Luft, vatten och saltvattens inverkan på asfalt över tid

Sammanfattning

This study aims to investigate how salt solution affects typical road wear courses in contrast to how air and water affect road surfaces. The wear layers are represented by the asphalt concrete Porous Asphalt (PA or ABD11 70/100) which is a draining road surface and Stone Mastic Asphalt (SMA or ABS11 70/100) which is a dense road surface. PA and SMA were used as contrasts to use in the experiment because PA has a much larger cavity than SMA and the influence of external substances can differentiate the wear layer types. To be able to compare how the wear layer types are affected by the different media of storage, a total of 62 asphalt samples were produced, of which 31 were of the PA type and 31 of the SMA type. An asphalt specimen has a cylindrical form and has approximately dimensions of ᴓ102mm and a normal height of 60-75mm. Of the respective 31 asphalt samples, four were initially tested after manufacture as reference values and then nine were placed in a closed air vessel, nine in a closed water vessel and nine in a closed saltwater vessel with a salt concentration of 23%. The saltwater concentration of 23% was determined based on the eutectic properties of salt solution, where salt theoretically can melt ice down to -21oC.The asphalt samples were produced over four days, where the first SMA-samples were produced over two days. Six days later, the PA-samples were produced over two days. In the manufacturing process, accepted methods and international standards were used. During the experiment, three of each air-stored, water-stored, and salt-water-stored specimens were tested after 6, 14 and 28 days for both the PA and SMA samples. The samples were tested with Marshall stability tests and the asphalt samples were preheated in a water bath to 40.0oC. An inconsistency occurred when preheating the reference samples where they were heated to 46.6oC. Before each test, the asphalt samples were studied visually. The ocular assessment shows that the asphalt samples stored in saltwater get small air bubbles around and that the salt water is very clear, while the asphalt samples stored in water initially acquire occasional air bubbles around them at the 6th day of storage but later are completely gone at the 14th day of storage. The asphalt samples resting in water alone acquire a browner colour over time, this observation is the same for both PA and SMA, but there was a certain time difference in when and how much the different changes occur. The water which SMA rested in, became browner than the water containing the PA. The results of the Marshall stability test show that the weight of the specimen plays a major role in the force that the asphalt specimen can withstand. For the air-stored samples, the results show that the PA tests after 6 and 14 days have similar Marshall stability, but that there is a deterioration for the samples tested after 28 days. For the PA samples, there is a minor decrease in stability for the tests performed after 14 and 28 days. The SMA samples show better stability in air. For the water-stored asphalt samples, the SMA samples show the highest Marshall stability both after 6 and 14 days. In contrast, the SMA samples show a reduced stability after 28 days in water. The PA samples, on the other hand, show a worse stability than the SMA samples for 6 and 14 days, but better after 28 days. The PA samples show that the largest break point in stability is found in the tests performed after 14 and 28 days in comparison with the 6-day test. The saltwater-stored specimens for both PA and SMA showed similar stability throughout all storage times. On the other hand, they performed worse than the SMA samples in air and water after 6 and 14 days, respectively, but perform better than the other samples, apart from the air-stored ABS samples, after 28 days. In general, it can be said that the saltwater-stored specimens maintained consistent Marshall stability over time, a possible reason for this difference is suggested to be osmosis.