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The present study aimed to understand the impact of inert-active filler combinations on cracking and resistance of asphalt mastic using work of fracture approach. A control grade asphalt binder (VG-30) and three fillers (inert: basalt (B); active: hydrated lime (HL) Nano hydrated lime (NHL)) were considered. The HL and NHL were added from 0% to 20% at 5% increment rate by weight of binder. The dosages of B were adjusted with respect to specific filler to binder ratios (0.6 to 1.2). The study focused on the influence of NHL on cracking resistance of mastic by means of ductile and fracture behaviour, evaluated using double edge notched tension test (DENT) at intermediate temperature condition. Findings indicated a beneficial impact in improving the cracking and fracture resistance of mastic due to reduction in the size of HL (NHL). The results signify that both HL and NHL can enhance the resistance to withstand ductile failure and fracture. Also, mastic prepared with B-NHL can be less susceptible to fracture over B-HL and hence, possessed improved ductile properties. Consequently, a lower dosage of NHL found to be superior over a higher dosage of HL in improving the cracking and fracture resistance of asphalt mastic. [ABSTRACT FROM AUTHOR]

This study explored a new simple monotonic Marshall rutting test (Marshall-RT) to evaluate the rutting resistance of asphalt mixtures. The Marshall-RT test setup combines the Marshall fixture (at the bottom) and the IDT fixture (at the top). The rutting resistance of asphalt mixtures was evaluated using peak load (Pmax) and work done for the deformation damage obtained from the load-displacement curve. Nine plant-produced asphalt mixtures having different types of binders (unmodified, crumb rubber modified binder (CRMB)), and polymer modified binder (PMB)) and gradations having different nominal maximum aggregate sizes (NMAS) were evaluated. The Marshall-RT test parameters (i.e. Pmax and $W_{P_{{\rm max}}}$ W P m a x ) have shown a strong correlation with fundamental (i.e. Flow Number (FN)), simulative (i.e. Hamburg wheel tracking test (HWTT)), and simple monotonic (i.e. Ideal rutting test (IDEAL-RT)) rutting tests. Moreover, the Marshall-RT test has shown good repeatability, the highest differentiation potential, and consistent ranking with other rutting tests. Furthermore, for high traffic levels (i.e. 100 MSA (Million Standard Axle)), at 50°C preliminary minimum threshold criteria were proposed for Marshall-RT (Pmax and $W_{P_{{\rm max}}}$ W P m a x ), and IDEAL-RT (RTIndex) as 5 kN, 14 kN-mm, and 90, respectively, to avoid premature rutting failure. Thus, the newly developed monotonic Marshall-RT test can also be used as a surrogate simple performance test to estimate the rutting potential of asphalt mixtures during the mix design and plant production phases as quality control (QC)/quality assurance (QA). [ABSTRACT FROM AUTHOR]

Higher energy requirement for asphaltic layer construction with asphalt binder containing reactive elastomeric terpolymer (RET) and poly phosphoric acid (PPA) can be addressed to a greater extent with the addition of warm mix asphalt (WMA) additives. However, moisture damage related problem is one of the concerns with such addition, which further aggravates with an increase in ageing level. The addition of lime may help in addressing moisture damage related problems in such cases. Previous research works show that based on the interaction between asphalt binder and particular WMA additive, the viscosity may undesirably increase also. So far, the influence of different WMA additives (wax, chemical surfactant (CS) and water-based (WB)) on the workability related properties of asphalt binder containing RET and PPA is not understood. It is also not clear if such warm mix additives with/without lime can help in improving long-term bonding with different aggregate types or not. Therefore, this research work aimed at identifying the appropriate WMA additive (with/without lime) which can help in (a) addressing the workability related problem and (b) improving long-term bonding with different aggregate types. To achieve this, different types of WMA additives (with/without lime) were added to RET and PPA modified binder. Viscosity-based measurement and chemical analysis using Fourier transform infrared spectroscopy were performed to understand workability and underlying chemical changes. Results indicated that although wax and CS-based warm mix additives can help in reducing energy demand, the addition of WB warm mix additive will have a negative impact from the workability perspective. Likewise, dynamic contact angle for different binder combinations was measured to evaluate the surface free energy components, which further helped to examine the long-term bonding with different aggregate types. Among different WMA additive types, the use of wax-based WMA additive was found to be most effective in improving compatibility with different aggregate types. Also, irrespective of the binder combination, the addition of lime improved the long-term bonding with considered aggregate types. [ABSTRACT FROM AUTHOR]

