Återvunna material i obundna lager i vägöverbyggnader

Sammanfattning: In an industry that is increasingly affected by sustainability and environmental matters, it is becoming more and more important to find ways to recycle and reuse materials rather than producing new materials. An example of this is when it comes to unbound pavement materials, such as the base and subbase layers. For these layers, mineral aggregate and natural gravel is traditionally used, which are obtained through quarrying. These materials are not infinite, and they are also important to help with purification of groundwater. Therefore, it is interesting to look for recycled materials that could replace them. Two such materials are crushed concrete and crushed asphalt, and this report aims to examine how these materials compare to mineral aggregate when it comes to bearing capacity, stability and impact on climate and environment. The report also examines which other recycled materials are available for this purpose. Based on this aim, the following questions are asked: • How is the bearing capacity affected with respect to degree of compaction with recycled materials in the unbound layers, compared to the reference case? • How is the stability affected with respect to degree of compaction with recycled materials in the unbound layers, compared to the reference case? • What savings of the climate and environment can be made whit the use of these materials? • Are there any other recycled materials that can be used? The method used to examine this is a literature study, to gain basic knowledge about road construction today, about the attributes of the materials, and also to find out what previous research on the subject has concluded. This is combined with a practical experiment, where three pavement structures consisting of different materials are tested with static plate load test, to examine the bearing capacity and degree of compaction of the different layers. The results show that both crushed concrete and crushed asphalt are comparable to mineral aggregates when it comes to bearing capacity. According to the literature the bearing capacity might even be better for the recycled materials in many cases, however this was not shown in the practical experiment. When it comes to stability, crushed concrete has similar attributes as mineral aggregate, but only until the load exceeds 1,2 MPa. After that, the material shows a tendency of crushing. For crushed asphalt, the stability is worse, but it could be improved by mixing more mineral aggregate in the material, or by allowing traffic on the layer for at least two weeks before the layers above are applied. The literature states that both crushed concrete and crushed asphalt has a binding effect, which makes the layer bind together over time, causing increased bearing capacity and stability. This was not possible to show with the practical experiment. The recycled materials’ impact on the climate and environment is positive compared to the mineral aggregates, since no quarrying is needed for new material, which means that finite resources are saved. There is also potential to decrease transports by using recycled materials. The materials themselves has no negative impact on the climate and environment worth mentioning through for instance leaching or emissions.