1999 Catalog of Practical Papers

Design and Construction of Transportation Facilities

Click on any of the headings below to link to articles on that subject.

  1. Bridge Design and Performance
  2. Construction: General
  3. Construction: Pavements
  4. Construction: Structures
  5. Bituminous Materials
  6. Cement and Concrete
  7. Mineral Aggregates
  8. Pavement Management, Design and Performance
  9. Roadside Safety
  10. Soils, Geology and Foundations

Do you have suggestions or comments about/ this catalog? Write us: mailto:fejl@nas.edu

991118 "Analysis of Paving Construction Quality for Urban Highway Weekend Closures"
Phillip S. Dunston, Bonnie M. Savage, and Fred L. Mannering

991497 "Evaluation of Rigid Pavement Joint Seal Movement"
Dennis A. Morian, Nadarajah Suthahar, and Shelley Stoffels

991442 "A Regression Model for Resilient Modulus of Subgrade Soils"
Louay N. Mohammad, Baoshan Huang, Anand Puppala, and Aaron Allen

I. BRIDGE DESIGN AND PERFORMANCE

990008 "Construction Of A Full-Scale Soundwall Using Recycled Plastic"

Abstract: A full-scale, recycled plastic soundwall is constructed and its structural behavior analyzed to determine the feasibility of using recycled plastics in place of conventional building materials. A design process that allows selection of recycled plastic support columns that limit lateral deflection of a prototype soundwall due to wind loading is introduced as are techniques that are used to fabricate and install components of the barrier. Analysis of the prototype structure includes monitoring of response to environmental factors such as exposure to ultraviolet radiation and testing of acoustic insertion loss. Conclusions: A modularized form of design was developed that allows construction of a soundwall that has a variety of modules. With exception of concrete footings, steel reinforcing bars inside plastic columns, and a modest number of metal connections, the barrier utilizes 100% recycled plastic products. Structurally, all modules in the prototype barrier have maintained their integrity over the course of approximately one year. An exception, mostly aesthetic, is the warping of some plastic sheet panels. In contrast, plastic lumber boards show no detrimental effects from weathering and exposure to ultraviolet radiation. Also, there is no noticeable deformation of the structure indicating that the internal framework is capable of withstanding long-term thermal loadings. Acoustically, insertion loss of the recycled plastic soundwall is exceptional giving a noise reduction of approximately 17 A-weighted decibels. This reduction far exceeds insertion loss for soundwalls specified by state transportation agencies. Given the adequate levels of performance, both structurally and acoustically, implementation of the proposed design for a recycled plastic soundwall is recommended.

Paul N. Roschke, Associate Professor, Department of Civil Engineering, Texas A&M University, College Station, TX 77843-3136, Telephone: (409) 845-1985, FAX: (409) 845-6554, Email: p-roschke@tamu.edu; and Steven T. Esche, Engineer-In-Training, J. Ray McDermott Engineering Houston, L.L.C., 801 N. Eldridge Street, Houston, TX 77079, Telephone: (281) 870-5000, FAX: (281) 870-5045, Email: steve.esche@mcdermott.com.

990028 "Quality Improvement Review of Jointless Bridges and Bridge Deck Joints in Washington State"

