IMPROVED CHARACTERISTICS IN SULFATE SOILS TREATED WITH BARIUM COMPOUNDS BEFORE LIME STABILIZATION

Abstract

Some sulfate-bearing soils stabilized with calcium hydroxide (lime) have developed heave over periods of time. This heave is thought to result from reactions of soluble sulfates, calcium hydroxide, and free aluminum in the soil or groundwater, or both, to form ettringite (3CaO.Al2O3.3CaSO4.32H2O), a highly water-expansive mineral. Laboratory testing, using the California bearing ratio (CBR) method, has indicated increased bearing strength values and decreased swell when barium hydroxide or barium chloride was added to sulfate-rich soils before lime application. A California soil containing sodium sulfate had increased strength values when either barium compound was used with lime as compared with specimens with lime only. A barium hydroxide treatment followed by lime application to a Texas soil containing sodium sulfate was successful, showing increased CBR values and a decrease in percent swell. Potential volume change tests were conducted on a Colorado soil and the California and Texas soils using lime only and lime added to soils treated with barium hydroxide or barium chloride. The barium hydroxide plus lime treatment showed a marked decrease in swell pressure when compared with lime-only treatment. The mix of barium chloride plus lime decreased in swell pressure, but not as significantly as the mix of barium hydroxide plus lime. The presence of ettringite in the treated soils was determined using scanning electron microscopy. Ettringite formation was not detected in the California or Colorado soils for either combination of barium hydroxide or barium chloride plus lime. The Texas soil contained an abundance of ettringite in the mix of barium chloride plus lime, and it was present, but sparse, in the mix of barium hydroxide plus lime.