•A strain level of 15% should be included in comparing and/or ranking of binders with respect to fatigue resistance.•The fatigue lives (Nf) at various aging levels are described by a simple function ...of aging at any strain level.•The effect of aging on asphalt binder LAS model parameters can relate to changes in complex modulus.•The proposed G*-related prediction model can used to estimate the fatigue life any aging and strain level.
The linear amplitude sweep (LAS) test is considered a useful tool for evaluating fatigue of asphalt binders. It has been confirmed that a good correlation exists between fatigue performance of binders and mixtures in a few studies. While the change in binder fatigue with load or strain level is well studied and modeled, the effects of oxidative aging remain difficult to explain or to model in a simple format. In this paper, the combined effects of strain and aging are investigated and a method for estimating binder fatigue behavior after different aging durations from limited measurements is introduced. LAS tests were conducted on eight binders at three different aging periods in the PAV. It is found that binder fatigue damage parameters C1 and C2 have a good linear relationship with aging level when using the dissipated pseudo-strain energy approach. The results also show that LAS parameters A and B at different aging duration maintain a linear relationship with the binder complex modulus (G*) measured at corresponding aging conditions. Therefore, a new fatigue life (Nf) model accounting for strain level and aging effect is proposed using a power function of the binder G*. To verify the model, its parameters are fitted using test data at first two aging conditions and used to extrapolate and predict the fatigue life at extended aging conditions. This study findings offer a simpler and reliable method to predicted values of fatigue life at new aging condition using both 35% damage level and maximum stress failure criteria that are recommended in AASHTO TP101-12 and AASHTO TP101-14, respectively. The new model will allow use of the LAS procedure to a wider range of aging and strain level conditions for which binders could be subjected to in the pavement.
•The dry Hamburg Wheel Tracking (HWT) test is proposed in measuring the rutting resistance of asphalt mixtures.•The dry HWT test can simulate rutting mechanisms including densification and shear ...failure analyzed by image processing analysis system 2 (IPAS2).•The dry HWT test shows a strong correlation of creep slope and cumulative strain with equivalent cycles observed for FN test.
Rutting is one of the most important failures occurring in hot mix asphalt (HMA) especially in the summer season and slow moving traffic areas. Rutting is a pavement surface failure compromising the safety and ride comfort of traveling and thus needs to be accurately evaluated in a laboratory. Although the flow number (FN) test is commonly used for evaluating the rutting resistance of HMA in a laboratory, there are some shortcomings in using FN test such as the costly and complicated equipment. Another potential test that is likely to be more advantageous than the FN test for evaluating the rutting resistance is the Hamburg Wheel Tracking (HWT) test, however, it is typically conducted in wet condition, and inadequate results in dry condition have been reported. The objective in this study is to optimize the HWT test subject to dry condition to be one potential method in measuring rutting resistance in a laboratory. Two rutting mechanisms (densification and shear failure) of HMA samples conducted in the HWT device were determined by Image Processing and Analysis version 2 (IPAS2). Results indicate that HMA samples under the dry HWT test can exhibit both rutting mechanisms in which typically occur in the field. Also, the dry HWT test shows a very good R2 for a relation of creep slope with the confined and unconfined FN test. As a result, the dry HWT can be an effective tool of quantifying rutting potential with better simulating to field behavior, lower cost of equipment, and less complicated geometry that can also accommodate field cores.
The linear amplitude sweep (LAS) test has been used widely in the last decade as an effective tool for evaluating the fatigue behavior of asphalt binders. However, a simple to follow criteria to be ...included in a standard specification has not been proposed yet. Recently, the Glover-Rowe (G-R) parameter has also been introduced with limiting values as a measure of binder cracking resistance and its change with oxidative aging. These two approaches differ in the time required for testing, the range in strain used and temperature of the tests required to derive the binder acceptance parameters. In addition, there is confusion about what could be the specification acceptance limits to be used and how to consider the temperature of pavement, and traffic volume and traffic speed in the specification criteria. In this study, the calculation procedure of the G-R parameter is simplified by using the data from the strain amplitude sweep, and the frequency sweep, used in the LAS test (AASHTO TP101). This new method of calculation eliminates the need for the time-consuming procedure that requires lower temperatures and low frequency conditions. The calculation procedure is also used to determine the dependency of the G-R parameter on strain level during the test and to derive acceptance criteria as a function of traffic speed and volume similar to the MSCR criteria. Thirty-six types of modified asphalt subjected to PAV aging are used in this study. For eight types of these asphalts, mixtures were prepared and subjected to three periods of oven aging conditions. By comparing the G-R index with the LAS fatigue life of the asphalt binder and the Flexibility Index value of the asphalt mixture, it is shown that there is a strong correlation between the selected binder fatigue parameters and mixture performance. It is also confirmed that strain levels play a very important role in defining the fatigue life of a binder. Following the concept of Jnr limits for different traffic grades used for the MSCR test, the threshold values of the allowable strain in LAS results, or a maximum allowable G-R limits, under different traffic volume and speed conditions are defined. The approach used in the study allows a determination of which traffic and speed conditions an asphalt binder can tolerate can be made in a relatively short time. Similar to the MSCR, four fatigue grades including S, H, V, and E are used in the proposed criteria.
