The combination of direct waves and coda waves could exploit the complementary merits in various pitting corrosion configurations. To overcome the limitations of coda waves for severe pitting corrosion and remedy the low sensitivity of direct waves for incipient pitting corrosion, a feature-level data fusion strategy is proposed to integrate the two probing waves to monitor all-stage pitting corrosion of steel bars. The decorrelation coefficient (DC) values are calculated to quantify the variations of both direct waves and coda waves.

Coda wave technique, a very sensitive method to subtle changes in medium using later arrival wave packets, is innovatively introduced to monitor pitting corrosion of steel bars, especially in the early stages. Conventional ultrasonic method, utilizing direct waves to detect damage, is adequate for severe pitting corrosion but suffers from low sensitivity to incipient pitting corrosion.

Corrosion monitoring of steel bars has drawn extensive attention in recent decades.

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