Frost Heave Test

Frost Heave Testing

The British Standard (BS 812-124) outlines a method for evaluating the frost resistance of unbound aggregate mixtures used in the construction of roads and other paved areas that may be subject to frost penetration. The procedure involves compacting a cylindrical specimen of the mixture at a specified water content and density, and then subjecting it to freezing temperatures. This method can also be applied to assess hydraulically bound aggregate mixtures, though the standards for acceptable frost heave may differ from unbound mixtures. Additionally, the use of comparator specimens is an option to ensure the accuracy of the test chamber.

What is Frost Heave?

Frost heave is a phenomenon that occurs when soil or other porous material is subjected to freezing temperatures. As the water in the soil freezes and expands, it pushes upward on the soil above, causing it to rise and form mounds or ridges. This process, known as frost heaving, can cause damage to structures, such as roads and buildings, that are built on top of the soil. It can also cause problems with drainage, as the frost can impede the flow of water through the soil or sub-base. The amount of frost heave that occurs depends on factors such as the type and composition of the soil, the amount of water present, and the severity of the freezing temperatures. It is more common in places that are susceptible to cold temperatures, and within materials absorb water, such as clay or recycled concrete fines.

Ice Lensing

Ice lensing

Ice lensing is a phenomenon that occurs in soil and sub-base materials when they are subjected to freezing temperatures. It occurs when water within the soil or sub-base material freezes and expands, forming thin, flat layers of ice. These ice lenses can be formed by the freezing of water that is present in the soil or sub-base, or by the infiltration of water from the surface.

The ice lensing process is driven by the freezing of water in the soil pores. As the water freezes, it expands and pushes against the surrounding soil particles, causing them to move apart. The result is the formation of thin, flat layers of ice within the soil or sub-base material. Over time, these ice lenses can grow and become thicker, causing the soil or sub-base material to expand and heave.

To prevent ice lensing, it is important to ensure that soil and sub-base materials are well-drained and that the groundwater table is low. In cold climates, it's also common to use de-icing chemicals to prevent the formation of ice lenses on roads and other surfaces.

Frost susceptibility of recycled concrete

Water absorption and frost heave can lead to severe damage on highway construction elements, resulting in bearing capacity reductions and accelerated pavement distress. These issues are particularly problematic in Nordic countries where controlling the frost susceptibility of road building materials is crucial.

In recent years, there has been a growing interest in using crushed concrete materials in road construction. However, concerns have been raised regarding the frost susceptibility of these materials. Limited experiences with crushed concrete materials in road construction in Norway have made it difficult to determine their level of frost susceptibility.

To address this issue, the Norwegian Public Roads Administration (NPRA) initiated the Recycling R&D Program, which aimed to test the frost heave properties of dense-graded crushed concrete materials. The program included the materials used at the Melhus test road, which were subjected to a 96-hour laboratory freezing test.

Studies in Norway suggest that while there were some variations in frost heave results, recycled concrete materials exhibited a higher degree of frost susceptibility than expected based on their grading curves alone. This highlights the importance of considering the potential consequences of frost heaves when utilizing these materials.

Is recycled concrete a good sub-base material?

Unbound crushed concrete aggregates have demonstrated excellent performance as base and sub-base materials, even on high-volume roads, as indicated by their high elastic stiffness and stability in laboratory tests. This suggests that these materials have a high bearing capacity and good resistance to permanent deformation.

Field measurements have confirmed the laboratory results, showing that recycled concrete aggregates have very high bearing capacities and layer stiffness.

However, the potential consequences of frost heaves should be considered when using these materials. Norwegian guidelines for road construction do not recommend using recycled concrete aggregate in submerged conditions where freezing could occur.

Recycled concrete aggregates appear to have satisfactory durability properties for most exposure conditions. However, the composition of the material requires tailored test methods, including tests of freeze-thaw durability that incorporate de-icing salts for Nordic climate conditions.