Vehicle traffic has been subjecting modern pavements to many millions of load cycles. All these repetitive stresses slowly deteriorate layers of pavement, despite the fact that the loads of single layers are far less than the maximum strength of the material. Fatigue testing is created to investigate such cumulative destruction and determine the duration of a pavement before cracking begins. Fatigue testing gives a realistic evaluation of the pavement durability by emphasizing material endurance and not the short-term strength. It promotes the use of performance-based pavement design methods and assists engineers in coming up with more durable road designs.
Principle and Methodology
The fatigue testing principle is founded on the repeated cyclic effect of loads or strains on pavement materials until failure sets in. Tests on asphalt mixtures or bound layers are carried out in the laboratory under controlled stress or strain levels that are related to the field traffic. The fatigue life is documented as the number of load cycles necessary to induce the development of a crack or to decrease the stiffness. The results of such tests are used to come up with fatigue equations that associate levels of stress or strain with pavement life. The methodology enables the engineers to foresee the accrual of damages under different circumstances in terms of traffic and environmental conditions.
Significant Considerations during Fatigue Testing
Fatigue testing measures some of the important parameters affecting pavement durability. These are applied stress or amplitude of strain, loading frequency, temperature, and material stiffness. The interaction of these factors will determine the rate at which the fatigue damage accumulates. With the parameters studied, it is possible to compare dissimilar materials and to choose mixtures that demonstrate greater resistance to cracking during repetitive loading.
Industrial Use
Fatigue testing is common in the pavement industry in the process of selecting materials, optimizing mix design, and structural pavement design. The results of fatigue tests are used by road agencies and construction companies to compare asphalt mixtures and modified binders, and recycled materials. The data are used in making decisions regarding the thickness of the layers, anticipated traffic loads, and maintenance. Quality control programs also employ fatigue testing, which is done in order to have consistent pavement performance.
