AN EVALUATION OF BASE COURSE MATERIALS IN FLORIDA WITH AN EMPHASIS ON PREDICTING STRENGTH GAIN ASSOCIATED WITH CEMENTATION OF HIGH CARBONATE AGGREGATES

An investigation of base course materials was performed to ascertain if cementation produced by high carbonate aggregates could be evaluated for the purpose of quantifying its effect on the structural coefficient (a₂) for use in pavement design. One goal of this research was to develop a laboratory test or series of tests that could be applied to a range of material types in order to quantify or predict strength and stiffness gains. Materials of varying carbonate content were characterized (mineralogy, gradation, and percent carbonates), prepared at optimum moisture content, and compacted by modified proctor for testing at different curing ages. Both Limerock Bearing Ratio (LBR) and Triaxial Resilient Modulus (M_R) tests were performed and evaluated for this study. Replicate specimens were prepared and tested with 1% lime (by weight) in an attempt to accelerate cementation or stablize clay contained in the aggregate.

Results show poor correlation between carbonate content and strength gain for both 1% lime treated and untreated samples. This indicates that the tests used for this study were unable to quantify the effect of cementation as a consequence of other sample variables. Variations in carbonate mineralogy (low-Mg calcite, high-Mg calcite, aragonite, and dolomite) and gradation of aggregate materials, as well as variations in test specimen dry density (g_d) exhibit correlations with strength gain, impacting test results. Furthermore, poor test precision added further to the difficulty in identifying a relationship, if any, between carbonate content and strength gain in the materials tested. As a result, use of a higher layer coefficient for high carbonate aggregates strictly based on percent carbonates may not be appropriate.