Ramya Sri | Indian institute of Technology,Hyderabad (original) (raw)

Papers by Ramya Sri

The performance of conventional or reclaimed asphalt pavement (RAP) mixes depends on the properti... more The performance of conventional or reclaimed asphalt pavement (RAP) mixes depends on the properties of the virgin and RAP binders. The fundamental characteristics of different materials often are used to explain the mechanical performance. Surface free energy (SFE) is one such property that can be considered to explain the fracture and rutting performance and moisture damage resistance of bituminous binders and mixes. The correlation between different rheological properties of binders (virgin as well as RAP blends) and the SFE, determined by the sessile drop technique, was explored in this study. Two commonly used virgin binders and different virgin-RAP binder blends (prepared by varying the RAP content in the blend) were evaluated. Penetration, softening point, viscosity, Superpave rutting and fatigue parameters, multiple stress creep and recovery (MSCR), and linear amplitude sweep (LAS) test parameters of the binders were measured and correlated with SFE. Total cohesive surface free energy of the binders was found to correlate well with (1) cohesive/stiffness properties of the virgin and RAP binders represented by penetration, softening point, and G Ã (complex shear modulus); (2) the viscoelastic response indicated by phase angle and percentage strain recovered; (3) rutting resistance, represented by the Superpave rutting parameter (G Ã = sin δ) (where δ is phase angle) and non-recoverable compliance measured in the MSCR test; and (4) fatigue performance indicators such as the Superpave fatigue parameter (G Ã sin δ) and the fatigue life estimated from LAS test. The study clearly established the correlation between SFE and the mechanical parameters evaluated in the study and indicates the need to conduct a more-detailed and exhaustive experimental program to develop generalized relationships applicable to a wider range of binders than considered in this study. The fact that a single binder parameter measured by a simple method can explain multiple aspects of performance is a promising prospect.

Bituminous mixes are generally designed with gradation and air void content ranges adopted by dif... more Bituminous mixes are generally designed with gradation and air void content ranges adopted by different agencies. The selected gradation and binder content are permitted to vary within specified tolerance limits. This leads to the possibility of a wide range of mixes with varying mix performance. Thus, it is essential to understand the influence of variation in these parameters on the performance of mixes. The present study aims to examine the sensitivity of the mix performance to variation within the specified gradation and air void ranges. Five aggregate gradations were considered for designing mixes for the volumetric design criterion of 4% air voids. For three of the five gradations, mixes were also designed for two additional design air void contents, 3% and 5%. Rutting resistance of the mixes was measured using a rut tester and moisture resistance was evaluated in terms of Tensile Strength Ratio (TSR). The densification characteristics represented by voids in mineral aggregate (VMA) values of the mixes prepared using the five aggregate gradations are similar to those of the corresponding aggregate packing characteristics (dry aggregate air voids, DAAV). A good relationship was observed between mix rutting and minimum voids in mineral aggregate and DAAV. Sensitivity analysis carried out with different aggregate gradations, design air void contents and tolerances, indicated that rut depth as well as TSR vary over a wide range for the combinations of mixes considered (all within the gradation, air void content and tolerance limits).Compared to the design air void content, aggregate gradation is found to have significantly larger effect on rut depth whereas both gradation and design air void content have similar effect on the TSR value. Using the results obtained from the present investigation, the Indian Marshall mix design criteria (MoRTH 2013) for stability and flow were revisited and new criteria are proposed. ARTICLE HISTORY

The present study aims to explain the dependency of different mechanical properties [penetration,... more The present study aims to explain the dependency of different mechanical properties [penetration, softening point, viscosity, and dynamic shear rheometer (DSR) parameters] and chemical parameters of reclaimed-asphalt pavement (RAP) binder. Viscosity grade (VG30) and VG40 virgin binders, RAP binder, and different VG30 + RAP blends, were investigated. Complex shear modulus and phase angle were measured at different temperatures, and creep compliance and percent recovery were evaluated at 60°C. Functional groups were evaluated using Fourier-transform infrared spectroscopy. Aging parameters ICO, ISO, and ICC increased with RAP proportion, whereas ICH decreased. No trend could be observed for OH/CH. The ICO, ISO, ICC, and ICH parameters correlated well with the mechanical properties of the blends. This study will be useful for better understanding of the relationship between the mechanical and chemical properties of RAP binders. The demonstration of the applicability of the rule of mixes for different mechanical and chemical parameters will be useful in the design of RAP mixes.

