Serji N. Amirkhanian

Laboratory Investigation of Moisture Damage in Warm-Mix Asphalt Containing Moist Aggregate

In recent years, rising energy prices, global warming, and more stringent environmental regulations have generated interest in warm-mix asphalt (WMA) technologies as a means to decrease energy consumption and emissions associated with conventional hot-mix asphalt. In this study, a laboratory investigation was conducted of moisture damage in WMA mixtures containing moist aggregates. Indirect tensile strength (ITS), tensile strength ratio, deformation, and toughness tests were performed to determine the mixtures’ moisture susceptibilities. The experimental design included two percentages of moisture content (0% and ∼0.5% by weight of the dry mass of the aggregate), two WMA additives (Asphamin and Sasobit), and three aggregate sources. In this study 15 mix designs were performed, and 180 specimens were tested. Test results indicated that, as expected, dry ITS values were affected by aggregate moisture and hydrated lime contents, whereas a WMA additive did not significantly alter the dry ITS and toughness values. Statistical analysis showed no significant differences in the wet ITS values of WMA mixture of three types of mixtures (control, Asphamin, and Sasobit) under identical conditions (same moisture and lime contents). Statistical analysis also showed that wet ITS values, generally, were statistically different for mixtures made with various aggregate sources. The deformation resistance values of mixtures containing moisture were lower than those of mixtures made with dry aggregate. However, the results indicated that the addition of hydrated lime increased the deformation resistance of all mixtures.

The influence of crumb rubber modifier (CRM) microstructures on the high temperature properties of CRM binders

Many physical and chemical factors affect the rheological properties of crumb rubber modifier (CRM) binders. This study is aimed at understanding the influence of CRM microstructure on one of the rheological properties, the high temperature properties of the CRM binders. To this end, the high temperature properties of the binders that were modified by two types of CRM with different microstructures, three different sizes, two percentages as well as three different mixing times, were evaluated by dynamic shear rheometer (DSR) test on samples before and after RTFO aging. A series of scanning electron microscope (SEM) were taken on the two types of CRM of three different mesh sizes. Results from this study showed that: (1) ambient CRM has porous surfaces and cryogenic CRM has angular with smooth cracked surfaces; (2) an addition of 10–15% of CRM in the binder can increase one and two PG grades at high temperature for either ambient or cryogenic CRM regardless of the microstructure of CRM; (3) when a high percentage and coarser CRM is mixed, the microstructures of CRM have significant influence on the high failure temperature and (4) change in mixing time from 15 to 45 min did not alter much in the failure temperature, suggesting that a mixing time of 15 min interact completely for 15% CRM with the binder.

Evaluation of Rutting Resistance in Warm-Mix Asphalts Containing Moist Aggregate

In recent years, rising energy prices and more stringent environmental regulations have resulted in an interest in warm-mix asphalt (WMA) technologies to decrease the energy consumption and emissions associated with conventional hot-mix asphalt production. In this study, the objective was to conduct a laboratory investigation of rutting resistance in WMA mixtures containing moist aggregates. Rut depth, weight loss, and gyration number of dry and conditioned specimens were measured for all of the mixtures. The experimental design included two aggregate moisture contents (0% and ∼0.5% by weight of the dry mass of the aggregate), two lime contents (1% and 2% lime by weight of dry aggregate), three WMA additives (Aspha-min, Sasobit, and Evotherm), and three aggregate sources. Thirty-six mixtures were prepared, and 216 specimens were tested in this study. Test results indicated that the aggregate source significantly affects the rutting resistance regardless of the WMA additive, lime content, and moisture content. In addition, rut depth of the mixture containing moist aggregate generally satisfies the demand of pavement performance without additional treatment. The mixture with Sasobit additive exhibited the best rutting resistance. The mixtures containing Aspha-min and Evotherm additives generally showed a rut resistance similar to that of the control mixture.

Influence of Antistripping Additives on Moisture Susceptibility of Warm Mix Asphalt Mixtures

Rising energy prices, global warming, and more stringent environmental regulations have resulted in an interest in warm mix asphalt (WMA) technologies as a means to decrease the energy consumption and emissions associated with conventional hot mix asphalt production. However, the utilization of the hydrated lime and liquid antistripping agents (ASA) in WMA mixture makes these issues more complicated. The objective of this study was to investigate and evaluate the moisture susceptibility of the mixtures containing ASA and WMA additives. The experimental design for this study included the utilizations of one binder source (PG 64-22), three ASA additives and control, two WMA additives and virgin, and three aggregate sources. A total of 36 types of mixtures and 216 specimens were fabricated and tested in this study. The performed properties include indirect tensile strength (ITS), tensile strength ratio (TSR), flow, and toughness. The results indicated that the hydrate lime exhibits the best moisture resistance for WMA mixtures, the liquid ASA additives can increase the ITS values of the mixtures but the liquid ASA generally exhibits a weak moisture resistance compared to the hydrate lime regardless of WMA and aggregate types in this study. In addition, the wet ITS values of mixtures containing WMA additives were lower than that of the mixtures without WMA additives.

