ABSTRACT
This paper presents some of the key finding in a series of in-situ measurements and laboratory tests aimed at investigating the effect of seasonal changes on the strength and deformation properties of unbound and bound road aggregates. The investigations have included monitoring, for two years, of the long-term variations in the temperature and moisture content of a pavement section located in Koskenkylä, near Rovaniemi in Northern Finland. In addition, short-term variations in the electrical properties of the various pavement layers were recorded while a heavy truck made passes of the measurement site. In addition, the mechanical behavior of various types of aggregates, including those taken from the different pavement structure layers at the measurement site, were studied in laboratory conditions where they were exposed to simulated variations of seasonal conditions.
The research results have given clear indications that the most significant problem for Finnish base course aggregates is the development of permanent deformations during frost thawing periods. During the most critical time period these deformations can be caused by a fairly low number of load repetitions, in fact, less than 10 passing heavy vehicles could cause permanent deformation. Meanwhile, especially when tested in laboratory conditions the resilient properties of all the aggregates were relatively good, and their resilient modulus values were not lowered significantly, even during the thawing phase. The results also suggest that suction properties of aggregates have a very significant effect on deformation behavior. Suction properties, in turn, are determined, above all, by fines content and also by the chemical and mineralogical properties of the aggregate. Further, a fairly simple Tube Suction test seemed to function well in the identification of problematic aggregates and in defining appropriate binder types and their required amounts.
