The morphological, mineralogical, and stress-strain properties of compacted bentonite-fly ash-lime, bentonite-fly ash, and bentonite-lime cured at 23 deg C and 50 deg C were compared. The development of microstructure and cementitious crystals was observed by scanning electron microscopy, energy dispersive spectral analysis, and x-raydiffractometry. The elastic moduli and compressive strengths were obtained from unconsolidated, undrained triaxial and unconfined compression tests. Curing at 50 deg C increased the rate of strength development. Similar elastic moduli were obtained for specimens cured for one day at 50 deg C and 28 days at 23 deg C. However, strain at failure after one day of curing at 50 deg C was considerably higher than that obtained after 28 days of curing at 23 deg C. The samples cured at 50 deg C yielded higher compressive strengths relative to the samples cured at 23 deg C. Cementitious minerals formed at both curing temperatures were similar except that the cementitious minerals observed after 50 deg C curing had a higher degree of crystallinity. Short-term, high-temperature curing may be substituted for the prediction of long-term design parameters; however, the relationship between short-term, high-temperature curing versus long-term, low-temperature curing must be statistically established by further testing.
Abstract