From the beginning of asphalt mixture design it was desired to understand the interaction of aggregates, asphalt, and the voids created during their compaction. In asphalt mixture design, guidance is lacking in the selection of the design aggregate structure and understanding the interaction of that aggregate structure and mixture volumetric properties. Asphalt mixture design concepts are presented that use aggregate interlock and aggregate packing to develop an aggregate blend that meets volumetric criteria and provides adequate compaction characteristics. The concepts rely on coarse aggregate for the skeleton of the mixture with the proper amount of fine aggregate to provide a properly packed aggregate structure. The objective is to use aggregate packing concepts to analyze the combined gradation and relate the packing characteristics to the mixture volumetric properties and compaction characteristics. The new concepts presented for asphalt mixture design and analysis include an examination of aggregate packing and aggregate interlock, blending aggregates by volume, a new understanding of coarse and fine aggregate, and analysis of the resulting gradation. These concepts are the result of many years of field experience and are the backbone of the Bailey method for asphalt mix design. These methods are under continued development as the improved method for asphalt mixture design, which will assist with the transition to contractor mix design.
Pavement roughness is an expression of the irregularities in a pavement surface that adversely affect the ride quality of a vehicle. Roughness also affects vehicle delay costs, fuel consumption, tires, and maintenance costs. Roughness is predominantly characterized by the international roughness index (IRI), which is often measured with inertial profilers. Inertial profilers are equipped with sensitive accelerometers, a height-measuring laser, and a distance-measuring instrument for measuring vehicle vertical acceleration data and the pavement profile. Modern smartphones are equipped with several sensors including a three-axis accelerometer, which was used in this project to collect vehicle acceleration data with an Android-based application. In the study, acceleration data were double integrated numerically to obtain a pavement profile, which was input into the software program ProVAL. The pavement roughness was then calculated. For the initial validation, pavement profile and acceleration data were collected with both an inertial profiler and the newly developed smartphone application from three test sites. The initial validation results suggest that the newly developed smartphone application can measure IRI with good correspondence to the inertial profiler and with good repeatability between measurement replications. However, calibration is needed for rougher pavement sections because the current analysis techniques do not directly account for acceleration damping resulting from vehicle suspension systems. With improvements in analysis that consider the vehicle suspension effects and additional validation, the approach could be used to reduce the cost of acquiring pavement roughness data for agencies and to reduce user costs for the traveling public by providing more robust feedback about route choice and its effect on estimated vehicle maintenance cost and fuel efficiency.
This paper quantifies the environmental improvements in current versus past pavement materials and construction practices employed by the Illinois State Toll Highway Authority (tollway authority). Improvements in sustainability performance were measured with a life-cycle assessment (LCA) approach. Three scenarios were generated to evaluate tollway authority practices on the basis of eight 2013 Interstate reconstruction and rehabilitation projects. The first scenario, 2013 projects, analyzed the actual pavement material and designs of the 2013 projects. The second scenario, materials baseline, was based on the 2013 projects but modified to include mix designs with less-sustainable materials used by the tollway authority circa 2000. The third scenario, design and materials baseline, considered both mix designs and pavement design practices used circa 2000. To improve the spatial and temporal relevance of the analyses, two regional databases of life-cycle inventories representing processes from 2013 and 2000 were developed and applied to the 2013 projects and 2000 baselines. A tool developed by the Illinois Center for Transportation (ICT) of the University of Illinois at Urbana–Champaign, the pavement ICT-LCA 0.95, was used to evaluate the sustainability performance indicator (SPI), global warming potential (GWP), and cumulative energy demand (CED) for each scenario. The resultant savings in SPI, GWP, and CED from the first scenario ranged between 17% and 28%, 12% and 16%, and 13% and 26%, respectively, compared with the second scenario, and 12% and 33%, 8% and 26%, and 11% and 32%, respectively, compared with the third scenario.
The advancement of the Superpave gyratory compactor (SGC) has led to a recognized need for a simple test that preferably can be performed on SGC samples during mix design that would rank performance potential of the mixtures if used in a pavement. Although it has proved difficult to find one test that can rate mixture potential for rutting and fatigue cracking and modulus, a limited study was conducted on Illinois mixtures that provides evidence that a simple test performed during mix design has the potential to predict a diverse set of performance characteristics. The results are presented for 10 Illinois dense-graded mixtures of surface and binder (9.5 and 12.5 mm) gradations that were tested in an asphalt pavement analyzer (APA) and subjected to flexural beam fatigue, unconfined repeated load permanent deformation, and diametral resilient modulus testing. The mixtures were further subjected to a rapid triaxial test procedure using SGC compacted samples, as taken from the SGC machine, and tested at 50°C in a triaxial stress reversal mode. The triaxial testing provides data that predicts resilient modulus, APA rutting results, fatigue coefficients, and permanent deformation characteristics of accumulated strain at tertiary failure, loads to tertiary failure, and the exponent to the standard logarithmic permanent deformation curve. The excellent correlations obtained from this study provide direct evidence that this test protocol may provide a structural evaluation procedure to supplement the volumetric mix design process and warrants further study.
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