Volume 19, Issue 2 (March 1991)
Comparison of Methods for Measuring Moisture Content of Aggregate and Asphalt-Aggregate Paving Mixtures
Residual moisture in hot asphalt-aggregate paving mixtures is a function of aggregate type, environmental conditions, and production rate. This moisture is detrimental to pavement performance. Residual moisture can be controlled, but a simple method is needed to measure the moisture content of asphalt-aggregate paving mixtures during the construction process. Currently the only standardized method for determining moisture content of asphalt-aggregate mixtures is the distillation procedure (ASTM D 1461), a method generally too cumbersome for routine production testing and hence not used in field laboratories. Moisture content measurements on a variety of materials (aggregates and asphalt-aggregate mixtures) with the distillation procedure and with conventional and microwave ovens for drying were compared and analyzed. Drying with a microwave or conventional oven gives slightly higher moisture contents than the distillation procedure. Efficiency of drying is apparently the primary reason for the differences. Considering the magnitude of the observed differences in measured moisture content and the relative difficulty of the D 1461 test procedures, the microwave method is recommended for routine moisture content determination for asphalt-aggregate mixtures.