Reclaimed asphalt pavement (RAP) mixes generally have good moisture and rutting resistance. Howev... more Reclaimed asphalt pavement (RAP) mixes generally have good moisture and rutting resistance. However, the fatigue performance of the RAP mixes is a matter of concern because the RAP binder is generally brittle because of age hardening. Asphalt mixes can heal and recover from the fatigue damage caused by repeated wheel load application. The healing characteristics of the mix depend to some extent on the flow characteristics as well as the chemical makeup of the binders. Linear amplitude sweep (LAS) testing was performed for evaluating the fatigue performance of RAP binders. The fatigue and healing characteristics of different virgin-RAP binder blends were measured in an oscillation fatigue test conducted with varying rest periods using dynamic shear rheometer. The slopes of the fatigue life versus rest period plots were taken as indicators of the effect of rest period on fatigue life or healing indices (HI). Different rheological and chemical parameters measured in terms of surface free energy and the indices calculated using Fourier transform infrared (FTIR) spectroscopy correlated well with the healing potential of RAP binders.

Utilization of reclaimed asphalt pavement (RAP) materials in the asphalt layer construction has e... more Utilization of reclaimed asphalt pavement (RAP) materials in the asphalt layer construction has emerged as an important rehab ilitation option for asphalt pavements. The properties of reclaimed asphalt material will be different from those of the initial (virgin) asphalt mixture due to the aging of the binder. Resilient modulus is an important material parameter used for the design of pavements. The mechanical behaviour of th e mix and the binder is expected to be influenced by the chemical composition of the binder. In this study, the effect of the chemical composition of virgin an d reclaimed asphalt pavement (RAP) binders on the resilient modulus (Mr) of RAP mixes has been evaluated. This is done by testing d ifferent RAP mixes prepared using bitumen samples containing different proportions of RAP binder. The RAP mixes prepared using one aggregate gradation (mid-point gradation recommended by the Ministry of Road Transport and Highways for Bituminous Concrete-1) and different RAP contents (0, 15, 25, 35 and 45 %) with VG-30 as virgin binder, were tested for their resilient modulus values at different temperatures (15, 25 and 35°C) and frequencies (0.5, 1, 1.5 and 2 Hz). The chemical composition of the binder blends was evaluated with the help of Fourier transform infrared spectroscopy (FTIR). The relationship between the chemical indices and the rheological parameters has been examined. Ketones, aliphatics and aromatics are found to have good correlatio n with rheological properties. The chemical indices also are found to have good correlation with the resilient moduli of the mixes. .

The healing properties of bituminous mixes prepared using reclaimed asphalt pavement (RAP) materi... more The healing properties of bituminous mixes prepared using reclaimed asphalt pavement (RAP) material are different from those of virgin mixes because the chemical characteristics of RAP binder blends are different (depending on the extent of aging) compared to virgin binders. Very limited research work has been reported in the literature on the healing potential of RAP mixtures. The current study aims to examine the fatigue and healing characteristics of RAP mixtures with varying rest periods between loads. To this end, different blends of RAP and virgin binders (VG30) were prepared at varying proportions (0%, 15%, 25%, 35%, and 45%) of RAP material in mix. The fatigue lives of different RAP mixes were evaluated by varying the rest period (400, 650, 900, and 1,400 ms) between load pulses. The healing potential of the mixes was evaluated in terms of the slopes of the lines drawn between fatigue life and rest period. The fatigue life of a mix increased with increases in the proportion of RAP in the mix. The degree of healing indicated by the slope of log (fatigue life) versus log (rest period) line was found to depend on RAP content and rest period. Mix time lag (between the peaks of stress and strain), a viscoelastic property of the mixes, was determined from the stiffness modulus test. Different rheological and chemical characteristics of the binder blends and the time lag values of the mixes were correlated with the fatigue lives and healing indexes of the mixes. The Superpave binder fatigue parameter (G Ã sin δ) and the mix time lag were observed to have good correlation with the fatigue life of RAP mixes. Surface free energy and different aging indexes of the binders (ICO and ICH) showed good correlation with the healing index of the mixes. Flow (consistency) parameters, such as softening point and viscosity at 60°C, correlated well with the healing index. These correlations are expected to improve understanding of the fatigue and healing behavior of RAP mixes.