Moisture-induced stress tester (MIST) has been recently developed to simulate the dynamic stresses that cause moisture damage. In the current study, asphalt mixes containing 0%, 10%, 20%, 30%, and 40% RAP were subjected to 0, 1000, 2000, 3500, 5000, and 10,000 stress cycles of MIST and IDT strength test was conducted. The test results were analysed using the concepts of survival and atrophy to propose a damage mechanism and suggest an alternative to TSR. In unconditioned state, the control mix depicted a superior survival as compared to RAP mixes with <20% RAP, and an inferior survival as compared to RAP mixes with >20% RAP. Rate of atrophy indicated that the control mix has a higher instantaneous potential to fail (2.34 MPa in unconditioned state for control mix) than RAP mixes (0.90, 1.07, 1.13 and 1.21 MPa for 10%, 20%, 30%, and 40% RAP mix, respectively, in the unconditioned state). Stiffness and peak stress carrying capacity for control mix in unconditioned state was 310.87 and 1.47 MPa, respectively, which was higher than RAP mixes. For RAP mixes, MDRs based on rate of atrophy and TSR were > 80% thereby indicating that RAP has the potential to improve the moisture-induced damage resistivity of asphalt mixes. [ABSTRACT FROM AUTHOR]

The present study was undertaken to evaluate the effects of different warm mix asphalt (WMA) additives on bonding behaviour of asphalt binder and aggregates using two different approaches: (i) The surface free energy (SFE) method and (ii) The asphalt bond strength (ABS) test. The study involved two phases, the first phase involved measurement of the SFE of control, and WMA (Sasobit, Advera, and Rediset) modified asphalt binders by the Wilhelmy plate method, and aggregate's (limestone and granite) SFE by the dynamic vapour sorption (DVS) method. Thereafter, bond energies were computed using SFE method for understanding the bonding behaviour of WMA modified binders with different aggregates in dry and wet conditions. The second phase involved direct measurement of bond strength and failure pattern between asphalt binder and aggregate combinations by the ABS test in both dry and wet conditions. Furthermore, bond strength of all combination of asphalt binder and aggregates were compared by SFE and ABS methods. The results indicated that Sasobit and Advera effectively contributed in enhancing the cohesive energy of control binder, whereas Rediset decreased the cohesive energy of control binder. Bond strength of WMA modified binder depends on both aggregate type and WMA additives. The results show that asphalt binder with Sasobit can have better bonding performance with limestone (basic) aggregate, whereas, asphalt binder after addition of Advera showed better bonding performance with granite (acidic) aggregate. After wet conditioning, asphalt binders with limestone (basic) aggregate combinations exhibited cohesive failure showing minimal effect of water on bond strength compared to binders with granite (acidic) aggregate combinations which showed adhesive failure. The comparison of bond strength by mechanical ABS test and energy based SFE methods have shown a fair correlation between bond strength ratio (BSR) and energy ratio (ER). [ABSTRACT FROM AUTHOR]

This study evaluates important functional characteristics such as dispersion, aging resistivity potential, temperature susceptibility, and high temperature storage stability of Carbon Nano Tube (CNT) modified asphalt binders. CNT content was varied as 0%, 0.4%, 0.75%, 1.5% and 2.25% by weight of control binder (AC-10). Scanning Electron Microscopic (SEM) images was captured to get direct observation of CNT dispersion. Viscosity was further measured to understand the workability and dispersion characteristics. Further, viscosity temperature susceptibility parameters (A and VTS), activation energy and Penetration Index (PI) values were estimated to evaluate temperature susceptibility. SEM images and viscosity data showed that CNT content up to 1.5% may be recommended without potential problem of entanglement/clustering. Similarly, analysis of softening point, complex modulus and phase angle data showed positive effect of CNT on aging resistivity potential. Such improvement in functional characteristics can be attributed to high specific surface area (190 m2/gm), higher aspect ratio (length/diameter = 645) and excellent mechanical properties of CNT. Likewise, high temperature storage stability was evaluated using softening point and Multiple Stress Creep Recovery (MSCR) tests. Though softening point test method showed sufficiently stable nature of CNT under high temperature storage condition, settling of CNT (unstable nature) was observed from MSCR testing approach. [ABSTRACT FROM AUTHOR]

