air exchange rate do not take into account equipment abundance in modern offices and heat input of the office equipment is rather significant value. The paper contains an analysis and comparison of the existing air exchange rates for the Republic of Belarus, Russian Federation, European countries and USA. Calculation of heat input and air exchange for public building premises during warm season of the year for assimilation of evident heat excess has been made at various orientations of curtain walls. The paper provides structure of heat input into premises. The required rate of air supply volume per one person has been determined on the basis of air exchange and it has been compared with the existing air exchange rate. The required rate averagely exceeds the standard one by 12-fold. But this does not mean that there is necessity to increase the rate in such a way because it entails an increase in capital and operational costs. In this connection the paper reviews variants for improvement of micro-climate in the building premises with large area of translucent structures: automatic regulation of heat transfer in heating appliances during cold period of the year; usage of air conditioning and increase in temperature difference of input and output air during warm period.

The existing normative documents consider 100%-wear as an extreme limit for operation of constructional element or structure. While using probabilistic rate of physical wear and determining the necessity in repair 100%-wear is assumed on the basis of physical state of constructional elements and structures that corresponds to minimum allowable reliability level. The paper contains description of a new method for determination of necessity in repair and its type for building and its elements on the basis of probabilistic assessment of their physical wear which is mated with residual reliability. Such method of calculation is carried out by determination of initial and threshold limit values for failure or destruction probabilities and density of probability distribution. According to these values time wear rate is selected and it ensures higher specific growth of failure and destruction probabilities at initial running period of the element operation. Then a planned wear assessment of building elements is carried out on a periodical basis. In the case when the planned rate of probability growth is equal to 0.4–0.5 from the critical value it is necessary to execute a mean current repair and when the probability level reaches value of 0.8 or even more in comparison with a critical one then it is necessary to carry out a capital repair in order to reduce probability value which will be close to the initial one. Such planned assessment of physical wear is made according to regulatory indirect indicators and in the case when intensity of physical wear exceeds the planned level it is necessary to determine strength characteristics of building elements while using instrumental physical methods. Taking into account a relative novelty of probabilistic assessment of necessity in repair and its type for building and its elements during operational period it is recommendable to carry out additional theoretical and statistic investigations in order to include this method in normative technical construction documents. 

The paper reports on peculiar features pertaining to execution of construction works during reconstruction of buildings. Practical experience on replacement of load-bearing structures has been analyzed for illustrative purposes. Attention has been concentrated on peculiarities in respect of organizational and technological solutions resulting from installation of temporary reinforcement structures. This is due to the fact that it is necessary to ensure spatial rigidity and stability of adjacent and existing construction structures of the building. In other words, when certain construction structures are replaced for some period of time the adjacent structures are without any support that ensure position stability for individual structural elements and building as a whole. Such a situation may lead to deformation of structures or their failure. In this regard, works must be performed in accordance with work zones that ensure stability in the adjacent structures. The paper presents examples of practical solutions concerning replacement of load-bearing floor structures and outer portion of a bearing wall in one of the buildings under constraint conditions. In this context when replacing intermediate floor works have been carried to strengthen temporarily reinforced concrete columns. Spacer steel beams providing column stability from plane have been used for this purpose. While making partial dismantling of the wall a variant presupposing installation of temporary vertical bearing structure in the form of a portal has been used in the paper. The given structure has been bearing loads from floor slab up to completion of re-bricking of bearing wall portion and arrangement of other structures in accordance with design solutions. The presented organizational and technological solutions will be useful for builders and designers while making development of design and technological documentation for reconstruction of buildings.

Construction of concrete road paving which was started in the 30-ies of the last century in the United States has proved its perspectiveness from the viewpoint of service life. In addition to that an analysis of road usage has shown that concrete paving is a deformation tendency due to some reasons and the tendency entails some difficulties in their repair after rather long operation. The deformations appear more intensively after 5-10-year road operational period. The following negative effects are practically unavoidable: micro-crack formation, scaling, deformation due to freezing of angular edges in concrete plates, destruction of deformation joints etc. The defects are characterized by rather large scope and they are present practically on all the roads. It is necessary to note the fact that a great number of the above-mentioned defects can be avoided on the condition that measures on strengthening surface layer of concrete paving will be undertaken in time. The measures presuppose application of impregnating method while using compositions that contain hydrophobisator and silicon dioxide sol. Industry-produced potassium methyl siliconate, oligomethyl hydride siliconate, tetraethoxysilane have been used as hydrophobisator and they form not easily soluble film on the surface of concrete pores which prevents penetration of water into concrete. Calcium hydrate being formed in the dissolution and hydrolysis process of cement clinker minerals is bound in hydrosilicates which are contained in the solution impregnated by silicon dioxide sol. These hydrosilicates culmatate concrete pores and strengthen its surface layer due to additional hard phase and according to chemical composition it is related to calcium hydrosilicates formed as a result of concrete hardening.

