Khalid A. Ghuzlan

Energy-Derived, Damage-Based Failure Criterion for Fatigue Testing

Determination of the failure limit in a repeated-load fatigue test in the laboratory has relied entirely on the arbitrary selection of a fixed criterion. The constant strain and constant stress modes of fatigue loading have been described by a consistent definition of failure in flexural fatigue testing because of the distinctly different application of energy during the loading history. The most widely accepted definition is a decrease in initial stiffness by 50 percent. Procedures examining energy input and dissipated energy have required different schemes for each mode in an attempt to describe similar states of damage in the mixture. A proposed method is presented for examining dissipated energy to select a consistent level of material behavior that is indicative of the damage accumulation in the mixture. This procedure shows the similarity between the constant stress and constant strain modes of testing and is shown to provide the potential for unifying the now phenomenological description of fatigue with a more rational energy-based description.

FATIGUE ENDURANCE LIMIT FOR HIGHWAY AND AIRPORT PAVEMENTS

The existence of a fatigue endurance limit has been postulated for a considerable time. With the increasing emphasis on extended-life hot-mix asphalt pavement, or perpetual pavement, verification of the existence of this endurance limit, a strain below which none or very little fatigue damage develops, has become a substantial consideration in the design of these new multilayered full-depth pavements. Fatigue data are presented that were collected on a surface mix and a binder mixture tested for an extended period from 5 million to 48 million load repetitions at strain levels down to 70 microstrain. The fatigue results are analyzed in the traditional manner and using the dissipated energy ratio. This analysis shows that there is a difference in the data at normal strain levels recommended for fatigue testing and at the low strain levels. This difference cannot substantiate an endurance limit using traditional analysis procedures, but the dissipated energy approach clearly shows a distinct change in material behavior at low flexural strain levels, which supports the fact that at low strain levels the damage accumulated from each load cycle is disproportionately less than what is predicted from extrapolations of fatigue testing at normal strain levels. This reduced damage may be attributed to the healing process. The conclusion of this study is that laboratory testing can verify the existence of a fatigue endurance limit in the range of 90 to 70 microstrain below which the fatigue life of the mixture is significantly extended relative to normal design considerations.

Evaluation of international roughness index for asphalt overlays placed over cracked and seated concrete pavements

Crack, seat and overlay (CS&O) is a rehabilitation technique that has been used on jointed plain concrete pavements. Only a few studies have evaluated the surface roughness of pavement sections rehabilitated using this technique. The purpose of this paper was to evaluate the roughness of roadway sections rehabilitated employing the CS&O technique. The data extracted from the long-term pavement performance database were separated based on the weather region and analysed. Then, international roughness index (IRI) prediction models were developed. A separate model was developed for pavement sections in California. For sections with bound bases, thick overlays provide a smoother surface (lower IRI). However, the effect of the overlay thickness on the IRI for sections with unbound bases does not appear to be considerable. Prediction models developed in this study are shown to provide adequate predictive capabilities. Sections in California have initial IRI values that are lower than those found for sections in the wet-with-freeze (WF) and wet-with-no-freeze (WNF) regions. However, California sections are predicted to develop higher IRI values over time, when compared to those sections in the WF and WNF regions.

Sasobit-Modified Asphalt Binder Rheology

AbstractThis research discusses the effect of Sasobit on asphalt binder rheology and how different percentages of Sasobit affect its performance. Evaluation is performed according to the Superpave ...

Performance of warm asphalt mixtures using Sasobit

ABSTRACT The performance of limestone warm mix asphalt mixtures using Sasobit over control mixtures was investigated. The Superpave mixture design method was used to prepare control and Sasobit-modified mixtures. The indirect tensile and dynamic creep tests were used for fatigue and rutting evaluation, respectively. The main findings of this research were the noticed lower accumulated strains and resilient modulus for Sasobit-modified mixtures over control mixtures in rutting performance testing. On the other hand, higher creep stiffness values in fatigue testing for Sasobit-modified mixtures were observed over control mixtures for deviator loads that ranges from 1 to 2 KN. Moreover, better fatigue resistance at lower temperatures was also observed for both control and Sasobit-modified mixtures.

Selection and verification of performance grading for asphalt binders produced in Jordan

Selection of proper binder is one of the most important factors considered in mixture design. Three different asphalt grading systems are normally used; they are penetration grading system, viscosity grading system and performance grading (PG) systems. PG system is a method of measuring asphalt binder performance; it was originally developed during strategic highway research program in the early 1990s in order to accurately and fully characterise asphalt binders for use in hot mix asphalt pavements. PG system is based on the idea that the properties of an asphalt binder should be related to the conditions under which it is being used. This involves expected climatic conditions, pavement temperature as well as ageing conditions. Performance-graded asphalt binders are selected to meet expected climatic conditions as well as traffic speed and load conditions. Therefore, the PG system uses a common set of tests to measure physical properties of the binder which can be directly related to field performance of the pavement at its service temperatures. In order to adopt the Superpave system in Jordan, it is essential to develop climatic zones for Jordan and to select the proper performance-graded binder to be used in different regions in Jordan. Selection of performance-graded binder is based mainly on the air temperature of the desired location. Several models were used to calculate the pavement temperature. Different reliability levels were used in developing the climatic zones in Jordan. Finally, Jordan was divided into different zones and specific binder type to be used there. On the basis of analysis, binder grade having designation PG 64-10 can be used in most parts of Jordan. The only source for asphalt binders used in the construction of flexible pavements for Jordans highways and streets is the Jordan Petroleum Refinery (JPR). Typically, the JPR produces two main types of original asphalt binders; these are 60/70 penetration grade asphalt binder and 85/100 penetration grade asphalt binder. On the basis of laboratory test and according to the Superpave asphalt binder classification system, the 60/70 penetration grade asphalt binder can be classified as PG 64-16 and the 85/100 penetration grade asphalt binder as PG 58-16.

Predicting the Complex Modulus for PAV Aged Asphalt Binder Using a Master Curve Approach for Sasobit Modified Asphalt Binder

This study is focused on the prediction of the asphalt binder complex modulus at various temperatures and various loading frequencies. The master curve approach was used to predict the asphalt binder behavior for a wide range of temperatures and loading frequencies by applying the time-temperature superposition principle for pressure ageing vessel (PAV) aged asphalt binder mixed with different percentages of sasobit asphalt modifier. The complex modulus was measured using the dynamic shear rheometer (DSR) with a wide range of loading frequencies (0.1 Hz-10 Hz) and a wide range of testing temperatures (16 C-31 C). The results showed an increase in the complex modulus with increasing the loading frequency as well as with increasing the sasobit percentage. However, the results showed a decrease in the complex modulus with increasing the testing temperature. The use of the master curve approach showed a high degree of accuracy in predicting the complex modulus for the asphalt binder.