The results presented in this paper are part of NCHRP Project 9-40 on the Optimization of Tack Coat for Hot-Mix Asphalt Placement. This paper presents the development of a new test device, the Louisiana Tack Coat Quality Tester (LTCQT), for evaluating the quality of the bond strength of tack coat in the field. LTCQT is a modification of the ATacker device. A test matrix was developed to evaluate the reliability and the repeatability of the LTCQT in the field. Three emulsified tack coats (CRS-1, SS-1h, and Trackless) and an asphalt cement (PG 64-22) were evaluated over a wide range of temperatures and at a residual application rate of 0.23 L/m2. Two key test parameters were determined to characterize the mechanical responses of tack coats: the optimum testing temperature and the maximum tensile strength test. Results indicated that the LTCQT can successfully be used in the field to measure the quality of the bond strength of tack coat and to distinguish between the responses of the evaluated tack coats. A good correlation was observed between the absolute viscosity of residual tack coat material and the tack coat tensile strength. This study shows that the softening point can be an adequate parameter to determine the optimum temperature for the tack coat pull-off test, and therefore pull-off testing at the softening point temperature of the residual binder material is recommended for field tack coat evaluation.

The effect of fine aggregate morphologic properties on asphalt mixtures' behavior is well recognized. However, the current procedures for measuring fine aggregate properties are at best indirect indicators of these properties. The indirect nature of the current measurements has led to inconsistency in predicting the extent to which the measured properties influence pavement performance. Two independent methods that integrate several aspects of image-analysis techniques are presented for quantifying angularity and texture of fine aggregates. The first technique relies on the change of aggregate shape as it is subjected to a number of erosion-dilation morphologic operations. The second technique uses the change of an object perimeter with its shape. The analysis shows that the two methods are able to capture aggregate shape at two different scales. Angularity is captured using low-resolution images, whereas surface texture is captured using highresolution images. The presented image-analysis techniques have potential benefit in quantifying the effects of texture and angularity on asphalt pavement performance.

The objective of this study was to quantify the effects of tack coat type, tack coat application rate, and surface type (i.e., hot-mix asphalt versus portland cement concrete) including milled versus unmilled surfaces on the interface shear strength based on full-scale test application. The variation of interface shear strength between field- and laboratory-prepared samples was also investigated. To achieve this objective, five types of tack coat materials were applied at three application rates on four types of surfaces at the Pavement Research Facility site of the Louisiana Transportation Research Center. Samples were cored from the constructed test lanes, and the interface shear strength was measured using the Louisiana Interface Shear Strength Tester. Results of this study showed that a direct relationship was observed between the roughness of the existing surface and the developed shear strength at the interface. A small amount of water seemed to negatively affect interface shear strength with PG 64-22 used as a tack coat material. However, the effect of surface wetness on interface shear strength was less evident for emulsion-based tack coat materials. Laboratory-prepared samples grossly overestimated the interface shear strength when compared with field-extracted cores. While a decreasing trend was observed in the laboratory, an increasing trend in the measured interface shear strength was observed in the field.

This study summarizes the experimental and analysis methods used in characterizing and quantifying the internal structure of hot-mix asphalt (HMA) paving mixtures. The implications of the internal structure analysis for the design, compaction, and performance of HMA are also discussed. The methods can be divided into two categories: volumetric analysis methods and imaging methods. The volumetric analysis methods rely on bulk measurements of the percentage of air voids in certain aggregate sizes or in the whole mix as indicators of packing. These concepts are currently used in the Superpaver design system for densegraded HMA, stone matrix asphalt design, and the Bailey method for selection of aggregate gradations in HMA. The imaging methods quantify the distribution of the aggregate skeleton, voids in the mineral aggregate, and air voids by analyzing images of the internal structure. These images can be captured two-dimensionally with a simple setup of a microscope connected to a camera or three-dimensionally with an X-ray computed tomography system.

This paper provides complete guidelines for using geosynthetics with hot-mix asphalt overlays to reduce reflective cracking. Definitions of the various types of geosynthetics that are commercially available along with some of their advantages and disadvantages are also provided. These guidelines address the following: when to consider a geosynthetic product, how to select and store geosynthetics, cost considerations, pavement design with a geosynthetic, overlay construction with a geosynthetic, construction inspection, and potential construction problems.