Abstract: This paper summarizes highlights of a 1997 Quality Improvement Review of jointless bridges and bridge deck joints in Washington State. The purpose of the QIR is to determine, assess, and disseminate the current state of the practice and to share this information with the other FHWA Region 10 states and other FHWA regions. The inspection team included personnel from FHWA, Oregon DOT (ODOT), and Washington DOT (WSDOT). Interviews were conducted with design, construction, inspection, and maintenance personnel. During the QIR, eighteen WSDOT bridges were inspected in the field to gauge the performance of jointless bridges and bridge deck joints. Background information on jointless bridges is given and current bridge deck joint practices are presented. The use of jointless bridges eliminates the need for expansion joints and the need for joint maintenance. The QIR found WSDOT's semi-integral jointless bridges with overall lengths of 122 m and skews less than 30 degrees to have performed well. Approach slabs are recommended for jointless bridges to minimize the effects of approach settlement. Quality improvement recommendations are presented. WSDOT has developed a new sawcutting procedure for compression seals as well as a second generation fatigue-based modular bridge expansion joint specification to improve long-term durability. Conclusions: Joints: WSDOT should continue to have a full-time expansion joint specialist to serve as an expert and resource contact. New joints, design, and detailing require more time and understanding than can reasonably be expected of bridge designers. Provide education and training for WSDOT's construction inspectors and contractor's personnel. One education approach is to use videos to emphasize critical preparation and installation procedures to ensure high quality and a durable joint. Develop construction inspection guidelines on joint installation for the WSDOT Construction Manual. Proper joint installation appears to be the single most important factor in determining satisfactory long-term performance of joints. Consider using warranties for joints to improve quality during installation. Warranties were used on two contracts. The use of warranties may be beneficial to obtain a quality installation. Reconsider the use of steel finger joints and sliding plate expansion joints. Although WSDOT's current policy is to provide a sealed deck system for environmental reasons, these older joint systems have a good overall performance history. Maintenance personnel and bridge inspection personnel favor their use. The minimal damage caused by joint leakage may be offset by their simple design and good performance. Invite WSDOT construction project personnel to the annual WSDOT bridge maintenance meetings and encourage bridge maintenance personnel to attend yearly construction conferences. The interviews suggest that both parties will benefit from this exchange of concerns, information, and ideas. These annual meetings can be very effective in transferring information to a wide range of users. Provide construction tolerances in specifications for preparing concrete surfaces and installation of expansion joints. This will enable both designers and construction personnel to use reasonable construction tolerances for joints. Continue to develop innovative methods for constructing reliable joints such as the sawcutting procedure for compression seals. Additional work still remains to refine this procedure into a standard method. However, this quality improvement process will help improve the long-term durability of compression seal joints. Place WSDOT's Qualified Products List on the WSDOT Internet home page as a resource to other state DOTs. Develop one day training seminars for FHWA Region 10 DOT joint specialists, construction inspectors, bridge inspectors, and maintenance personnel. This provides a networking opportunity to share lessons learned in improving the quality and durability of expansion joints.

Jointless Bridges: Encourage the use of jointless bridges. This review confirms that jointless bridges types are preferred to jointed designs for the short to medium span ranges. The maximum skew limit of thirty degrees seems an appropriate upper limit for skew angle. The semi-integral abutment detail is performing very well. The decision to install an approach slab should be made by the bridge designers after consultation with the Geotechnical Branch. This decision should be based upon long-term performance and life cycle costs, rather than initial first cost to the project. There was unanimous support from all disciplines for using approach slabs on jointless bridges.

John A. Van Lund, Bridge and Structures Office, Washington State Department of Transportation, Olympia, WA 98504-7340, Tel: 360-705-7217, Fax: 360-705-6814, Email: VanLunJ@wsdot.wa.gov.us; Barry B. Brecto, Region10 FHWA - Washington, 711 South Capitol Way, Suite 501, Olympia, WA 98501-0943, Tel: 360-753-9482, Fax: 360-753-9889, Email:

Barry.Brecto@fhwa.dot.gov.us.

990065 "Bending Tests of Bridge Deck Planks"

Abstract: This paper presents results of timber plank tests, for planks used in highway bridge decks. They are oriented and loaded flat-wise. Tests were carried out to determine the flat-wise use factor, which is represented by the ratio of modulus of rupture (MOR) for flat-wise loading to MOR for edge-wise loading. The tests were carried out at the University of Michigan on the most common species used for plank decks in Michigan, Red Pine. Four sizes were tested, two are typical for bridge planks: 100x250mm (4"x10") and 100x300mm (4"x12"), and the other two sizes have good potential for future applications: 100x150mm (4"x6") and 100x200mm (4"x8"). A total of 169 edge-wise and 177 flat-wise specimens were tested. The resulting MOR's are presented in the form of cumulative distribution functions on normal probability paper. For comparison, MOR values were calculated, using actual dimensions and dressed sizes. The tests confirmed that MOR for flat-wise loading is considerably larger than for edge-wise loading for the larger planks tested and that flat-wise use factor increases for larger plank width. The flat-wise use factor in the current bridge design code is overly conservative for typical plank sizes. Conclusions: The wood plank tests performed at the University of Michigan confirmed that the modulus of rupture (MOR) for flat-wise loading is considerably larger than for edge-wise loading for the larger plank sizes tested. Flat-wise use factor increases for larger plank width. The flat-wise use factor in the current bridge design codes is overly conservative, for typical bridge plank sizes. New flat-wise use factors are recommended for the design of wood plank decks for highway bridges. The recommended values vary from 1.10 for 100x150mm (4"x6") to 1.6 for 100x300mm (4"x12").