•Power law model was used to determine the creep stage in Hamburg wheel tracking (HWT) test.•Wet HWT can be deployed as a substitute to the dry HWT test in the creep stage.•Bitumen Bond Strength ...(BBS) test can also verify the moisture sensitivity occurred in the dry and wet HWT.
Hamburg wheel tracking (HWT) is prominently used for rutting resistance test. The HWT is a versatile device to determine moisture susceptibility and permanent deformation, which has been widely used in many states and agencies in the United States. However, the standard of the test for the HWT device conducted in water is not related to a primary result of rutting, which is due to repeated traffic loading cycle especially in the dry condition. In this study, the HWT test in different conditions (i.e. dry and wet) was conducted to compare the behavior of hot mix asphalt (HMA) during testing. The objective is to determine the comparison between the dry and wet condition testing in HWT test, and to evaluate relative effect of moisture conditioning in wet HWT on the creep stage. Fitting curve using Francken model was applied to determine the tertiary point of HWT curve. Power law model was used to determine the effect of the moisture conditioning in wet HWT on the creep stage. The moisture damage in the wet HWT test was also verified by the Bitumen Bond Strength (BBS) test. The results indicated that the wet HWT currently specified in the AASHTO 324 can be deployed as a substitute to the dry HWT test in the creep stage (before the stripping inflection point) since the difference in creep slope estimated for both conditions is within the experimental error. The wet HWT results after the creep slope remain useful for detecting the moisture sensitivity with the confirmation by the measured cohesion/adhesion of asphalt mastics from each mixture. The BBS test can also verify the moisture sensitivity occurred in the dry and wet HWT with the creep slope and tertiary/stripping slope well correlated to mastic cohesion change in BBS test.
Understanding moisture damage mechanisms in asphalt pavements and evaluating the right combination of materials that are resistant to moisture damage are important. Moisture damage is the loss of ...strength or stiffness in asphalt mixtures caused by a combination of mechanical loading and moisture. Many test methods have been developed to evaluate loss of adhesion and cohesion in binders. However, a simple procedure to address moisture damage in the asphalt–aggregate interface is not available. The feasibility of the newly developed bitumen bond strength (BBS) test for moisture damage characterization was investigated. An experimental matrix that included various binders, modifications, and aggregates to account for the chemical and physical conditions in the aggregate–asphalt interface was completed. A statistical analysis was performed to verify reproducibility of the BBS test. The results indicated that the bond strength of asphalt–aggregate systems was highly dependent on modification and moisture exposure time. Polymers were found to improve the adhesion between asphalt and aggregate as well as the cohesion within the binder. Results from this study indicated that the BBS test was repeatable and reproducible. To further validate the effectiveness of the BBS test, a comparison of the BBS test results and the modified dynamic shear rheometer strain sweep test was conducted. The comparison showed that the BBS test could rank materials similarly to a more sophisticated and time-consuming test.
The linear amplitude sweep (LAS) test is useful for evaluating the fatigue of asphalt binders. In this paper, the combined effects of strain and temperatures are investigated, and a method for ...estimating binder fatigue behaviour is introduced at different temperatures from limited measurements. LAS tests were conducted on several different PG-grade binders at four different temperatures. The results show that LAS parameters A and B at different temperatures maintain a linear relationship with the binder complex modulus (G*) measured at corresponding temperatures. Therefore, a fatigue life model, accounting for strain level and temperature, is proposed using a power function of the binder G*, which can account for temperature effects. To verify the model, its parameters are fitted using test data at two temperatures were used to predict the fatigue life at additional temperatures. This study findings offer a simpler and reliable method to predict the values of fatigue life at new temperatures using both 35% damage level and maximum stress failure criteria that are recommended in AASHTO TP101-12 and AASHTO TP101-14, respectively. The new prediction method will allow a wider use of the LAS procedure regarding the effects of temperature and strain level for which binders are subjected to the pavement.
