Committee Research Problem Statements

Transcription

1 Transportation Research Board Technical Activities Division Committee Research Problem Statements Group 2, Design and Construction of Transportation Facilities Section D - Bituminous A2D02 Committee on Characteristics of Nonbituminous Components of Bituminous Mixtures Preface An important function of the Transportation Research Board (TRB) is the stimulation of research toward the solution of problems facing the transportation community. One of the techniques employed by technical committees in support of this function is the identification of problems, and the development and dissemination of research problem statements. The aim of this activity is to provide information to governmental agencies, research institutes, industry, the academic community and others in allocating scarce resources to the solution of transportation problems. The problem statements listed below were developed by the TRB committee indicated above. Collectively they should not be considered an all inclusive recognition of research needs in the committee's technical area, but represent a portion of the overall needs identified by committee members. It is likely that some current research in progress or recently completed research was overlooked which may have altered the listings. Statements Problem Problem Statements Number 1 Development Of Improved Methods For Measuring Fine Aggregate Angularity 2 Evaluation Of Opto-Electronic Techniques For Measuring Aggregate Shape 3 Development Of A Mix Design Procedure For Open Graded Asphalt Friction Courses 4 Aggregate Morphology Needed For Stone Matrix (SMA)/Gap-Graded And Other Rut Resistant Asphalt Mixtures 5 Crumb Rubber Modified (CRM) Stress-Absorbing Membrane Interlayers For New Pavement Construction, Maintenance And Repair Of Existing Pavements And Bridge Decks 6 CRM Fiber As Reinforcement In HMA, Membranes Or SMA 7 Reclaimed/Reprocessed Materials In HMA 8 Aggregate Structure In Asphalt Concrete Mixtures Related To Pavement Performance PROBLEM 1: DEVELOPMENT OF IMPROVED METHODS FOR MEASURING FINE AGGREGATE ANGULARITY Fine aggregate angularity (FAA) specifications were designed by SHRP to promote high internal friction in hot mix asphalt and, thus, resistance to asphalt pavement rutting. FAA for Superpave mixtures is determined as the percent air voids in a loosely compacted sample of a standard grading (AASHTO TP 304, ASTM C 1252). This test is based on the assumption that more fractured faces and higher texture of the faces will result in higher void contents in the loosely compacted sample. This is not always true. Many sources of fine aggregates that have a history of excellent field performance do not meet the Superpave FAA criteria. As a result, some agencies have met extreme difficulty in achieving the specified FAA values. Typically, these problem fine aggregates are 100% crushed, cubical, calcareous materials. In cases where FAA requirement has not been met, the requirement has either been waived (avoid the problem) or complying fine aggregate has been imported (throw money at the problem). A major concern is that no aggregate research was included in SHRP to validate and verify the FAA procedure and limits selected. A novel test protocol for directly measuring FAA along with meaningful criteria needs to be developed. Researchers should identify fine aggregate properties related to internal friction and rutting in

2 pavements. The current test does not directly measure aggregate angularity, but techniques are available that can directly do so. Image analysis techniques include fractal dimension analysis, Hough transform, Fourier analysis, image digitizing and others. In fact, studies have shown good correlations between particle shape and texture measured by fractal analysis and creep test results of asphalt concrete paving mixtures. Examine variables affecting SHRP procedure for measuring FAA (e.g. specific gravity, particle shape cubical or not, particle size and distribution, etc). Analyze the data from previous laboratory and field research to determine appropriateness of the angularity test procedure and the Superpave criteria. Develop a new or revised procedure and criteria that are capable of directly measuring angularity and surface texture of fine aggregates that consistently relate to pavement performance. Two related studies began in The International Center for Aggregates Research (ICAR) is sponsoring a study to compare FAA to other measures of angularity and compare FAA in asphalt mixtures with pavement rutting performance using the LTPP database. A pooled-fund study at the North Central Superpave Center in Indiana is examining laboratory rutting performance of asphalt mixtures containing different levels of FAA. These studies will provide valuable information to help assess the magnitude of the problem as well as important databases for this proposed study. This research is critical to the highway industry and the taxpaying public. If the Superpave FAA test routinely eliminates locally available aggregates of good quality, costs of HMA will increase significantly and unnecessarily. Results of this research will establish the appropriateness of the current Superpave test and criteria as well as revise or replace the test. The deliverable will be capable of immediate implementation in the Superpave asphalt mixture design process. $400,000 over 3 years. PROBLEM 2: EVALUATION OF OPTO-ELECTRONIC TECHNIQUES FOR MEASURING AGGREGATE SHAPE Aggregate shape is believed to be an important factor in the performance of hot-mix asphalt (HMA). Superpave specifies three tests to measure aggregate shape: coarse aggregate angularity, flat and elongated particles and fine aggregate angularity. The coarse aggregate angularity test requires the operator to examine numerous particles and visually determine the number of fractured faces. The test is subjective and no precision statement exists. The flat and elongated test requires the operator to evaluate numerous particles including mm material using proportional calipers. Recent research indicates the test has poor precision. No research has been done to link flat and elongated particles to performance of HMA. Both coarse aggregate tests are extremely time consuming and difficult to use for aggregate quality control. Some have stated that the fine aggregate angularity test indicates better results for poorly shaped flat and elongated particles than cubical fine aggregates. Opto-electronic devices have been developed to measure aggregate shape. Some are commercially available. These devices could result in significant time savings as well as improved precision. Research is needed to develop these tests as surrogates for the currently accepted hand tests and relate their properties to performance.

