HR: 1340h
AN: B53A-0984    [Abstracts]
TI: Spatial Distribution of Sulfate and the Formation of Ettringite in Lime-Amended Soils of Central Texas
AU: * Kuo, L
EM: ljkuo@geo.tamu.edu
AF: Texas A and M University, Department of Geology and Geophysics, College Station, TX 77843-3115 United States
AU: Markley, C T
EM: cmarkley@neo.tamu.edu
AF: Texas A and M University, Department of Geology and Geophysics, College Station, TX 77843-3115 United States
AU: Herbert, B E
EM: herbert@geo.tamu.edu
AF: Texas A and M University, Department of Geology and Geophysics, College Station, TX 77843-3115 United States
AU: Little, D N
EM: d-little@tamu.edu
AF: Texas A and M University, Department of Civil Engineering, College Station, TX 77843-3135 United States
AB: During road construction, the use of calcium-based stabilizers, such as calcium oxide (lime), in sulfate-bearing clay soils has historically lead to distress and heave due to the formation of ettringite and possibly thaumasite. Ettringite (Ca6(Al(OH)6)2(SO4)3*26H2O) is a hydrous calcium alumino-sulfate mineral that precipitates in environments with high pH and high sulfate activity. Field surveys of soil conductivity quantified using electromagnetics (EM31), geochemical characterization of soils, geochemical modeling of ettringite precipitation in lime-amended soils, and landscape characterization using existing geospatial databases were coupled to prediction the potential for ettringite formation along the SH 130 corridor, a new toll road being constructed in central Texas. Electromagnetic surveys of soil conductivities were conducted at two sites near HWY 290 and HWY 79, in the SH 130 corridor. Soil conductivities at the two sites were correlated extractable SO42- and other soil properties (extractable Al, Ca, and Mg) quantified by water extracts at two pHs (pH 8-9 and 12). At the HWY 290 site, the soil conductivity ranged from 111 to 184 ms/m, while the conductivity ranged from 34-48 ms/m at the HWY 79 site. The concentration of extractable SO42- in HWY 290 and HWY 79 sites are up to 7269 mg/kg and 406 mg/kg, respectively. Soils at these sites are dominated by smectitic clay with relatively high amounts of carbonate. Information from STATSGO, the USDA soil database, and the comparisons between the results of the field surveys and laboratory soil analyses show that variations in sulfate levels at the two sites are strongly influenced by topography. The HWY 79 site is fairly level and there are only very weak trends in the sulfate composition of the soils. The HWY 290 site, on the other hand, is fairly hilly, with a dry stream channel, whose soil and sediments exhibited very high sulfate concentrations. The strong topographic slope influences hydrologic flow, including both surface runoff and subsurface flow, which transports sulfate down slope. In addition, evapotranspiration during the dry season would also help accumulate sulfate in low-lying areas due to solute transport from near-surface ground waters. This study demonstrates that electromagnetics can be used for in-situ, field-scale survey of sulfates. Coupled with the application of geochemical speciation models, we assess the potential of ettringite formation in the SH 130 corridor.
DE: 9820 Techniques applicable in three or more fields
DE: 5100 PHYSICAL PROPERTIES OF ROCKS
DE: 1894 Instruments and techniques
DE: 1615 Biogeochemical processes (4805)
DE: 0694 Instrumentation and techniques
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting