EFFECTS OF RESIDUAL AGGREGATE MOISTURE ON STRIPPING POTENTIAL OF ASPHALT CONCRETE MIXTURES

For some asphalt concrete mixes in Alabama, correlations between field stripping performance and stripping test predictions have been poor. One of the possible causes of this inconsistency appears to be the inability of the laboratory stripping tests to simulate field conditions, particularly the drying of aggregates before mixing with asphalt cement. In the field, highly absorptive saturated aggregates may not be effectively dried by rapid heating in drum dryers. Laboratory preparation of test samples, however, begins with well-dried aggregates. Moisture content measurements of hot bin aggregates and freshly mixed hot asphalt concrete occasionally confirm the presence of residual moisture at levels that are likely to have an effect on the moisture damage susceptibility of the mix. The amount of moisture retained in plant-produced mix is highly dependent on ambient temperature and the moisture content of aggregate stockpiles. Wet-dry indirect tensile stripping tests indicate that the effect that residual moisture has on tensile strength depends on aggregate type. On the basis of tensile strength ratios of conditioned specimens to unconditioned specimens, residual moisture can be detrimental to mixes containing primarily siliceous aggregate. However, mixes containing limestone as the dominant aggregate did not appear to be adversely affected by residual aggregate moisture.