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Description: Concrete technologists interested in durability in sulfate environments will find this report invaluable. It documents a 16-year research project carried out to evaluate the performance of concrete in field and laboratory exposures to sulfate solutions. Variables studied included cement composition, water to cement ratio, cementitious materials, and surface treatments. The work affirmed the importance of controlling the water to cement ratio and permeability of concrete in maximizing concrete durability. Traditional mechanisms for sulfate attack are questioned and alternative mechanisms involving salt crystallization are suggested. This report is also found on DVD021.
A long-term test program (16 years) was carried out to evaluate concrete performance in field and laboratory sulfate exposures. Variables included cement composition, water-cement ratio, cement replacements and additions, surface treatments, and exposure conditions. A severe exposure consisting of either partial immersion in a 6.5% sulfate concentration (65,000 ppm) with alternate wetting and drying, or continuous immersion at constant temperature was employed.
Long-term results confirmed the importance of ratio of water to total cementitious materials and resulting permeability as the primary factors determining performance in outdoor exposures. Cement composition was of limited importance. Cement replacements were of lesser importance, depending on type of replacement material. Surface treatments, particularly silicon-based waterproofing materials, were generally beneficial with some dependence on relative permeability of the concrete design mixture.
Continuous immersion in the same sodium sulfate concentration resulted in superior performance of the concrete prisms compared with companion concrete beams. These prisms all were in excellent condition after 12 years immersion, regardless of materials or treatments.
These findings call into question the traditional explanation of sulfate reaction and deterioration of concrete. Continuous immersion in sulfate solution resulted in essentially no deterioration, whereas cyclic immersion resulted in progressive scaling and loss of aggregate.
The following conclusions are drawn based on findings from this study:
1. Use of low ratios of water to total cementitious materials provided the greatest resistance to sulfate attack on the concrete.
2. Composition of portland cement was less important as it relates to performance in sulfate solutions.
3. The salt crystallization process was a major cause of concrete distress compared with the traditional hypothesis of chemical reaction of aluminates from cement hydration and sulfates from external sources.
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