Rutting in asphalt mixes is a common type of distress in pavements with thick asphalt layers. It ... more Rutting in asphalt mixes is a common type of distress in pavements with thick asphalt layers. It is more severe for pavements subjected to high pavement temperatures, slow moving, uphill in mountainous areas and heavy traffic loads. A number of binder rutting parameters have been proposed by different researchers for ranking/grading of the binders in terms of their rutting resistance. The suitability of different binder rutting parameters for explaining the rutting resistance of unmodified binders as well as modified binders has been a topic of research for several years. Considering that asphalt mixes in pavement layers are subjected to different conditions of temperature, loading time/frequency and stresses/ strains, it is expected that these conditions will affect the way binder rutting resistance is judged. This study was conducted to examine the suitability of different binder rutting parameters for ranking of binders (unmodified as well as polymer and crumb rubber modified), distinguish modified binders from unmodified binders and for their ability to correlate with mix rutting. For this purpose, nine binders (four unmodified and five modified) were evaluated in oscillation and creep and recovery modes and various rutting parameters were examined. Oscillation tests were performed at varying frequencies and multiple stress creep recovery test was performed at different stress levels. The binder parameters were correlated with wheel tracking rut depths of bituminous concrete mix with NMAS of 19 mm. The frequency sensitivity of oscillation parameters and stress sensitivity of creep and recovery parameters were examined. J nr and% recovery have been found to be stress sensitive whereas |G⁄|, d and |G⁄|/sind were frequency sensitive. Some of the binder parameters have distinctly different ranges of values for unmodified and modified binders. The rankings produced by ZSV and J nr closely matched the ranking of the mixes identified based on wheel tracking rut depths. While both oscillation and MSCR parameters correlated well with mix rutting for unmodified binder mixes, the correlation of oscillation parameters with mix rut depth was not good for modified binder mixes.

The performance of conventional or reclaimed asphalt pavement (RAP) mixes depends on the properti... more The performance of conventional or reclaimed asphalt pavement (RAP) mixes depends on the properties of the virgin and RAP binders. The fundamental characteristics of different materials often are used to explain the mechanical performance. Surface free energy (SFE) is one such property that can be considered to explain the fracture and rutting performance and moisture damage resistance of bituminous binders and mixes. The correlation between different rheological properties of binders (virgin as well as RAP blends) and the SFE, determined by the sessile drop technique, was explored in this study. Two commonly used virgin binders and different virgin-RAP binder blends (prepared by varying the RAP content in the blend) were evaluated. Penetration, softening point, viscosity, Superpave rutting and fatigue parameters, multiple stress creep and recovery (MSCR), and linear amplitude sweep (LAS) test parameters of the binders were measured and correlated with SFE. Total cohesive surface free energy of the binders was found to correlate well with (1) cohesive/stiffness properties of the virgin and RAP binders represented by penetration, softening point, and G Ã (complex shear modulus); (2) the viscoelastic response indicated by phase angle and percentage strain recovered; (3) rutting resistance, represented by the Superpave rutting parameter (G Ã = sin δ) (where δ is phase angle) and non-recoverable compliance measured in the MSCR test; and (4) fatigue performance indicators such as the Superpave fatigue parameter (G Ã sin δ) and the fatigue life estimated from LAS test. The study clearly established the correlation between SFE and the mechanical parameters evaluated in the study and indicates the need to conduct a more-detailed and exhaustive experimental program to develop generalized relationships applicable to a wider range of binders than considered in this study. The fact that a single binder parameter measured by a simple method can explain multiple aspects of performance is a promising prospect.

