Effects of laboratory elevation on rolling thin film oven test results.

摘要

Asphalt is the most commonly used material for road pavement. Asphalt pavement provides low cost, high durability, superior waterproofing abilities, and rapid construction. Before laying down the actual pavement, a series of tests are performed to make sure the asphalt can meet the requirements on specifications. The tests are usually conducted twice. One is provided by the asphalt supplier, the other one is provided by the buyer to make sure the quality of the asphalt meets their requirements. The asphalt aging process is unavoidable and starts when the asphalt is produced. The Rolling Thins Film Oven test (RTFO) is used to simulate the aging from production to asphalt laydown. The Dynamic Shear Rheometer (DSR) is used to quantify asphalt's elastic and viscous properties, which can reflect asphalt's ability to resist deformation during its service life. The goal of this paper is to identify any trends with respect to elevation, including which binders are influenced by elevation change. The general hypothesis is that elevation can affect both test results from DSR and Ductility tests. If this is true, then the test results from specs might need to be adjusted when bringing asphalt from one elevation to another. E.g. If the supplier is at sea level and the buyer is at 6000 feet, the supplier's test results may perfectly match the specs at sea level, but when the asphalt is tested in the same way at 6000 feet, the result cannot meet the requirements. This means the supplier is at the risk of not getting paid. In this case, the specs need to be adjusted for a situation like this.;By analyzing the test parameters from DSR and ductility test, my research showed that the elevation can affect the test results. The DSR test parameters are G*, δ, G*/sin δ, G*-6C, δ-6C, and G*/sin δ -6C.;Complex modulus (G*) reflects the specimen's total resistance to deformation when repeatedly sheared. The bigger the G* value, the stiffer the asphalt binder is. Phase angle (δ) indicates the lag between the applied shear stress and the resulting shear strain. G*/sin δ is the rutting parameter. When DSR was conducted at -6C, it can achieve G*-6C, δ-6C, G*/sin δ -6C. The seven different performance grades of asphalt specimens were PG 64-22, PG 64-28, PG 64-34, PG 70-22, PG 70-28, PG 76-22 and PG 76-28. Results showed that test parameters of certain asphalt performance grades present linear regression as elevation goes up. E.g. G* value decreases as elevation goes up, in the corresponding asphalt binders PG 64-22, PG 64-34, PG 70-28, and PG 76-22. Parameter G*, δ, G*/sin δ, G* -6C, δ -6C, G*/sin δ -6C shows clear linear regression as elevation goes up. Ductility did not present obvious linear regression as elevation goes up, therefore, is omitted from the summary. The discrepancy may have resulted from insufficient test data. The recommendation is that the researchers continue collecting data on ductility properties test. When using PG 70-28 for DSR test, test parameters presented linear regression as elevation goes up. The test parameters are G*, δ, G*-6, δ- 6C. When using PG 76-22 in the DSR test, test parameters presented linear regression as elevation goes up. The affected test parameters are G*, δ, G*/sin δ, G*-6C, and G*/sin δ -6C. Logically, if δ is affected by elevation, then δ-6C should also be affected by elevation. Thus, the assumption that δ-6C does not present linear regression as elevation goes up was because of the insufficient data volume. If there had been three times more data pool than the data set in this paper, the assumption may be proved right.