Sulfate attack can occur in concrete due to external sulfate ions reacting with hydrated cement paste. The sulfate attack resistance of portland-limestone cements (PLCs) has been questioned due to their high limestone content, which has the potential to initiate a rare type of sulfate attack that forms thaumasite. This research evaluates the performance of portland-limestone cements in sulfate prone environments by investigating changes in the physical, chemical, and mechanical properties of specimens. Mortar and paste specimens prepared by replacing Type I/II and Type V cement with 4.4, 10, 14.6 and 20 percent of calcitic and dolomitic limestone powders and fly ash are examined for their sulfate resistance. An accelerated cube test for measuring strength loss due to sulfate attack was developed using 33,800 ppm sodium and magnesium sulfate solutions at 5°C and 23°C. Results from this testing are compared to ASTM C1012 expansion measurements. The physical and chemical transformation in paste specimens are analyzed using visual observation, mass loss measurements, and X-ray diffraction.
All mixtures prematurely exceeded the ASTM C1157 12–month expansion limit. Results revealed higher expansion of Type I/II cement with increased calcitic limestone contents, especially in sodium sulfate solution. Type V cement showed greater sulfate resistance in both expansion and strength measurements compared to Type I/II, and the addition of calcitic limestone to Type V cement decreased its expansion. Increased calcitic limestone contents did not significantly impact strength loss for either cement. The addition of a small dosage (4.1% by mass) of dolomitic limestone improved sulfate resistance by exhibiting less strength loss in magnesium sulfate and lower expansion in both solutions in part due to ettringite stabilization. The incorporation of Class F fly ash with 14.6% PLCs showed higher sulfate resistance than other mixtures. Higher expansion (up to 80%) at 180 days and greater strength loss (up to 62%) at 120 days was observed in sodium sulfate compared to magnesium sulfate. Higher strength loss (up to 62%) was observed at 5°C compared to 23°C for most mixes in both solutions, especially for magnesium sulfate exposure. More surface deterioration, including extensive cracking at the corners and along the edges, bulging on the surfaces, and spalling was found in the paste samples at 5°C. Samples with higher limestone contents, in general, showed greater deterioration. At 5°C, thaumasite was detected in all samples in addition to gypsum and ettringite.
|School:||South Dakota School of Mines and Technology|
|Department:||Civil and Environmental Engineering|
|School Location:||United States -- South Dakota|
|Source:||MAI 58/04M(E), Masters Abstracts International|
|Subjects:||Geology, Geological engineering, Civil engineering|
|Keywords:||Cement, Limestone, Performance, Portland-limestone, Sulfate|
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