Laboratory Investigations of Frost Susceptibility of Aggregates Applied to Road Base Courses

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In order to ensure the bearing capacity and durability of road pavements in cold climate areas, it is necessary to use materials which are resistant to harmful frost impact, known as frost heaving. Frost heave cause adverse volume changes, the upwards swelling of a pavement after freezing and deterioration of the bearing capacity of the structure after thawing. In winter, road carriageway temperatures may reach tmin = −30 ˚C 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 unbound pavement structural layers. Road bases made of unbound mixtures of continuously graded aggregates may be frost susceptible. Potential frost susceptibility of road materials and soils is determined by laboratory testing. Frost susceptibility is connected directly with the content and quality of fine particles in an aggregates. Frost heave can be predicted on the basis of different properties of soils or aggregates. The article presents the results of laboratory tests of 14 typical natural aggregate road mixtures, continuously graded 0/31.5mm and practically applied to road base courses. Frost susceptibility of the aggregates was determined during laboratory testing of the following properties: content of fine-grain fractions <0.002 mm, <0.02 mm, <0.075 mm, plastic limit, liquid limit and sand equivalent. The aggregates were also compacted and frozen in a cylinder and then their frost heave value was determined. Correlations between fine-grain fractions, plastic limit, liquid limit, plasticity index, sand equivalent and frost have of the aggregates were analysed. The tests showed no correlations between plastic limit or plasticity index and frost have of the aggregates. Differences were also noted in criteria applied for predict frost susceptibility of aggregates based on fines content. The conclusions of the tests can be used in practice to determine or verify requirements for aggregates or their mixtures applied to road base courses.