Laboratory evaluation of stiffness, low-temperature cracking, rutting, moisture damage, and fatigue performance of WMA mixes

Despite the environmental and compaction benefits of warm mix asphalt (WMA), several researchers have expressed concerns over laboratory and field performances of WMA mixes. In this study, a wide range of laboratory tests, namely, dynamic modulus, creep compliance, fatigue, moisture damage, and rutting, was conducted to evaluate the performance of different types of WMA mixes. For this purpose, three WMA mixes, consisting of one mix produced using a zeolite-based WMA additive (containing water), one surface course mix, and one base course mix, the latter two produced with a chemical-based WMA additive with surfactant technology, were collected from different field projects in Texas. In addition, three hot mix asphalt (HMA) mixes with aggregate gradations similar to those of the collected WMA mixes were produced in the laboratory to compare the performance of WMA and HMA mixes. Overall, the WMA mixes yielded lower stiffness, reduced potential of low-temperature cracking, lower fatigue resistance, and a higher rutting potential compared with their HMA counterparts. However, a mixed trend of moisture-induced damage potential was observed for WMA and HMA mixes, when evaluated using retained tensile strength ratio (TSR) and stripping inflection point (SIP) obtained from the Hamburg wheel tracking (HWT) test. In other words, no correlation was found between TSR and SIP values, indicating that passing a TSR test does not guarantee better performance of a mix when tested using an HWT. The results from this study reveal that performance of a WMA mix widely depends on the technology and the type of other additives (e.g. anti-stripping agent) used. The findings of this study are expected to be useful to pavement professionals to better understand the performance of WMA mixes and to develop a database of input parameters for the Mechanistic-Empirical Pavement Design Guide

Micro-Structural Analysis of Moisture-Induced Damage Potential of Asphalt Mixes Containing RAP

This study was undertaken to evaluate the effects of reclaimed asphalt pavement (RAP) on moisture-induced damage potential of asphalt mixes using two different approaches: (i) micro-structural analysis of aggregate-asphalt bonding based on the surface free energy (SFE), and (ii) mechanical testing of asphalt mixes using retained indirect tensile strength ratio (TSR) and Hamburg wheel tracking (HWT). This study involved two phases. In the first phase, the SFE (non-polar, acidic and basic) components of a virgin PG 64-22 binder mixed with 0, 25, and 40 % of simulated RAP binder and aggregates (limestone, rhyolite, RAP extracted aggregate) were measured using a dynamic contact angle (DCA) device and a universal sorption device (USD), respectively. Thereafter, composite work of adhesion and composite work of debonding, and composite energy ratios for each combination of asphalt binder and aggregates were determined to assess the moisture-induced damage potential of the mixes containing different percentages of RAP (0, 25, and 40 %). In the second phase, the TSR and HWT tests were conducted on asphalt mixes containing different percentages of RAP (0, 25, and 40 %) to evaluate their moisture-induced damage potential. Both the methods showed that the moisture-induced damage potential decreased with increasing amount of RAP in asphalt mixes. A strong correlation was found to exist between the moisture-induced damage potential predicted using the micro-structural method and laboratory performance tests. It was found that the micro-structural energy approach, as a mechanistic framework, can be successfully used as an indicator of moisture-induced damage potential of the asphalt mixes. It is expected that the present study would be helpful in understanding the moisture-induced damage potential of flexible pavements containing RAP

Effect of Shape Parameters and Gradation on Laboratory-Measured Permeability of Aggregate Bases

The current study was undertaken to evaluate the effect of aggregate shape parameters (i.e., angularity, sphericity, form, and texture) and gradation on the permeability of commonly used aggregate bases in Oklahoma. Aggregates used in this study were collected from three different quarries. For each aggregate type, upper and lower limits of three different gradations, modified AASHTO #57, Oklahoma Aggregate Association (OKAA) Type M, and Oklahoma DOT (ODOT) Type A, were selected. Permeability of 18 different combinations of aggregate types and gradations (three aggregate types x three gradations x two gradation limits) were tested using a falling-head permeability approach. For a selected gradation, the lower limit exhibited higher permeability values than the upper limit. Also, permeability was found to increase with an increase in effective diameter and void ratio. An increased coefficient of uniformity and fine content resulted in lower permeability, as expected. Furthermore, the shape parameters of different aggregate types were measured using an aggregate imaging system (AIMS). The coefficient of permeability was found to increase with reduced gradient angularity and increased sphericity. The texture index was found to have minimal impact on the coefficient of permeability. A regression model was developed using aggregate shape and gradation parameters to estimate permeability of aggregate bases. (C) 2014 American Society of Civil Engineers

