EVALUATION OF AGGREGATES FOR BASE COURSE CONSTRUCTION

An investigation of limestone base course aggregates was performed to ascertain if strength and stiffness changes in carbonate aggregates could be evaluated for the purpose of quantifying their effects on the base structural layer coefficient used in pavement design. One of the goals of this approach was to develop a laboratory test or series of tests, which the Florida Department of Transportation might use to quantify or predict strength and stiffness gains, that could be generally applied to a range of materials types given field operating conditions. Materials of varying carbonate content were selected, prepared at optimum moisture content and compacted by modified proctor for testing at different ages after curing by two methods (soak and moisture room). Replicate specimens were prepared with 1.0% lime and tested for the purpose of accelerating cementation or modifying clay contained in the aggregate to simulate observed increases in field based strength performance. Limerock Bearing Ratio, cohesion and angle of internal friction, triaxial resilient modulus, and gyratory shear tests were performed and evaluated. Based on the data accumulated with this study, carbonate content does not necessarily relate to higher strength gain. This does not mean that high carbonate content materials cannot achieve cementation and greater strength, rather that the series of tests included in this report were unable to quantify and/or accurately reproduce the effect of cementation within a curing time of 60 or less days. However, it does suggest that use of a higher layer coefficient for high carbonate aggregates strictly based on percent carbonates may not be appropriate.