In this study, geometric features (e.g. road and shoulder width), pavement characteristics (e.g. shoulder type, skid number, and international roughness index), and traffic parameters (e.g. posted speed limit and average daily traffic) were extensively analyzed to identify the significant predictors and develop better-fit 85th percentile speed prediction models for the tangent sections of two-lane rural highways. Three models, representing all highways, lower speed limit highways, and higher speed limit highways, were developed using stepwise multiple linear regression analysis. About 80% data from 251 locations in the State of Oklahoma, United States, was used in model development and 20% for validation. The all highways model is the best-fit among the three. Two most significant parameters of this model are posted speed limit and skid number. Additionally, international roughness index is significant in the higher speed limit highway model. The lower speed limit highway model depends only on the posted speed limit. [ABSTRACT FROM AUTHOR]

The present study evaluates the effects of three different stages of crushing mechanism, namely two stage (2S), three stage (3S) and four stage (4S) on various morphology parameters (i.e. angularity, texture, flatness & elongation, sphericity and form2D) of aggregates. The 2S crushing consisted of primary and secondary crushers as Jaw and HSI (horizontal shaft impactor), respectively, while 3S crushing was composed of primary, secondary and tertiary crushers as Jaw, Jaw and HSI, respectively. In other word, 3S consisted of an additional jaw crusher compared to 2S crushing. Likewise, 4S crushing had primary, secondary, tertiary and quaternary crushers as Jaw, Jaw, HSI and VSI (vertical shaft impactor), respectively. The 4S had an additional VSI crusher to 3S crushing. Three coarse and three fine aggregate sizes were used in the study. A digital device, Aggregate Image Measurement System was used to measure various morphology parameters of aggregates and to assess the effects of stage crushing. The coarse aggregates were subjected to angularity, texture, sphericity and flatness and elongation, while fine aggregates were studied for angularity and form2D. A systematic statistical analysis was conducted to compare the mean value of aggregates shape parameters and draw logical conclusions. It was observed that effects of crushing on aggregate shape are a cumulative function of stage crushing, crushing mechanism and aggregate size. The outcome of the present study may be helpful in understanding effects of stage crushing mechanism on shape parameters of aggregates for quality production. Further, the study can assist in selection of an appropriate source of aggregate and crusher health monitoring via morphological characterisation of aggregates. [ABSTRACT FROM AUTHOR]

Crumb rubber modified (CRM) binder has high working temperatures, which may be reduced with addition of warm mix additives (WMA). The dynamic mechanical analysis of CRM binder containing three different WMA additives, namely Fischer–Tropsch wax-based (FT), water-based (WB) and chemical surfactant-based (CS) additive, was undertaken in the present study. The CRM binder was blended with different percentages (by weight of asphalt binder) of WMA additives, i.e. FT (1, 2 and 3%), WB (4, 6 and 8%) and CS (1, 2 and 3%). The viscosity, rutting and fatigue performance of CRM binder with and without WMA additives were evaluated using Brookfield viscosity, multiple stress creep recovery and linear amplitude sweep tests, respectively. The FT modification effectively reduced the viscosity of CRM binder, while the inclusion of CS showed similar viscosity and WB increased the viscosity of CRM binder. The WB modification observed to create foaming effect in asphalt binder. The FT- and WB-modified CRM showed same High Superpave performance grade (PG), however, the addition of CS degraded high PG of CRM binder (from PG88 to PG82). The CRM binder showed reduced Jnr value and improved R-value after FT and WB modification, indicating improved rutting resistance. Whereas, CS-modified CRM indicating poor rutting performance (high Jnr and low R). Asphalt binder combinations showed significantly different rutting performance parameters (Jnr and R-value), whereas they were graded as E. Therefore grading of asphalt binders based on AASHTO MP 19 should be relooked. All WMAs improved the Nf i.e. fatigue resistance of CRM binder. The 2% FT dosage observed to be optimum for CRM binder. The study showed that selection of WMA additives should not only be based on viscosity criterion but also rheological performance parameters are to be looked into for making appropriate conclusions about their effectiveness. [ABSTRACT FROM AUTHOR]