Laboratory characterisation of asphalt mixes containing RAP and RAS

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

Mechanistic Evaluation of the Effect of WMA Additives on Wettability and Moisture Susceptibility Properties of Asphalt Mixes

This study used a mechanistic framework (i.e., surface free energy) to evaluate the moisture susceptibility of warm mix asphalt (WMA) with three different WMA additives, namely, Sasobit, Advera, and Evotherm. The surface free energy (SFE) components of modified PG64-22 asphalt binder with different percentages of WMA additives and selected aggregates were measured in the laboratory. The wettability, the work of adhesion, the work of debonding, and energy ratios were estimated in order to assess the moisture-induced damage potential of combinations of modified asphalt binders and different aggregates. The results indicate that Sasobit and Advera are able to reduce the moisture susceptibility potential of the mixes, but their use is not recommended with highly acidic aggregates such as granite. Evotherm resulted in the highest increases in wettability, total surface free energy, and increased work of adhesion and a reduction in the work of debonding, resulting in a better possible aggregate coating with asphalt binder and lower moisture susceptibility with all types of tested aggregates relative to those of other WMA additives. Furthermore, tensile strength ratio (TSR) tests were conducted on Advera and Evotherm-modified and neat (unmodified) asphalt mixes, and the results were compared with those from the SFE test. It was found that the SFE approach is a better indicator of moisture susceptibility than the traditional TSR test. The findings of the present study would help the highway engineers and agencies to better understand the moisture damage potential of flexible pavements constructed with WMA technologies

An alternative analysis of indirect tensile test results for evaluating fatigue characteristics of asphalt mixes

Fatigue cracking is one of the major distresses responsible for the failure of asphalt pavements. The widely-accepted Superpave (R) volumetric mix design method does not consider screening the asphalt mixes based on their fatigue resistance. Based on a survey conducted in this study, it was found that many state Departments of Transportations (DOTS) do not perform a fatigue test during mix design, mainly due to lack of specialized equipment, trained personnel and consensus about the most appropriate test method. This present study was undertaken to suggest a simple, quick and effective fatigue test method and the corresponding data analysis procedure. It was found that the indirect tension test, which is usually conducted in the DOTs on a regular basis, can be used to characterize the fatigue resistance of asphalt mixes as well. A simplified data analysis approach has been proposed. The fatigue resistance of asphalt mixes can be determined by using a newly derived parameter called Fatigue Index (f(i)). Fatigue resistance of five different asphalt mixes were evaluated using this new parameter, f(i). It was found that the fi parameter were able to statistically discriminate five selected asphalt mixes with respect to their fatigue resistance. The effectiveness of the f(i) parameter was verified by investigating its correlations with the results of the semi-circular bend and four-point beam fatigue test results. Published by Elsevier Ltd

Comparison of laboratory performance of asphalt mixes containing different proportions of RAS and RAP

Despite environmental and economic advantages associated with incorporating recycled asphalt shingles (RAS) and reclaimed asphalt pavement (RAP) in hot-mix asphalt (HMA), concerns focus on fatigue and low-temperature cracking potential of pavements containing RAS and RAP. This study was undertaken to identify the areas in need for research through conducting a national survey among departments of transportation and to evaluate the effects of RAS and RAP on fatigue, low-temperature cracking and stiffness of HMA. National survey results indicated that while the fatigue cracking is the major concern when RAS and/or RAP are used in mixes, no specific test is recommended for fatigue evaluation of these mixes at the mix design stage. It was found that, fatigue life of mixes with a non-polymer-modified binder containing a blend of 5% RAS and 5% RAP led to the maximum increase in fatigue life. However, incorporation of 6% RAS decreased the fatigue life of mixes, when compared with virgin mix. Also, it was found that addition of RAS and/or RAP to asphalt mixes increased their dynamic moduli which may result in a better rutting performance. From creep compliance test results it was concluded that use of RAS and/or RAP may lead to a higher low-temperature cracking potential when compared with the virgin mixes. Findings of this study can be used to develop/update guidelines/special provisions for design of HMA containing RAS and RAP. (C) 2016 Published by Elsevier Ltd