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 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.

The objective of this study was to investigate tack coat interface shear bond characteristics at various temperatures and to relate tack coat characteristics in the field to the rheological test results in the laboratory. Interface shear strength (ISS) of two emulsified asphalt tack coats (CRS-1 and trackless) was evaluated at temperatures ranging from −10°C to 60°C. Two emulsified tack coats were applied on full-scale pavement test sections at application rates of 0.14, 0.28, and 0.70 L/m2. Cores were then extracted from the full-scale test sites to be tested in the laboratory while simulating different field conditions. Tests were conducted with a newly developed direct shear device. The binder grade for the residue of CRS-1 emulsion was PG 58-28. The high temperature grade for the residue of the trackless emulsion was PG 82. Trackless material was brittle at a low temperature, and its low temperature PG grade could not be determined. Within the evaluated temperature range, the ISS of the tacked interface increased with the decrease in temperature. Generally, bonding performance, as measured by the ISS, of the trackless emulsion was superior to CRS-1 emulsion, specifically at temperatures greater than 40°C. In addition, results show that interface shear strength for both tack coat materials at each application rate increased with an increase of the binder rheology parameter G*/sin δ. This relationship can be used to establish a laboratory design threshold for this parameter, to ensure that the selected application rate and tack coat material will perform adequately in the field.

An approach to a practice paving technique using building information modeling (BIM) was developed. When planning hot mix asphalt (HMA) overlay on a concrete slab, in-advance paving simulations can help to preemptively evaluate pavement quality, such as HMA thickness, and prevent excessive HMA quantity. The BIM technique has the capabilities of ‘in-advance simulation’, ‘3-D visualization’, ‘interference identification’, and ‘quantification’. Building information modeling could be successfully implemented to optimize milling quantity and improve HMA pavement quality in an actual paving project. Based on the established BIM model, alternative paving levels were derived and paving sequences were simulated. Through 3-D visualized images, locations where HMA thickness was inadequate could be effectively identified. Quantified information for simulation results enabled optimization of milling and paving options. Milling was selectively conducted for the identified undulations. The cost was reduced by approximately 12%. Paving thickness and density had coefficients of variation (CV) of approximately 15% and 0.2%, respectively.

The exclusive effects of microsurfacing on thermal cracks were quantified in terms of IRI. In addition, vehicle operating costs related to the IRI were estimated. For the MnROAD project, using a measurement device with high resolution, pavement surfaces with thermal cracks were profiled before and after microsurfacing. The crack profiles were transferred into longitudinal profiles with no cracks so that the exclusive contribution of original and microsurfaced cracks to roughness could be analyzed. Then, vehicle operating costs corresponding to the exclusive roughness were evaluated. Applying the given amount of microsurfacing materials, the IRI resulting from cracks with 0.7 cm depth and 0.58 m width was reduced by about 80 percent for serviceable roughness levels. The IRI resulting from cracks with 1.5 cm depth and 0.61 m, and 1.8 cm depth and 0.80 m width were decreased by about 60 percent and about 45 percent, respectively. By examining vehicle operating costs, it was found that a small difference in crack severities results in a greater increase in cost. Therefore, it was concluded that prompt operation of microsurfacing for any crack severity levels is no less important than earlier operation for low severity cracks. In addition, it was concluded that microsurfacing can be a costeffective maintenance technique for cracks for a year. If more than 3 cracks would be detected in the field, microsurfacing would be still a cost-effective maintenance method for any severity crack level.