Asphalt Penetration Testing


Penetration testing of bitumen measures the consistency and stability of pure bitumen, oxidized bitumen (blown bitumen), and the residue of emulsion bitumen. The test provides an established method for classifying bitumen according to its penetration value. Penetration values between 40 and 300 have been grouped into five different hardness grades, which are listed in the specifications: AASHTO M 20 and ASTM D946. This test is used to classify the hardness value of bitumen based on penetration value, which helps in determining, which bitumen to use in various weather conditions for proper road construction. Soft bitumens (higher penetration) are used in cold weather to avoid cracking. In hot weather, a hard bitumen (lower penetration) is used to avoid it getting too soft in the heat.

Penetration value is measured by applying the needle with a load of 100 grams that vertically penetrates into the bitumen for 5 seconds at 25 degrees Celsius. The amount of needle movement is referred to as the penetration value and is measured in tenths of a millimeter. The higher the penetration of the needle in the bitumen, the higher the bitumen grade. Grades of bitumen are designated by two penetration values, for example, 40/50, 60/80, 80/100 etc.; the penetration of an actual sample of the bitumen in any grade should fall between the lower and upper value given.

Required Equipment

  • Water bath: it contains at least 10 liters of water at a temperature of 25 °C. The sample is immersed in a depth with more than 100 mm from the top. Moreover, the supported perforated shelf, which is the sample placed on it, should be above 50mm from the bottom of the bath.
  • Sample container: a small cylindrical dish with a flat bottom which its material is metal or glass.
  • Transfer dish or Tray: It helps in keeping the container immersed in the water bath.
  • Penetration needle: stainless steel needle which is cylindrical and high polished
  • Stopwatch: an automatic timer with an accuracy of 1/10 seconds.
  • Thermometer: it shows the temperature in the range of 0-44 °C.
  • Penetrometer: the device contains a needle. It is used to release and lock the needle in any position and allows measuring the penetration by applying a load of 100 grams with the least friction. It is important to calibrate accurately.

Humboldt Penetrometers
Humboldt’s penetrometers for asphalt binder testing are known for their durability, precision and economical design. These penetrometers are used extensively in asphalt binder evaluations, and other bituminous materials, cement, mortar, petrolatum, waxes, as well as food, cosmetics and pharmaceutical products. Their simple and easy-to-use design, provide years of dependable service in labs around the world.

Humboldt penetrometers come in 3 designs:
The H-1200 - Universal Penetrometer
This unit provides a basic precision penetrometer function with its 5-inch diameter, dial indicator, which is graduated in 400 divisions of 0.1mm, corresponding to a 40mm penetration reading. It provides a zero preset for eliminating reading errors. A large variety of penetration needles are available to accommodate any type of penetration testing.

The H-1240 - Electric Penetrometer
This unit builds on the basic design by adding an automatic, digital timer. The timer’s release mechanism is switchable between seconds, minutes and hours and accommodates setting to 1/10th of a second intervals. The penetrometer’s plunger is released with a simple button push and automatically stops at the preset time duration.

The 1240DA - Digital Penetrometer
This unit incorporates a digital gauge for the penetrometer, as well as an auto, digital timer. The use of a digital timer and gauge provides accurate timing of tests with an auto stop feature, as well as precise, at-a-glance readings during and at the end of the a test.

All three of these Humboldt Penetrometers can accommodate any needle or cone plunger that has a 1-1/8th in. (3mm) diameter stem. All three feature a 47.5g plunger assembly, two additional loading weights (50g and 100g) and a standard 2.5g ASTM D 5 needle.

Humboldt also has a Portable Penetrometer, which is lighter and smaller than the other penetrometers.

Humboldt Penetrometer Needles
Humboldt provides a range of penetration needles to fit almost any penetration testing application. For bitumen penetraton testing, Humboldt provides four models of needles.

Needles for Bituminous Materials
The H-1280 is a fully hardened and tempered stainless steel needle with a total length of 50mm and an exposed length of 40-45mm. Needle diameter is 1.00 - 1.02mm. Needle complies with ASTM D5 and AASHTO T49 Standards.

The H-1290 is a long version of the standard needle with a total length of 60mm and an exposed length of 50-45mm. Needle diameter is 1.00 - 1.02mm. Needle complies with ASTM D5 and AASHTO T49 Standards.

Humboldt’s H-1300 and H-1302 needles are Certified versions of the two needles above.

Humboldt also offers an array of other penetration needles for various needs, such as: waxes, battery pastes, firmness of fats, grease testing, joint sealents, as well as food, paste and paints.

Humboldt also offers various sample containers, moisture boxes and transfer dishes for use in penetration testing.

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