Page 12 - Дисертація ГРЕДІЛЬ_ФМІ

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crack origin appears in the centre of the wire due to residual tensile stresses, with

further coalescence of two crack paths.

The factors of bond strength degradation in reinforced concrete during its

long-term operation have been elucidated and modelled by applying the external

current to a reinforced concrete specimen to speed up electrochemical processes

at the rebar surface. The method is developed for assessing bond strength in

reinforced concrete under the action of corrosive-hydrogenating environments. It

is based on the determination of bond strength parameters under the tensile testing

of a cylindrical concrete specimen reinforced with two coaxially placed rebar

rods, one of which is subjected to cathodic polarisation. It evidenced a significant

impact of hydrogen evolution on adhesive strength in reinforced concrete due to

hydrogen embrittlement of steel and concrete cover exfoliation.

Scientific novelty of the obtained results
1. For the first time, a hydrogen-deformation mechanism and sequence of

damage development in low-alloyed pipe steels have been disclosed, which

consist in weakening of adhesion between the matrix and non-metallic inclusions

with their further delamination and deformation-driven growth of formed pores
due to rising pressure of recombined hydrogen, and causes steel embrittlement

and increased susceptibility to the hydrogen action.
2. A method for accelerated pipe steel degradation has been developed,

based on the combination of hydrogen and deformation factors for damage
initiation in steel, similar to operational, and makes it possible to predict the

resistance of operated steel to corrosion-mechanical fracture.

3. A new semi-field method has been developed for assessing hydrogen

embrittlement of carbon steels under simulated operational conditions for above-

ground pipeline sections. The method implies prolonged exposure of pre-loaded

specimens to hydrogen gas under pressure in a pipe at a test stand, subjected to

climatic temperature variations, simulating operational ones. Its effectiveness has

been confirmed by a drastic increase in hydrogen content in metal, and a decrease

in fracture toughness and brittle fracture resistance.