Investigation of the benefits of carbonate cementation due to addition of low percentage of hydrated lime in the base courses of pavements

Abstract

Carbonate cementation is a natural phenomenon. Constant fluctuation of the chemical conditions in the nature causes calcium carbonate to dissolve and reprecipitate as a cementing agent. Research showed that this natural tendency of carbonate cementation can be enhanced by adding lime to the system. Lime is used in many places and especially in Texas to stabilize base and subgrade materials. Base course aggregates are normally stabilized with very low percentage of lime. While pozzolanic reaction is expected to occur in heavily stabilized subgrade, carbonation reaction is likely to be prominent in base courses stabilized with low percentage of lime because of little or no clay in them. In this research, two base course materials commonly used in South Texas, limestone and caliche soil, were tested extensively to examine the effect of carbonate cementation due to the addition of small percentages of lime. Testing included mineralogical analysis of the two materials, strength analysis in terms of texas triaxial strength, atterberg limit testing, scanning electron microscopy examinations, resilient moduli determination of the materials in the lab and in the field. Caliche and limestone base materials stabilized with either I or 2 percent hydrated lime were compared to control (unstabilized) materials in terms of the anal yses 1 i sted above. In addition, Falling Weight Defectometer was used to back calculate moduli values of the pavement layers using the program MODULUS. Mineralogical analysis revealed that quartz-rich limestone and caliche aggregate contained little, if any, clay minerals and it was unlikely for these aggregates to experience pozzolanic reaction for that reason. Strength increases due to the addition of low percentage of lime to both of these aggregates which were observed in Texas triaxial compression tests were most likely to be the result of carbonation reaction. Laboratory and field testing for resilient moduli also demonstrated that the addition of hydrated lime increased the moduli values of the aggregate regardless of material type, curing time, and moisture condition.