Traditional asphalt mixture design practices recognize the need for laboratory parameters, which relate to field performance throughout the life of the pavement. However, many design methodologies consider volumetric proportions and strength characteristics of the mixtures, which may not provide adequate insight into mixture performance. Laboratory testing that can ascertain an asphalt mixture's capability to resist common distresses is needed to complement current design methodologies. Distresses commonly associated with flexible pavement failure are fatigue cracking and permanent deformation (rutting). The Louisiana Department of Transportation and Development proposed specification modifications for 2013 to address the need for balanced mixtures (i.e., mechanistic laboratory evaluation to complement volumetric criteria). This paper presents Louisiana's experience with specification modifications to develop a balanced mixture as evaluated through the use of the Hamburg loaded wheel tester (HLWT) and semicircular bend (SCB) tests. Laboratory performance of 11 mixtures produced with the 2013 proposed specification modifications was compared with that of 40 mixtures produced under the 2006 specifications. Laboratory tests included HLWT and SCB to evaluate rutting and intermediate temperature cracking, respectively. The research showed that specification modifications did not adversely affect rutting or fatigue cracking resistance of the mixtures.

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The Louisiana Department of Transportation and Development (DOTD) began developing open-graded friction course (OGFC) mixtures in the late 1960s and early 1970s. Then, in the late 1980s, a moratorium was imposed on their use because of some early failure issues. However, OGFC mixture performance and service life have improved significantly since a new generation of OGFC mixture was promoted in the United States in the late 1990s. Inspired by the success of other state agencies, the Louisiana DOTD modified the earlier mix design and constructed four new OGFC sections during the past decade to evaluate pavement performance and safety benefits. This paper includes a comprehensive evaluation of Louisiana OGFC mixtures based on their laboratory and field performance. Laboratory work entailed material and mixture design in addition to numerous laboratory tests, namely permeability, draindown, tensile strength ratio, and loaded wheel test. Field evaluation involved visual inspection, pavement condition survey, skid resistance, and traffic safety. With few exceptions in the laboratory, the selected OGFC mixtures showed the potential to meet current Louisiana DOTD specifications, as well as various performance standards established by previous studies. The field analysis indicated that the OGFC test sections showed improved rutting, cracking, and skid performance when compared with typical Superpave® roadway sections. This performance evaluation will likely support the ongoing use of OGFC mixtures in the state of Louisiana. Additionally, the evaluation provides an opportunity to continually improve the current OGFC specification and mix design procedures adopted by the Louisiana DOTD.

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This study included five different recovery methods for six emulsions (CRS-2, CRS-2P, CRS-2L, SS-1, SS-1L, and SS-1H) and their corresponding unaged base binders. These five recovery methods consisted of different curing times, temperatures, and vacuum pressures. The goal of this study was to understand the effect of these variables on the rheological properties of the recovered asphalt emulsion residue during the recovery process. Rheological properties such as G*/sin δ, phase angle, and average percent strain recovery were determined to quantify stiffness, oxidative aging, and change in creep recovery due to polymer modification. One new recovery method using a vacuum drying oven was explored in this study. This method reduced the effects of oxidative aging and reduced the recovery time to 6 h. The results show that this newly proposed vacuum drying method ensured better drying of the sample and produced residue that was not unnecessarily aged and was similar to unaged base binder in stiffness, whereas with ASTM D7497 oxidative aging plays a significant role in residue stiffness by almost doubling the stiffness relative to unaged base binder. Also, this 6-h vacuum drying method allowed us to clearly identify the presence of polymer. Overall, this report explains the reasons for the differences between the stiffnesses of unaged base binder and emulsion residue, considering oxidative aging, remaining moisture, emulsifier, and polymer modification.