The Influence of Mixing Conditions on the Macro-Scale Homogeneity of Asphalt Mixtures Blended with Reclaimed Asphalt Pavement (RAP).

Quan Liu,Markus Oeser

doi:10.3390/ma14154137

Abstract

The homogeneity of asphalt mixtures blended with reclaimed asphalt pavement (RAP) is affected by many factors. Due to the complicated compositions of recycled asphalt mixtures, the inhomogeneity issue might cause insufficient mechanical properties of asphalt mixtures, even though a design method was appropriately adopted. Therefore, it is of great significance to study the influence of mixing conditions on the homogeneity of asphalt mixtures blended with RAP materials. This study focused on the macro-scale homogeneity of produced asphalt mixtures. Specifically, asphalt mixtures incorporated with 40% RAP content were produced in a laboratory using different mixing times and mixing temperatures. A multi-direction indirect tensile stiffness modulus (ITSM) test was proposed to quantify the homogeneity of produced samples. In addition, the digital image processing (DIP) method was used to identify the distribution of aggregates and RAP binder. The results indicated that the influence of mixing time on the macro-homogeneity of asphalt mixtures indicated that a longer mixing time was favorable for the material dispersion. The influence of mixing temperature mainly rested on two perspectives. One was that the temperature variation induced the change of binder viscosity. The other was that the temperature influences the diffusion process between RAP binder and new bitumen, which further affected the mechanical performance of produced asphalt mixtures.

Highlights

Asphalt mixtures have been extensively used in the construction of pavements
The other was that the temperature influences the diffusion process between reclaimed asphalt pavement (RAP) binder and new bitumen, which further affected the mechanical performance of produced asphalt mixtures
Coefficient of variation (CoV) of indirect tensile stiffness modulus (ITSM) were calculated for each mixing condition

Summary

Introduction

Asphalt mixtures have been extensively used in the construction of pavements. when pavement suffers severe distress and, as a result, no longer functions with satisfactory quality, pavement has to be reconstructed [1]. The homogeneity of asphalt mixtures is estimated by quantifying the segregation of air voids and aggregates [6,7,8]. Studies addressing the homogeneity of asphalt mixtures can be simplified as the distribution of aggregates and air voids. Many technologies have been developed to characterize the distribution of aggregates and air voids. Yue et al applied DIP to calculate the distribution, orientation, and shape of coarse aggregates in mixtures [12]. Their results indicated that major cross-sections of coarse particles preferred to lie horizontally in mixtures. An aggregate homogeneity index was introduced and it verified a good correlation with penetration strength

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