Strength increases resulting from carbonate cementation in compacted sands and cemented coquina highway base course materials of variable quartz-calcite composition were investigated through the use of limerock-bearing-ratio (LBR) testing. Quartz and calcite sands were mixed in various proportions, compacted into LBR molds, soaked for time periods from 2 days up to 60 days, and tested to determine strength increase with time. For comparison, cemented coquina highway base course materials of variable quartz-calcite composition were also compacted, soaked, and tested. In addition, duplicate sets of specimens were tested that had 1 percent ca(oh)2 (hydrated lime) mixed with the dry materials before compacting and soaking. This was done to provide a source of ca2+ ions for formation of additional carbonate cement. Results of the LBR testing program showed that more strength developed as the calcium carbonate composition of both the quartz-calcite sand mixes and the cemented coquina samples increased. Addition of ca(oh)2 to the samples enhanced carbonate cementation effects, with large strength increases occurring in high-carbonate materials. Scanning electron microscopic examinations of the tested LBR materials, base course materials scored from in-service highways, and naturally occurring calcite-cemented quartz sandstones and limestones revealed different bonding characteristics between calcite cement-calcite particle and calcite cement-quartz particle systems, which would explain the strength development patterns observed in LBR testing.
Abstract