Andrzej S. Nowak, Department of Civil and Environmental Engineering, 2370 G.G. Brown Building, University of Michigan, Ann Arbor, MI 48109-2125, tel. (734) 764-9299, fax (734) 764-4292; Pawel Stankiewicz, ADAPT Corp., Redwood City, CA 94061, tel. (650) 306-2400, fax (650) 364-4678; and Michael A. Ritter, Forest Products Lab, Madison, WI 53705, tel. (608) 231-9229, fax (608) 231-9303.

990133 "Simplified Method for Shear Design of Prestressed Concrete Girders"

Abstract: The new AASHTO LRFD Bridge Design Specifications incorporate the modified compression field theory for shear design of prestressed and non-prestressed concrete members. This method is based on the variable-angle truss analogy model and takes into account the inclination of diagonal shear cracks, strain in longitudinal steel and the applied shear stress on a section. This is a realistic approach to predict the shear resistance of any section of a concrete member. However, for prestressed concrete sections, an iterative process is required to determine the shear resistance of the sections. In an effort to simplify the process, Washington State DOT has completed a parametric study, resulting in a simplified method using fixed shear design parameters for WSDOT standard girders. A detailed step by step shear design based on the current AASHTO LRFD Specifications and the simplified method is given. The simplified method saves significant time in shear design of prestressed girders, especially when it is applied to standardize the shear reinforcement in a series of standard prestressed concrete girders. Shear cracking is a complex problem because of the complexity factors that contribute to the cracking mechanism. Some of the controlling factors are: the compressive and tensile strength of the concrete, the span to depth ratio of the member, the magnitudes of axial force, shear and moment at the section, the amount of shear and longitudinal reinforcement, and so on. Conclusions: The LRFD Specifications predict the shear resistance of prestressed girders more accurately than the LFD Specification and resulting in higher shear capacity of the sections. The LRFD requires less shear reinforcement in prestressed girders than LFD for the current WSDOT Standard prestressed girders. A simplified method using fixed shear design parameters of q and b may be utilized to simplify the LRFD shear design of prestressed girders. For the WSDOT Standard Prestressed Girders, q equal to 35 degrees and b equal to 2.4 are found to meet the shear design requirements of the LRFD. Similar fixed design parameters may be obtained for other sets of standard prestressed girders used by other states. The simplified method saves significant time in shear design of prestressed girders using the LRFD. Further time and cost savings may be realized by applying the simplified method of using fixed shear design parameters to standardize the shear reinforcement in a set of standard prestressed girders. The vertical components of harped or draped strands contribute as much as 10% of the total shear resistance of the section.

M. Myint Lwin, Bridge and Structures Office, Washington State Department of Transportation, Phone: (360) 705-7207, Fax: (360)705-6814, and Email: lwinm @wsdot.wa.gov; and Bijan Khaleghi, Bridge and Structures Office, Washington State Department of Transportation, Phone: (360) 705-7181, Fax: (360) 705-6814, and Email: khalegb@wsdot.wa.gov.

