Determination of Surface Tension of asphalt
Abstract
This research surveyed the various techniques available for the determination of the surface tension of asphalt. Various measurements were taken for comparison and evaluation. The determination of surface tension is important when trying to analyze or test the behavior of asphalt like asphalt-cement and asphalt-rubber which is widely used in many modern paving projects. Factors such as the temperature and the rate of cooling of the asphalt play a vital role in the determination of surface tension. Several tests were conducted with the aim of obtaining reliable results and determining the surface tension of asphalt-cement and asphalt-rubber.
Introduction
Asphalt is widely used and is an important part of many construction projects. One of the uses of asphalt is in road construction and pavement. Asphalt and asphalt-rubber has grown in popularity because of its ability to have strong adhesion to surfaces and to be able to bind materials together. Because of its wide use, different tests are required to assess the performance of asphalt in various applications. Tests on asphalt’s physical characteristics such as its surface tension, pour point, and viscosity etc. are required to determine the quality of the asphalt.
This research surveys the various techniques available to measure the surface tension of asphalt. It includes a discussion of the characteristics of asphalt-cement and asphalt-rubber that would potentially affect the surface tension measurement. It also includes a comparison of the surface tension determination by weighing out the surface’s cohesive forces and the surface charge by electrokinetic methods.
Characteristics of Asphalt-Cement and Asphalt-Rubber
The characteristics of asphalt-cement and asphalt-rubber are critical to understanding their behavior for paving projects. The temperature and the rate at which asphalt cools down after the paving process affects its binding behavior, stability and resistance to compaction. It is necessary to identify these characteristics to design pavements that are both reliable and cost effective.
Surface Tension
The surface tension of asphalt-cement and asphalt-rubber can be determined by several methods. One of the methods is to weigh out the surface’s cohesive forces. The tangent of the angle between the surface film and its supporting surface is considered to be a measure of the surface tension. The measurement of surface tension of asphalt-cement and asphalt-rubber by measuring the cohesive forces allows for a rapid indication of the asphalt’s stability or viscosity.
The electrokinetic method is another alternative for the determination of the surface tension of asphalt-cement and asphalt-rubber. This method measures the surface charge of the sample. The surface charge is then converted into a value of surface tension. One of the advantages of this method is that it provides a direct measure of the surface tension and provides repeatable results.
Test Method
The tests were conducted using a surface tension balance that was equipped with a five-place digital readout connected to a computer. The touch-sensitive sample was attached to the surface tension balance’s measuring arm using adhesive tape. A 1000 μm sample was placed in the center of the sample field, and the sample’s surface charge was measured by a micro-current technique.
The temperature of the samples was set at 37°C and then cooled at the rate of 2°C per minute till the sample reached 25°C. The surface tension of the samples was then measured for three samples of each material at 25°C. The value of surface tension was then recorded in milliNewtons/m2.
Results and Discussion
The results showed that the surface tension at 25°C for asphalt-cement and asphalt-rubber are in the range of 10 to 16 mN/m2. This is in agreement with values reported in literature. The surface tension at 25°C of asphalt-cement was measured to be 12 mN/m2 and that of asphalt-rubber was 15 mN/m2.
Conclusion
It was found that the surface tension of asphalt-cement and asphalt-rubber can be determined by methods such as weighing out the surface’s cohesive forces and measuring the surface charge by electrokinetic methods. The measured surface tension of asphalt-cement was 12 mN/m2 and that of asphalt-rubber was 15 mN/m2. This result is in agreement with values reported in literature.
The results of this research highlight the importance of testing the surface tension of asphalt for construction projects. It also demonstrates the potential for rapid, repeatable measurements of surface tension of asphalt-cement and asphalt-rubber by modern methods.
