Title page for ETD etd-0409102-112238


Type of Document Dissertation
Author Wang, Lan
Author's Email Address lwang2@lsu.edu
URN etd-0409102-112238
Title Cementitious Stabilization of Soils in the Presence of Sulfate
Degree Doctor of Philosophy (Ph.D.)
Department Civil and Environmental Engineering
Advisory Committee
Advisor Name Title
Roger K. Seals Committee Chair
Amitava Roy Committee Member
Clint Willson Committee Member
John Metcalf Committee Member
John Sansalone Committee Member
Roy Dokka Dean's Representative
Keywords
  • soil stabilization
  • supplementary cementitious materials
  • sulfate attack
Date of Defense 2002-03-19
Availability unrestricted
Abstract
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 40C, 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 40C 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.

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