Ghazi G. Al-Khateeb

Laboratory Study for Comparing Rutting Performance of Limestone and Basalt Superpave Asphalt Mixtures

The primary objective of this research effort was to conduct a rutting performance-based comparison between limestone and basalt Superpave asphalt mixtures using dynamic creep rutting tests. Two sets of mixtures were prepared using limestone and basalt ag- gregate, mixed with one asphalt binder having a Superpave performance grade of PG 64-10. To overcome the stripping potential of the Superpave basalt asphalt mixtures, 1% by total weight of the basalt aggregate was replaced by hydrated lime for the filler portion of the aggregate. Rutting was evaluated at four different temperatures (40, 50, 60, and 65°C) and one loading frequency of 8 Hz. Rutting test results indicated that the basalt Superpave asphalt mixtures exhibited superior performance relative to the limestone Superpave asphalt mixtures. The difference in the rut depth at 19,200 loading cycles between the limestone and basalt asphalt mixtures was statistically sig- nificant at levels of α ¼ 1, 5, 1, and 0.5% for the temperatures 40, 50, 60, and 65°C, respectively. The difference in the rut depth at 200,000 loading cycles between the two asphalt mixtures was statistically significant at levels of α ¼ 1, 5, 0.1, and 0.1% for the temperatures 40, 50, 60, and 65°C, respectively. In addition, the difference in the number of loading cycles to rutting failure between limestone and basalt asphalt mixtures was also statistically significant at a level of α ¼ 0.1% for all temperatures. DOI: 10.1061/(ASCE)MT.1943-5533.0000519.

A Simple Quantitative Method for Identification of Failure due to Fatigue Damage

A simple quantitative method is presented which is applicable to any type of fatigue testing that uses sinusoidal strain/stress input and which will work for experimentally identifying points of failure due to fatigue damage of any kind of material being tested. The present work utilizes strain-controlled bending beam fatigue test on asphalt mixtures to demonstrate the efficacy of this method. Distortions in the hysteresis loop or waveform are tracked to pinpoint the appearance of initial microcracks and final point of complete failure due to fatigue damage. Relationship between output signals for consecutive cycles with reference to initial stable cycle is used for computing ‘R 2’. The ‘R2’ drops sharply from initial stable value of 1 to less than 0.5 and eventually to almost 0 with increasing loading cycles. The number of cycles determined from the fitted equation at ‘R2’ = 1 marks the point of first fatigue failure N fff and ‘R2’ = 0 marks the point of complete fatigue failure Ncff.

Comparison of Simple Performance Test |E*| of Accelerated Loading Facility Mixtures and Prediction |E*|: Use of NCHRP 1-37A and Witczak's New Equations

The dynamic modulus, |E*|, of asphalt mixture has recently drawn much attention in the asphalt community. The |E*| test has been suggested by NCHRP Projects 9-19 and 9-29 as the simple performance test (SPT) to verify the performance characteristics of Superpave® mixture design. In addition, it has been recommended as the potential quality control-quality assurance parameter in the field. The dynamic modulus, |E*|, is an input to the Mechanistic-Empirical Pavement Design Guide (M-E PDG) and also supports the predictive performance models developed as part of NCHRP Project 1-37A. The importance of this parameter on one hand and its time-consuming determination on the other hand necessitated reliable prediction of dynamic moduli of asphalt mixtures at different temperatures and loading frequencies. In this respect, a number of predictive equations have been developed. The most widely used model is the NCHRP 1-37A, which is currently used for calculation of |E*| in Levels 2 and 3 of M-E PDG. The model has a reasonably good prediction capability of high modulus values; however, it tends to over-predict the moduli at the lower spectrum. This study shows that a recent modification to the NCHRP 1-37A model has improved the overall prediction of |E*| but has not significantly improved the overprediction of the lower moduli. While the replacement of the binder viscosity, η, with the binder shear modulus, |G*|, has increased the accuracy of the model, the inclusion of the binder phase angle, δ, in the revised equation was not found to have a significant effect.

