Tejash Gandhi

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.

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.

Laboratory investigation of moisture susceptibility of long-term saturated warm mix asphalt mixtures

Moisture damage in flexible pavements might cause stripping in asphalt pavements and ultimately result in premature failure. Warm mix asphalt (WMA) technology as a means to decrease the energy consumption and emissions associated with conventional hot mix asphalt production is broadly being used recently. However, the utilisation of the hydrated lime and liquid anti-strip additives in WMA mixtures makes these issues more complicated. The objective of this study was to investigate and evaluate the moisture susceptibility of mixtures containing anti-stripping agents (ASAs) and WMA additives after long-term saturated durations. The experimental design for this study included the utilisations of one binder source (PG 64-22), three ASA additives and control, two WMA additives and hot mix, and three aggregate sources. A total of 36 types of mixtures and 540 specimens were fabricated and tested in this study. The performed properties included indirect tensile strength (ITS), tensile strength ratio, flow and toughness. The results indicated that the aggregate source has an effect on dry ITS and flow values but had no effect on wet ITS, wet flow and toughness values. In addition, hot mixture generally had higher dry and wet ITS values, and there were significant differences in flow and toughness values between hot and warm mixtures. Moreover, the hydrated lime exhibited the best moisture resistance in WMA mixtures; the liquid ASA additives could increase the ITS values of mixtures but exhibited a weak moisture resistance in this study. Furthermore, the storage and saturated duration generally had no effect on ITS values, and statistical analysis results did not show any differences among these mixtures.

A Comparison of Warm Asphalt Binder Aging with Laboratory Aging Procedures

Warm asphalt has been gaining increasing popularity in recent years; however there are several characteristics about warm asphalt that are still unknown. While several studies have been conducted to study 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 limited study to evaluate the aging characteristics of two WMA binders artificially aged in the rolling thin film oven (RTFO) and the pressure aging vessel and comparing them with binder extracted from freshly prepared and artificially aged warm asphalt mixtures. RTFO aging was performed at 163°C and a lower temperature to simulate warm asphalt aging. Tests on binders aged in the laboratory and binders extracted from freshly mixed and aged mixtures indicated that the WMA binders extracted from WMA mixtures had significantly lower viscosities and G∗/sin δ compared to binders extracted from hot mix asphalt (HMA) and binders aged in the RTFO at 163°C (325°F). This indicates that the lower mixing and compaction temperatures reduce the aging of the warm asphalt binders. Also, binders extracted from WMA had significantly lower creep stiffness values and significantly higher m-values compared to warm asphalt binders aged in the RTFO at 163°C (325°F) and binders extracted from HMA. Binders containing WMA additives did not have higher G∗ sin δ values, indicating that the warm asphalt additives do not negatively affect the fatigue properties of the binders. Gel permeation chromatography analysis indicated that the addition of the warm asphalt additives did not have any significant effect on the %LMS of the binders used in this study.

Laboratory Simulation of Warm Mix Asphalt (WMA) Binder Aging Characteristics

As warm asphalt has been gaining increasing popularity in the recent years, there are still several characteristics about warm asphalt that are unknown. While several studies have been conducted to study the performance of warm asphalt mixtures, aging characteristics of warm asphalt binders are not known in great detail as the technology is relatively new, and there are no old pavements to study the aging behavior of warm asphalt. This paper presents the results of a study conducted to simulate the aging of warm asphalt binder in the laboratory by preparing asphalt mixtures containing two different binder sources and three different warm asphalt additives (Control, Asphamin® and Sasobit®). The mixtures were artificially aged in the oven, and the binders were extracted for testing. The binders extracted from freshly prepared samples were considered being short term aged binders and binders extracted from oven aged mixtures were considered being long term aged binders. Results of several tests (e.g., viscosity, high and low temperature properties, Gel Permeation Chromatography, etc.) are presented in this study. The results indicated that the binders extracted from the warm mix asphalt (WMA) had significantly lower aging index (ratio of the viscosity of extracted binders to original binders) compared to the binders extracted from control hot mix asphalt (HMA). It was also observed that the binders extracted from the WMA had aged significantly lower compared to binders extracted from control HMA. The results indicated that the warm asphalt additives did not have any significant effect on the fatigue cracking parameter (G*.sin δ) or the creep stiffness of the binders. However, Asphamin® significantly increased the m-value of the binders.