E Ray Brown

Laboratory Study of Full-Depth Reclamation Mixes

Full-depth reclamation (FDR) is the technique of in-place recycling of the asphalt-bound layer of a pavement along with part of the underlying unbound layer to produce an improved base material. The objective was to develop a mix design system for FDR and evaluate the performance of designed reclaimed materials from the western part of Maine. Mixes were prepared in the laboratory, and samples were compacted with the Superpave® gyratory compactor. The samples were then tested for bulk specific gravity and resilient modulus. Samples of mixes prepared with asphalt emulsion, water, emulsion plus lime, emulsion plus cement, and emulsion plus lime and cement were also tested for their resilient moduli at different cure times and for their shear strengths. Rut tests were also conducted with the samples under water to evaluate the stripping potentials of the different mixes. The test results showed that maximum density and resilient modulus criteria can be used to select the optimum additive content for water and asphalt emulsion mixes. Comparison of performance testing results showed that mixes with additives develop strength faster and show significantly higher shear strength and stripping resistance than mixes with water only. For the materials tested, addition of lime and cement with asphalt emulsion appears to increase the rate of gain in strength and, hence, to result in faster curing and to increase the shear strength as well as resistance against moisture damage. It is recommended that FDR sections with asphalt emulsion, lime, and cement be constructed and evaluated for in-place performance.

Online Tools for Hot-Mix Asphalt Monitoring

The feasibility, realistic possibility, and practicality of developing and deploying, on a local or national scale, an online database to monitor hot-mix asphalt projects throughout their life cycles are demonstrated. Such a tool allows the real-time acquisition and monitoring of mix design, field construction, and performance data, as well as archiving of such data. Monitoring functions include browsing, searching, and analysis of data ranging from mix design and quality assurance/quality control data from the field to performance measures such as roughness, cracking, and rutting. In particular, early implementation via Washington State’s Superpave® project data is demonstrated. The database includes quantitative design and construction data, field instrument readings, infrared and video images, and performance information. Analysis and search capabilities are provided, including a map-based front end to support spatial searches and location-based data entry.

Evaluation of Two Compaction Levels for Designing Stone Matrix Asphalt

Current stone matrix asphalt (SMA) design guidelines list two compaction options to design SMA, 50 blows Marshall or 100 gyrations with the Superpave® gyratory compactor (SGC). However, some states have found that 100 gyrations with the SGC is excessive for their materials. In this study a lower compaction level of 65 gyrations was used to compare with the standard 100 gyrations to design SMA mixtures. Results showed that mixtures designed by 65 gyrations had an average of 0.7% higher optimum asphalt content and 1.5% higher voids in mineral aggregate (VMA) than those designed by 100 gyrations. All mixtures designed by 65 gyrations met the minimum asphalt content and VMA requirements for SMA, whereas only eight of 15 mixtures designed by 100 gyrations met those two requirements. Compaction at 100 gyrations resulted in an additional 0.62% average aggregate breakdown at the critical sieve as compared with 65 gyrations. SMA mixtures designed by 65 gyrations and 100 gyrations had an average asphalt pavement an...

An Overview of Fundamental and Simulative Performance Tests for Hot Mix Asphalt

Numerous fundamental and simulative test methods are being used to evaluate the performance of Hot Mix Asphalt (HMA). Permanent deformation, fatigue cracking, thermal cracking, loss of surface friction, and stripping are the 5 main distress types for HMA pavements. All of these distresses can result in loss of performance, but rutting is the one distress that is most likely to be a sudden failure as a result of unsatisfactory HMA. Other distresses are typically long term and show up after a few years of traffic. This paper provides a general overview of the fundamental, empirical, and simulative tests for HMA corresponding to each of these 5 distresses. All test methods have been evaluated in terms of advantages and disadvantages. However, major emphasis has been placed on tests for evaluating permanent deformation.

Evaluation of remaining fatigue life model for hot-mix asphalt airfield pavements

Several design criteria exist for predicting the fatigue life of hot-mix asphalt (HMA) pavements. Researchers previously developed an Aged Asphalt fatigue criterion from laboratory testing of aged field HMA airfield pavements. This criterion is unique because the majority of the existing fatigue criteria were developed from laboratory-prepared specimens. In this paper, a comparison of the Department of Defense (DoD), the Asphalt Institute (AI) and the Aged Asphalt fatigue models was completed for the HMA surfaces. The analysis showed that the Aged Asphalt fatigue criterion was more conservative than the DoD and AI fatigue criteria at low strain levels and low pavement modulus values. Furthermore, the Aged Asphalt fatigue criterion revealed that fatigue life decreased with increasing strains but increased with increasing modulus values. After evaluating the potential causes of this unexpected trend in detail, it is reasonable to expect that stiffer in situ mixes will have a longer fatigue life than less stiff mixes.

