SULPHIDE, SULPHATE AND SULPHURIC ACID CORROSION OF CONCRETE IN LABORATORY TESTS
School of Engineering, University of Guelph, Guelph, ON, Canada N1G 2W1 E-mail: jjofriet@uoguelph. ca
Portland cement (PC) concrete is generally a highly durable structural material. Nevertheless, certain chemical actions and aggressive environments in a livestock building can cause deterioration and total collapses of structures have occurred long before they have reached their design life.
The sulphide and sulphate resistance of three replicates of eight different reinforced concrete mixes were investigated in a laboratory study in which one half of the 48 specimens were half submerged in a sodium sulphate solution (20,000 ppm SO42-) and also exposed to hydrogen sulphide gas (1,000 ppm H2S). The other half of the 48 specimens was subjected to hydrogen sulphide gas only. The mixes included PC concrete with W/CM ratios of 0.4 and 0.5 and six mixes with cement replacements of slag, fly ash or silica fume, all with water/cementitious material (W/CM) ratio of 0.4.
After 23 cycles of testing over about 36 months, the electrochemical potential results and visual inspection of the reinforcing bars indicate that the PC concrete with 0.5 W/CM ratio was the least resistant against steel corrosion. Corrosion of the concrete was more critical than that of the steel. All treatments containing silica fume performed much better than PC40. Treatments that contained fly ash performed worse than plain PC concrete with the same W/CM ratio. Sulphate resistant cement concrete was more resistant than Type 10 Portland cement concrete, in both sets of tests. In general the samples that were exposed to hydrogen sulphide and sulphate corroded at a higher rate then those exposed to the H2S gas only.
In subsequent tests 6 of the 8 mixes were exposed to 7% sulphuric acid for about one year. Preliminary results indicate the greatest mass loss for the concrete with 0.5 W/CM ratio and very similar amount of loss for the 5 mixes with W/CM ratio of 0.4. The least amount of mass loss was experienced by the mix with sulphate resistant cement.
Keywords: concrete corrosion, livestock building, manure, hydrogen sulphide, sulphate, sulphuric acid
Reinforced concrete for the use in agricultural facilities often exposed to aggressive environment conditions. Temporary storage of liquid manure underneath barn floors produce corrosive agents generated from aerobic and anaerobic fermentation, causing premature corrosion of reinforcement steel and degradation of the concrete. The rehabilitation of reinforced concrete structures due to corroding steel reinforcing bar is quite expensive compared with the use of good quality concrete at the time of construction.
For Canadian climatic conditions, storage of manure for a period of six months, or even longer, is generally required so that manure spreading can be avoided during winter. Anaerobic fermentation produces several gases of which hydrogen sulphide is the most corrosive leading to rapid deterioration of concrete floors in barns (Frenay and Zilverberg, 1993). Sulphate-reducing bacteria, known to thrive in animal confinement buildings, generate sulphuric acid as the end product of their metabolism. The sulphuric acid strength has been measured in the laboratory as equivalent to 7% (by volume) H2SO4 (Hewayde 2005).
High humidity, the concentration of various gases above the liquid manure and the continuous wetting of concrete floor slats are all contributing factors (Svennerstedt et al., 1999). As a
M. Pandey et al. (eds), Advances in Engineering Structures, Mechanics & Construction, 55-65.
© 2006 Springer. Printed in the Netherlands.
consequence of the concrete degradation in some instances slatted floor have deteriorated to the point of requiring replacement in less than five years. In some swine barns in Ontario a 50% loss of expected service life was reported, when regular concrete mixes were used. It is estimated that an average annual cost of depreciation on all structures is about $250 million and about $100 to 150 million is spent on repairs.
In order to improve the durability of concrete recent investigations have been made in an attempt to reduce the rate of deterioration by changing the concrete composition (De Belie et al. 1997; Idriss 2000; Jiang 2002; Berge and Verhardsson, 2002). This study involves concrete made with various combinations of Portland cement, slag, fly ash and silica fume, subjected to hydrogen sulphide gas and sulphate solution.
The experimental part of the project will be described in this paper. The results of this research will help finding the most cost-effective solution in Ontario for reducing concrete corrosion to a minimum and enhance the service life of reinforced concrete in livestock buildings there.