Pavement Life-Cycle Cost and Asphalt Binder Quality: Theoretical and Experimental Investigation

Quality control/quality assurance tests can be used to demonstrate that an as-constructed pavement has characteristics different from the contracted specifications of the as-designed pavement because the bitumen employed was of insufficient quality. Many different issues affect asphalt binder quality. Such problems can significantly increase the pavement life-cycle cost, which means that a pay adjustment (PA) is needed. Unfortunately, the quantitative analysis of this issue is very complex. The objectives of this study were to model the dependence of the pavement life-cycle cost on asphalt binder quality and to determine the quantitative relationship between bitumen viscosity and the PA for a given class of boundary conditions. In addition to modeling this problem theoretically, experiments and simulations were carried out through the use of the Mechanistic-Empirical Pavement Design Guide. We then derived the consequences of these effects on life-cycle cost by using a specific life-cycle cost model. Our results demonstrate that asphalt binder viscosity can strongly affect the expected pavement life and the PA, and thus needs to be taken into account in contract and construction management.     

Construction Quality Control for Asphalt Concrete Hydraulic Barriers

Asphalt concrete has been used for low permeability barriers in numerous applications over many centuries. In recent times, asphalt concrete barriers have been used for waste containment applications. The hydraulic conductivity of asphalt concrete specimens can be measured in the laboratory; however, there is no expedient, efficient way of accurately measuring the in situ hydraulic conductivity of low permeability asphalt concrete shortly after its placement and compaction in the field. A method has been developed to efficiently check the in situ hydraulic conductivity of asphalt concrete in the field. Asphalt concrete specimens with varying asphalt cement contents and unit weights were prepared in the laboratory and their hydraulic conductivity measured. The measured hydraulic conductivity data were grouped into different ranges and plotted as a function of unit weight and asphalt cement content. An acceptable zone was specified for a combination of asphalt cement content and unit weight that resulted in a specified hydraulic conductivity. In the field, a quality control inspector can check the unit weight and asphalt cement content of the in-place barrier to make sure it lies within the acceptable zone. The asphalt cement content and unit weight can be readily measured, thereby allowing rapid acceptance or rejection of the asphalt concrete barrier shortly after compaction.     

Evaluation of Full-Depth Asphalt Pavement Construction Using X-Ray Computed Tomography and Ground Penetrating Radar

In the past few years, a number of full-depth or perpetual pavements have been designed and constructed in the State of Texas. A study was conducted to examine the quality of the compaction of the thick asphalt layers within these pavements using advanced forensic tools such as X-ray computed tomography (X-ray CT) and ground penetrating radar (GPR). The GPR is a nondestructive tool for evaluating the uniformity of density in pavements at highway speed. X-ray CT is a laboratory tool that is used to conduct detailed analysis of air void distribution and uniformity in asphalt pavement cores. This paper presents the results of analyzing one of the perpetual pavements constructed in State Highway 114 (SH-114). In this project, two different structural asphalt pavement sections were placed, one included a 1?in. (25.4 mm) stone filled (SF) Superpave mix and the other included a traditional dense graded Type B material. The dense graded Type B material was found to be uniformly compacted. However, major compaction problems were identified with the coarse SF Superpave mix. The poor compaction and associated high percent air vsoids were found to permit moisture infiltration, which could potentially lead to rapid pavement deterioration. The analysis showed very good agreement between the GPR and X-ray CT results and demonstrated the efficiency of using GPR and X-ray CT in the evaluation of asphalt pavement compaction.     

Finite Element Studies of Asphalt Concrete Pavement Reinforced with Geogrid

Many geotechnical applications are becoming more sophisticated and solutions derived from simplistic procedure are no longer reasonable or solutions do not exist. This paper describes two-dimensional finite element studies that analyzed the behavior of reinforced asphalt pavement under plane strain conditions and subject to monotonic loading. The asphalt material and soils were expressed using triangular elements of elastoplastic behavior that obeys Mohr–Coulomb criteria with associated and nonassociated flow rules. The geogrid was modeled using a one-dimensional linear elastic bar element. The finite element procedure was validated by comparing the results of analysis with the results obtained from a series of model tests. The load–settlement relationships, settlement profile, and strains in the geogrid were compared. The failure load obtained by assuming subgrade foundation with nonassociated flow rule was smaller than that of associated flow rule. There was only minor difference between the results obtained from the associated and nonassociated plastic models. The finite element procedure was capable of determining most measured quantities satisfactorily except the tensile strain in the geogrid, which was assumed linear elastic. The effects of the stiffness of geogrid reinforcement, thickness of asphalt layer, and strength of subgrade foundation were also investigated. The finite element procedure is a versatile tool for enhanced design of reinforced pavement systems.     