Criteria for using the Superpave gyratory compactor to design airport HMA mixtures

Asphalt concrete pavements for commercial airport applications in the USA are constructed according to guidelines in Item P-401, ‘Plant Mix Bituminous Pavements’, Federal Aviation Administration (FAA) Advisory Circular 150/5370-10E. Item P-401 specifies the material characteristics and construction requirements for airport asphalt pavements, but does not currently provide guidance for using the Superpave gyratory compactor (SGC) in the preparation of specimens used in the design of hot mix asphalt (HMA) mixtures. Nearly all state departments of transportation in the USA use the SGC along with the Superpave mix design procedure. Since most HMA mixes are used in roadways, many asphalt contractors no longer maintain expertise and equipment for conducting the Marshall mix design procedure currently used by the FAA. The lack of contractors familiar with the Marshall method may become a significant problem for the FAA in the future. This paper describes a laboratory study of the HMA mix design for airport pavements, which uses the SGC. The purpose of the study was to determine the number of gyrations with the SGC needed to design asphalt pavement mixtures for airports. A value of 70 gyrations is recommended for further evaluations based on the comparisons of volumetric measurements of HMA mixture specimens compacted using Marshall compaction with specimens from the same mixture compacted using Superpave gyratory compaction.

Flowable Fill for Rapid Pavement Repair

The federal, state, and local highway authorities in the United States invested

The FHWA’s Demonstration Project for Enhanced Durability of Asphalt Pavements through Increased In-Place Pavement Density

3.9 billion in the rehabilitation of roughly 8,000 mi of pavement in 2008. This significant investment emphasizes the importance of ensuring that rehabilitation techniques perform well to help reduce the high annual cost for repairs. The repair of pavement base layers with compacted lifts of crushed aggregate requires specialized labor and equipment, contributes significantly to total construction time, is very difficult to perform—particularly in restricted access areas—and often results in a poorly constructed repair and loss in performance. Flowable fill technology has shown some success when used for backfilling patches and utility cut repairs. The purpose of this paper is to present performance and cost advantages of using preblended flowable fill for rapid repair of damaged areas in highway and airfield pavements. Eleven commercially available flowable fill blends were evaluated with laboratory and field testing methods. The laboratory evaluation consisted of standard material characterization testing including compressive strength, flowability, hardening time, and excavatability. Field testing included constructing and trafficking simulated utility cuts and full-depth patches in existing pavements. An examination of structural capacity, surface deformation, and visible surface distress was conducted for each repair at regular traffic intervals. In addition, construction time, difficulty, and cost were compared with those of a traditional aggregate repair. Testing results indicate that backfilling utilities and patches in pavements with flowable fill reduce the potential for premature failure, reduce construction time, and reduce total project cost while increasing repair performance.

DENSITY OF ASPHALT CONCRETE--HOW MUCH IS NEEDED?

Recognizing the importance of in-place density in building cost-effective asphalt pavements, a Federal Highway Administration (FHWA) Demonstration Project was created for “Enhanced Durability of Asphalt Pavements through Increased In-Place Pavement Density.” The objective of the demonstration project was to determine the benefit of additional compaction and show that additional density could be obtained through improved techniques. This project effort included two major components: (1) a literature search to serve as an educational component regarding the best practices for increasing density, and (2) the construction of 10 field demonstration projects. Eight of the 10 states improved densities by at least 1% compared to a control section on their field demonstration projects. There were at least two pavement sections (a control and at least one test section) constructed within each of the 10 states that participated in this field demonstration project. Many of the states constructed more than two pavement sections for a total of 38 sections. There were many variables, including mixture type, construction equipment, and procedures between states and within states. A summary of the methods that states used to obtain increased density generally fell into one of five categories: (1) improving the agency’s specification by including or increasing incentives and increasing the minimum percentage density requirements; (2) making engineering adjustments to the asphalt mixture design to obtain slightly higher optimum asphalt content (although not part of the original goal of the demonstration project); (3) improving consistency as measured by the standard deviation; (4) following best practices; and (5) using new technologies.