Accelerated Mixture Performance Test (AMPT)
One of the newest tests to the asphalt industry is the AMPT. The AMPT was developed under the NCHRP 9-29 research following guidance from the NCHRP 9-19 research. It is considered a more simple and practical method of measuring the dynamic modulus (E*) and rutting potential, called Flow Number, of a mixture.AMPT dynamic modulus (E*) data is used in the Mechanistic Empirical Pavement Design Guide (MEPDG) for pavement thickness design and performance prediction. AMPT Flow Number test is a new and upcoming rutting test that predicts rutting potential well. It pulses the sample and then allows relaxation to simulate a tire moving over a pavement. The Flow Number is a destructive test.2
Disk-shaped Compact Tension ([DC(t)] Test
The DC(t) test was developed by University of Illinois to measure the fracture energy of round gyratory or core samples. A round sample is pulled apart to measure the crack initiation and prorogation. By measuring the area under the load and displacement curve, fracture energy is calculated for the sample. This test helps us understand a mixture’s ability to resist cracking. This test can be run on road cores.
Indirect Tension Test (IDT) – Creep and Strength
Used during the SHRP research, the IDT creep and strength tests measure the low temperature compliance (ability of a mixture to relax at cold temperatures) and the fracture strength of a mixture at temperatures well below freezing. This test when used in conjunction with models is used to predict the low critical cracking temperature of a mixture. The fracture strength is a destructive test.2
Flexural Beam Fatigue
Researched during SHRP, the 4-point flexural beam fatigue apparatus allows one to measure the flexibility of a mixture usually through repeated strain cycles. Commonly used for understanding fatigue failure, it is not limited to only classic pavement fatigue. This test is also used to understand the brittleness of a mixture in comparison to other mixtures. At extreme high strains, this device may be used to simulate the joint movement of Portland cement concrete (PCC) joints. This is a destructive test.2
Superpave Shear Test (SST)
Developed through the Strategic Highway Research Program (SHRP), the SST can run:
- Repeated Shear at Constant Height (RSCH) at highway pavement layer temperatures usually around 50 to 60 degrees C. The RSCH pulses the sample for a given stress and then allows it to relax for a more accurate rutting response. The loading cycle is usually repeated for 5,000 cycles. This test is thought by some asphalt technologists to be the best predictive rutting analysis available. This is a destructive test.
- Frequency Sweep at Constant Height (FSCH) test to measure the shear complex modulus (G*)1 of a mixture. The FSCH is a strain-controlled test where the resultant stress is measured over a range of temperatures and frequencies. The modulus data is used to understand a mixture’s ability to respond to slow and fast loads at high and low temperatures.
- Simple Shear Test at Constant Height test measures shear force required to shear a sample. This is a destructive test.2
Resilient Modulus (Mr)
Probably one of the older and most widely used of the modulus tests. The resilient modulus test configuration allows samples to be tested on their side, making it popular for pavement cores. A sample is pulsed with a load determined from a fracture test. The sample is then allowed to relax; thus named the resilient modulus.
Asphalt Pavement Analyzer (APA)
The APA originated in Georgia from the concept of microsurface/slurry rut testing. GA developed the APA so it could measure the rutting risk of asphalt mixtures before placement. The APA is still used by the GA DOT for proof testing of mixtures. This test seems to be most widely used in the Eastern U.S. This is a destructive test.
Hamburg Wheel Tracker (HWT)
The HWT test was developed in Hamburg, Germany and used to measure both rutting and stripping risk. If passing, mixtures were accepted in Germany for five-year warranties. This test was first adapted for the US by Colorado DOT. This test is most widely used in the mid-western and western U.S.
1. Modulus = stress/strain. This measures a mixture’s stress in response to a movement (strain).
2. The sample cannot be re-used for other testing
Back to SST
Request more information about any of the Asphalt Institute Laboratory services.