Recommended Practice for Stabilization of Sulfate-Rich Subgrade Soils

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Recommended Practice for Stabilization of Sulfate-Rich Subgrade Soils

Author: Little, Dallas N Texas A&M University, College Station Nair, Syam Texas A&M University, College Station | Size: 1.08 MB | Format: PDF | Quality: Original preprint | Publisher: Transportation Research Board | Year: 2009 | pages: 66 | ISBN: -

Calcium-based stabilizers (CaO-based stabilizers) develop a high pH environment when mixed with water during construction. This high pH condition and the presence of lime (CaO) introduce an environment favorable to the formation of two expansive minerals, ettringite and possibly thaumasite, when sulfate-bearing salts are present in soil. The success of a lime stabilization project depends heavily on the accuracy of predictions regarding the potential of the native soils to form these disruptive minerals. This report describes the nature of these minerals and the mechanism of their formation in soils stabilized with lime, cement, or fly ash. The key issue for the engineer in deciding how to properly stabilize sulfate-bearing soils is to quickly and efficiently determine: (1) the sulfate content of the soils and (2) the threshold quantity of sulfates likely to cause damage. This report addresses both issues but focuses on the methods used to quantify sulfate content. Quick and effective field techniques and more precise laboratory tests are compared and evaluated. Recommendations are presented regarding the appropriate testing protocol to use. Specific recommendations for changes to the American Association of State Highway and Transportation Officials (AASHTO) test method T-290-95 (methods A and B) are made. The report also outlines techniques for effective risk assessment including reconnaissance, topographical assessment, pedological and geological assessment, climatic assessment, and soil sampling plans. The report also outlines construction tests that can reduce risks for various levels of sulfate determined using a method such as AASHTO T-290-95 (revised) or equivalent.

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