The results of the analysis and monitoring of normative and technical documents (NTD) in the field of design and construction of mechanical butt joints of high factory readiness for precast concrete and reinforced concrete structures of buildings are presented. The normative documents regulating the requirements in the field of design and detailing of mechanical butt joints of high factory readiness, including an analysis of the regulatory, methodological and technical documents available both in our country and abroad, are considered. The shortcomings of regulatory documents are analyzed: repeated technical requirements, references to canceled NTDs, contradictions in various standards of requirements for structures. Proposals were formed on the feasibility of performing additional scientific research work in the form of RW and R&DW, as well as proposals for updating existing and developing missing BS and standards in the NTD system.

Keywords: butt joints, structural system of building, frame structural system of building, frameless structural system of building, prefabricated monolithic structures.

For citation: Kozelkov M.M., Lugovoy A.V. Monitoring of the regulatory framework in the field of design and construction of mechanical butt joints of high facto- ry readiness for precast concrete and reinforced concrete structures of buildings. Beton i Zhelezobeton [Concrete and Reinforced Concrete]. 2021. No. 3 (605), pp. 3–11. (In Russian).

On the basis of the analysis of experimental studies, brittleness criteria for high-strength concrete at high temperatures are proposed and their threshold values are recommended, which are determined by the developed method for concrete at t=20°C. The brittleness criteria for high-strength concrete at high temperature for operational structures are determined on the basis of the dependence of the elastic modulus E and the critical stress intensity coefficient KIC on the surface hardness H. On the basis of the experimental data obtained, the value of the surface hardness (at t=20°C) of high-strength concrete H>450 MPa is proposed, when heated, brittle fracture will occur.

Keywords: high-strength concrete, brittleness, crack resistance, ultimate strength, fracture toughness, durability.

For citation: Leonovich S.N., Litvinovsky D.A., Budrevich N.A. Assessment of concrete resistance to high temperature based on State Standard 29167–2020. Beton i Zhelezobeton [Concrete and Reinforced Concrete]. 2021. No. 3 (605), pp. 14–18. (In Russian).

The new state standard GOST R “Concretes. Acoustic emission control method”, which establishes methods for monitoring concrete and reinforced concrete products and monolithic structures in order to assess damage and early diagnosis of the formation and development of operational (power) cracks by acoustic emission (AE) method, is considered. Unlike traditional methods of non-destructive control and technical diagnostics, the AE method does not require scanning the surface of an object to search for defects, the source of information is the defect itself. Damages are detected long before the onset of the limit state, which makes it possible to plan preventive measures for preventing accidents.

Keywords: concrete, reinforced concrete, monolithic structures, cracks, concrete destruction, acoustic emission, defects.

For citation: Sagaidak A.I. Standard for the method of acoustic-emission control of concrete and reinforced concrete products and monolithic structures. Beton i Zhelezobeton [Concrete and Reinforced Concrete]. 2021. No. 3 (605), pp. 19–24. (In Russian).

With the development of 3D printing technology in construction, the development of effective building materials with specified performance properties for extrusion molding is becoming increasingly relevant. The article presents the results of the study of the influence of two prescription factors on the properties of light concretes on hollow microspheres by means of mathematical planning of the experiment. Experimental and statistical models describing the depend- ences of changes in the mobility of the concrete mixture, average density, bending strength, compression and shrinkage deformations of light concrete on the content of a solution of superabsorbing polymer (SAP), which provides hydration of Portland cement under unfavorable hardening conditions, and a dispersed reinforcing additive-polypropylene fiber, are obtained. The optimal ranges of fiber and SAP content were established, which are (in %): CFI[1.19; 1.38] and CSAPI[0.81; 1.25], respectively. The composition of light concrete on hollow microspheres, containing 1.25% fiber and 1.25% SAP, has the best physical and mechanical properties.

Keywords: lightweight concrete, structural lightweight concrete, hollow microspheres, superabsorbing polymer, polypropylene fiber, 3D printing.

