To perform the test, first, a needle with a 100-gram load is vertically penetrated into the bitumen for five seconds at 25 degrees Celsius to measure the initial penetration value. The amount of needle movement is noted in 0.1 mm.
In the next step, put the bitumen in the oven at 163 degrees Celsius for 5 hours. Again measure the penetration value. The reduction amount is reported as a percentage.
What is the Importance of the Drop in Penetration After Heating Test of Bitumen?
In construction, bitumen is heated and mixed with aggregates. When the bitumen binder is exposed to heat, its volatile content evaporates, causing the bitumen to harden.
The more volatile the bitumen content, the more sensitive it is to heat. Because its contents evaporate more and faster, and as a result, the binder becomes harder.
Hard bitumen is not ductile enough. It can not stick the aggregates well together. Moreover, it cannot tolerate the load on the asphalt and temperature changes.
Would you like to know which types of bitumen are mixed with aggregates? Read the article which is about different types of bitumen that can be used in road construction.
Apparatus and Procedure of Dop in Penetration after Heating Test of Bitumen
This test is described based on two standard methods ASTM D5 & ASTM D6.
– Component of Apparatus
- Oven
- Digital balance
- Thermometer
- Metal or glass container
- Transfer dish or Tray
- Penetration needle
- Stopwatch
- Penetrometer
– Sample preparation
Stir the bitumen well until it is uniform and free of air bubbles. Note that the bitumen sample is free of water.
For a solid sample, heat it to become liquid. Do not overheat the sample since the component will change.
Pour it into a container and let the sample cool at room temperature. Place it in the water bath at 25 degrees Celsius.
– Test procedure
- Fill the transfer dish with water from the water bath. Place the sample in the transfer dish and place the whole assembly under the stand of the penetrometer apparatus for applying penetration test of bitumen.
- Release the needle with a 100-gram load for only 5 seconds on the sample surface.
- Note the penetration depth in 0.1 mm.
- For 5 hours, place the container of bitumen sample in the oven at 163 degrees Celsius. Consider it as D1.
- Then take out the sample from the oven and let it cool at room temperature.
- After that, repeat the penetration test. Note the penetration depth in 0.1 mm. Consider it as D2.
Drop in penetration value (%) = [ (D1 – D2)/D1 ] * 100