Construction Management of a Small-Scale Accelerated Pavement Testing Facility

Research in accelerated pavement testing (APT) facilities has traditionally focused on the pavement performance such as rutting and fatigue cracking, but documentation on construction management and information of the actual pavement construction quality is limited. There are typically four critical factors that need to be considered to achieve the best possible outcome in construction: cost, schedule, construction process, and quality control, and management. With the objective of developing guidelines for planning and executing construction of a small-scale APT facility, this paper presents a case study documenting and evaluating the construction process and construction management efforts of two sensor-instrumented hot mix asphalt pavement test sections built in a small-scale APT facility. The focus of the experiment was to study bottom-up fatigue cracking of the flexible pavement structure. The presented information and lessons learned serve as a template and guide for agencies pursuing this type of research and pavement construction.     

Evaluating Cost Overruns of Asphalt Paving Project Using Statistical Process Control Methods

While some projects will experience changes to the contracted cost by deduction or additions, construction cost overruns are becoming a common problem in the construction industry. Steps need to be taken to minimize cost overrun through cost and quality control techniques. This paper presents a study conducted to evaluate construction cost overruns of asphalt paving operations performed by the Illinois Department of Transportation (IDOT). The main objective is to analyze the main causes of cost overruns and evaluate the amount of cost overrun of asphalt paving operations, using statistical process control (SPC) techniques. Real data from projects in the year 2000 were collected from IDOT. These data contain cost information of 219 projects. The results indicate that the average cost overrun for the sample collected was 4% above the bid price. Reasons for cost overruns are analyzed and a Pareto chart and a cause and effect diagram are constructed. Individuals and Moving Range (MR) control charts are developed and their interpretation and use are discussed. Furthermore, the benefits and limitations of using the individuals and MR chart in cost control applications are pointed out. It is recommended that SPC analysis be an integral part in managing and controlling project costs.     

Application of Graded Finite Elements for Asphalt Pavements

Asphalt paving layers, particularly the surface course, exhibit vertically graded material properties. This grading is caused primarily by temperature gradients and aging related stiffness gradients. Most conventional existing analysis models do not directly account for the continuous grading of properties in flexible pavement layers. As a result, conventional analysis methods may lead to inaccurate prediction of pavement responses and distress under traffic and environmental loading. In this paper, a theoretical formulation for the graded finite element method is provided followed by an implementation using the user material subroutine (UMAT) capability of the finite element software ABAQUS. Numerical examples using the UMAT are provided to illustrate the benefits of using graded elements in pavement analysis.     

Accuracy of Ground-Penetrating Radar for Concrete Pavement Thickness Measurement

Core extraction is the most common method for measuring concrete layer thickness in pavement construction. Although this method provides a very accurate thickness measurement, it is destructive, time-consuming, and does not provide adequate representation of the concrete layer thickness variability. Ground-penetrating radar (GPR) is a nondestructive evaluation technique that has been successfully used in several transportation applications, such as subsurface exploration and condition assessment. The main objective of this research is to investigate the accuracy and cost-effectiveness of using GPR in thickness measurement of concrete pavement for quality assurance purposes. A high-resolution 1.6-MHz ground-coupled antenna was used to perform grid scans and measure concrete thickness for several laboratory and field experiments. Results indicated that the use of metal objects underneath the concrete layer to improve bottom surface reflectivity was necessary for a reliable thickness measurement. Also, the use of calibration cores to determine the actual dielectric properties of the concrete was essential for accurate thickness calculation. An average accuracy of 98.5% was achieved when steel plates were used underneath the concrete layer and two cores were extracted for calibration. The effect of concrete age on GPR thickness measurement accuracy was also investigated.     

