Corrosion of Steel Reinforcement in Mortar Specimens exposed to Hydrogen Sulphide, Part 1: Impressed Voltage and Electrochemical Potential Tests

Reinforced concrete in livestock buildings is subject to severe corrosion if manure is stored below slatted floors. Many chemicals associated with manure are identified as having a detrimental effect on concrete and the reinforcing steel embedded in the concrete. The major problem, however, is the effect of hydrogen sulphide and its derivatives, such as biogenic sulphuric acid corrosion. Experiments were conducted to compare the corrosion resistance of six different cement mortar specimens under long-term exposure to hydrogen sulphide. There are a number of apparent solutions such as using sulphate resisting cement, silica fume cement, fibre mesh addition to the cement and treatment of the concrete with linseed oil. These various treatments were tested in the laboratory using impressed voltage tests and electrochemical potential tests. In impressed voltage test, specimens made with 8% silica fume cement replacements (SFC) performed best and similar Portland cement mortar specimens with a watercement ratio of 0·55 (PC55) poorest. The other four treatments (Portland cement, Portland cement with fibre mesh, Portland cement coated with linseed oil, and sulphate resistant cement), all with water-cement ratios of 0·45, were less effective in preventing corrosion than treatment SFC. The electrochemical potential tests determined the minimum concentration of sulphides (threshold level) that initiates corrosion in the reinforcement bars for each of the six treatments. Again, treatment SFC performed best and PC55 poorest. The performance of treatment PC55 was poor because the permeability of the cement paste increased due to the higher watercement ratio, and the presence of additional water reduced the electrical resistance. The early failure of the linseed oil coated treatment provided a corrosion threshold of 3 g kg-1(sulphur-tomortar weight) at the steel/mortar interface.