3 Conduct a literature review to identify existing opto-electronic devices that may be used for aggregate shape measurement. Evaluate existing research. Choose a suitable device or devices. Evaluate a wide range of aggregates with both acceptable and unacceptable properties as determined by the current hand test procedures. Compare the evaluation of the hand methods to the opto-electronic device. Estimate criteria level based on the existing hand methods. Verify the proposed criteria by testing mixes produced from a subset of the above aggregates using performance tests (SST wheel trackers etc.) Prepare test methods and specifications in AASHTO format Virginia Transportation Research Council, University of Illinois at Urbana-Champaign and University of Arkansas are all conducting small scale studies. However, studies linking the proposed devices to performance or wide spread testing with numerous aggregate sources may not exist. There is an urgent need for better aggregate shape measurement techniques. These techniques need to be less time consuming and have better precision. These tests are an issue in many states implementing Superpave. $250,000 over 1.5 years. PROBLEM 3: DEVELOPMENT OF A MIX DESIGN PROCEDURE FOR OPEN GRADED ASPHALT FRICTION COURSES Open graded friction courses (OGFC) have been used since 1950 in different parts of North America to improve the friction resistance of asphalt pavements. The OGFC provides good, high-speed frictional qualities; reduces the potential for hydroplaning; reduces the amount of splash and spray, and also reduces the noise at the pavement/tire interface. The Federal Highway Administration (FHWA) developed a mix design procedure in 1974 for OGFC (FHWA Report No. FHWA-RD-74-2, January 1974 Design of Open-Graded Asphalt Friction Courses ) and promoted the use of OGFC in the 1970s for improving the friction resistance of asphalt pavements. Many state DOTs utilized this mix design procedure. However, experience of states with OGFC has been widely varied according to a recent survey conducted by the National Center for Asphalt Technology (NCAT) published as Transportation Research Board Circular Number E-C005 dated December 1998 Open-Graded Friction Course: State of the Practice. Whereas many states have reported good performance, other states have stopped using OGFC due to poor performance. The following problems were experienced by the states reporting poor performance: premature raveling of the surface, debonding, filling up of voids from sanding during winter time, stripping in underlying layers, and generally lower durability compared to dense-graded hot mix asphalt (HMA) overlay. Although, the FHWA revised the mix design procedure in 1990 (FHWA Technical Advisory T dated December 26, 1996 Open Graded Friction Courses ) most states who had unsatisfactory experience did not resume the use of OGFC. The NCAT survey has indicated that a vast majority of states reporting good experience with OGFC in recent years use polymer modified asphalt binders. Also, gradation of aggregates used by these states tend to be somewhat coarser than those used earlier based on the FHWA recommendations. This new generation of OGFC has also higher asphalt content than the OGFC used in the past. High asphalt content can be incorporated in the OGFC without any draindown problems because of polymer modification and/or introduction of fiber in the mix. It appears that good mix design and construction practice is the key to improved performance of OGFC mixes. The FHWA mix design procedure is no longer adequate for the new generation of OGFC. An improved, standard mix design