It has been found that four reinforced concrete flue stacks being constructed in late 80-ies and early in 90-ies of the 20^th century and being operated at various thermal power stations show practically no settlement, and this fact is not taken into account by any applicable regulatory documents. Foundations of these stacks were designed at the same time and they have been protected by patents of Russian Federation and Republic of Belarus. They represent circular bases made of reinforced concrete piles buried tightly together and forming so-called “slurry wall” with common monolithic reinforced concrete grillage. The grillage presents a direct extension of the stack shaft. One of these stacks has been built in Russia, and three – in Belarus. Due to significant differences in soil conditions and loads in each case, it is a fair assumption to say about regularity of the observed phenomenon. Notwithstanding the fact that circular foundations significantly decrease steel and concrete consumption, construction period and labour input, they have not yet received adequate attention from the side of scientific community and designers. While considering specific examples of the constructed stacks the paper reveals an opportunity to apply calculations which efficiently use passive soil resistance. The presented calculations and designs of the existing foundations make it possible to assess probability of the proposed methodology for the foundations which are analogous in design and which have closed in-plane structure not only for industrial buildings and structures.

Nowadays we observe rather rapid growth of energy accumulators market. There are prerequisites to their extensive application in Belarus. In spite of technology development problems pertaining to optimization of electric power and their operation under conditions of specific systems “generator – accumulator – consumer” (GAC) have not obtained proper consideration. At the same time tuning and optimization of the GAC system may provide competitive advantages to various accumulating systems because application of accumulator batteries in non-optimal charge – discharge conditions reduces its operating resource. Optimization of the GAC system may include utilization of hybrid accumulator systems together with heterogeneous chemical and mechanical accumulators, tuning of system controller parameters etc. Research papers present a great number of empirical and analytical methods for calculation of electric loads. These methods use the following parameters as initial data: time-averaged values of actual electric power consumption, averaged apartment electric loads, empirical and statistical form coefficients, coefficients of maximum electric load for a group of uniform consumers. However such models do not meet the requirements of detailed simulation of relatively small system operation when the simulation must correspond to non-stationary, non-averaged, stochastic load nature. The paper provides a simple approach to the detailed simulation of electric loads in regard to small projects such as multi-unit apartment building or small agricultural farm. The model is formulated both in physical and algorithmic terms that make it possible to be easily realized in any programming environment. The paper presents convergence of integral electric power consumption, which is set by the model, to statistically averaged parameters. Autocorrelation function has been calculated in the paper that shows two scales for autocorrelation of simulated load diagrams. The paper contains of an analysis on Fourier spectra for generated electric load diagrams. The model of electric load may be used separately or as a component of a general model in the GAC system. It may also be applied for tuning of automatic systems for control and accounting of power resources and various research purposes. 

Magnetic mode for 3-phase transformer with symmetrical magnetic conductor of frame design has been investigated on schematic model. The scheme consists of three non-linear coils having star-connection without zero wire. Weberampere characteristics correspond to similar parameters of separate frames of a magnetic conductor. It has been accepted that a magnetic flow of every frame is closed on itself without passing into other frame of the magnetic conductor. Electromagnetic state of equivalent diagram has been described by a system of differential equations which were solved with the help of MathCad program. Investigations have resulted in calculation of functions for magnetic frame induction and magnetizing current and their harmonic compositions; dependence of actual amplitude for magnetic field induction on amplitude of the main harmonic induction has been determined in the paper. While executing experiments it has been revealed the following: induction amplitude of the main harmonic in the magnetic field within frames of the magnetic conductor is higher in comparison with the design induction value by 15.5 %; due to non-linearity of weber-ampere characteristics in frames and properties of 3-phase system harmonic components, which are multiple of three, are initiated in the functions of magnetic induction for separate frames; high-order harmonics of function for magnetic frame induction being imposed on the main harmonic decrease an actual amplitude of magnetic field induction practically up to the design induction value within the operational range of the actual amplitude and in this context coefficients of high-order harmonics change insignificantly; harmonic components, which are multiple of three, are absent in magnetizing currents.