>The work was executed under support of the Grant of the President of the Russian Federation for state support of young Russian scientists – Candidates of Sciences MK-1394.2020.8.

For citation: Duong Thanh Qui, Korolev E.V., Inozemcev A.S. Complex modification of light concretes on hollow microspheres for 3D printing technology. Beton i Zhelezobeton [Concrete and Reinforced Concrete]. 2021. No. 3 (605), pp. 25–29. (In Russian).

On May 27–28, 2021, Gelendzhik hosted the II RUCEM Conference «Open Dialogue of Cement Makers, Manufacturers of Construction Chemicals and Concretes», which is traditionally organized by the online magazine about cement RUCEM.ru and «GK POLYPLAST» JSC with the information support of the industry media and the National Association «Union of Concrete Manufacturers».

The optimum compositions of fiber-reinforced concrete with glass-polymer composite fiber of compressive strength classes B20, B40 and B60 have been devel- oped. Their complex studies demonstrate that based on concrete mixtures with an average density of 2320–2360 kg/m3, air entrainment of 2.5–3.5%, and work- ability (slump) of 21–22 cm, the concrete with the following properties can be obtained: average compressive strength of concrete – 28, 54.7 and 83.3 MPa; the average bending tensile strength – 3.5, 4.4 and 5.6 MPa; the breaking strength – 2.92, 5.78 and 6.92 MPa; prismatic strength – 20.1, 40.4 and 60.4 MPa; modulus of elasticity – 35393, 46146 and 51366 MPa; Poisson’s ratio – 0.17, 0.18 and 0.18, respectively. The addition of glass-polymer composite fiber into concrete mix- tures in an amount of 0.5, 1.5 and 2.5% vol. slightly reduces the average density of the mixture by 7–72 kg/m3, increases the air content of mixtures by 0.1–0.6%, reduces slump by 3–8 cm, and has little influence on the compressive strength. The data on the ultimate bending tensile strength at the moment of crack formation, as well as residual bending tensile strength corresponding to the crack opening in the range 0.5–3.5 mm, were obtained. The shape of a single fiber surface was the determining factor when it broke out of concrete matrix. Three main types of deformation mechanism were identified. The characteristics of fiber-reinforced con- crete durability were determined. Overall, the results indicate that fiber-reinforced concrete can be produced with properties that are suitable for wide application.

Keywords: glass-polymer composite fiber, fiber-reinforced concrete, performance, adhesion, sustainability.

For citation: Nurtdinov M.R., Soloviev V.G., Buryanov A.F. The use of composite fibers in heavy concrete. Beton i Zhelezobeton [Concrete and Reinforced Concrete]. 2021. No. 3 (605), pp. 33–39. (In Russian).

The methodological manual “Calculation and Construction of Concrete and Reinforced Concrete Pressure-free Pipes” is developed in the development of the provisions of SP 63.13330.2018 “SNiP 52-01–2003 Concrete and Reinforced Concrete Structures. Basic Provisions”, which establishes general requirements for the calculation and design of reinforced concrete structures, and SP 35.13330.2011 “SNiP 2.05.03–84* Bridges and Pipes” in terms of the calculation and design of concrete and reinforced concrete non-pressure pipes used in outdoor underground drainage and sewerage networks. The manual contains recommendations for the calculation and design of non-pressure concrete and reinforced concrete non-stressed pipes with a round hole, taking into account their design features and operating conditions in non-pressure pipelines mounted by the open (trench) method and closed (trenchless) microtunneling method. The theoretical provi- sions, engineering methods and recommendations set out in the manual are illustrated by a number of detailed examples of determining the loads on pipes and internal forces in the structure, designing and calculating concrete and reinforced concrete pipes according to the limit states.

Keywords: concrete pipes, reinforced concrete pipes, pressure-free pipes, strength calculation, crack formation calculation, designing.

For citation: Melikhov V.I., Sokolov B.S. Design of concrete and reinforced concrete pressure-free pipes. Beton i Zhelezobeton [Concrete and Reinforced Concrete]. 2021. No. 3 (605), pp. 40–44. (In Russian).