Conclusions and Recommendations
After 23 cycles of exposure to sulphate and/or sulphide 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 (PC50) is the least resistant to steel corrosion, as might be expected. All treatments containing silica fume are performing much better than PC40. Treatment FAC, and FASF stand out as performing worse than plain PC concrete with the same W/CM ratio confirming the fact that Class C fly ash, most commonly available in Ontario, does not provide improvement in sulphate resistance. SR was more resistant than Type 10 Portland cement, 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.
Exposed to (1.000 ppm) Hydrogen Sulphide Gas Only
Fig. 6b. Pictures of specimens after the 23rd cycle showing the concrete loss.
Exposed to (20,000 ppm) Sulphate Solution and (1.000 ppm) Hydrogen Sulphide Gas
The results of this study show that, in the sulphide/sulphate environment of manure storage and handling structures made of reinforced concrete, concrete corrosion is the critical factor, steel corrosion is less of a problem. The results indicate that the quality of concrete is the key to the best protection for the steel against sulphate and sulphite attack. It is relatively simple to produce such concrete by making an impermeable, well-cured concrete using a reasonably low W/CM ratio. However, the results also indicate that high Portland cement content creates a problem. Therefore, partial replacement of the Portland cement or the use of sulphate resistant cement will benefit the durability of the concrete of manure structures against the sulphates present in manure.
In summary, it is recommended that reinforced concrete in areas in a livestock building exposed to corrosive materials from manure should be specified to have:
1. high quality, with a maximum W/CM ratio of 0.45, 0.40 if feasible;
2. a maximum Portland cement content of 350 kg/m3 in order to limit C3A content;
3. 8% of the cementitious material to be silica fume, or 35% to be slag;
4. adequate (50 mm) concrete cover over the reinforcement