Kamyar C. Mahboub

Pilot Study in Sampling-Based Sensitivity Analysis of NCHRP Design Guide for Flexible Pavements

The mechanistic–empirical pavement design guide (MEPDG), developed under the recently completed NCHRP Project 1–37A, is a complex tool. Sensitivity analyses typically vary a single input parameter while holding other parameters constant. A pilot project is outlined to identify the feasibility of a global sensitivity analysis of the design process by using random sampling techniques over the entire input parameter space. This study sampled the following flexible pavement input variables: hot-mix asphalt (HMA) base nominal aggregate size, climate location, HMA thickness, annual average daily truck traffic (AADTT), subgrade strength, truck traffic category, construction season, and binder grade “bump.” A total of 100 design sections were randomly sampled from these input parameters. The resulting predicted performance of longitudinal and alligator cracking, HMA and total rutting, and international roughness index were analyzed by using the Pearsons and Spearmans correlation coefficients. These coefficients indicate that AADTT, HMA thickness, and subgrade strength have a significant impact on performance, whereas the remaining parameters have lesser impacts. The performance predicted with trial designs with default values of the least significant variables was compared with the original performance predictions using the original input factors. This comparison indicated that the default parameters produced similar performance to designs using all the input parameters. These results demonstrated that this type of sensitivity analysis may be used to identify important input parameters across the entire parameter space. The utilization of a “bumped” binder grade did not appear to have a significant influence on the performance predicted by the MEPDG models. These results indicate that further research to refine the MEPDG performance models may be necessary.

Pervious Concrete: Compaction and Aggregate Gradation

Pervious concrete is very different from traditional portland-cement concrete (PCC). Therefore, there are open questions regarding the suitability of the current standard concrete testing protocols as they may be applied to pervious concrete. There are unique features associated with pervious concrete that may require special testing considerations. This paper examines the compaction and consolidation of pervious concrete. This study presents cylindrical specimen preparation techniques that will produce laboratory specimens that are similar to the field pervious concrete slab. Additionally, a simple correlation is provided that allows concrete designers to estimate the porosity ofpervious concrete based on its aggregate bulk density when crushed limestone is used. This practical tool saves time when designing pervious concrete mixtures.

Interfacial Bond between Reinforcing Fibers and Calcium Sulfoaluminate Cements: Fiber Pullout Characteristics

The results of an experimental investigation on the influence of the interfacial bond of reinforcing fibers embedded in a calcium sulfoaluminate matrix on the fiber-pullout peak load and energy consumption are presented. Bonding at the fiber-matrix interface plays an important role in controlling the mechanical performance of cementitious composites - in particular, composites formed from sulfate-based systems (calcium sulfoaluminate [CSA] cements), as opposed to the silicate systems found in portland cement. Various types of fibers were selected, including polyvinyl alcohol (PVA), polypropylene, and copper-coated steel. The fibers were embedded in three different matrixes: two sulfate-based cements including one commercially available CSA cement and a CSA fabricated from coal-combustion by-products. The third matrix was a silicate-based ordinary portland cement (OPC). In this study, the results of the single-fiber pullout test were coupled with scanning electron microscopy (SEM) to examine the interfacial bond between the fiber and CSA matrix for evidence of debonding and possible hydration reaction products.

Evaluation of Aspects of E* Test by Using Hot-Mix Asphalt Specimens with Varying Void Contents

A dynamic modulus master curve for asphalt concrete is a critical input for flexible pavement design in the Mechanistic–Empirical Pavement Design Guide developed in NCHRP Project 1-37A, which has drawn much attention among asphalt technologists. The objectives in this study were (a) to consider and compare different analysis techniques for construction of the master curve and (b) to measure and analyze the effect of permanent strain on samples that have been evaluated with one of the simple performance tests, dynamic modulus. It was found that differences existed in the calculated asymptote values and the shape of the master curve, depending upon which method was adopted. Recommendations are made for modifications to the testing protocol and for further work to determine the effect of permanent strain at higher test temperatures.

Superpave® Laboratory Compaction Versus Field Compaction

Laboratory compaction is an important part of asphalt mix design. For the mix design process to be effective, laboratory compaction must adequately simulate field compaction. In this study mechanical properties measured with the Superpave® shear tester were used to evaluate field compaction and laboratory compaction. The field compaction consisted of three test sections with different compaction patterns. The laboratory compaction used the Superpave gyratory compactor with adjustments to several parameters. Results of this study indicate that current gyratory protocol produces specimens with significantly different mechanical properties than those of field cores produced with the same material and compacted to the same air voids. Results also show that adjustments to certain parameters of the gyratory can produce specimens that better simulate the mechanical properties of pavement cores.

