Cementitious Stabilization of Soils in the Presence of Sulfate

by Lan Wang

Institution: Louisiana State University
Department: Civil and Environmental Engineering
Degree: PhD
Year: 2002
Keywords: soil stabilization; supplementary cementitious materials; sulfate attack
Record ID: 1730367
Full text PDF: http://etd.lsu.edu/docs/available/etd-0409102-112238/


Winn Rock (anhydrite, CaSO4) comes from a quarry in Winn Parish in north Louisiana. Gravel from the quarry has been used extensively as a surface course on local parish and logging roads. Stabilization of these roads with Type I Portland cement followed by an overlay by asphaltic concrete sometimes resulted in heaving. The causes for heaving and possible solutions were investigated. In the laboratory 2" x 4" molds of Winn Rock containing soil were prepared and cured in water bath at 40°C, sealed plastic bag at room temperature, and air. Molds were prepared with 5% to 20% cementitious material. The cementitious materials were Type I Portland cement, lime, and supplementary cementing materials (SCM) such as granulated blastfurnace slag (BFS), Class C fly ash (CFA), and an amorphous silica (AS). The expansion of the molds over time was monitored. Mineralogical and micro-structural analysis of the molds was also performed over time and correlated to expansion. The characterization methods included X-ray diffractometry, thermal analysis and scanning electron microscopy. A set of molds was also prepared with soil from a well-characterized site west of Baton Rouge (the Accelerated Loading Facility site), free of any sulfate minerals, to distinguish the effect of internal and external sulfates. The Winn Rock gravel partially weathered in the soil to gypsum which was detected in all size fractions. The highest amount of expansion occurred in Winn Rock soil stabilized by lime cured at 40ºC in water bath. The magnitude of the expansion is directly proportional to the amount of Type I portland cement, the amount of available moisture, and the curing temperature. Replacement of a part of the Portland cement by BFS reduced the expansion by almost an order of magnitude even at the highest moisture content. No expansion was detected when CFA and AS were used as replacement. The average length and amount of ettringite crystals, in general, inversely correlated with the magnitude of expansion. A three-stage expansion model was developed to explain increased sulfate attack resistance provided by the SCMs, attributable to their consumption of calcium hydroxide and a morphology change of ettringite crystals.