Mechanistic Analyses of FHWA's Accelerated Loading Facility Pavements: Primary Response

In-depth details are provided for mechanistic analyses conducted for the asphalt pavements of the FHWA accelerated loading facility (ALF) by using available programs, including KENPAVE, WINLEA, EVERSTRS, EVERFLEX, and VESYS 5W. These pavements were constructed by using highly modified and unmodified asphalt binders. The described analyses focused on primary response under the ALF pavements. This study included multilayer elastic theory (MLET) solutions, finite element analysis, and analysis using the VESYS 5W program. Predictions of the primary response for the fatigue mode included the horizontal tensile stress and strain at the bottom of the hot-mix asphalt (HMA) layer and for the rutting mode included the vertical compressive stress and strain on top of each pavement layer. The impact of loading frequency and stress sensitivity (nonlinearity) on fatigue primary response, rutting primary response, and principal stresses was investigated. The frequency did affect the fatigue tensile stress and strain, primarily at the bottom of the HMA layer. It also affected the major and minor principal stresses, particularly at the bottom of the HMA layer. The frequency effect on the rutting compressive stress was insignificant, whereas it was considerable for the compressive strain within the HMA layer. The MLET solutions that used a linear elastic base provided reasonable predictions for the measured tensile strains for highly modified and unmodified asphalt pavements with an absolute percentage error in the range of 0% to 15% percent in most cases. The solutions of the MLET and VESYS 5W programs were capable of providing good predictions of the vertical deformation within the HMA layer that correlated well with the measured permanent deformation values.

Target and Tolerance Study for Angle of Gyration Used in Superpave Gyratory Compactor

Five companies offer eight models of the Superpave® gyratory compactor (SGC) in the United States. Each model uses a unique method of setting and inducing the specified angle of gyration. However, all angles are set externally relative to the mold and none of the manufacturer’s calibration systems can be universally applied to all models. The specified external angle of gyration (α) is 1.25° FHWA, in partnership with Test Quip, Inc., developed a dynamic angle validation kit that measures the dynamic internal angle (DIA) of gyration during loading. The DIA accounts for equipment compliance issues, such as bending of the platens during compaction, which is not apparent when the angle is measured externally. Differences in specimen density produced by different compactors have been attributed to differences in compliance. Thus, the SGC test method needs to be revised to obtain uniformity. However, it would be inappropriate to assign the external angle of 1.25° to the DIA because the internal angle is always lower than the external angle. Use of a 1.25° internal angle would result in an increase in the compactive effort applied by all SGCs, which would invalidate the Ndesign table. FHWA investigated the DIA by using the original two SGC models. These models were used to refine the Ndesign table that is in use today. The study found that the DIAs for these original SGCs were 1.176° and 1.140°, which resulted in a proposed DIA of 1.16° The proposed tolerance is ±0.03°.

Studying rutting performance of Superpave asphalt mixtures using unconfined dynamic creep and simple performance tests

This study aimed at evaluating asphalt mixtures for rutting using two test procedures. The first procedure was the dynamic creep test, which was performed using the 5-kN Pneumatic Universal Testing Machine (UTM-5P). The second procedure was the flow number test which was performed by the Superpave Simple Performance Tester (SPT), currently known as the Asphalt Mixture Performance Tester (AMPT). Test specimens were prepared using crushed limestone aggregate and 60/70-penetration-grade asphalt binder having a performance grade (PG) of 64-10. Two aggregate gradations were used and compared in this study: a gradation passing above the restricted zone (ARZ) representing a fine gradation, and another gradation passing below the restricted zone (BRZ) representing a coarse gradation. Asphalt mixtures were compacted using the Superpave Gyratory Compactor (SGC). The SGC samples were then cored and sawed to produce fabricated test specimens of the desired height (150 mm) and diameter (100 mm). Specimens were tested at four temperature levels: 40°C, 50°C, 55°C, and 60°C. For comparison purposes, identical test parameters were used for both tests including: specimen dimensions, load frequency, load and rest periods, contact stress, and deviator stress. Test results were analysed to investigate the permanent deformation behaviour of the asphalt mixture with the temperature. The results for fine-graded mixtures and coarse-graded mixtures were analysed and compared. A comparison between the two test procedures was made based on the test results. The analysis and comparison were made based on the number of cycles at failure, the strain at failure, the number of cycles to reach 1.5% strain, and the strain at 1000 cycles. Both one-way ANOVA and two-way ANOVA procedures were used in the comparison. Results showed that a significant difference between ARZ asphalt mixtures and BRZ asphalt mixtures in the measured properties existed. The significance level was found to be strongly related to the test temperature. Results also showed that the flow number test and the dynamic creep test results had different behaviour with test temperature and sometimes opposite behaviour. The significance of the difference was also found to have an interaction with the test temperature. Based on the results and the comparison, it was clear that the SPT flow number test showed better accuracy and reproducibility of test results. The flow number test results also showed better fitting and no departures from the expected trend, unlike the dynamic creep test results.