4 procedure is needed to help the transportation agencies start using OGFC, and obtain satisfactory durability and performance. The primary objective of this research project is to develop a standard mix design procedure for the new generation of OGFC mixes. The mix design should take the following factors into consideration: Resistance to permanent deformation. This can be achieved by ensuring a stone-on-stone contact similar to stone matrix asphalt (SMA). Durability. High asphalt binder contents should be used (requiring the use of polymer modified binders and/or fibers) to ensure satisfactory durability. Tests such as Cantabro abrasion test used in South Africa can be used to quantify durability. Draindown of asphalt binder. Draindown tests such as NCAT draindown test should be utilized to quantify the draindown. Permeability. A permeability test should be a component on the mix design process. Resistance to aging. Susceptibility of the OGFC mix to premature aging, which may cause raveling problems, should be evaluated. Key Words Open-graded friction course, OGFC, porous asphalt, mix design, durability Mix design procedures developed in Europe, South Africa, and Australia for porous asphalt (this term is used for OGFC in these countries) need to be evaluated. OGFC provides safety to motoring public in terms of high surface friction, reduced potential for hydroplaning, and reduced splash and spray. There is a need to have a standard mix design procedure for OGFC like we have for Superpave and SMA mixes. The availability of a standard mix design will encourage the transportation agencies to start using OGFC without any durability and performance problems. $500,000 over two years. PROBLEM 4: AGGREGATE MORPHOLOGY NEEDED FOR STONE MATRIX (SMA)/GAP-GRADED AND OTHER RUT RESISTANT ASPHALT MIXTURES The U.S. is importing European asphalt mix technology to produce rut resistant mixes. These SMA mixes, as well as Superpave and even some conventional dense-graded HMA mixtures for pavements with critical traffic volumes, require high quality aggregates to perform. A test or procedure is needed to identify aggregates of different rock types that are acceptable for use, since generic specifications tend to eliminate many rock types that have proven service records. Availability of high quality aggregates is limited and likely to become more so in the future. Develop an aggregate specification by rock type (morphology) for SMA/gap-graded and other asphalt mixtures for areas that allow and do not allow studded snow tires.

5 Many areas of the United States do not have access to aggregates that meet the quality requirements of SMA aggregates. The U.S. does have aggregates that have produced long-lasting pavements without meeting SMA specifications. The SMA/gap-graded and coarse Superpave gradations appear to be effective in minimizing rutting on high volume pavements. This research is needed so that more rut-resistant pavements can be placed using good quality local aggregates. Approximately $100,00-200,000 over 12 to 24 months. PROBLEM 5: CRUMB RUBBER MODIFIED (CRM) STRESS-ABSORBING MEMBRANE INTERLAYERS FOR NEW PAVEMENT CONSTRUCTION, MAINTENANCE AND REPAIR OF EXISTING PAVEMENTS AND BRIDGE DECKS Asphalt concrete overlays are a primary method of rehabilitating distressed asphalt and portland cement concrete pavements, including bridge decks. Reflective cracking is often the first distress that occurs in overlays, and it provides a path for surface water to infiltrate the pavement structure. Stress-absorbing membrane interlayers (SAMIs) have demonstrated the potential to significantly improve performance and serviceable life of the overlays by improving resistance to reflective cracking, keying the overlay to pavement, and providing a waterproof seal over the underlying pavement. Evaluate the design and performance of CRM SAMIs placed throughout the United States, including the coarser rubber systems developed by McDonald and the finer rubber systems developed by Rouse Rubber Industries. Consider factors ranging from aggregate gradation to construction operations. Use the information to develop and/or refine SAMI design and construction methods to further improve performance, serviceable life, and cost effectiveness of asphalt concrete overlays. Known current activity is limited to construction done in Florida, Arizona, Texas and California. Work in California and Arizona includes high mountain locations of alpine climate, subject to both high and low temperature extremes. During the 1990s, CRM SAMIs were constructed in various locations throughout the US and records of some were included in the NCHRP Synthesis of Practice for CRM paving materials. However relatively little has been done to document the performance of most SAMIs. There is an urgent need to improve performance, serviceable life, and cost effectiveness of rehabilitative asphalt concrete overlays of roadway and bridge pavements. Approximately $100,000 over 12 to 24 months