990266 "Simplified Method for LRFD Shear Design"

Abstract: Determination of the shear strength of prestressed concrete beams has become complicated in recent years. Much of the complexity comes from determining the concrete contribution, Vc, to the overall shear resistance. Because of the empirical nature of Vc calculation by various codes and specifications and because of the insignificant cost impact of shear reinforcement, the complexity is not warranted. A simplified shear design method is proposed. A detailed example is given to demonstrate design based on the current AASHTO LRFD Specifications and the proposed method. Another important issue in shear design of thin-web precast prestressed concrete members is the maximum allowed shear reinforcement. AASHTO Standard Specifications require that Vs not exceed (fc’ in MPa) (fc’ in psi). This limit has become a controlling design factor when wide beam spacing and high performance concrete are utilized. It is almost always a controlling parameter in the design of post-tensioned I-beams. Recent experiments have shown that: (1) This limit is too conservative; and (2) The limit of 0.25fc’bvdv on (Vc + Vs) in the AASHTO LRFD Specifications can be reached if adequate anchorage of the prestressing steel at member ends is provided. A summary of the full-scale test results is presented. Conclusion: In conclusion, the proposed simplified LRFD shear design method is a safe and simple method that does not require any iterative process as the current AASHTO LRFD does. There is no need for tables and charts. It is a more reasonable method in the sense that it predicts a uniform shear reinforcement pattern which follows the factored shear force diagram. It is simple to understand and to use in both simply supported bridge beams and continuous bridge beams. In comparison with our full-scale tests as well as other experimental data available in the literature, with proper reinforcement the maximum shear capacity of 0.25 fc’ bvdv can be easily reached. This limit represents a lower bound fit to the experimental results when the longitudinal reinforcement has enough anchorage as specified. The maximum shear reinforcement limit specified in AASHTO Standard Specifications is too restrictive.

Zhongguo (John) Ma, University of Nebraska-Lincoln, Engineering Building, Room # 129, 60th & Dodge Streets, Omaha, NE 68182, Tel: (402) 554 – 2820, Fax (402) 554 – 3288, Email: zma@unomaha.edu; Maher K. Tadros, University of Nebraska-Lincoln, Engineering Building, Room # 129, 60th & Dodge Streets, Omaha, NE 68182, Tel: (402) 554 – 2985, Fax (402) 554 – 3288, Email: mtadros@unomaha.edu.

990331 "Verification of Girder Distribution Factors for Short-Span Bridges by Field Testing"

Abstract: This paper presents the procedure and results of field tests that were performed on five simply supported short span steel girder bridges to verify girder distribution factors. Prior analytical studies have shown that in most cases currently used girder distribution factors are too conservative. However, these studies also showed that for short spans and short girder spacings, the girder distribution factors can be too permissive. Therefore, this paper focused on experimental evaluation of girder distribution factors for short span steel girder bridges. The research work involved formulation of the testing procedure, selection of structures, installation of equipment, measurements, and processing of the results. Strains and deflections are measured and filtered to calculate girder distribution factors. The results were compared with the distribution factors specified by AASHTO Standard (1996) and AASHTO LRFD Code (1994). It has been found that the measured girder distribution factors are lower than AASHTO values in all cases. Conclusions: Five short-span two lane bridges were tested. The field measurements confirmed that the actual (measured) girder distribution factors are smaller than those specified by AASHTO Standard (1996) and AASHTO LRFD Specifications (1994). For three bridges, the measured GDFs for two side-by-side 11-axle trucks were close to but less than S/3.36 (where S is in meters), and for two other bridges they were approximately S/5. FEM analyses provided GDFs close to S/3.36. For comparison, the GDF's obtained in field tests as a part of this study, are plotted versus analytical values calculated using AASHTO Specifications (1996), and AASHTO LRFD Code (1994). The results are presented for a single truck (one lane loaded), and for two trucks (two lanes loaded).

Andrzej S. Nowak, Junsik Eom and Ahmet Sanli, Department of Civil and Environmental Engineering, 2370 G.G. Brown Building, University of Michigan, Ann Arbor, MI 48109-2125, tel. (734) 764-9299, fax (734) 764-4292. Roger Till, Michigan Department of Transportation, P.O. Box 30049, Lansing, MI 48909, tel. (517) 322-5682, fax (517) 322-5664.

