Terrasstabilisering - frostbeständigheten i stabiliserade jordar

Sammanfattning: The thesis examines various stabilised soils resistance to frost and to increase understanding in the field. By variation of soil materials, binders and water content, the expectation is to find a link between the various factors and frost resistance. Soil stabilisation is not a new method as it has been used since Roman times but even more recently, the U.S. military used the stabilisation at the construction of highways and airport areas. In today's society were environmental questions has got an increasingly significant role, this method can bring environmental and transport savings and a better sustainable use of natural resources. A stabilised subgrade creates incentives for reduced pavement and can thereby reduce the need for crushed rock. The approach is that the binder is milled into an otherwise unusable soil material to obtain the desired strength. Soils with less grain fraction and a high clay content is beneficially stabilised with lime where the mixture causes pozzolan effects while cement is better suited in soil materials with coarser grain fractions. Strength is obtained quickly when mixed with cement, while in lime mixtures strength isn’t achieved until long after. There are different theories of how the stabilised material reacts when exposed to frost conditions, one of the theories is the mortar theory based on the water which is trapped by the reaction products which aren’t freezable so it’s only the capillary bound water that’s exposed. Stabilised soil is therefore less prone to icing, while the occurrence of residual products from reactions decreases the probability of water saturation. French experiences has shown that a compressive strength of 2.5 MPa with lime stabilisation and 0.25 MPa tensile strength with stabilisation by hydraulic binders have been assessed to be regarded as frost resistant. However, there are divided opinions about what’s considered to be frost resistant. To get a structure of the study, standards were followed. The ground materials that were chosen to study was sandy clay till, and silty clayey moraine sand. The till contained high levels of lesser fractions while the silty till contained a high proportion of larger fractions. The following test parameters were considered to be of interest: • Binder type • Binder amount • Earth materials • Water content These parameters were varied by either type or content. When the binder content was varied, the water ratio were constant (optimum water content) and vice versa. Manufacture of test specimens were performed using modified proctor in PVC moulds as in the purposed European freeze-thaw standard. Curing of test specimens were performed in an oven of temperature of 40 ° C. After curing in oven, the specimens were placed in a water bath to obtain water saturation followed by freeze-thaw tests. The samples were placed in a climate chamber, where they underwent temperature cycles while the compressive strength test was performed on the first reference sample. Once the procedure had been completed, strength tests were performed on reference samples 2 and frost test. To get a good overview of the frost effect on the blends, a ratio between the mean value of the reference samples 2 and frost samples were compiled and studied. Results from this study demonstrated that binder content between 3 and 4 % gave a high frost resistance. Upon further examination of the water contents effect on frost resistance, significant difference were found between 6 and 9 % water content at which the mixture of lower water content had minimal frost damage. The strength change between 9 and 12 % were insignificant which could be explained by that the amount of water contained within the specimen didn’t increase from 9 to 12 % water content.