Applicability of Superpave to Modified Asphalts: A Mixture Study

Superpave binder and mixture specifications are currently being reviewed for their applicability to modified asphalts. This study was designed to evaluate a series of modified binders with the same Superpave performance grade (PG 76-22). The experiment was based on the following hypothesis: The performance characteristics for a given asphalt mixture will be the same for all PG 76-22 binders. The performance indicators analyzed in this study were obtained from a suite of laboratory mixture performance tests. The study, which also included a PG 64-22 asphalt to serve as the control, revealed that the hypothesis may be rejected. That is, mixture performance potential would be significantly different for various modified asphalts of the same performance grade. Loading frequency and strain dependency were noted as the most significant behaviors to address. Finally, recommendations were made for possible modifications of Superpave specifications to address these issues.

Comparison of Performance Properties of Terminal Blend Tire Rubber and Polymer Modified Asphalt Mixtures

Incorporation of used tires in asphalt mixtures has been a major advancement in the using recycled materials in asphalt pavements. Tires contain some of the polymeric components that have been used to modify the asphalt binders for decades, but in a solid form. This paper presents the result of a research to examine whether or not the proper application of the tire rubber in asphalt mixtures can enhance the pavement’s mechanical properties to the same degree that the traditional polymeric binder modifiers do. The performance of a terminal blend tire rubber mixture was compared to a polymer-modified mixture through mechanical testing at the Asphalt Institute laboratory. Two mixtures in this study were designed with the same gradation in accordance with the California standard specifications, one with polymer, and the other with terminal blend asphalt. Flexural beam fatigue test, Superpave shear test, and disk-shaped compact tension test were conducted to evaluate the performance of the mixtures with respect to fatigue cracking, rutting, and low temperature cracking, respectively. The results revealed that the terminal blend mixture would have a better rutting performance. Furthermore, the terminal blend mixture exhibited a slightly more ductile behavior at the low temperature of -12°C. The two mixtures showed a similar performance with respect to fatigue cracking at 20°C.

Contractor Performed Quality Control on KyTC Projects

This report addresses issues related to transferring the responsibility for quality control from the Kentucky Transportation Cabinet (KyTC) to construction contractors. Surveys of the KyTC, other state departments of transportation, and Kentucky highway contractors were done to identify the advantages, concerns, and modifications of the Contractor Performed Quality Control (CPQC) program. An advisory committee of experienced KyTC engineers, Federal Highway Administration representatives, and contractor representatives met periodically to identify approaches for handling key issues of the program. Several key topics related to CPQC are presented in this report, with emphasis on quality control/quality assurance (QC/QA) administration, QC/QA procedures, quality acceptance and verification testing, and CPQC training. Specific issues related to CPQC pay items in Kentucky are also discussed. Several recommendations have been proposed to enhance the program. If properly implemented, CPQC can improve a contractors work performance and help relieve the States burden for inspection. Additional monitoring of the program is necessary to make further improvements and to include other pay items.

USE OF SCRAP TIRE CHIPS IN ASPHALTIC MEMBRANE

Findings of a study involving the use of scrap tire chips in an asphaltic membrane are reported. The research project was designed with two objectives in mind: investigate the effectiveness of an asphaltic membrane on top of a subgrade for maintaining moisture equilibrium in subgrade and study the potential use of scrap tire chips in asphaltic membranes. The effectiveness of the membrane as a moisture barrier needs to be evaluated over a long period of time. However, the method proved to be a cost-effective way of recycling waste tires in pavements. It is hoped that this study will contribute to various efforts in the area of cost-effective and sound use of waste materials in construction.

A study of the suitability of the KENTORT II eastern shale oil for asphalt paving applications

Abstract The uncertain future of petroleum reserves has fuelled the search for alternative resources. A feasibility study was conducted to determine potential paving applications of the oil extracted from eastern shale by the KENTORT II process. The eastern shale oil (ESO) in this study was separated into two drastically different viscosity portions, designated as ‘hard’ and ‘soft’ ESO. It was hypothesized that the ‘hard’ portion might enhance the asphalt performance by increasing the stiffness. It was discovered that the ‘hard’ ESO modified asphalt properties deteriorate significantly with time. On the other hand, the ‘soft’ ESO was found to exhibit desirable properties in an asphalt recycling application. Further studies are recommended to fully characterize the binder and mixture properties of ESO modified/rejuvenated asphalts.