Bituminous mixes are generally designed with gradation and air void content ranges adopted by dif... more Bituminous mixes are generally designed with gradation and air void content ranges adopted by different agencies. The selected gradation and binder content are permitted to vary within specified tolerance limits. This leads to the possibility of a wide range of mixes with varying mix performance. Thus, it is essential to understand the influence of variation in these parameters on the performance of mixes. The present study aims to examine the sensitivity of the mix performance to variation within the specified gradation and air void ranges. Five aggregate gradations were considered for designing mixes for the volumetric design criterion of 4% air voids. For three of the five gradations, mixes were also designed for two additional design air void contents, 3% and 5%. Rutting resistance of the mixes was measured using a rut tester and moisture resistance was evaluated in terms of Tensile Strength Ratio (TSR). The densification characteristics represented by voids in mineral aggregate (VMA) values of the mixes prepared using the five aggregate gradations are similar to those of the corresponding aggregate packing characteristics (dry aggregate air voids, DAAV). A good relationship was observed between mix rutting and minimum voids in mineral aggregate and DAAV. Sensitivity analysis carried out with different aggregate gradations, design air void contents and tolerances, indicated that rut depth as well as TSR vary over a wide range for the combinations of mixes considered (all within the gradation, air void content and tolerance limits).Compared to the design air void content, aggregate gradation is found to have significantly larger effect on rut depth whereas both gradation and design air void content have similar effect on the TSR value. Using the results obtained from the present investigation, the Indian Marshall mix design criteria (MoRTH 2013) for stability and flow were revisited and new criteria are proposed. ARTICLE HISTORY

The present study aims to explain the dependency of different mechanical properties [penetration,... more The present study aims to explain the dependency of different mechanical properties [penetration, softening point, viscosity, and dynamic shear rheometer (DSR) parameters] and chemical parameters of reclaimed-asphalt pavement (RAP) binder. Viscosity grade (VG30) and VG40 virgin binders, RAP binder, and different VG30 + RAP blends, were investigated. Complex shear modulus and phase angle were measured at different temperatures, and creep compliance and percent recovery were evaluated at 60°C. Functional groups were evaluated using Fourier-transform infrared spectroscopy. Aging parameters ICO, ISO, and ICC increased with RAP proportion, whereas ICH decreased. No trend could be observed for OH/CH. The ICO, ISO, ICC, and ICH parameters correlated well with the mechanical properties of the blends. This study will be useful for better understanding of the relationship between the mechanical and chemical properties of RAP binders. The demonstration of the applicability of the rule of mixes for different mechanical and chemical parameters will be useful in the design of RAP mixes.

Reclaimed asphalt pavement (RAP) mixes generally have good moisture and rutting resistance. Howev... more Reclaimed asphalt pavement (RAP) mixes generally have good moisture and rutting resistance. However, the fatigue performance of the RAP mixes is a matter of concern because the RAP binder is generally brittle because of age hardening. Asphalt mixes can heal and recover from the fatigue damage caused by repeated wheel load application. The healing characteristics of the mix depend to some extent on the flow characteristics as well as the chemical makeup of the binders. Linear amplitude sweep (LAS) testing was performed for evaluating the fatigue performance of RAP binders. The fatigue and healing characteristics of different virgin-RAP binder blends were measured in an oscillation fatigue test conducted with varying rest periods using dynamic shear rheometer. The slopes of the fatigue life versus rest period plots were taken as indicators of the effect of rest period on fatigue life or healing indices (HI). Different rheological and chemical parameters measured in terms of surface free energy and the indices calculated using Fourier transform infrared (FTIR) spectroscopy correlated well with the healing potential of RAP binders.

Utilization of reclaimed asphalt pavement (RAP) materials in the asphalt layer construction has e... more Utilization of reclaimed asphalt pavement (RAP) materials in the asphalt layer construction has emerged as an important rehab ilitation option for asphalt pavements. The properties of reclaimed asphalt material will be different from those of the initial (virgin) asphalt mixture due to the aging of the binder. Resilient modulus is an important material parameter used for the design of pavements. The mechanical behaviour of th e mix and the binder is expected to be influenced by the chemical composition of the binder. In this study, the effect of the chemical composition of virgin an d reclaimed asphalt pavement (RAP) binders on the resilient modulus (Mr) of RAP mixes has been evaluated. This is done by testing d ifferent RAP mixes prepared using bitumen samples containing different proportions of RAP binder. The RAP mixes prepared using one aggregate gradation (mid-point gradation recommended by the Ministry of Road Transport and Highways for Bituminous Concrete-1) and different RAP contents (0, 15, 25, 35 and 45 %) with VG-30 as virgin binder, were tested for their resilient modulus values at different temperatures (15, 25 and 35°C) and frequencies (0.5, 1, 1.5 and 2 Hz). The chemical composition of the binder blends was evaluated with the help of Fourier transform infrared spectroscopy (FTIR). The relationship between the chemical indices and the rheological parameters has been examined. Ketones, aliphatics and aromatics are found to have good correlatio n with rheological properties. The chemical indices also are found to have good correlation with the resilient moduli of the mixes. .