Conceptualizing the asphalt film thickness to investigate the Superpave VMA criteria

Abstract Asphalt binder film thickness (FTb) is the key factor that is responsible for durability of asphalt mixtures. Mixtures with coarse aggregate gradations have difficulty meeting the Superpave minimum voids in mineral aggregate (VMA) criteria even though they tend to have thick asphalt films. In this study, the concept of asphalt binder film thickness (FTb) was used to investigate the Superpave VMA criteria. Superpave aggregate gradations of three nominal maximum aggregate sizes (NMAS): 9.5, 12.5 and 19.0 mm, were used. Aggregate gradations passing above, below, crossover through, humped, and through restricted zone were all considered. Superpave Gyratory Compactor test data of 126 compacted asphalt mixtures were used in the study. The current Superpave VMA criteria relate the mixture durability with VMA and set the same VMA value for mixtures with the same NMAS regardless of other parameters. However, a poor relationship was found between VMA and FTb (a durability measure) with an R 2 ≅ 0.01, and yet a relatively good relationship (R 2 ≅ 0.38) was found between voids filled with asphalt (VFA) and FTb although the VFA volumetric phase is part of the VMA volumetric phase in the mixture. This result was justified by the poor relationship between VFA and VMA (R 2 ≅ 0.13). Despite that the effective binder content (P be ) as a volumetric phase represents the VFA in the mixture, the relationship between FTb and P be was found to be more significant (higher R 2) than the relationship between FTb and VFA. In this study, asphalt mixtures that did fail the Superpave VMA criteria in some cases had adequate asphalt FTb, and mixtures that passed the criteria did not necessarily have adequate FTb. In conclusion, although the current Superpave VMA criteria are significant, findings of this study support the tendency to modify the current criteria.

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.

Mechanical Behavior of Asphalt Mastics Produced Using Waste Stone Sawdust

This study intended to evaluate the use of waste stone sawdust filler with asphalt binders and compare the mechanical properties of the waste filler-asphalt mastic with those of the asphalt mastic produced using the typical limestone filler. The mastics were prepared at four filler-to-asphalt ratios by volume of asphalt binder: 0.05, 0.10, 0.20, and 0.30. A dynamic shear rheometer (DSR) strain-controlled frequency sweep test was used to evaluate the properties of the control asphalt binder and the mastics. The test used a constant strain of 10% and loading frequencies of 10, 5.6, 3.1, 1.78, 1.0, 0.56, 0.31, 0.178, and 0.1 Hz and was conducted at wide range of temperatures: 10, 20, 30, 40, 50, 60, and 70°C. The test measured the complex shear modulus ( ) value and the phase angle for the binder and the mastics. The findings of this study showed that the stone sawdust filler demonstrated higher resistance to fatigue and rutting behavior than the limestone filler. However, the elastic behavior of the two asphalt mastics was nearly similar and increased with the increase in volume ratio. It was also found that the best-fit model described the relationship between the volume ratio and each of and , and the mastic-to-binder modulus ratio was the exponential model with high coefficient of determination ( ). The differences in the value between the limestone filler and the stone sawdust filler were relatively insignificant particularly at low loading frequencies and high temperatures. Finally, the mastic-to-binder modulus ratio decreased with the increase in loading frequency.