Polymer impregnation of concrete as a means of improving corrosion resistance
The service life of concrete in particularly extreme bacteriological environments has long been a problem that has been facing engineers and concrete materials experts. This is particularly relevant for the case of concrete sewer pipes, the useful life of which is critically limited by corrosion due primarily, and ultimately, to sulphide attack. Sulphides are formed from the sewage sulphates, by bacteria in the slime layers on the walls of the pipe. These diffuse, firstly into the liquid, and then into the sewer atmosphere as hydrogen sulphide, which is then in turn oxidised to sulphuric acid. Hydrogen sulphide gas is well known for its characteristic "rotten eggs" odour, but more important although less known, for its extreme toxicity. The maximum safe concentration in air is only twice that of hydrogen cyanide. It also has the dangerous side effect that the ability to sense it by smell is quickly lost after first encountering the gas, and deaths have occurred in sewers that can be both directly and indirectly attributed to hydrogen sulphide poisoning. The corrosion discussed in this thesis refers primarily to that caused by this bacteriologically created sulphuric acid attack in the space above the liquid, as opposed to sub-liquid level corrosion due to aggressive chemicals, more commonly associated with industrial effluents. This is all discussed more fully in later sections.
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