Due to its economic and environmental benefits, using reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS) in new hot-mix asphalt (HMA) has become an integral part of today's asphalt industry. The advantages of using RAP and RAS in HMA are not limited to economic and environmental benefits, and may result in improving a number of mix performance characteristics including rutting and resistance to moisture-induced damage. Despite aforementioned benefits, concerns over premature pavement distresses resulting from using RAP and RAS limit their usage in HMA. Furthermore, because of the lack of mechanistic performance data, use of new mixes containing RAP and RAS remains limited. Therefore, the present study was undertaken to investigate the effects of using different amounts of RAP and RAS on laboratory performance of HMA, and to generate valuable input design parameters for implementation of the mechanistic-empirical pavement design guide (M-EPDG), using local materials. Four types of base course mixes containing 0% RAP, 25% RAP, 40% RAP and 20% RAP+5% RAS, and three types of surface course mixes containing 0% RAP, 25% RAP and 20% RAP+5% RAS were tested. Laboratory tests were conducted to evaluate stiffness, low-temperature cracking, fatigue life, rut and moisture-induced damage potential of the mixes. It was found that dynamic modulus and creep compliance of the asphalt mixes increase and decrease, respectively, with an increase in the amount of RAP and/or RAS used in the mix. Fatigue life was found to increase with increasing RAP content up to 25%, and to decrease when the RAP and/or RAS content exceeded 25%, or when RAS was used in the mix. It should be noted that this conclusion was drawn based on a 15% increment in RAP content. Hamburg wheel tracking (HWT) test results showed increased resistance to rutting and moisture-induced damage, with an increase in the amount of RAP and/or RAS. However, the tensile strength ratio test results were not confirmed by HWT. The findings of this study are expected to be helpful in understanding the effects of using different amounts of RAP and RAS on the performance of asphalt mixes produced using local materials. Furthermore, valuable design input parameters, developed in this study for new mixes containing RAP and RAS, may be used for calibration of the M-EPDG input parameters, with local materials. [ABSTRACT FROM AUTHOR]

The performance of hot mix asphalt (HMA) greatly depends upon the aggregate shape characteristics, namely angularity, two-dimensional (2D) form, texture and sphericity. This paper presents the effect of plant production and sample preparation methods on the shape characteristics of coarse aggregate (CA) and fine aggregate (FA). Six different types of aggregates, namely original aggregate (OA), plant mix (PM) aggregate and aggregate retrieved from specimens compacted at four different air voids [6% (AV6), 8% (AV8), 10% (AV10) and 12% (AV12)] were used. Each type of aggregate was divided into two different sizes: coarse and fine. The sizes of CAs were passing a 19 mm sieve and retained on a 12.5 mm sieve (CA12), and passing a 9.5 mm sieve and retained on a 4.75 mm sieve (CA4). Similarly, the sizes of FAs were passing a 4.75 mm sieve and retained on a 2.36 mm sieve (FA8), and passing a 2.36 mm sieve and retained on a 1.18 mm sieve (FA16). The Aggregate Image Measurement System was used to measure the shape characteristics of each size of aggregate. A statistical method called analysis of variance was used to compare the mean of shape parameters. The analyses of the results indicate that the texture and 2D form of CA particles change significantly when they undergo different processes of HMA production and sample preparation. No significant difference was observed in angularity and sphericity for all types of CAs. Similarly, no significant changes were observed in FA shape parameters. The effect of aggregate size on the shape parameters is also discussed. It is expected that the present study would develop a better understanding of HMA mixture behaviour in light of aggregate properties pertaining to aggregate shape. [ABSTRACT FROM PUBLISHER]