A small-scale study was conducted to investigate the expansion of a simulated salt-cement wasteform made with a salt mixture containing sodium nitrate, sodium sulfate, and sodium chloride blended with water and Type I Portland cement. The total salt loading was 39.4% by mass of simulated wasteform. Samples cured at 23°C hardened within 90 h and showed strength averaging 11.67 MPa after 23 days. Samples cured at 23°C and 55°C expanded when subjected to temperature cycling from 1 to 25°C. The samples cured at 55°C required only four cycles to disintegrate after showing 14% expansion. Samples cured at 23°C required eight cycles before disintegrating after showing 16% expansion. X-ray diffraction patterns from 1-, 4-, 6-, and 21-day-old samples showed the characteristic patterns of halite, sodium nitrate, darapskite, and unreacted Portland cement. Samples older than 1 day also showed portlandite, sodium sulfate and calcium chloroaluminate hydrate which were not found in the younger sample. The results are consistent with the hypothesis that expansion is due to recrystallization of confined soluble salts. Results suggest that wasteforms containing such high loadings of soluble salts may disintegrate if subjected to thermal cycling.
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