Corrosive effect of hydrogen sulphide on cement mortar
Deterioration of concrete in livestock buildings due to corrosive environment is a very serious problem in Ontario. For instance, the cost of replacing slats due to corrosion in Ontario alone is of the order of multi-million dollars and pushed some producers to the edge of bankruptcy. The agents that cause deterioration of concrete in livestock housing buildings are not specifically known. There are numerous corrosive agents, such as hydrogen sulphide, ammonia, lactic acid and acetic acid that are generated due to the anaerobic fermentation of manure. In this study the effect of hydrogen sulphide on mortar cements was studied in detail. Six different treatments were tested, including Portland cement type 10 with 0.45 water-cementious material (W/C) ratio (PC45), Portland cement type 10 with 0.55 W/C ratio (PC55), sulphate resistant Portland cement type 50 with 0.45 W/C ratio (SRC), Portland cement type 10 with fibre mesh with 0.45 W/C ratio (FMC), Portland cement type 10 with 0.45 W/C ratio coated with linseed oil (PCL) and silica fume cement with W/C ratio of 0.35 (SFC). Field test, laboratory tests, and mathematical modelling were used in the study. In the field test specimens were suspended in both swine and dairy barns below the slatted floors. The laboratory tests comprised impressed voltage test, electrochemical potential test, and diffusion profiles test. Constant diffusion coefficient and non-constant diffusion coefficient models were used to determine the diffusion coefficients for the six treatments. A two-dimensional finite element analyses were carried out on a full scale slat to determine the time required to initiate corrosion. The results indicated the SFC treatment was consistently the best treatment while treatment PC55 was the poorest. The results of treatments with 0.45 W/C varied from test to test, however, FMC and SRC treatments performed slightly better in resisting corrosion from H2S than PC45 treatment. The PCL treatment did not perform well as indicated by the premature failure of specimens in the electrochemical potential test. The numerically estimated time to failure by the finite element analyses was longest for treatment SFC at 10000 days (about 27 years) followed by treatment FMC with 7500 days. PC45, PCL and SRC had duration of 5500, 4500 and 3700 days, respectively.