990411 "Subjective and Objective Evaluations of Bridge Damage"

Abstract: A decommissioned 40+ year old reinforced concrete deck on steel girder bridge was subjected to a series of induced damages, nondestructive field tests, and visual evaluations in order to compare objective and subjective methods of bridge condition assessment. Subjective evaluations of bridge condition produced highly variable results - inspectors with different backgrounds and field experience disagreed on how severely deterioration and damage influenced bridge behavior/safety and, consequently, generated different assessments of bridge condition. Furthermore, a load-rating of the as-is state of the bridge, e.g., the state prior to any induced damages, based on current Ohio DOT procedures indicated that the bridge could only support truck-loads of 227,804 N (51,192 lbf). However, for this particular bridge state and when subjected to truck-loads of 282,130 N (63,400 lbf), objective data acquired during nondestructive field testing revealed maximum superstructure deflections and live-load stresses of 0.190 cm (0.075 in.) and 15,985 kPa (2,320 psi), values well within AASHTO limits. These values also imply that the bridge can support loads much greater than those indicated in the load-rating. Comparing the subjective and objective assessments for the induced damage scenarios yielded results similar to those for the as-is bridge condition. Essentially, it was revealed that subjective bridge evaluation, unlike objective methods of condition assessment, was unable to properly characterize neither intrinsic bridge mechanisms nor the influence that such mechanisms have on bridge behavior. Condition assessment of typical reinforced concrete deck on steel girder bridges should therefore include objective evaluations of bridge condition and behavior. Conclusions: In-situ bridge mechanisms, such as flexibility, were successfully characterized from the objective data acquired through nondestructive field test methods such as dynamic impact testing and truck-load testing. Such data revealed that the decommissioned test-bridge could support service truck-loads - measured deflections and strains (stresses) were considerably less than AASHTO serviceability and stress requirements. However, the subjective results of an Ohio DOT inspection performed prior to any field research were used to decommission the bridge. This and other numerous subjective evaluations performed on the bridge during the course of this research apparently did not capture the true nature of intrinsic bridge mechanisms nor the influence that such mechanisms have on bridge behavior such as load distribution and structural flexibility. Using a 3-D field-calibrated finite element model to incorporate the objective characterizations of these mechanisms into the load-rating process consequently yielded ratings that indicated the bridge could support truck-loads greater than those predicted by current Ohio DOT load-rating procedures. Objective methods of bridge assessment, such as nondestructive field test methods, should therefore be included as part of the condition assessment process.

Michael S. Lenett, University of Cincinnati, Dept. of Civil and Environmental Engineering, 741 Baldwin Hall, Mail Location #71, Cincinnati, Ohio 45221-0071, email: lenettms@email.uc.edu, phone: 513-556-3687 or 513-556-3679, fax: 513-556-2599.

990430 "Steel Orthotropic Decks - Developments in the 1990's"

Abstract: Paper summarizes recent developments in the field of orthotropic decks which are indispensable in the design of very long span bridges. European research results and recommendations are discussed. Fatigue susceptibility of decks with closed ribs and thin deck plates is highlighted by catastrophic cracking of decks in Holland in 1997. The writer discusses the cause which is stress flow constriction in the deck plate not previously considered and proposes a solution for future designs. Open rib decks are less efficient but have much better fatigue resistance. Such decks are widely used on railway bridges in Europe. Surfacing failures are due to excessive deck flexibility. Conclusions: 1. In decks with closed ribs internal diaphragms at intersections with floorbeams eliminate stress concentrations in floorbeam webs and in the deck plate. V-shaped ribs are more efficient than traditional trapezoidal ribs. 2. Open-rib decks deserve more consideration in future designs. 3. Stresses in surfacing due to composite action with the deck must be considered and rib deflections minimized as required by AASHTO LRFD specifications. Thick surfacings are more vulnerable to effects of deck flexibility. Surfacings with low elastic modulus and little variability with temperature are desirable. 4. Practical design for fatigue should be based on semi-empirical rules for "distortion-induced" fatigue.

Roman Wolchuk, Consulting Engineers, 26 Journal Square, Jersey City, NJ 07306, Tel. 201 659-7428, Fax 201 659-6370, Email: wolchukeng@juno.com.