The effects of rejuvenating agents on recycled aged CRM binders

The recycling of asphalt pavements containing crumb rubber modifier (CRM) modified binders is increasing in areas having these types of asphalt pavements more than 10 or 15 years old. The performance and physical and rheological properties of the blends of aged CRM binders containing rejuvenating agents due to the presence of CRM have not been considered in detail. In this study, two CRM binders and one control binder of PG76-22 were artificially aged and then used as recycled materials by adding different rejuvenating agents, i.e. a rejuvenator and a softer binder. The properties of the blends of the three aged binders containing various percentages of the rejuvenating agents were evaluated using Dynamic Shear Rheometer (DSR), Bending Beam Rheometer (BBR) as well as viscosity tests. The test involved three different aging states of the blends: original, RTFO residual and RTFO+PAV residual. Results from this study show that: (1) the aged CRM binders can be rejuvenated back to a targeted PG grade; (2) the rejuvenating agents investigated are effective in changing the properties when used with the aged CRM binders; (3) the presence of crumb rubber in the modified binders enhances their aging resistance; (4) the target grade is more easily reached by adding the rejuvenating agents to the aged CRM binders rather than the aged control PG76-22.

Laboratory investigation of moisture damage in rubberised asphalt mixtures containing reclaimed asphalt pavement

In many parts of the world, highway officials are utilising crumb rubber and reclaimed asphalt pavement (RAP) in order to save money, protect the environment, and improve the life of asphalt pavement. However, due to the use of these materials, the effects of moisture damage should be investigated for rubberised asphalt concrete (RAC) mixtures containing RAP. The objective of this research involved investigating the moisture susceptibility of RAC containing RAP. The testing conducted included the determination of binder viscosity, toughness and indirect tensile strength (ITS) analysis. Several mixtures containing different crumb rubber types, two different RAP sources and various percentages of rubber and RAP were evaluated. The results indicated that, in general, the additional of RAP was beneficial in improving the ITS values and reducing the moisture susceptibility of the mixture although the addition of crumb rubber had a slightly negative effect.

Influence of Carbon Nanoparticles on the Rheological Characteristics of Short-Term Aged Asphalt Binders

Nanotechnology has the potential to create many new materials and devices with wide-ranging purposes. Nano-sized particles have been used in numerous applications to improve the properties of various materials. The utilization of nanotechnology in civil engineering is expected to increase and may become an attractive alternative for asphalt binder modification. The objective of this study was to investigate and evaluate the rheological properties of binders containing various percentages of carbon nanoparticles after a short-term aging process. The experimental design for this study included five binder sources (three grades including PG 64-22, PG 64-16, and PG 52-28), three nano percentages (0.5, 1.0, and 1.5% by weight of the virgin binder), and control binders. The rheological characteristics of the rolling thin film oven (RTFO) binders, including failure temperature, performance grade, creep and creep recovery, viscous flow, and frequency and amplitude sweep, were tested. The results of the experiments indicated that the addition of nanoparticles was helpful in increasing the failure temperature, complex modulus, and elastic modulus values and in improving rutting resistance of the RTFO binder. The phase angle of the binders generally decreased with an increase in nano content and RTFO aging procedure. In addition, statistical analysis indicated that the asphalt binder source plays a key role in determining the rheological properties because of significant evaluations.

Recycling of Laboratory-Prepared Reclaimed Asphalt Pavement Mixtures Containing Crumb Rubber-Modified Binders in Hot-Mix Asphalt

The recycling of reclaimed asphalt pavements (RAP) containing crumb rubber—modified binder is an important issue because some of these types of pavements are more than 10 to 15 years old in some areas in the United States. In this study, a laboratory investigation was conducted on the possibility of laboratory-prepared crumb rubber—modified RAP being recycled in Superpave® mixtures according to a normal recycling practice. Six mixtures (three recycled mixtures containing laboratory-prepared crumb rubber—modified RAP and three control virgin mixtures) were designed and tested. Three types of aggregates and two types of crumb rubber—modified binders were used for the mixtures. The crumb rubber-modified RAP used in the study was artificially aged in the laboratory with an accelerated aging process. The percentage of the RAP incorporated into the recycled mixtures was 15%. Evaluation of all mixtures included the following testing procedures: indirect tensile strength, asphalt pavement analyzer, and resilient ...

Laboratory Evaluation of Warm Asphalt Binder Aging Characteristics

As warm asphalt has been gaining increasing popularity in recent years, there are still several characteristics of warm asphalt, which are unknown. While several studies have been conducted to analyse the performance of warm asphalt mixtures, aging characteristics of warm-mix asphalt (WMA) binders are not known in great detail. This paper presents the results of a study to evaluate the aging characteristics of WMA binders artificially aged in the rolling thin film oven (RTFO) and the pressure aging vessel. RTFO aging was performed at 163°C and a lower temperature to simulate warm asphalt aging. The results of this study indicated that reducing the aging temperature reduced the aging index and increased the m-values, but had no significant effects on G*/sin δ, G*sin δ and stiffness of the binders. Also, the addition of warm asphalt additives significantly increased the G*/sin δ values and lowered the m-values of the binders.

Laboratory evaluation of warm mix asphalt ageing characteristics

Since warm asphalt technology is relatively new, there are no old pavements to study the ageing behaviour of warm mix asphalt (WMA). While several studies have been conducted to study the properties of WMA, its ageing characteristics are yet to be evaluated in detail. This paper presents the results of a laboratory study conducted to evaluate the ageing characteristics of WMA. Laboratory-prepared samples were aged artificially in the oven to simulate long-term ageing and then compared with unaged samples. Results of this study indicate that the warm asphalt additives improved the moisture susceptibility of the mixes and the mixes containing Sasobit® exhibited lowered rutting. Also, Aspha-min® lowered the resilient modulus (M R) values of the mixes at 25 and 40°C. The additives did not seem to have any significant effect on the moisture susceptibility or the rutting resistance of the mixes as they aged, but significantly increased the M R values of the mixes as they aged.