Freezing-induced water migration in compacted base-course materials
Canadian Geotechnical Journal
Abstract and Figures
Ramped-freezing tests were conducted on three base-course materials with fines contents of less than 7% and compacted at different initial states but always at degrees of saturation near or well below 60%. Three different quarries were studied. The natural fines from crushed gneiss with biotite, limestone, and monzonite were all frost susceptible. Frost heave was relatively small, but significant water intake occurred in all samples during freezing with access to an external water source, regardless of initial saturation level. The frost susceptibility of coarse-grained soils cannot be solely evaluated with respect to frost heave but needs also to consider the amount of water drawn to the freezing front during the freezing process and the consequences of this water during thaw. The normalized heave of the base-course layer of pavements is a practical and efficient indicator of the frost susceptibility of the base-course aggregates. If it is larger than 1%, the base-course material can be considered as frost susceptible leading to a significant increase in the degree of saturation once frozen. Current base-course material specifications based solely on grain-size distribution are not adequate to differentiate materials that are nonfrost susceptible from those that are frost susceptible. Hence, an additional criterion based on the fines frost susceptibility should be considered.
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The influence of fines on the frost susceptibility of base-course crushed aggregates was established by laboratory freezing tests simulating closely the thermal conditions in the field. The frost susceptibility of the fines was varied by use of different mixtures of granitic fines and commercially available kaolinite clay. A total of 13 samples with fines content of 5%, 10%, and 15% and kaolinite fractions of 10%, 50%, 75%, and 100% were subjected to four freezethaw cycles. The frost susceptibility of well-graded crushed aggregates increases with increasing fines content and increasing kaolinite fraction. From a quantitative point of view, for a given kaolinite fraction, the segregation potential increases linearly with fines content, until the fines create a matrix in which the coarser particles are embedded. For the material studied, this occurs when the fines content is higher than 15%. For a given fines content, it was also established that the segregation potential increases linearly with kaolinite fraction, indicating the importance of mineralogy. It was also established that appropriate thermal testing conditions need to be adopted to prevent undue pore water extraction from the unfrozen soil close to the frost front during laboratory freezing of unsaturated coarse-grained soils.Key words: coarse grained, soil, frost susceptibility, pavements, laboratory, fines.
This paper presents the results of a comprehensive laboratory investigation program on the influence of the properties of fines particles on the hydraulic characteristics of granular base-courses. The soil-water characteristic curve and the hydraulic conductivity were determined for three types of well-graded crushed aggregates (granite, limestone, and schist) with different amounts of fines (3.512.5%). A porosity model that considers the uniform dispersion of fines is proposed for well-graded material. Empirical relationships have been developed between the hydraulic parameters (i.e., the saturated hydraulic conductivity, the air entry value, the pore-size distribution index, the fines fraction porosity) and their specific surface area. A methodology is proposed for the assessment of the saturated and unsaturated hydraulic characteristics of base-course materials.Key words: pavement, drainage, base-course, fines, soil-water characteristic curve, hydraulic conductivity.