New Mechanistic Procedure to Predict the Critical Cracking Temperature of Asphalt Concrete from Bending Beam Rheometer and Indirect Tension Test Data

This study presents a new mechanistic procedure for determining the critical cracking temperature of asphalt concrete (AC) using data from bending beam rheometer (BBR) test of asphalt binder and indirect tension (IDT) test of AC. This new procedure uses BBR creep data to generate the mixture relaxation modulus mastercurve by utilizing the Hirsch model, time-temperature superposition principle, and Prony series-based interconversion method. The Hirsch model parameters are calibrated by comparing creep data from BBR and IDT creep tests performed at the same temperature. Boltzmann hereditary integral and second-order heat equation are then used to calculate thermal stress from the developed relaxation modulus mastercurve. IDT strength data is transferred from test strain rate to thermal strain rate using the viscoelastic continuum damage model. Since a strain gauge is not attached for traditional laboratory IDT strength testing, this study derived an analytical equation based on the Hondros solution to compute the horizontal strain rate from the applied vertical displacement rate. Finally, the critical cracking temperature is determined by coupling the thermal stress and strength profiles. Using the procedure presented in this paper, the critical cracking temperatures of four AC mixtures were predicted from BBR and IDT data. Their actual critical cracking temperatures were measured using thermal stress restrained specimen test performed in the laboratory to validate the method. The predicted critical cracking temperatures are found to be very close to the laboratory measured values. The developed procedure has substantial practical and technical importance in predicting the critical cracking temperature of AC because it utilizes widely available BBR and IDT tests.

Evaluation of recycled asphalt mixture at low temperature using different analytical solutions

Using reclaimed asphalt pavement (RAP) in road infrastructures is crucial for mitigating the environmental impact while controlling the construction costs. However, poorer low temperature performance may be experienced for mixtures containing RAP. In this paper, the effect of RAP on the material response at low temperature is investigated through mixture creep testing with the bending beam rheometer. Three different mathematical approaches are selected for further evaluation in combination with simple statistical analysis. Based on the experimental data, creep stiffness, m-value, relaxation modulus, thermal stress, and critical cracking temperature are computed and compared. As a result, no differences are found between the virgin mixture and that designed with 15% of RAP. Poorer performance is observed when more than 25% of RAP is incorporated; however, no significant variation was observed for a further increase up to 40% suggesting that higher amount RAP could be used depending on traffic level and climate.

Investigation on the cooling medium effect in the characterization of asphalt binder with the bending beam rheometer (BBR)

In this paper, the possibility of using air as an alternative cooling medium for testing asphalt binder in the bending beam rheometer (BBR) is considered and evaluated. For this purpose, five asphalt binders were characterized with the BBR; creep stiffness, m-value, performance grade (PG), thermal stress, and critical cracking temperature were computed both for ethanol and air. In addition, the rheological Huet model was fitted to the experimental measurements to further investigate the effect of the cooling medium. It was found that air measurements result in stiffer materials, with higher low PG, higher thermal stress, and critical cracking temperature. The parameters of the Huet model confirm such a stiffening effect when air is used. Based on the material response observed in this study, further research is recommended before potentially replacing ethanol with air in the BBR, as the latter appears to provide a substantially different material grading.

Analysis of Methods and Criteria for Evaluation of Bitumen Performance at Low Temperatures

Thermal cracking is the dominant pavement failure in the cold regions. After each winter, the newly appeared cracks have to be sealed. However, after a few years depending on the sealing method the previously sealed cracks have to be resealed. It results in high maintenance budget and human resources. The appropriate bitumen selection on the basis of bitumen performance at low temperatures can reduce the effect of thermal cracking. For this purpose, number of methods are developed such as Fraass test, bending beam rheometer (BBR) test, direct tension (DT) test, asphalt binder cracking device (ABCD), dynamic shear rheometer using 4 mm diameter parallel plates (4-mm DSR) test, single-edge-notched bending (SENB) test, doubleedge- notched tension (DENT) test and spectral analysis of acoustic emission (AE). This paper presents the analysis of different tests for the evaluation of the bitumen performance at low temperatures, highlights their advantages and disadvantages and gives their limiting criteria. These limiting criteria are usually used to determine the critical cracking temperature, which is defined as the lowest temperature at which bitumen can withstand induced thermal stresses.

Applied Technology in Asphalt Low Temperature Performance Evaluation

Through BBR, DTT and independently developed Asphalt Thermal Cracking Test, several asphalt low temperature performance indexes(SHRP critical cracking temperature, Asphalt Thermal Cracking temperature, SHRP creep stiffness, m value, conventional ductility) were evaluated. The TSRST test was used as low temperature evaluating standard indicator. The theory of grey correlation is adopted to reach that TSRST fracture temperature has the highest correlation degree with Asphalt Thermal Cracking temperature. The SHRP critical cracking temperature has the second place of correlation degree with TSRST. Low temperature ductility has the lower correlation. Therefore it is more reasonable to adopt thermal cracking temperature than other general evaluations.

Evaluation of Low-Temperature Properties and the Fragility of Asphalt Binders with Non-Arrhenius Viscosity–Temperature Dependence

Rotational viscosities of different asphalt binders were determined at temperatures between 80°C and 185°C. Viscosity–temperature dependence of asphalt binders was described with the use of the Vogel–Tammann–Fulcher (VTF) and the William–Landel–Ferry (WLF) equations. The Vogel temperature ( Tv) and the glass transition temperature ( Tg) for different asphalt binders were determined by fitting experimental values of viscosity at different temperatures with these two equations. For asphalt binders, the difference between Tv and Tg was about 40K. Effects of asphaltenes, aging, chemical modification, and polymer content on these temperatures were evaluated. As asphaltene content increased, both temperatures, Tv and Tg, increased. Different polymers showed different effects on these temperatures. The values of Tv and Tg were correlated with the critical cracking temperature ( Tcr) determined through use of a bending beam rheometer and a direct tension tester. The results suggested that the correlations between Tv, Tg, and Tcr could be used to determine Tcr from the rotational viscosity results tested at high temperature. With simple rotational measurements, a quick estimation of Tcr of asphalt binders could be obtained. Liquid fragility theory was also used to study Tg of asphalt binders. Parameters determined with the VTF and WLF equations indicated that asphalt binders behaved as fragile liquids because of their non-Arrhenius behavior in the temperature range studied.

Processing of Thick Dielectric Films for Power MEMS: Stress and Fracture

ABSTRACTThis paper presents residual stress characterization and fracture analysis of thick silane based PECVD oxide films. The motivation for this work is to elucidate the factors contributing to residual stress, deformation and fracture of oxide films so as to refine the fabrication process for power MEMS. It is shown that residual stress in oxide films strongly depended on thermal processing history. Dissolved gases were found to play an important role in governing intrinsic stress. The tendency to form cracks is a strong function of film thickness and annealing temperature. Mixed mode fracture mechanics was applied to predict critical cracking temperature, and there is a fairly good match between theoretical predictions and experimental observations.