Effect of micromorphological development on the elastic moduli of fly ash-lime stabilized bentonite
The mineralogical and micromorphological changes occurring in fly ash-lime stabilized bentonite were observed and related to changes in elastic moduli of the stabilized mixture. Compacted fly ash, fly ash-lime, bentonite-lime, bentonite-fly ash, and bentonite-fly ash-lime mixtures were prepared and cured at 23C and 50C, for 1, 28, 90 and 180 days. The development of microstructure and cementitous crystals were observed by a scanning electron microscope, and energy dispersive spectrum analyzer and a X-ray diffractometer. The elastic moduli and strengths were obtained from unconsolidated undrained triaxial and unconfined compressive strength tests. The physical test results were compared with changes observed by scanning electron microscopy and X-ray diffraction. CSH gel Type I, II and III, ettringite, afwillite and tetracalcium aluminate thirteen hydrate crystals were identified in the cured specimens. The elastic modulus of the fly ash-lime stabilized bentonite was higher than the untreated bentonite and the increase in elastic modulus corresponded to the curing times when new cementitious crystals were observed. Acicular crystals (CSH Type I and II) and ettringite crystals spanned the pores and increased the contact points where blocky aggregates of equant crystals (CSH III) engulfed the fly ash grains providing support. The compressive strength increased, and the strain at a failure decreased resulting in an increase in the elastic modulus. Some fly ash grains providing support for montmorillonite aggregates dissolved and created weak spots in the matrix, causing a decrease in elastic modulus at longer curing periods. At 50C curing temperature the same cementitious crystals were observed as at 23C. However, the rate of the reactions increased considerably.
- Research Organization:
- Louisiana State Univ. and Agricultural and Mechanical Coll., Baton Rouge, LA (USA)
- OSTI ID:
- 5573471
- Country of Publication:
- United States
- Language:
- English
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010800* -- Coal
Lignite
& Peat-- Waste Management
AEROSOL WASTES
ALKALINE EARTH METAL COMPOUNDS
ASHES
BENTONITE
CALCIUM COMPOUNDS
CALCIUM OXIDES
CHALCOGENIDES
CLAYS
COHERENT SCATTERING
COMPRESSION STRENGTH
CRYSTAL STRUCTURE
CURING
DIFFRACTION
DISPERSIONS
ELASTICITY
ELECTRON MICROSCOPY
FLY ASH
MECHANICAL PROPERTIES
MICROSCOPY
MICROSTRUCTURE
MINERALOGY
MIXTURES
MORPHOLOGICAL CHANGES
OXIDES
OXYGEN COMPOUNDS
RESIDUES
SCANNING ELECTRON MICROSCOPY
SCATTERING
STABILIZATION
TEMPERATURE DEPENDENCE
TENSILE PROPERTIES
TIME DEPENDENCE
WASTE PRODUCT UTILIZATION
WASTES
X-RAY DIFFRACTION