The article proposes the simplified method for determining stresses in massive monolithic foundation slabs arising from the heat release of concrete during the hardening process. The proposed technique makes it possible to reduce a three-dimensional problem to a one-dimensional one based on the features of the distribution of stresses and strains in the structures under consideration, identified during finite element modeling in a three-dimensional setting. The resulting resolving equations take into account the creep and shrinkage of concrete, the coefficient of reinforcement of the structure. The strength and deformation characteristics of concrete are assumed as functions of the degree of maturity of the concrete, which in turn is determined by the time and temperature of curing. Approbation of the developed model is carried out by comparison with the calculation in a three-dimensional setting in the ANSYS software package. The influence of creep and contraction shrinkage of concrete, the degree of concrete maturity and the coefficient of reinforcement on the stress-strain state of structures is investigated.

A model describing the variation in autogenous shrinkage and drying shrinkage of portland cement concrete, depending on the volume of aggregates and the shrinkage of hardened cement paste, is presented. The equation to calculate shrinkage of concrete as a function of the volume of aggregates and shrinkage of a hardened cement paste was proposed. Formulas are proposed that describe the change in the shrinkage of hardened cement paste as a function of water/cement. The results of studies of the effect of superplasticizers and mineral additives on the autogenous shrinkage and the drying shrinkage of hardened cement paste are presented. Concretes made with superplasticizer and mineral additive may have the potential lower the value of drying shrinkage. The shrinkage value can be lowered from 30% till 70%. Concretes containing superplasticizers and mineral additives can potentially have the autogenous shrinkage reduced to 75%, or increased to 180%.

The creation of the efficient reinforced concrete structures, that allows to reduce the material consumption as well as the labor costs, is the most important task today. One of the possible ways of solving this problem is the design and wide application of multilayer structures in which high mechanical, heat engineering and acoustic properties are provided due to the combination of high strength of heavy concrete and low strength of light concrete with low heat conductivity. The advantages of three-layer reinforced concrete structures are shown. The proposals have been made to take into account the sag and the classes of lightweight concrete of such elements.

The article deals with the method for calculating the three-layer bent reinforced concrete elements, taking into account the total deformation diagrams of different concrete layers. There are formulas and calculations in cases of presence and absence of cracks in the tension zone.

No abstract

The RPP introduction has been established up to 3% by weight of the dry concrete mix is ​​accompanied by a decrease in the fine-grained concrete tensile strength in compression to 40% and in tension during bending to 15%. The relationship between the tensile strength limit in bending and compression for the studied materials is invariant to the cement and RPP type. With the concrete tensile strength in tensile bending increase, there is a weak tendency to a decrease in the adhesion ratio value to the concrete base and tensile strength. The adhesion amount to the concrete base with RPP increasing dosage can either increase or decrease after a certain limit, depending on the cement properties. The maximum increase in adhesion to the concrete base was 37%, while the decrease in the concrete elasticity initial modulus was 26%.

The relationship between the creep factor of concrete and hardened cement paste and the E-modulus of aggregate and evaluation of the effects of some modifiers on the creep factor of the hardened cement paste was determined. The influence of the SP on the creep factor of hardened cement paste is ambiguous: SP may increase, decrease, or not change the creep factor. The possible deviation of creep factor of hardened cement paste with the SP in certain cases can be up to 4 times. The average statistical increase in the creep factor of hardened cement paste may be 7 to 35%. The creep factor of regular concrete is equal 0.43 - 0.9 value of the creep factor of hardened cement paste. Superplasticizers may increase the creep of concrete up to 30% and in some cases - up to 3 times. Silica fume, metakaolin, white ash, including when used with the superplasticizers, may reduce the creep of concrete from 15 to 50%. An equation was suggested to calculate the E-modulus of concrete with the volume of hardened cement paste of 0.27 - 0.35 as a function of E-modulus of hardened cement paste and E-modulus of the aggregates.

Concretes with frame structure produced by using the technology of separate concreting by immersing a coarse aggregate in a low-viscosity mortar matrix due to an increased concentration of coarse aggregate have an increased E-modulus, reduced creep coefficient and cement volume in concrete compared to traditional vibrational compaction concretes. Production concrete using separate concreting technology by immersing a coarse aggregate in a mortar matrix with low-viscosity allows to obtain a frame structure of concrete with a concentration of coarse aggregate up to 0.7 when a voidness of coarse aggregate is equal 0.28. The real concentration of coarse aggregate in a concrete structure depends on the particle size of the coarse aggregate, the cross-section dimensions of the structure, and the reinforcement coefficient. The influence of geometric dimensions and the coefficient of reinforcement on the concentration of coarse aggregate in the concrete with frame structure is studied. The concentration of coarse aggregate decreases with the growth of the S/V modulus (S – area, m2, V – volume, m3) and the reinforcement coefficient, but the decrease in the E-modulus does not exceed 5%. Conclusion: regardless of the type of construction and reinforcement, the concrete of the frame structure must have a sufficiently high uniformity of deformation properties.