Salt Weathering Distress on Concrete Exposed to Sodium Sulfate Environment

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Title: Salt Weathering Distress on Concrete Exposed to Sodium Sulfate Environment

Author(s): Harvey Haynes, Robert O’Neill, Michael Neff, and P. Kumar Mehta

Publication: Materials Journal

Volume: 105

Issue: 1

Appears on pages(s): 35-43

Keywords: deterioration; physical salt attack; salt hydration distress; salt weathering; sodium sulfate; sulfate attack.

DOI: 10.14359/19205

Date: 2/1/2008

Abstract:
Under certain environmental exposure conditions, rocks and stone monuments are known to exhibit salt weathering or physical salt attack. A similar phenomenon is found with ordinary porous concrete exposed to soils containing sodium sulfate. This type of physical attack on concrete was overlooked by past researchers who focused on chemical sulfate attack, which is potentially far more harmful. Physical attack is the primary focus of research investigation in this paper. To promote physical attack, a concrete mixture was made with a low C3A, ASTM Type II portland cement, using a water-cement ratio (w/c) of 0.65. After curing, cylindrical concrete specimens were partially submerged in a 5% sodium sulfate solution for periods up to 3.1 years. Tests were conducted under temperature and humidity cycles simulating various ambient conditions, one of which promoted alternate cycles of conversion between thenardite (Na2SO4) and mirabilite (Na2SO4·10H2O). Overall, the results showed that concrete scaling occurred at evaporation surfaces directly above the solution level, and significant scaling occurred when concrete was subjected to numerous cycles of thenardite-mirabilite conversion.


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