Highway base course materials composed of crushed limestone aggregates have been observed to increase in strength with time under both field and laboratory conditions. Studies have shown that this is due primarily to the movement of calcium and carbonate ions, which produces a natural cementation process in these materials. Testing ofmaterials with variable silica-carbonate compositions indicated that the amount of strength developed from the carbonate cementation process is a function of the mineralogic composition of the materials, with more strength developed as calcium carbonate composition increased. Scanning electron microscopic studies suggest that this is dueto differences in bonding characteristics between calcite cement-calcite particle and calcite cement-quartz particle systems. Treatmentof the silica-carbonate material with ca(oh)2 (hydrated lime) before testing enhanced strength development by furnishing calcium ions, which carbonate to form an additional source of calcium carbonate cement. This treatment allows for a more rapid test method to determine the potential strength development in silica-carbonate materials from natural cementation processes. This paper appears in transportation research record no. 1250, Innovation in aggregate testing.
Abstract