Durability of Magnesia-Phosphate Grouts in Sulfate Solutions


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Title: Durability of Magnesia-Phosphate Grouts in Sulfate Solutions

Author(s): J. Pera, E. Soudee, and J. Ambroise

Publication: Special Publication

Volume: 212


Appears on pages(s): 341-352

Keywords: ammonium sulfate; durability; magnesia-phosphate cement; magnesium sulfate; schertelite; struvite

Date: 6/1/2003

Two different magnesia powders (MgO) were used to prepare magnesia-phos- phate cements in combination with equal quantities of mono-ammonium phosphate (NH4H2PO4 or MAP). Two grouts containing 5O% of each magnesia-phosphate cement and 50% Class F fly ash were prepared at a water to solids ratio of 0.25 and submitted to three wetting-drying cycles in the following solutions: - de-ionized water, - 20% ammonium sulfate solution - 20% magnesium sulfate solution Each cycle was composed of four weeks of immersion and one week of drying at 20°C. The samples were subjected to the following investigations: mass loss, compressive strength, and microstructure (X-ray diffraction, scanning electron microscopy and differential thermal analysis). The results obtained show a very good behavior of these grouts in magnesium sulfate solution. Their behavior in ammonium sulfate solution depend upon the initial porosity of the grout: expansive schertelite appears and develops without disorder when the grout is very porous. When the porosity is limited, the grout disintegrates after three cycles in the aggressive solution.