Properties of Asphalt Modulus

Elasticity

• A material's elasticity refers to its ability to return to its original shape after being bent. Every material is elastic to some extent; the more elasticity, the longer it can be bent or deformed and still retain its shape. For asphalt, it is known as the elastic modulus. This property is the ratio of stress to strain: increase either factor and the elastic modulus shortens.

Resilient Modulus

• Resilient modulus measures how much of a change in the asphalt can be recovered. It is a function of elasticity. Drive a heavy load, like a truck, over the asphalt and it bends, forming a temporary rut. Resilient modulus indicates how the asphalt responds and whether it will return to its original shape. A method of determining resilient modulus is a stiffness test. The results indicate how well asphalt holds up under certain weight loads, and it also shows the effects of temperature on the asphalt.

Dynamic Modulus

• Sometimes the result of an action is not immediate, a condition known as hysteresis. Tracking the time from causation to effect for asphalt is dynamic modulus. The cause in this case is a heavy load on the asphalt and the effect is deformation, or rutting. Specifically, dynamic modulus measures how long it takes for the deformation to occur after the load is applied. A study titled "Dynamic and Resilient Modulus of MN/DOT Asphalt Mixtures" conducted from 2001 to 2003 for the Minnesota Department of Transportation indicates that dynamic modulus increases with frequency of load and decreases in temperature.

Temperature

• Temperature has a significant impact on asphalt modulus. Walk on asphalt on a very hot day and it becomes apparent. The surface retains heat, which weakens the stiffness. Resilient modulus falls as the temperature increases. An increase of 100 degrees Fahrenheit, or 56 degrees Centigrade, changes resilient modulus by a factor of 100, according to the "Pavement Guide" that the University of Washington publishes.