Evaluation of fatigue performance of asphalt materials based on their relaxation behavior

Abstract

Although the fatigue properties of asphalt materials have been extensively studied, the relationship between the rheological properties and road performance of asphalt mixtures remains underexplored. In this study, we have examined the relaxation properties of asphalt binders through relaxation tests conducted on asphalt and its mastic under different conditions. A repeated stress relaxation-recovery test is designed for assessing both the relaxation and elastic properties, and a set of reasonable test parameters is recommended, thereby establishing a novel test method for measuring the relaxation and elastic behaviors of asphalt. In addition, we have proposed evaluation indexes, such as relaxation time, relaxation rate, and strain recovery rate, to assess the stress relaxation performance and strain recovery ability. It is observed that the relaxation rate and strain recovery rate of the material can be used to characterize the material's relaxation and elasticity properties, respectively. Thus, the proposed indexes can be used to comprehensively evaluate the viscoelastic performance of the material. The fatigue performance of the selected materials is further examined using the linear amplitude sweep (LAS) test, and the correlation between the relaxation properties and fatigue performance (as indicated by fatigue parameters) is explored. Furthermore, a fatigue performance prediction equation based on the repetitive stress relaxation-recovery test is established. The findings reveal a strong correlation between the relaxation properties and fatigue performance, suggesting that the stress relaxation test can accurately assess the fatigue performance of asphalt materials.

Keywords: Asphalt mastic; Fatigue performance; Fatigue prediction equation; Relaxation index; Stress relaxation.

Fig. 1

Schematic of the stress vs. strain curve obtained from the stress relaxation-recovery test.

Fig. 2

Schematic of the loading time vs. strain curve obtained from the repeated stress relaxation-recovery test.

Fig. 3

Strain load and stress response obtained from the LAS test.

Fig. 4

Relaxation curves under five different strain conditions for 90# aged asphalt.

Fig. 5

Definition of relaxation time. Stress relaxation completion time of various types of asphalt.

Fig. 6

Stress relaxation completion time of various types of asphalt.

Fig. 7

Variation rate of strain at 50 s for various types of asphalt samples in the recovery stage.

Fig. 8

Complex modulus curves for different asphalt materials.

Fig. 9

Phase angle curves for different asphalt materials.

Fig. 10

Relaxation curves of various asphalt materials.

Fig. 11

Relaxation curves of various asphalt materials.

Fig. 12

Material damage curve.

Fig. 13

Fatigue parameters of different types of asphalt.

Fig. 14

Fatigue life of asphalt at various strain loads.

Fig. 15

Relationship between the complex modulus and fatigue parameters A and B.

Fig. 16

Relationship between the phase angle and fatigue parameters A and B.

Fig. 17

Strain recovery rate vs. fatigue parameter A .

Fig. 18

Strain recovery rate vs. fatigue parameter B.

Fig. 19

Fitted curves of fatigue parameter B vs. relaxation rate.

Fig. 20

Fitted curve of fatigue parameter A vs. strain recovery rate for asphalt material.

Fig. 21

Fitted curves of fatigue parameter B vs. relaxation rate for each material.