6 PROBLEM 6: CRM FIBER AS REINFORCEMENT IN HMA, MEMBRANES OR SMA It is well know that fibers can provide excellent reinforcing aids in asphalt mixtures. Fibers from scrap tires offer an excellent low cost alternative or supplement to virgin fibers. As no good use has been found for these high quality fibers, they are being disposed of in landfills or in some cases incinerated. To evaluate the performance and cost effectiveness of adding tire fibers to supplement virgin fiber for use in asphalt paving materials. No research has been conducted on the use of tire fibers in asphalt paving materials High quality fibers are being wasted when they could be used as relatively low cost, value-added reinforcing components in asphalt paving materials. Substituting such excellent materials in fiber-reinforced or filled mixes, including SMA, could reduce materials costs. The growing use of ground recycled tire rubber in a number of applications is producing considerable volumes of tire fibers. Approximately $75,000 over 12 to 24 months. PROBLEM 7: RECLAIMED/REPROCESSED MATERIALS IN HMA The HMA Industry has for many years used Reclaimed Asphalt Product (RAP), slag, baghouse fines, and recycled PCC, as well as a host of other, lesser quantity reclaimed and/or reprocessed materials such as roofing shingles and ceramic toilets. Most research that has been done relates to the use of RAP, and most of that work was done in the 1970s and early 1980s. Given the changes in plant equipment, mix design approaches, use of modifiers/additives, use of non-dense graded mixes, and the ongoing difficulty in recovering recycled asphalt binder, a thorough review of the effect of using reclaimed/reprocessed materials on the performance of HMA pavements needs to be conducted. The objective of this project is to develop improved mix design and construction evaluation techniques for the use of reclaimed/reprocessed materials in hot mix asphalt mixtures, addressing the key issues of health, safety, and environmental concerns, recyclability, mix design, and construction. NCHRP Project 9-12 is to develop guidelines for incorporating RAP in the Superpave system and prepare a manual that can be used by laboratory technicians. The National Center for Asphalt Technology is evaluating the use of RAP screenings in HMA.

7 The highway industry has been a strong user of recycled materials and is often looked at as a potential user of other waste materials. It is important that we understand the influence of these materials on the performance, future recycling of the pavement and the health and safety of our workers. $350,000 over 2 years. PROBLEM 8: AGGREGATE STRUCTURE IN ASPHALT CONCRETE MIXTURES RELATED TO PAVEMENT PERFORMANCE Asphalt concrete (AC) is a strongly heterogeneous material that consists of asphalt cement, air voids, fine aggregate and coarse aggregate. Examination of the literature reveals that the investigations of AC largely concentrate on the macroscopic behavior of the material based on the assumption that the mixture is homogeneous. Most of these investigations assume that an aggregate gradation, determined on a mass basis, accurately reflects aggregate structure, even though it is composed of particles of widely differing specific gravities. In other words, the stated mix gradation may not accurately reflect the aggregate structure of the mix. Very little basic or applied research has been conducted that considers the aggregate skeleton in terms of a true distribution of particle sizes. No standardized methodology exists to evaluate or specify the true distribution of aggregate particle sizes. Yet it is widely recognized that aggregates and their true size distribution and associated packing characteristics play a key role in the stability and other performance characteristics of AC. Establish relationships between aggregate particle size distribution and AC performance in pavements. Develop a methodology for the quantitative measurement of aggregate particle size and structure in AC mixtures. Establish quantitatively the characteristics of aggregate distribution in different types of AC currently used in the U.S. and Canada such as dense-graded asphalt concrete, stone matrix asphalt, porous friction courses, etc. The National Research Council of Canada performed an investigation on the application of digital image processing to quantitatively study aggregate distribution in AC. Other related activity includes a study funded by SHRP (88-A- IIR-13) pertaining to microscopic analysis of voids in AC mixtures that was carried out by the Danish Roads Institute. This study was redirected by SHRP to the University of California at Berkeley (A-003A) to analyze homogeneity of air voids produced in test specimens fabricated by rolling wheel and gyratory test equipment. A high level of AC performance necessitates consideration of the heterogeneous nature of the mixtures, in particular, the aggregate structure as reflected by its actual distribution of particle sizes. Gradation specifications, such as the new Superpave method based on the 0.45 power chart, need to be analyzed in terms of their ability to relate a well-performing aggregate structure. There is no quantitative knowledge on aggregate distribution in AC mixtures, in particular, in the differences of aggregate distribution in specialty mixes such as SMA, etc. Such new knowledge will improve AC mixture design, compaction quality, and pavement performance. Approximately $300,000, for 24 months.