Corrosion Investigation of Rock Anchors Served over 10 Years in Underground Powerhouse of a Hydropower Station

Table 6

Evaluation and rating system for corrosion on wire (Hopwood & Havens, 1984 [27]).

Rating	Rating standard
Stage 1	Wire surfaces have a shiny metallic appearance, though some signs of white zinc corrosion product may be visible in spots.
Stage 2	Wire surfaces dull as zinc corrodes. The wires eventually are covered with white corrosion product. However, there is no ferrous corrosion under the white corrosion product.
Stage 3	The signs of ferrous rust are visible on wire surfaces. Zinc coating is almost completely consumed. Random wire cracking is possible in this stage.
Stage 4	Ferrous rust stains or displaces most of the white corrosion product on wires. Wire surfaces become very rough and pitted. Wire cracking is anticipated at this stage of deterioration