Guidelines for treatment of sulfate-rich soils and bases in pavement structures

In general, the use of calcium-based additives (lime, cement, and Class CS fly ash) to treat soils and bases has been performed with success over many years. Over the past 20 years, a phenomenon has surfaced in which many subgrade soils treated with calcium-based additives experience heaving problems due to the chemical reactions with sulfate and/or sulfide minerals and calcium-modified soils, as illustrated in Figure 1. Field observations indicate that the reactions can be very rapid and occur overnight following a single rainfall event