查看更多>>摘要：Load transfer is an important aspect of portland cement concrete joint design. To date, aggregate interlock and round steel dowels have been used to accomplish load transfer. Research was done to examine the use of steel dowels of alternative shapes to provide load transfer. A field research project in Iowa has used two elliptical bars of different sizes at three spacings and numbers of bars per joint. Test sections included bars across the entire joint and sections using bars only in the wheelpaths. The impact of cut, fill, and transition sections was also factored into the experimental design. This paper documents the construction of the project, testing that is being done, and the initial results of the work.
M. Stroup-GardinerAlan CarterThomas DasBrian Bowman...
p.105-112页
查看更多>>摘要：Ride quality assessed with an inertial profiler on flexible pavement was used to provide initial information on the following key issues: repeatability associated with international roughness index (IRI) values for a wide range of hot-mix asphalt (HMA) material variables, timing of acceptance testing for initial ride quality, IRI changes with type of roadway, influence of stops and starts in the paving operation on ride quality, identification of "bump," and effect of grinding on IRI. IRI was calculated for 25-ft intervals instead of the standard 0.1 mi (528 ft) for all testing to highlight local anomalies such as bumps due to paving stoppages. Results indicate that the standard deviation of three replicate passes with an inertial profiler is 5 in./mi (includes 46 HMA mixes on the Auburn University National Center for Asphalt Technology test track). IRI measurements with time suggest that initial acceptance testing can be conducted within 7 days, which allows more flexibility in scheduling by the agency. Limited traffic also slightly reduces the IRI values, which is to the contractor's advantage. IRI values are suggested for two-lane county roads and medium- to high-traffic facilities. Separate IRI ranges are indicated for each of these categories on the basis of the type of HMA construction: new, repair and overlay, and mill and overlay. These ranges are set for best and good practices (continuous paving, no stoppages; consistent supply of trucks, very short stops). IRI values greater than 125 in./mi in any given 25-ft interval indicate a bump; bumps can be ground so that these areas have IRI values of less than 100 in./mi.
查看更多>>摘要：Cold milling operations have been used for more than two decades in Indiana, but little attention was given to the quality of the operations. Several alternatives for evaluating surface macrotexture were considered as a quality measure. ASTM E965-96 was selected as the best procedure on which to base evaluation of milled surfaces. The Indiana Department of Transportation developed Test Method ITM 812-03T to make the ASTM procedures workable for milled surfaces. The initial quality of hot-mix asphalt (HMA) construction directly affects the long-term performance and the service life of a transportation facility. It is directly dependent on the quality of the aggregates and binders and the production and laydown operations. Construction concerns include surface preparation, which is the removal of distressed materials to develop a stable working platform on which HMA materials can be placed. Indiana HMA contractors were experiencing numerous problems in meeting volumetric and density quality requirements on highway construction projects. A significant number of HMA mixtures were either being accepted with partial payment or replaced before being accepted. Investigation of the problem included observing the contractor's certified HMA plant production operations, mixture components (i.e., aggregates, binders, etc.), mixture transportation, laydown and compaction, and mixture sampling procedures. It was discovered that more problems occurred when cold milling of the existing surface was included in the project. A solution to these issues resulted in the development of improved milling design and construction requirements, which include quality measurement techniques for the milling operations.
查看更多>>摘要：Testing of asphalt concrete samples was conducted by using the asphalt pavement analyzer test, the Superpave~® shear tester (SST) frequency sweep test, and the SST repeat shear at constant height test to determine the rutting susceptibility that might be expected from samples that have different levels of segregation. Previous research had divided segregation into four levels: none, light, medium, and high. Test results suggest that samples with different segregation levels might show similar rutting susceptibility. Therefore, performance-related models were established in which segregation was divided into three levels: good, fair, and unacceptable. The performance-related models were applied to field data, and examination indicates that the modified models are capable of assessing segregation in field projects. Examination also found that fine segregation was present. Fine segregation can be predicted by extrapolating the developed model from the coarse part to the fine part. However, more data should be investigated to develop acceptable criteria for fine segregation. A methodology was developed to improve pavement quality by controlling aggregate segregation and poor compaction in placed mats. With the models and the proposed methodology, realistic construction uniformity could be assessed by agencies and contractors, which is the first step in obtaining pavements with high performance and longer service life.
查看更多>>摘要：Four methodologies for determining the asphalt content of mixtures containing high-loss aggregates in the ignition furnace were evaluated: the standard method using the Thermolyne furnace (control), the Troxler NTO infrared furnace, the Ontario method, and a Tempyrox glass-cleaning oven. Six aggregate sources with high ignition furnace aggregate corrections were obtained from around the country: four dolomites, a basalt, and a serpentine/chlorite. Calibration factors were determined for each method at optimum asphalt content. Additional samples were then tested at optimum plus 0.5% asphalt content, and the measured asphalt content was calculated by using the correction factor determined for that method and aggregate source. The Tempyrox Pyro-Clean furnace, commonly used for cleaning laboratory glassware, produced the lowest aggregate correction factors. The standard method and the Ontario method, both using the Thermolyne ignition furnace, produced the smallest bias or error in measured asphalt content. The standard deviation of the corrected asphalt contents for these high-loss sources was higher than the within-laboratory standard deviation reported for AASHTO T308. The only exception was the Alabama source using the standard method. The Ontario method and Tempyrox oven generally reduced the variability of asphalt content measurements for high-loss aggregates. None of the methods evaluated statistically reduced aggregate breakdown on the nominal maximum aggregate size and 4.75-mm sieves. The Ontario method significantly reduced, but did not eliminate, aggregate breakdown on the 0.075-mm sieve. The Ontario method is the best method for immediate implementation for determining the asphalt content by the ignition method for high-loss aggregates.
Gregory A. SholarGale C. PageJames A. MusselmanPatrick B. Upshaw...
p.135-144页
查看更多>>摘要：The Florida Department of Transportation uses long-established test procedures to determine the maximum specific gravity (G_(mm)) and bulk specific gravity (G_(mb)) of asphalt mixtures and the bulk specific gravity (G_(sb)) of aggregates. The CoreLok, a vacuum-sealing device that can be used to determine these properties, was evaluated by the department for these test procedures. With respect to the G_(mm) test procedure, for mixtures containing nonabsorptive granites, the CoreLok determined results equivalent to those of the department's test procedure. However, for mixtures containing absorptive limestones, the CoreLok determined higher G_(mm) values than did the department's test procedure. The apparent reason for the discrepancy is that the CoreLok does not determine a saturated surface dry condition of the sample. With respect to the aggregate specific gravity test procedures, the CoreLok provided test results equivalent to the department's test procedure for the nonabsorptive fine aggregates only. For the absorptive fine aggregates and all of the coarse aggregates, the CoreLok determined G_(sb) test results significantly different from those of the department's test procedures. The CoreLok may be suitable for determining G_(mb) for coarse-graded compacted specimens with high porosity and air voids. There are concerns with the accuracy of the CoreLok results because of the bridging effect of the plastic bag over the large surface voids and because of the CoreLok's significant underestimation of the specific gravity of a solid aluminum cylinder.
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