An approach for dynamic stiffness evaluation in asphalt concrete

• A theoretical approach for evaluation of dynamic stiffness modulus.
• Stiffness and phase angle follow cyclic variations with exponential decay.
• Evaluation of dynamic modulus under cyclic loading and considering material damage.

Stiffness modulus is a fundamental parameter for fatigue evaluation in asphalt concrete (AC). It is evaluated with different considerations like static or dynamic loading, elastic or visco-elastic material etc. Asphalt being visco-elastic and fatigue being due to dynamic loading, the modulus parameter happens to be time dependent complex variable. This is named as complex modulus (E∗E∗) and the absolute value of E∗E∗ is known as dynamic stiffness modulus (|E∗||E∗|). The present paper focuses on the development of a theoretical approach for E∗E∗ and |E∗||E∗| based on principles of linear visco-elasticity. The expression of |E∗||E∗| and phase angle (ψψ) for generalized Maxwell model under constant strain amplitude sinusoidal loading has been derived. It is seen that both |E∗||E∗| and ψψ as function of time (tt) follow cyclic variation with exponential decay due to viscous effect. Numerical analysis has been performed using Maxwell parameters (under relaxation condition) of AC at 10 °C and -20 °C. It is observed that |E∗||E∗| and ψψ variations with time are significantly different at different temperatures. Their rate of decay depends upon the relaxation time of mix. The present work also explores the evaluation of dynamic modulus, while considering decay due to material damage.