Microstructural Viscoplastic Continuum Model for Permanent Deformation in Asphalt Pavements

Permanent deformation is one of the major distresses in asphalt pavements. It is caused mainly by high traffic loads associated with high field temperatures. An anisotropic viscoplastic continuum damage model is developed in this study to describe permanent deformation of asphalt pavements. The model is based on Perzyna’s formulation with Drucker–Prager yield function modified to account for material anisotropy and microstructure damage. The material anisotropy is captured through microstructural analysis of aggregate distribution on two-dimensional sections of hot mix asphalt. A damage parameter is included in the model to quantify the nucleation of cracks and growth of air voids and cracks. A parametric study was conducted to demonstrate the sensitivity of the model to strain rate, aggregate distribution, and microstructure damage. Triaxial strength and static creep measurements obtained from the Federal Highway Administration Accelerated Loading Facility were used to determine the model parameters.     

NJTxtr—A Computer Program Based on LASER to Monitor Asphalt Segregation

Abstract: This paper describes the research funded by the New Jersey Department of Transportation to develop an automated technology to monitor segregation during construction of hot-mix asphalt concrete pavements. A Laser-based system was used to measure surface texture and to detect segregation. Two segregated test sections and a control test section were tested to evaluate the applicability of Laser texture method to detect and quantify segregation. Laser texture data were gathered from all three sections. Ratios of texture in segregated areas to that in nonsegregated areas were set as the basis for detection of different levels of segregation. By combining the level of segregation and extent of segregation, an AREA index was developed to determine the acceptability of a pavement section. Based on AREA index, pay adjustment factors were proposed to reduce the payment to account for loss of pavement life due to segregation. Further remedial actions were proposed to correct segregated pavement sections with acceptable AREA index. Based on the above concepts, Windows-based computer program NJTxtr was developed to detect and quantify segregation. This computer program uses the Laser-equipment-collected pavement texture data and determines whether the pavement section is acceptable or unacceptable based on the level of segregation within a pavement section, and provides bonus or penalties to the contractor. The paper describes a novel technology using laser and associated software for construction quality control of asphalt concrete pavements. The proposed methodology was applied to detect segregation in an interstate highway section in New Jersey, and this section was repaved based on visual observation and recommendation from this study.     

Effect of Specifications Type on the Quality of Paving Contracts in New Brunswick

Construction specifications are used by transportation agencies to define the client’s requirements of the final product. The primary motivation of adopting the newer end result specification (ERS) or performance related specification over method-based specification (MBS) is to reduce clients’ costs, encourage contractors’ innovation, and improve overall quality. However, some transportation agencies have been reluctant to fully implement ERS due to lack of demonstrated evidence on whether they achieve comparable level of quality or performance. This paper investigates if the specification type has any effect on quality. The case study presented is based on data from New Brunswick Department of Transportation (NBDOT) from years 2003–2007. NBDOT generally uses ERSs to call paving contracts equal to or larger than 8,000 t. MBSs are used for all other smaller paving contracts. The most prevalent indicator variables for accepting asphalt paving jobs in North America [that is, percent theoretical maximum relative density, asphalt binder content, air voids, voids in mineral aggregates, percent passing 4.75 mm (No. 4), and 75?μm (No. 200) sieves] were investigated. Statistical analysis was performed to compare the deviation of the quality indicator variables from their respective job mix formula values for paving projects that used MBS or ERS. ANOVA results revealed that there were no significant differences between the qualities achieved from the two specification types. Also, no significant differences were found from within-specification comparisons over the time frame examined. Given the possible cost advantages from agency’s point of view, the flexibility of the contractors to innovate and the fact that this study demonstrates quality is not compromised, there is an opportunity for agencies to expand or fully adopt the use of ERS specifications.     

The Pavement Enterprise at Michigan Technological University

A project-based student Enterprise program was established at Michigan Technological University as part of an effort, funded by the National Science Foundation, related to reform of engineering education. The Enterprise program represents a separate degree track available in all departments of the College of Engineering. The Pavement Design, Construction, and Materials (Pavement) Enterprise was established in the Department of Civil and Environmental Engineering in conjunction with the Thompson Scholars program. The Thompson Scholars program is an asphalt-paving-industry-supported scholarship program. The Pavement Enterprise is composed of a team of students that work in a businesslike setting on projects related to the asphalt paving industry. In addition to their project activities, students are required to participate in paid summer internships in associated industries and organizations. An Advisory Board composed of industry and government leaders meets three times a year to provide advice, guidance, and feedback to the students and associated faculty. The team project activities of the Pavement Enterprise prepares graduates for careers in the pavement engineering field with knowledge and skills well beyond their peers in the traditional civil engineering curriculum. These team projects incorporate “active learning” techniques into the program. The performance of the Pavement Enterprise is demonstrated using student attrition as well as a peer review. Lessons learned in the operation of the program are presented for those institutions considering a similar program.     

