The influence of admixtures on the strength and linear expansion of cement-stabilized phosphogypsum

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The effect of admixture content, dry density and curing condition on linear expansion of cement-stabilized phosphogypsum (CSPG) was studied over a ninety-day period. The phosphogypsum was stabilized using 8% Type I portland cement. Cylindrical CSPG specimens (51mm × 102 mm) were fabricated by static compaction (ASTM D 698) at three density levels: standard Proctor maximum dry density (13.7 kN/m ) and 5% on either side of this density with a moisture content (20%) corresponding to the maximum standard Proctor dry density. CaCl (1% and 2%) and Daraset (0.05% and 0.15%) as a percentage of the amount of cement, were added to CSPG. Curing conditions were (at ambient temperature): open to air, moisture-controlled and soaked. Selected specimens were analyzed by derivative thermogravimetry and scanning electron microscopy. When cured under moisture-controlled environment, CSPG had a short initial period of expansion irrespective of the dry density or admixture content. Increasing dry density led to a period of contraction following expansion. At the same dry density, the additon of CaCl led to a period of no length change while the addition of Daraset led to more initial expansion. The length change, over time, of air-cured CSPG specimens was negligible. The correlation between ettringite content and expansion was crude. For soaked specimens, ettringite growth was widespread and unusually high. Compacted at the lowest density (13.0 kN/m ) and cured in moisture-rich environments, CSPG deteriorated significantly. 3 3 2 2

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Cement and Concrete Research

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