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This paper presents a comparative study of both laboratory and field performance of several applications of crumb-rubber modified (CRM) hot-mix asphalt in Louisiana. Eight CRM asphalt pavement sections were constructed using eight different CRM processes or applications. These eight CRM sections were built at five state highway projects. A control section with conventional asphalt mixture was constructed at each project to compare the performance of pavement sections built with CRM asphalt mixtures.To evaluate the mixture characteristics of the CRM and conventional mixes, laboratory tests of Marshall stability and flow, indirect tensile strength (ITS) and strain, and indirect tensile resilient modulus (M R ) were conducted on field compacted Marshall specimens.Comparisons of the field performances of the pavements were achieved through roadway core air void analysis, rut-depth measurement, international roughness index (IRI), pavement structure numbers measured through the DYNAFLECT system, and visual inspections of cracks.The result of this study indicated that the conventional mixtures exhibited higher laboratory strength characteristics than the CRM mixtures. The pavement sections constructed with CRM asphalt mixtures showed overall better performance indices (rut depth, fatigue cracks, and IRI numbers) than the corresponding control sections after five to seven years of traffic.

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Effects of longitudinal compression before and after transection of the accessory ligament of the superficial digital flexor (SDF) muscle were measured in eight equine cadaver forelimbs. When compression was increased from 890 N to 3115 N, the metacarpophalangeal (MCP) and carpal joints hyperextended 20 degrees and 4 degrees, respectively, and strain in the SDF and deep digital flexor tendons was increased 3.5% and 1.4%, respectively. The accessory ligament did not elongate. Immediately after transection of the accessory ligament at 3115 N load, a 2.8 mm gap formed between the transected ends of the accessory ligament, and the muscle belly of the SDF elongated and moved distad. The MCP joint hyperextended 15.8% further and strain of the SDF tendon increased 11.2% further. These results show that the accessory ligament transferred load in the SDF musculotendinous unit away from the muscle belly and that desmotomy altered this function. Decrease in the MCP joint angle indicated that the accessory ligament contributed to the support of the MCP joint under load. Increase in SDF strain after desmotomy was probably influenced by the change in the moment about the MCP joint and increased length of the SDF musculotendinous unit.

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.

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Asphalt tack coat is a light application of asphalt, usually asphalt diluted with water. It is used to ensure a bond between the surface being paved and the overlying course. Normally, hot asphalt cements, emulsified asphalts, or cutback asphalts are used as tack coats. The objective of this study was to evaluate the practice of using tack coats through controlled laboratory simple shear tests and determine the optimum application rate. The influence of tack coat types, application rates, and test temperatures on the interface shear strength was examined. Four emulsions (CRS 2P, SS-1, CSS-1, and SS-1h) and two asphalt binders (PG 64-22 and PG 76-22M) were selected as tack coat materials. The residual application rates considered were 0.00 (0.00), 0.09 (0.02), 0.23 (0.05), 0.45 (0.1), and 0.9 (0.2) L/m 2 (gal/yd 2 ). A simple shear test was performed to determine the shear strength at the interface at two test temperatures, 25°C (77°F) and 55°C (131°F). The results indicated that CRS-2P emulsion was the best tack coat type and 0.09 L/m 2 (0.02 gal/yd 2 ) was the optimum application rate at which a maximum interface shear strength was measured for both test temperatures.