Saad Abo-Qudais

Monitoring fatigue famage and crack healing by ultrasound wave velocity

This paper presents the possibilities of using a simple ultrasonic method to estimate the fatigue life and crack healing of hot-mix asphalt (HMA). The ultrasound pulse velocity (UPV) was measured on cylindrical HMA specimens prepared using 60/70 asphalt cement and crushed limestone at three different aggregate gradations (maximum nominal aggregate size equal to 12.5, 19.0 and 25.0 mm). The UPV measurements were performed before and after first stage fatigue tests, after rest periods, and after a second stage fatigue tests that followed the rest period. The collected data were analyzed for the possibility of using UPV to predict fatigue life and crack healing of HMA. The results indicated that UPV can be used to predict fatigue life and crack healing especially after a relatively long rest period. The UPV was found to decrease consistently with an increasing number of constant stress fatigue cycles. UPV showed good capability in evaluating crack healing. The relationship between the percent of increase in UPV and the extended fatigue life caused by a rest period was much better than those between UPV and fatigue life before healing or between UPV and the type of aggregate used in preparing the HMA. Increasing of the rest period temperature caused an increase in both UPV and extended fatigue life. However, the percent of increase in UPV may be less than the percent of increase in fatigue life. Also, it can be noticed that the percent increase in UPV due to the use of different aggregate gradations is compatible to the percent increase in fatigue life due to the same reason. UPV was found to be higher in HMA prepared using higher sizes of aggregate. Based on the collected data, statistical models have the capability to predict fatigue life and crack healing in terms of measured UPV, healing temperature, rest period length and aggregate gradation used in preparing HMA were developed.

Method To Evaluate Rigid-Pavement Joint Sealant Under Cyclic Shear and Constant Horizontal Deflections

In recent years, the need for sealants in rigid pavement joints has become debatable, partly because of the unpredictable field performance of joint sealants. This inability to predict sealant performance stems from the fact that there is no laboratory evaluation method that accurately simulates field traffic and environmental loading conditions. A laboratory testing method was developed to predict the performance of rigid-pavement joint sealants. A research team at Virginia Tech designed a fixture that allows the evaluation of joint sealants under cyclic shear and static horizontal deflections. Shear deflection simulates vehicular loading, and horizontal deflection simulates expansion and contraction of concrete slabs due to temperature variation. Concrete specimens were prepared at a typical water-to-cement ratio of 0.45. Two aggregate types were used in the concrete mixes to evaluate the effect of aggregate type on sealant performance. Two commercially available sealants were investigated in the study. Sealant performance was evaluated for different joint widths and joint expansion. Specimens were loaded cyclically to failure; a 20 percent cohesive or adhesive debonding was considered a failure. A limited number of specimens were exposed to freezing and thawing cycles. The study showed quantitatively the effects of joint width, joint expansion, concrete aggregate type, and freezing and thawing cycles on sealant performance. Statistical models were developed to predict the number of loading cycles to failure for each sealant.

Time-temperature and time-aggregate gradation superposition in asphalt mixes

ABSTRACT This study was devoted to evaluate the effect of aggregate gradation, temperature, and type of asphalt cement on the permanent deformation of Hot-Mix Asphalt (HMA). An experimental program was conducted to characterize the viscoelastic deformation response of asphalt mixture using the static creep test. The specimen was exposed to a constant vertical stress of 100 KPa and the vertical deformation of the specimen was monitored through linear variable differential transducers (LVDTs). All tests were conducted within a temperature-controlled chamber to keep the temperature constant throughout the test. Time-temperature and time-aggregate gradation shift factors for each evaluated type of HMA were estimated using plots of log time versus log creep compliance. If the deformations under reference temperature or reference gradation are known, those under given temperature or any given gradation can be obtained using shift factor. Also, viscoelastic models were developed to represent the deformation behavior of HMA under constant stress. The collected data was analyzed to study the effects of aggregate gradation, testing temperature, and asphalt consistency on creep behavior. The effect of temperature variation on creep behavior was found to be more significant at low temperatures and long loading time than those at high temperatures and short loading time. Moreover, aggregate gradation found to has a significant effect on creep behavior, the lowest creep deformation was for HMA prepared using ASTM upper limit gradation. While HMA prepared using ASTM mid-limits aggregate gradation was the least affected by temperature variation.

Transient Thermal Behavior of Hot–Mix Asphalt Pavement

A heat transfer model was developed to predict a transient thermal behavior of asphalt concrete during service life at different weather conditions. The developed model has the capability to predict the distribution of temperature field with respect to time within the Hot-Mix asphalt body based on surrounding environmental conditions. This will greatly help pavement engineers to select the suitable asphalt grade to achieve the best pavement performance and avoid pavement distresses might be caused due to extreme pavement temperatures. These distresses include fatigue cracks, rutting, and thermal cracking. The resulted model required data on asphalt mixture, incident radiation, surface, and ambient temperatures in addition to thermal properties of Hot-Mix asphalt including absorptivity, heat transfer coefficient, and the emissivity. A sensitivity analyses wasperformed to study the impact of a number of thermalenvironmental and pavement geometric parameters on predicted temperature responses. The results of analysis indicated that the incident radiation, absorptivity, and the heat transfer coefficient have the most significant effect on Hot-Mix asphalt temperature. Also, the emissivity has insignificant effect on surface temperature Hot-Mix asphalt.