Moisture Retention Characteristics of Base and Sub-Base Materials

Project summary:

Soil water retention refers to the relationship between the amount of soil water and the energy with which it is held. This relationship is not only an indicator of the pore size distribution but also the volume occupied by various pore classes. The relationship is important for characterizing the rate at which water moves through a granular material under both saturated and unsaturated conditions. Important consequences of this relationship are the amount of drainage that may occur through soils, how deep the frost might penetrate, and how strength properties vary seasonally. Since soil particle packing leads to formation of many different size pore necks and pore bodies, water retention of granular material also varies depending upon the size distribution of the granular material, the shape of the particles, and how they are packed.

In this project, soil moisture retention data was generated on 18 non-recycled and 7 recycled materials used in pavement construction. The results showed that water retention of non-recycled materials was nearly similar. The major differences among the curves were in the inflection points (air entry values) and in the water contents either near saturation or at 15,300 cm of suction. Using this database, we also developed Pedo-transfer functions that can predict (1) water retention or (2) the parameters of functions that describe water retention from easily measurable properties of the pavement materials. Water retention of concrete with and without shingles was only slightly different. This is partially because shingle chips imbedded in the concrete were large. Traditionally, the influence of matric suction has not been directly considered in pavement design. The water retention data in this report will be helpful in developing resistance factors for Minnesota Flexible Pavement Design Program either through physical modeling or through statistical relationships between design criteria and the water contents.