Rouzbeh Ghabchi

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.

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.

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

AbstractThe 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×three gradations×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 o...

Effects of Regular-Sized and Nanosized Hydrated Lime on Binder Rheology and Surface Free Energy of Adhesion of Foamed Warm Mix Asphalt

Although foamed warm mix asphalt (WMA) offers many potential benefits, there are some performance concerns. Researchers are making efforts to study the usage of different additives as modifiers to meet standard specifications of asphalt mixes for paving applications; however, selection of an appropriate modifier is extremely important to better performing asphalt. In recent years, there has been a dramatic interest in research, technology, and production of nanoparticles (nanomaterials). The current study was conducted with the objective of addressing the potential benefits of using nanosized hydrated lime (NHL) compared with regular-sized hydrated lime (RHL) as a modifier to the WMA produced using an additive. This paper documents the findings of the effect of NHL and RHL on the asphalt binder rheology and provides an insight into their effect on the free energy of adhesion of the asphalt binder-aggregate system. The rheology of asphalt binder was investigated based on the dynamic shear rheometer (DSR) test, whereas the free energy of adhesion was quantified based on the surface free energy (SFE) measurements of the asphalt binders and aggregate. Rheology results showed that the addition of NHL in smaller amounts can provide improved characteristics as compared with RHL. In concurrence with the rheology results, the free energy of adhesion showed that the NHL is more competitive compared with the RHL. Foaming the asphalt binder adversely affects the asphalt binder-to-aggregate adhesion.

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 todays 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.

Effect of gradation and source properties on stability and drainability of aggregate bases: a laboratory and field study

A combined laboratory and field study was undertaken to evaluate the effect of gradation on resilient modulus (M R) and falling weight deflectometre (FWD) modulus (M FWD) as measures of stability and coefficient of permeability (k) as an indicator of drainability of aggregate bases. Aggregates from three different sources in Oklahoma and three gradations consisting of M-AASHTO #57, ODOT Type A and OKAA Type M were used. M R and k tests on compacted aggregate specimens were conducted in the laboratory. Also, a 152.4-m long test section was constructed with the aforementioned gradations and FWD and in-situ falling head permeability tests were conducted periodically. Results showed that denser gradations resulted in higher M R and M FWD and lower k values, both in the laboratory and in the field. M FWD and field k values were found to increase and decrease, respectively, with time, possibly due to traffic-induced compaction. Regression models were developed to estimate M R and k in terms of gradation and source properties of aggregates.

A Laboratory Study of Warm Mix Asphalt for Moisture Damage Potential Using Surface Free Energy Method

The moisture damage potential of an asphalt mix is generally determined using tensile strength ratio test (TSR), according to AASHTO T 283 test method. The basis of evaluating moisture damage potential of a mix using TSR is an empirical approach which does not represent moisture failure mechanism in real life of an asphalt pavement. This shortcoming of TSR method is more of concern when it comes to moisture susceptibility of warm mix asphalt (WMA), which is known for a possibbly higher moisture susceptibility. Recently, surface free energy (SFE) approach has been used as a mechanistic-based indicator of moisture susceptibility of the asphalt mixes.The present study was undertaken to evaluate the moisture susceptibility of Advera ® (synthetic zeolite) modified WMA mix using SFE approach. The SFE components of a selected asphalt binder, modified with different percentages of Advera ® and selected aggregates were measured in the laboratory and different energy parameters were calculated for the aggregate-asphalt binder systems. It was found that addition of Advera ® does not make the mix prone to moisture damage, , however, this additive did not show favourable properties with highly acidic aggregates like granite.

Numerical Analysis for a Realistic Support Design: Case Study of the Komurhan Tunnel in Eastern Turkey

AbstractThe aim of this study was to highlight the importance of the numerical approach in realistic support design for tunneling. The Komurhan Tunnel, which is to be constructed between the Elazig–Malatya highway, located east of Elazig City in eastern Turkey, was selected as the application site of this study. The lithology of this area consists of Late Cretaceous–age ophiolitic rocks, known as Komurhan ophiolites. Field and laboratory studies were performed to determine the geotechnical properties of rock mass and intact rock materials. Empirical and numerical approaches were used, and the results were compared, focusing on tunnel design safety. The rock mass was classified in terms of the rock mass rating (RMR), rock mass index (RMi), Austrian tunneling method, and geological strength index rock mass classification systems, and then the support systems for the tunnel were determined accordingly. The support systems obtained from the classification systems were also analyzed using software based on the...

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 performance grade (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 moistureinduced 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.

Influence of Tensile Strain at Failure on Flexural Properties of a Cementitiously Stabilized Subgrade Soil

AbstractFlexural properties of subgrade soils play an important role in the overall performance of pavements. In this study, a series of laboratory tests and finite-element analysis were conducted to evaluate the effect of the stress-strain behavior of cementitiously stabilized soil (CSS) on its flexural fatigue life. Three different amounts of cement kiln dust (CKD), namely 5, 10, and 15% (by weight), were mixed with soil, and beam specimens were prepared using these three mixes. Modulus of rupture (MoR) tests were conducted on the prepared specimens to measure flexural strength and tensile strain at failure. Four-point bending beam fatigue tests were conducted on CSS specimens to evaluate their flexural modulus and fatigue life of each mix. Also, finite-element models of the MoR tests were developed using a concrete damage plasticity model for the CSS material. The MoR test results showed that the flexural strength increases with an increase in the amount of CKD. However, the failure strain was not foun...