The marked brittleness with low tensile strength of plain concrete can be overcome by the addition of steel fibres (SF). This paper investigates the mechanical properties of steel fibre reinforced concrete (SFRC) and spiral steel fibre reinforced concrete (SSFRC). The properties included compressive and splitting tensile strength, modulus of rupture, and toughness index. The steel fibres were hook-ended shape with aspect ratio (l/d=50). The introduced shape was spiral steel fibres (SSF) with diameter of spiral=1.5 cm. The two shapes of steel fibres were added at the volume fraction of 0.5%, 1.0%,2.0%, and 3.0%. All the mechanica1 properties of SFRC enhanced up to 2.0% volume fraction of fibers, whereas the mechanical properties of SSFRC enhanced up to 3.0% volume fraction. The compressive strength of SFRC and SSFRC enhanced by 43.4% and 65% respectively relative to plain concrete. The splitting tensile strength of SFRC and SSFRC enhanced by 52.6% and 147% respectively relative to plain concrete. The modulus of rupture of SFRC and SSPRC enhanced by 137.5%, and 62.5% respectively relative to plain concrete. The toughness index of SPRC improved with increasing the fraction up to 2.0%. The indices I 5 , I 10 , and I 20 registered values of 10.7, 20.5, and 35.1 at 2.0% fraction. The toughness index of SSFRC improved with increasing the fraction up to 3.0%. The indices I 5 , I 10 , and I 20 registered values of 9.76, 18.78, and 35.8, respectively, at 3.0% volume fraction.

This review article provides general information about reinforced concrete corrosion and types of corrosion. The most dangerous consequence of corrosion processes in reinforced concrete is a decrease in the load-bearing capacity of the structure. Corrosion of reinforcing steel is one of the most common damages to reinforced concrete structures. The most dangerous type of rebar corrosion is chloride corrosion, since at a certain concentration of chlorides, the concrete immediately loses its protective properties in relation to the rebar, the corrosion develops locally and deep into the rod, leading to significant losses of its cross-section, often without visible damage to the concrete surface. Types of corrosion: physical corrosion, chemical corrosion, leaching corrosion, magnesian corrosion, carbon dioxide corrosion, sulphate corrosion, hydrogen sulfide corrosion, biological corrosion, electrochemical and electroosmotic corrosion, the destruction of cement stone. The article provides an overview of the mechanism of reinforcement corrosion, its initiation, progress and factors that expedite the process of reinforcement corrosion. Once the reinforcement corrosion is initiated, it shortens the service life of the structures by cracks initiation, propagation and subsequently spalling of the cover concrete due to expansion of corrosion steel. Corrosion of the embedded reinforcing steel is the most frequent cause for degradation.

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Earlier, authors considered the under-examined question of accuracy (error) in the theory of the diagram method for calculating reinforced concrete core elements. The notion of convergence of the numerical implementation of the method under consideration is closely related to it, which has so far remained undisclosed. The article presents a theoretical justification of the convergence criterion of a numerical diagram method for calculating the strength of reinforced concrete bendable elements. The resulting criterion coincides in form with the Chebyshev norm. It implies a criterion for stopping the iterative calculation process and an estimate of the error of the numerical diagram method. Using the example of a reinforced concrete element with a rectangular cross section and double reinforcement, the issue of convergence of iterative strength calculation with varying concrete class and percentage of reinforcement is investigated. It is established that for all the considered design variants, the iterative calculation process converges after the 6th iteration at the initial curvature approximation and after the 4th iteration at , with a relative calculation error of δ<1 %. In addition, it is found that with an increase in the percentage of reinforcement, the convergence of the calculation improves: with the number of iterations equal to 4, the error in the design variant B60, µ = 0.5 % is 10.3 %, and with B35, µ = 3.0 %–0.98 %.