Effect of the degree of corrosion damage in reinforcing bars on composite action with concrete

Introduction. The article examines the possibility of using steel reinforcement with instances of corrosion and determines the maximum degree of corrosion damage in reinforcing bars (rebars). Although long-term studies show that corroded reinforcement can be used in the manufacture of reinforced concrete structures, some studies and regulatory documents provide different conditions for the use of such rebars, as well as establishing different corrosion thresholds (thickness of the rust layer on the rebar surface).

Aim. To determine the maximum thickness of the rust layer on the surface of corrugated rebars, at which the physicomechanical characteristics of reinforcement are preserved and the capability for composite action with concrete is not hampered; to determine the degree of corrosion damage in rebars at which its use in reinforced concrete is permissible in order to revise the existing regulatory documents on the protection of structures against corrosion.

Materials and methods. The experimental studies were conducted on rebar specimens of two classes (A500 and A800) exhibiting different degrees of corrosion damage (rust layer thickness of 0, 150, 250, and 300 μm). In order to determine the composite action with concrete, B15 and B20 concrete was used. The physicomechanical characteristics of rebars with different rust layer thicknesses were determined on rebar specimens having a diameter of 12 mm and length of 400 mm according to the procedure specified in State Standard 12004-81. The reinforcing steel resistance to corrosion cracking was determined on rebar specimens having a diameter of 12 mm and a length of 400 mm as per the procedure given in State Standard 31383-2008. The passivating effect of concrete on steel reinforcement was determined on concrete specimens — 70 × 70 × 140 mm prisms, with rebars having a diameter of 12 mm and a length of 120 mm in the center — according to the procedure given in State Standard 31383-2008. The bond between rebars and concrete was determined on concrete specimens-cubes (150 mm on edge), with rebars having a diameter of 12 mm and a length of 500 mm in the center — using the procedure specified in State Standard 31938-2012.

Results. The study yielded experimental data on the physicomechanical characteristics of rebars exhibiting different degrees of corrosion damage; on the resistance of reinforcing steel to corrosion cracking; data on the passivating effect of concrete of two classes on steel rebars exhibiting different degrees of corrosion damage; data on the bond between rebars corroded to various degrees and concrete of two classes.

Conclusions. As part of the work, an experimental research program was developed and implemented, which involved the production and testing of rebar specimens of two classes exhibiting four degrees of corrosion damage with the use of concrete of two classes and. The experimental study results were used to determine the effect of corrosion damage of varying degree in rebars on the characteristics of reinforced concrete. The presence of a rust layer on the rebar surface of up to 150 mm in thickness was found not to degrade its physicomechanical characteristics, not to decrease its resistance to corrosion cracking, and not to reduce its composite action with concrete. Any further increase in the thickness of the rust layer on rebar surface reduces these characteristics, except for the bond to concrete. No dependence of rebar-concrete bond stress on the rust layer thickness was observed.

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