The healing properties of bituminous mixes prepared using reclaimed asphalt pavement (RAP) materi... more The healing properties of bituminous mixes prepared using reclaimed asphalt pavement (RAP) material are different from those of virgin mixes because the chemical characteristics of RAP binder blends are different (depending on the extent of aging) compared to virgin binders. Very limited research work has been reported in the literature on the healing potential of RAP mixtures. The current study aims to examine the fatigue and healing characteristics of RAP mixtures with varying rest periods between loads. To this end, different blends of RAP and virgin binders (VG30) were prepared at varying proportions (0%, 15%, 25%, 35%, and 45%) of RAP material in mix. The fatigue lives of different RAP mixes were evaluated by varying the rest period (400, 650, 900, and 1,400 ms) between load pulses. The healing potential of the mixes was evaluated in terms of the slopes of the lines drawn between fatigue life and rest period. The fatigue life of a mix increased with increases in the proportion of RAP in the mix. The degree of healing indicated by the slope of log (fatigue life) versus log (rest period) line was found to depend on RAP content and rest period. Mix time lag (between the peaks of stress and strain), a viscoelastic property of the mixes, was determined from the stiffness modulus test. Different rheological and chemical characteristics of the binder blends and the time lag values of the mixes were correlated with the fatigue lives and healing indexes of the mixes. The Superpave binder fatigue parameter (G Ã sin δ) and the mix time lag were observed to have good correlation with the fatigue life of RAP mixes. Surface free energy and different aging indexes of the binders (ICO and ICH) showed good correlation with the healing index of the mixes. Flow (consistency) parameters, such as softening point and viscosity at 60°C, correlated well with the healing index. These correlations are expected to improve understanding of the fatigue and healing behavior of RAP mixes.

Rutting in asphalt mixes is a common type of distress in pavements with thick asphalt layers. It ... more Rutting in asphalt mixes is a common type of distress in pavements with thick asphalt layers. It is more severe for pavements subjected to high pavement temperatures, slow moving, uphill in mountainous areas and heavy traffic loads. A number of binder rutting parameters have been proposed by different researchers for ranking/grading of the binders in terms of their rutting resistance. The suitability of different binder rutting parameters for explaining the rutting resistance of unmodified binders as well as modified binders has been a topic of research for several years. Considering that asphalt mixes in pavement layers are subjected to different conditions of temperature, loading time/frequency and stresses/ strains, it is expected that these conditions will affect the way binder rutting resistance is judged. This study was conducted to examine the suitability of different binder rutting parameters for ranking of binders (unmodified as well as polymer and crumb rubber modified), distinguish modified binders from unmodified binders and for their ability to correlate with mix rutting. For this purpose, nine binders (four unmodified and five modified) were evaluated in oscillation and creep and recovery modes and various rutting parameters were examined. Oscillation tests were performed at varying frequencies and multiple stress creep recovery test was performed at different stress levels. The binder parameters were correlated with wheel tracking rut depths of bituminous concrete mix with NMAS of 19 mm. The frequency sensitivity of oscillation parameters and stress sensitivity of creep and recovery parameters were examined. J nr and% recovery have been found to be stress sensitive whereas |G⁄|, d and |G⁄|/sind were frequency sensitive. Some of the binder parameters have distinctly different ranges of values for unmodified and modified binders. The rankings produced by ZSV and J nr closely matched the ranking of the mixes identified based on wheel tracking rut depths. While both oscillation and MSCR parameters correlated well with mix rutting for unmodified binder mixes, the correlation of oscillation parameters with mix rut depth was not good for modified binder mixes.