Visualization and Simulation of Asphalt Concrete with Randomly Generated Three-Dimensional Models

The objective of this study is to visualize and simulate microscale properties of asphalt concrete with three-dimensional discrete element models under mechanical loading. The microstructure of the asphalt concrete sample was composed of three ingredients: coarse aggregates, sand mastic (a combination of fines, fine aggregates, and asphalt binder), and air voids. Coarse aggregates were represented with the irregular polyhedron particles which were randomly created with an algorithm developed for this study. The gaps among the irregular particles were filled with air voids and discrete elements of sand mastic. The mechanical behaviors of the three ingredients were simulated with specific constitutive models at different contacts of discrete elements. Based on the geometric and mechanical models, visualization and simulation of asphalt mixtures were conducted in this study.     

Slippage Failure of a New Hot-Mix Asphalt Overlay

A premature pavement overlay failure had occurred only 1 day after it was opened to traffic. Crescent-shaped cracks were intermittently spread over a section about 3 mi in length. Dynamic cone penetrometer results demonstrated that the slippage cracks were not linked to weak base or subgrade. Loss of overlays on structurally sound pavements due to poor bonding is an expensive error. A tack coat is considered a simple, relatively inexpensive, yet essential step in the pavement construction process. It is theorized that the ineffective bonding due to poor quality tack coat and/or inappropriate application rate is the primary factor that led to the slippage cracks. Other contributing factors include low asphalt content and high aging ratio that reduced the effectiveness of the bond. The aging ratios exceed the maximum allowable 3.5 specified. Based the investigation results, the contractor did remove and replace the top 50 mm hot-mix asphalt (HMA) overlay at his own expense. Although selection of proper tack coat materials and quantities is essential, there is a lack of proper construction quality control and quality assurance procedure to ensure appropriate surface preparation prior to application of a HMA overlay.     

Use of an Infrared Joint Heater to Improve Longitudinal Joint Performance in Hot Mix Asphalt Pavements

Longitudinal joint cracking is one of the most prevalent forms of distress in asphalt concrete pavements. The joint area does not achieve the same density as the mat due to an unconfined edge on the initial pass and a cold joint during the second pass. The lower density allows water to penetrate and the material cracks, usually within one?year of construction. There are many techniques for constructing longitudinal joints, one being to preheat the joint prior to paving the second lane. This paper describes a field study conducted in New Hampshire using an infrared joint heater. Thermocouples were embedded in the pavement to determine the extent of heat penetration from the infrared heaters. Cores were taken along the joint and in the travel lanes for both the control and test sections. Density and strength measurements were taken on the cores. Permeability measurements along the control and test joints were performed. A cracking survey performed one?year after construction showed that the section of pavement where the infrared heater was used had significantly less cracking than the control section.     

Using Scanning Lasers to Determine the Thickness of Concrete Pavement

Due to limited budgets and reduced inspection staff, state departments of transportation are in need of innovative approaches for providing more efficient quality assurance on concrete paving projects. In Iowa, the current technique is to take core samples of the pavement, which is a labor intensive, destructive process. Due to these limitations, a limited number of cores are used to estimate the pavement thickness. Any method that can reduce or eliminate cores and increase the statistical accuracy of the thickness estimate will be beneficial. One method, which uses a laser to scan the surface of the base prior to paving and then to scan the surface after paving can determine the thickness at any point. Also, scanning lasers provide thorough data coverage that can be used to calculate thickness variance accurately and identify any areas where the thickness is below tolerance. The laser scanning methodology for this study involved the following: (1) investigating characteristics of the paving process; (2) using a laser scanner on three different sites; (3) processing the data to create clean surface models; (4) performing statistical analyses to determine thickness variability; and (5) summarizing the results.     