Air voids (density) is a key volumetric property of asphalt mixes and play an unignorable role in anti-cracking. While lower voids were expected to result in more durable asphalt mixtures, ...contradictory trends were found in lab testing. In this study, several plant-produced mixtures were compacted to three levels of air voids (7%, 9%, and 11%) and tested to evaluate the sensitivity to the crack resistance. The results indicate that the higher the air voids, the better the cracking resistance as measured by the CT
index
. To understand the cause, a stepwise regression analysis was conducted to model the IDEAL-CT parameters with volumetric and gradation parameters. The air void, percent passing the 0.6 mm (P
0.6
) and binder content (P
b
) are found to have significant effects on CT
index
and post-peak slope. The analysis of the CT change rate shows that the P
b
, dust to binder ratio (D/B), and P
0.6
can be used to predict the effect of the voids with a correlation factor (R
2
) of 0.96. For further understanding, the asphalt film thickness was calculated and found that compared with using film thickness as the single fitting parameter, combining the film thickness with D/B in modelling can dramatically increase the R
2
of correlation from 0.67 to 0.92.
Moisture damage of asphalt mixtures can be caused either by adhesive failure between asphalt binder and aggregate surface, or by cohesive failure within the asphalt mastic. There are limited studies ...on the effect of moisture on cohesive failure caused by asphalt mastic bonding deterioration measured by the Bitumen Bond Strength (BBS) test. The objective of this study is to determine the effects of different mineral fillers in asphalt mastic on moisture damage resistance using the BBS test. Results collected indicate that surface area and mineralogy of mineral fillers have significant effects on moisture damage resistance. Results also show that there is a significant effect of asphalt modification on moisture damage measurements. Thus, the concept of testing the mastic with the fillers and polymers intended for production of mixture appears to give an effective tool to predict the adhesion and cohesion performance before and after water conditioning.
Rutting is one of the main asphalt pavement distresses, and it is believed that binder properties play an important role in mixture's potential rutting resistance. Generally, in the Superpave design ...system asphalt binder is selected based on the binder PG grade required for the climate. However, to implement performance control through the traditional Superpave PG system during mix design faces more challenges due to the changes of oil refinery, asphalt binder modification, and the use of recycled materials in the mixture. This paper aims to investigate the role of asphalt binders and mix designs in the rutting resistance of asphalt mixtures. A total of 22 plant-produced mixtures from 10 states and 5 laboratory-produced mixtures were investigated for their rutting performance in this study. Those tested mixtures include various binder grades, aggregate sources, RAP contents, and mix designs. The Superpave binder rutting parameter G*/sinδ and Multiple Stress Creep and Recovery (MSCR) grade parameter Jnr3.2 are correlated with the mixture dynamic modulus and Hamburg Wheel Tracking (HWT) rutting parameters. In addition, the effects of other mix design variables on the rutting resistance are evaluated using a statistical analysis. The results show that by incorporating the binder properties and mix design variables, the stepwise regression fitting provides a much better prediction for HWT rutting parameters as compared to using only the binder properties. This indicates the importance of proper selection of the binder grade for mixture performance, and it also calls for justifying more focus on including mixture design variables to ensure acceptable mixture rutting performance. The statistical analysis can provide an insight into the use of artificial intelligence and machine learning by generating mathematical models for evaluating which mixture design variables are needed for better prediction of rutting performance.
Recently, there is a growing interest in increasing content of reclaimed asphalt pavement (RAP) material in the production of Hot Mix Asphalt (HMA) pavements to further reduce material costs and to ...preserve non-renewable resources. This study aims to evaluate the long-term performance of high RAP mixtures containing various softening oils. Both petroleum-based and bio-based oils were applied in preparing the 30% RAP and 50% RAP mixtures. The mixtures were subjected to the short-term oven aging (4 h), long-term oven aging (8 h), and extended-term aging (16 h) in the laboratory. Their performance, including the rutting, fatigue cracking at intermediate temperature, and low temperature cracking, were measured and compared with the control mixtures. The results indicate that the softening oils in this study can be used to produce asphalt mixtures containing high percentages of RAP with similar performance to a virgin mixture utilising the same aggregates and mixture design. In addition, the results show that making decisions to compare, qualify, or otherwise accept mixtures using the short-term aging results alone can be very risky. It is clearly shown in this study that relative ranking of mixture performance can change based on the level of aging.
