Frazier Parker

Aggregate Toughness/Abrasion Resistance and Durability/Soundness Tests Related to Asphalt Concrete Performance in Pavements

Numerous tests have been developed that empirically characterize aggregate without, necessarily, having a strong relationship to the performance of the final products incorporating these aggregates. This seems to be particularly true for aggregate toughness and abrasion resistance and durability and soundness. Toughness/abrasion resistance and durability/soundness tests for characterizing aggregate used in asphalt concrete were identified and evaluated, and those test methods that best correlate with field performance were determined. Based on a review of literature and specifications, laboratory tests for characterizing aggregate toughness/abrasion resistance and durability/soundness were selected. Sixteen aggregate sources with poor to good performance histories were identified for evaluation with the selected suite of tests. Performance histories of pavements containing these aggregates in asphalt concrete layers were established through personal contacts with state transportation agencies and performance evaluation questionnaires. Aggregate properties from laboratory tests were correlated with field performance. The micro-deval and magnesium sulfate soundness tests provide the best correlations with field performance of asphalt concrete and are recommended for characterizing aggregate toughness/abrasion resistance and durability/soundness.

CHARACTERIZATION TESTS FOR MINERAL FILLERS RELATED TO PERFORMANCE OF ASPHALT PAVING MIXTURES

Various studies have shown that the properties of mineral filler, especially the material passing through a 0.075-mm (No. 200) sieve (generally called P200 material), have a significant effect on the performance of asphalt paving mixtures in terms of permanent deformation, fatigue cracking, and moisture susceptibility. However, researchers have employed different characterization tests for evaluating the P200 materials. This study was undertaken to determine which P200 characterization tests are most related to the performance of asphalt paving mixtures. Six P200 materials representing a wide range of mineralogical composition and particle size were used. These P200 materials were characterized by six tests including Rigden voids, particle size analysis, and methylene blue test. Mixes were prepared with two fines to asphalt ratios (0.8 and 1.5) by weight. Mix validation tests included the Superpave shear test for evaluating permanent deformation and fatigue cracking, and the Hamburg wheel tracking test and AASHTO T283 for evaluating moisture susceptibility of the 12 mixtures containing different P200 materials and fines to asphalt ratios. The particle sizes in microns corresponding to 60 and 10 percent passing and the methylene blue test were determined to be related to the performance of asphalt paving mixtures.

Quality Assurance of Hot-Mix Asphalt: Comparison of Contractor Quality Control and Georgia Department of Transportation Data

Quality assurance is the process by which highway construction elements are sampled and tested to ensure compliance with specifications and other project requirements. The results of contractor-performed tests, originally performed for quality control purposes, are increasingly used in the acceptance decision in many states. The Georgia Department of Transportation (GDOT) uses contractor-performed tests in the acceptance decision on acceptable corroboration of GDOT-performed tests. Statistical analyses were performed to assess differences between tests conducted on hot-mix asphalt concrete by GDOT and its contractors during the 2003 construction season. Measurements of gradation and asphalt content taken by both parties were compared both across all projects and on a project-by-project basis for projects large enough to meet sample size requirements for this type of analysis. Both tabular and graphic representations of data are used to interpret the results. Statistically significant differences occur in some cases; these differences are much more common when comparing variability of these measurements than with the means. At the project level, on most projects in which statistically significant differences occur, the GDOT value typically is larger.

EFFECT OF SUPERPAVE DEFINED RESTRICTED ZONE ON HOT MIX ASPHALT PERFORMANCE

The effect of the Superpaver defined restricted zone on hot-mix asphalt rutting performance was evaluated. One gradation that violated the restricted zone (TRZ) and two gradations that did not violate the restricted zone (BRZ and ARZ) were evaluated. Evaluated mixes represented a range of maximum aggregate sizes (MASs), design traffic levels, and aggregate types. Three laboratory tests—asphalt pavement analyzer, rotary-loaded wheel tester, and Marshall test—were used to evaluate the rutting performance. From the analysis, it was found that mixes with gradations violating the restricted zone performed similarly to or better than the mixes with gradations passing outside the restricted zone with respect to laboratory rutting tests. This conclusion was drawn from the results of experiments with 12.5-, 19.0-, and 25.0-mm MAS gradations at Ndesign (design number of gyrations) values of 100, 75, and 50 gyrations. This conclusion is confirmed and supported by the recently completed NCHRP Project 9-14: The Restricted Zone in the Superpave Aggregate Gradation Specification. The results also showed that rutting performance of mixes having gradations below the restricted zone, which was commonly recognized to be rut resistant, appeared to be more sensitive to aggregate properties than mixes having gradations above or through the restricted zone.

TESTS FOR EVALUATING FINE AGGREGATE PARTICLE SHAPE, ANGULARITY, AND SURFACE TEXTURE

Particle shape, angularity, and surface texture are critical properties in assessing fine aggregate quality for asphalt concrete. The index for aggregate particle shape and texture and uncompacted voids tests indirectly measure these properties. Several sources of fine aggregate from Alabama were evaluated by both tests. Modifications to current test procedures to include all particle sizes normally included in fine aggregate are suggested. Particle index and uncompacted voids are affected by gradation, and this effect should be eliminated in assessing fine aggregate quality. Testing of individual size fractions and computation of composite indexes or void contents or testing of samples with standard gradations are viable options for elimination of gradation effects. Particle indexes or uncompacted voids of blends of two aggregates may be assessed by linear proportioning of values for individual components.