Dynamic Numerical Analysis of Antimoisture-Damage Mechanism of Permeable Pavement Base

As a permeable base material of pavement, the large stone porous asphalt mixture (LSPM) is used widely in China to lessen the moisture damage of the asphalt pavement. However, the dynamics mechanism of the inhibitory effect of permeable base on moisture damage is not clear yet. The dynamic fluid-solid coupling analysis of the saturated pavement with LSPM base course, considering the asphalt mixtures as the porous medium, was performed using the finite difference numerical code FLAC3D. Numerical results revealed that the positive and negative dynamic pore pressure alternated in the pavement with the approaching and leaving of the wheel loads. The phenomenon of water pumping out of and sucking into the pavement under the moving loads was proved. The flow of fluid in pavement can be regarded as the laminar flow. The presence of the LSPM base course greatly decreased the dynamic pore pressure and the scouring force in the surface course because of the large permeability coefficient of the LSPM. The location of the maximum dynamic pore pressure also changed due to the LSPM base course. Due to the permeable base, the dissipation of the dynamic pore pressure was accelerated and thus the moisture damage was lessened.     

Field Trial for Asphalt Pavements Reinforced with Geosynthetics and Behavior of Glass-Fiber Grids

This paper presents details of a large field trial and some observations conducted to evaluate the practical efficiencies of geosynthetically reinforced asphalt pavements in Shanxi Province, China. Three glass-fiber grids (LB2000 II, TGG-8080, GGA 2021), one plastic grid (Tensar AR1), two geotextiles (nonwoven needle-punched and nonwoven heat-bonded), and one geocomposite (Tensar AR-G) application were selected for evaluation. These geosynthetics were installed in the interface between new asphalt pavement layers (APL) and new cement-stabilized gravel–sand base courses coated by emulsified asphalt or within new APL in the reconstruction of asphalt pavement sections (Program I), or in the interface between old APL and new overlay layers in the asphalt overlay pavement sections (Program II). In each program, reinforced sections with different geosynthetics were compared with each other and with nonreinforced sections to determine relative performance. Inspections after construction showed that the integrated damage ratio and deflection in the pavement sections reinforced with glass–fiber grids were less than other pavement sections. Furthermore, after about 4?years of service, glass-fiber grids were dug out and no breaking and node movement were discovered. Nevertheless, observations indicated that geosynthetics may not be effective, if bearing capacity of the base course/subgrade is inadequate, or if the overlay thickness is too thin, or if preconstruction repair of distressed old pavement is incomplete.     

Neural Network–Based Intelligent Compaction Analyzer for Estimating Compaction Quality of Hot Asphalt Mixes

Continuous real-time estimating of compaction quality during the construction of a hot mix asphalt (HMA) pavement is addressed in this paper. The densification of asphalt pavements during construction usually is accomplished by using vibratory compactors. During compaction, the compactor and the asphalt mat form a coupled system whose dynamics are influenced by the changing stiffness of the mat. The measured vibrations of the compactor along with process parameters such as lift thickness, mix type, mix temperature, and compaction pressure can be used to predict the asphalt mat density. Contrary to existing techniques in the literature in which a model is developed to fit experimental data and to predict mat density, a neural network-based approach is adopted that is model-free and uses pattern-recognition techniques to estimate density. The neural network is designed to read the entire frequency spectrum of roller vibrations and to classify these vibrations into different levels. The intelligent asphalt compaction analyzer (IACA) is then trained to convert these vibration levels into a “number” indicative of the asphalt mat density at a given location. This two-step process eliminates the need for regression analysis and produces more accurate density measurements than those reported elsewhere in the literature. Compaction studies of HMA mixes on a stiff subgrade indicate that the changes in the vibration characteristics of the roller are attributable to an increased compaction of the HMA base. The results also show that, with the neural network working as a classifier, the IACA can estimate the density continuously, and in real time, with accuracy levels adequate for quality control in the field.     

Approaches to Rut Depth Prediction in Semirigid Asphalt Pavements

Rutting has an adverse effect on safety and riding comfort of pavement. Reliable prevention and prediction of rutting has been one of the major focuses in road research. This paper summarizes the methods available for rut depth prediction and performs a case study in two separate ways based on the data acquired from a full-scale indoor circular road test. One was to formulate the possible rut depth by integrating a four-element-five-parameter viscoelastic model and the layered strain approach. The other was based on an empirical method. It is verified that both methods are applicable in predicting rut depth within the near future after open to traffic. The empirical method, however, is also capable of predicting rut depth within the whole design life. And theoretical method proves inadequate because of the limitation of the model itself and also of the method for obtaining parameters.