Abstract:
The corrosion behavior of TMT steel bars in different corroding media such as rain water, storage atmosphere and concrete ponded in 10% sodium chloride solution has been investigated for a corrosion duration of 40 weeks. The corrosion rate of TMT steel bars corroded in the three media was measured at an interval of 4 weeks. Both macroscopy and microscopy were carried out to reveal different zones such as hardened case, soft core and transition zone in the cross-section and microstructure in these zones respectively of the TMT steel bars in the as received condition and after corrosion of 40 weeks duration. The depth of hardened rim of the corroded steel bars was measured at an interval of corrosion duration of 8 weeks by optical microscopy. The tensile test of the TMT bars were carried out by a universal tensile testing machine at an interval of corrosion duration of 8 weeks to obtain data on yield strength, tensile strength, % elongation and % reduction of area. The hardness of the surface of the TMT steel bars in the as-received condition and after corrosion for a duration of 40 weeks was measured by a Rockwell hardness testing machine.
It was found that the corrosion rate of the TMT steel bars in rain water decreases gradually with corrosion duration and reaches a minimum value at 24 weeks of duration after which the corrosion rate increases. The corrosion rate of the TMT steel bars in storage atmosphere initially increases and after reaching a maximum value at 16 weeks duration it starts decreasing. The corrosion rate of the TMT steel bars in concrete with 10% NaCl solution decreases very slowly and after reaching minimum value at 32 weeks of duration it starts increasing gradually. The corrosion rate of the TMT steel bars in rain water is much higher than that of the TMT bars in storage atmosphere and the corrosion rate of steel bars in concrete with NaCl solution is the lowest of all the media.
The depth of hardened rim of the TMT steel bars decreases considerably in rain water with corrosion time whereas the depth of hardened rim of the steels decreases slightly in storage atmosphere and concrete.
The yield strength and ultimate tensile strength of the TMT steel bars corroded in rain water decrease considerably with corrosion time whereas there is little decrease in YS and UTS of the steel bars corroded in storage atmosphere and concrete with 10% NaCl solution. The hardness of the TMT steel bars is found lower in rain water than that of the steel bars corroded in storage atmosphere and concrete with 10% NaCl solution.
