Laboratory Examination of Frost-heaving Properties of Road Unbound Mixtures Based on Fines Content and Plasticity Index

AbstractIn order to ensure the bearing capacity and durability of road pavement in cold climate areas, it is necessary use materials which are resistant to harmful frost impact, known as frost-heaving. Frost heave cause adverse volume changes, the upwards swelling of the pavement after freezing and deterioration of the bearing capacity of the structure after thawing. In winter, road carriageway temperatures may reach tmin = -30̊C under Polish conditions, which results in the freezing of the structural pavement and subgrade layers. Due to frost penetration into the pavement and the subgrade, heaves may form in soils and in structural layers (unbound mixtures), and during the thaw period a high level of moisture is maintained in the frozen layers, and therefore the structure has a low bearing capacity. The aim of this research was to evaluate frost susceptibility of aggregates mixtures based on content of fine-grain fractions and plasticity index IP. Potential frost susceptibility of road materials and soils is determined by laboratory testing. Frost susceptibility is connected directly with the content and quality of fines, which is why the basic test is that material grading. The criterion based on fines content is the most frequently used indicator in determining frost susceptibility for soils. The article shows whether the limit values adopted for this criterion are also applicable to aggregates. The results of frost-heaving properties are presented of 14 typical natural aggregate road mixtures, continuously graded 0/31.5 mm. Frost susceptibility was determined based on laboratory testing of the following features: content of fine-grain fractions, smaller than 0.002 mm, 0.02 mm, 0.075 mm, 0.125 mm, plasticity index IP and the value of the actual frost-heave of a compacted aggregate mixture frozen in a cylinder. The article shows the test results and their analyses according to the frost susceptibility evaluation criteria for unbound mixtures in road construction. The tests presented in the article were carried out at the Road and Bridge Research Institute in Warsaw