What is Ductility Testing?
Materials that are capable of deforming plastically before fracturing are defined as ductile. Ductile testing, therefore, involves measuring the amount of stress that can be applied to a material without fracture.
Why is Ductile Testing Important?
Ductile testing will tell you the tensile strength of your material and allow you to assign it a grade. In pavement construction, sufficient ductility must be present or the pavement may crack due to temperature variations or traffic stresses. Roads also expand or contract at different times of day, so without adequate ductility in the bitumen, cracking will eventually occur.
What materials are required for Asphalt Ductility Testing?
- Sample – Briquette of standard dimensions.
- Mold – The mold should be made of brass. Humboldt offers many different mold types to fit your needs: Elastic Recovery Mold, Ductility Briquette Mold, Base Plate for Single Ductility Mold or Base Plate for Three Ductility Molds.
- Water Bath – The water bath needs to maintain a specified test temperature and not vary any more than 0.1°C.
- Testing Machine – The specimen must be continuously immersed in water as the sample is separated and also must be separated at a uniform speed. Humboldt offers a variety of Ductility Machines that conform to industry standards.
- Thermometer – A thermometer having a range of 18-89°F (-8 to 21°C).
What is the Procedure for Ductility Test on Bitumen?
Preparing your sample for testing
- Assemble your brass molds. Humboldt’s molds have a recommended release agent of a glycerin and dextrin or talc mix. See product manual for specific instructions.
- The mold is then placed on a level plate.
- Melt the briquette of test material thoroughly until it becomes completely fluid.
- The liquid sample should be strained through a #50 sieve and carefully poured into the mold. It is helpful to pour slowly back and forth from end to end of the mold to fill evenly.
- Let the mold cool to room temperature for approximately 40 minutes. The mold can then be placed into a water bath (where your desired temperature is maintained) for 30 minutes. After this time, a heated straight edge knife can be used to remove any specimen outside of the mold container.
- Return your briquette to the water bath (at your specified temperature) and incubate for 90 minutes. After the allotted time, the briquette can be removed from the molding plate and immediately tested.
Testing your sample
- Attach both clips to both ends of your sample inside the testing apparatus.
- Note the measurement at the starting point of your sample.
- Select your uniform speed and start the pulling process.
- Note the measurement at the spot of rupture. Please be aware that a test is considered normal when the material ruptures near the center of the specimen. Ruptures occurring at either end of the sample are not normal and the test should be redone.
Humboldt ductility machines determine ductility of formed asphalt/cement or semi-solid bitumen by measuring the distance of elongation before reaching the breaking point of a briquette sample, which is pulled apart at a specific speed and temperature. The H-1068X is a three-speed machine designed for standard and force ductility tests. The unit tests three briquettes simultaneously and its DC, direct-drive motor maintains constant speed, entirely vibration-free. Speeds of 1/4, 1 or 5cm per minute are selected via lever shift on mechanical gear box. Humboldt provides a full line of USA-made ductility testing equipment, accessories and components.
A single stainless steel lead screw mounted above water level prevents agitation of water and premature rupture of specimens. A traveling pointer adjusts to zero starting position and indicates exact position of carriage on a linear centimeter scale attached to trough‘s front edge. Maximum carriage travel (elongation) is 150cm with an automatic stop.