SALT RELATED EXPANSION REACTIONS IN PORTLAND-CEMENT-BASED WASTEFORMS

A small-scale study was conducted to investigate the expansion of a si mulated salt-cement wasteform made with a salt mixture containing sodi um nitrate, sodium sulfate, and sodium chloride blended with water and Type I Portland cement. The total salt loading was 39.4% by mass of s imulated wasteform. Samples cured at 23 degrees C hardened within 90 h and showed strength averaging 11.67 MPa after 23 days. Samples cured at 23 degrees C and 55 degrees C expanded when subjected to temperatur e cycling from 1 to 25 degrees C. The samples cured at 55 degrees C re quired only four cycles to disintegrate after showing 14% expansion. S amples cured at 23 degrees C required eight cycles before disintegrati ng after showing 16% expansion. X-ray diffraction patterns from 1-, 4- , 6-, and 21-day-old samples showed the characteristic patterns of hal ite, sodium nitrate, darapskite, and unreacted Portland cement. Sample s older than 1 day also showed portlandite, sodium sulfate and calcium chloroaluminate hydrate which were not found in the younger sample. T he results are consistent with the hypothesis that expansion is due to recrystallization of confined soluble salts. Results suggest that was teforms containing such high loadings of soluble salts may disintegrat e if subjected to thermal cycling. Published by Elsevier Science B.V.