Statistics for Superpave Hot-Mix Asphalt Construction Quality Control/Quality Assurance Data

Asphalt content, air void content, and mat density measurements for Superpave® mixes were collected during 1997, 1998, 1999, and 2000 to develop statistics for a statistical quality control/quality assurance program for the Alabama Department of Transportation (DOT). Data were analyzed to determine if accuracy and variability improved and stabilized as contractors accumulated experience with Superpave mixes, to compare contractor and Alabama DOT measurements, and to assess the effects of maximum aggregate size and the design equivalent single-axle load range. Analyses indicated that the accuracy and variability of asphalt content measurements for Superpave mixes remained consistent and comparable to those for Marshall mixes. The variability of air void contents for Superpave mixes stabilized but remained higher than the variability of air void contents for Marshall mixes. The accuracy in achieving target air void contents for Superpave mixes deteriorated and stabilized at values poorer than those achieved for Marshall mixes. The variability of mat density measurements for Superpave mixes decreased and stabilized at values comparable to those achieved for Marshall mixes. The accuracy of mat density measurements for Superpave mixes improved but stabilized at values poorer than those achieved for Marshall mixes. There are significant differences between contractor measurements and Alabama DOT measurements. Asphalt content decreases as design traffic level and maximum aggregate size increase. The level of mat density achieved increases as maximum aggregate size increases.

Soil—Structure Interaction and Imperfect Trench Installations for Deeply Buried Corrugated Polyvinyl Chloride Pipes

The imperfect trench installation method has been used to reduce earth pressure on buried rigid pipes by inducing positive soil arching over the pipe. Because they are relatively flexible, corrugated thermoplastic pipes induce a small amount of positive soil arching. Therefore, there has been little research on the effects of imperfect trench installation on flexible pipes, such as those fabricated with corrugated thermoplastic. A study was done of the soil-structure interaction for corrugated poly-vinyl chloride (PVC) pipes and the efficiency of the imperfect trench method for their installation. The soil-structure model was simulated with the Duncan soil model and Selig soil parameters by using the finite element method. The geometry of a soft zone was optimized to maximize the earth load reduction effects for imperfect trench installations. The optimization process was based on parametric studies of the geometry and location of the soft zone, combined with bedding and sidefill treatments to reduce earth pressures. Predictor equations for earth load, maximum stress, and deflection of corrugated PVC pipes were formulated that incorporate the proposed optimum soft zone geometry and installation techniques. Parametric studies revealed that the optimum geometry of the soft zone in the proposed imperfect trench installations could reduce the maximum wall stress in corrugated PVC pipes by 85%.

Comparisons of Contractor and State Transportation Agency Quality Assurance Test Results on Mat Density of Hot-Mix Asphalt Concrete: Findings of Multistate Analysis

A typical component of highway construction quality assurance programs is the process by which highway construction elements are sampled and tested to ensure compliance with specifications and other project requirements. The results of contractor-performed tests on in-place properties of hot-mix asphalt are increasingly used in the acceptance decision in many states. Results of tests performed by contractors and state departments of transportation (DOTs) in North Carolina, Florida, and Kansas consistently indicate that differences between contractors and state DOT test results for hot-mix asphalt concrete mat density are statistically significant. Furthermore, these comparisons consistently indicate less variable and more favorable contractor test results, relative to specification limits, that give more favorable acceptance outcomes. Details of quality assurance processes (sampling and testing frequencies, test methods, verification procedures, and acceptance procedures) appear to have little if any effect on these comparisons. These findings provide information for state DOTs to consider in structuring their quality assurance programs, specifically the role of contractor-performed tests in acceptance decisions.

UNCOMPACTED VOIDS AND PARTICLE INDEX TESTS FOR EVALUATING COARSE AGGREGATE

Coarse-aggregate angularity and surface texture are properties specified under the SuperpaveTM mix design system. To control specification requirements, the fractured-face count test is suggested. The use of a more objective test was investigated. Uncompacted voids and index of aggregate particle shape and texture tests were studied to measure coarse-aggregate angularity. The gradation of the sample has an obvious influence on both test results. Ways to separate the effect of gradation from aggregate angularity were studied. Viable options include testing a standard graded sample and computing a weighted average from tests of individual size fractions based on the gradation of the blend. When comparing aggregate sources, either option produces a comparable evaluation, but testing standard graded samples saves time. On the other hand, the weighted average is more appropriate for evaluating an aggregate blend. The index of aggregate particle shape and texture test and the uncompacted voids test provide comparable measures of coarse aggregate angularity and surface texture.

Effect of Material Transfer Devices on Flexible Pavement Smoothness

The initial smoothness of a pavement is linked to both future pavement smoothness and pavement life. Research was conducted to study the effects of adding a material transfer device to the paving train. The focus was to determine if the use of a material transfer device improved flexible pavement smoothness. An automated data collection van was used to collect pavement profile data, and smoothness was quantified with the international roughness index in inches per mile. An infrared camera and a rolling wheel were used to detect and locate portions of the mat with temperature differences of more than 10°C (19°F). It was found that a material transfer device significantly improved flexible pavement smoothness. Fewer areas with temperature differences of more than 10°C were noted when a material transfer device was used, and areas with these temperature differences were found to be significantly rougher than locations that had more uniform temperatures. In an additional finding, unrelated to the use of a material transfer device, the extension of the screed to one side of the paver caused a significant increase in roughness in the wheelpath on that side.