The most significant problem related to base course aggregates in Finland and in many other countries affected by seasonal frost is the development of permanent deformation, especially during the frost-thawing period. From 1996 to 2000, a series of research projects was carried out to examine the mechanical, thermodynamic, electrical, and chemical factors that affect the seasonal variation of strength and deformation behavior of base course aggregates. The test series included frost heave tests and normal as well as long-lasting cyclic-loading triaxial tests performed in situations simulating seasonal conditions of dryness, moisture, and the period following a freeze-thaw cycle. Also, chemical and suction properties of the selected aggregates were examined. Results show clearly that even though the aggregates were reflecting significantly different permanent deformation behavior, the resilient deformation properties of all tested aggregates were relatively good, and their resilient modulus values were not significantly lowered even during the thawing phase. Meanwhile, the suction properties of aggregates appeared to have a significant effect on the deformation behavior. Suction properties, in turn, result foremost from the fines content but also from chemical properties of the aggregate. A fairly simple tube suction test proved to function well in identifying the problematic aggregates and in defining appropriate binder types and their required amounts. Further, the results suggest that the properties of aggregates bound with emulsified bitumen are not necessarily improved when binder content is increased.
Abstract