990485 "Steel Girder Bridge Field Test Procedures"

Abstract: Research has shown that in most cases, bridges exhibit capacities higher than analytical load capacity rating predictions. These rating procedures are based on conservative design assumptions that do not always represent the true bridge behavior. Testing bridges in the field has demonstrated this additional capacity and bridge field testing has become an acceptable means to determine a more accurate estimate of a bridge’s safe capacity. Many factors not considered in the design process contribute to the response of a tested bridge. Several of these, like the actual load distribution and additional system stiffness from curbs and railings, are welcome benefits and can be used to increase weight limits on bridges. However, there are also contributions from bearing restraint forces and unintended composite action that may not be reliable during the service life of the structure. Determining how much of the increase in capacity is acceptable is difficult. This paper presents systematic field test rating procedures that separates and quantifies these contributing factors so that owners may remove unwanted contributors and retain the reliable benefits. An efficient test plan is applied to a three-span steel girder bridge to demonstrate the procedures. Conclusions: Field testing provides the engineer with valuable knowledge of system response, load distribution, actual section properties, bearing restraint effects, and dynamic impact for the tested bridge. The standardize field testing procedures were developed from a series of diagnostic tests on the steel girder bridge to separate and quantify the factors tending to increase the load to (1) remove the unwanted contributions and (2) confirm the origin of the useable benefit. The results indicate that the current analytical single unit weight limit can be increased 67% after removing the questionable benefits from bearing restraint forces. The rating equation procedures presented have been optimized for time effort and cost.

Michael G. Barker, University of Missouri – Columbia, E2509 Engineering Building East, Columbia, Missouri, 65211, Tel: (573) 882-2467, Fax: (573) 882-4784, email: barkerm@missouri.edu.

990757 "Design Of An 11-Span Isolated Steel Structure For Serviceability, Puente Sobre El Rio Tempisque"

Abstract: The purpose of this paper is to discuss the design process and studies that were required to develop the design for the bridge across the Tempisque River in Costa Rica that would be serviceable under various seismic loads. Required levels of performance for various bridge components will be discussed. Costa Rica is located on the Caribbean tectonic plate - a very seismically active area that is currently in the midst of an intensive seismic cycle which began in 1982. The western coast is in a region of subduction between the Caribbean, the Cocos, and the Nazca Plates. The Tempisque River separates the resort laden western shores of Costa Rica from the country’s capital, San Jose, and the rest of the country east of the river to the Caribbean Ocean. While the country has relatively modest economic resources, a design must be developed that for this important transportation link that: meets the country’s stringent seismic design criteria; is relatively inexpensive; and, has a high potential of re-use following an earthquake. The bridge will be built and operated by the contractor. While this process reduces the initial costs for the owner, it can have implications on the required level of performance during the concession portion of the structure’s useful life. This will also be discussed. Conclusion: A design for a steel bridge that meets a "serviceable" performance criteria is discussed. Specific performance criterion for the structural components are defined. A strategy for achieving the serviceable design is elaborated on. Central issues to the serviceable design for a steel bridge are proposed to be; limiting the inertial loads in both the superstructure and substructure through the use of isolation bearing devices, tuning the structure through variation of substructure and bearing design, and addressing the performance requirements of the expansion joints. The reduced risk to the contractor during construction is shown, for this location, to be essentially defined by the same seismic event as the Design Earthquake. This implies that no additional analysis (other than for temporary works) is required by the designers to address the reduced risk during the construction and concession period. The design follows the philosophy that seismic design is not an exact science, that a bounded performance based design defines risks more clearly, and that a clear definition of risk is a strong foundation for any design.

Thomas R. Cooper, P.E., Senior Supervising Engineer, Parsons Brinckerhoff Quade & Douglas, Inc., 3840 Rosin Court, Suite 200, Sacramento, CA 95834, 916-567-2522, Fax: 916-925-3517, email: cooper@pbworld.com; and Cristoforo D. Subrizi, P.E, Lead Engineer, PBQ&D, Inc., Marathon Plaza, 303 Second Street, San Francisco, CA 94107, 415-243-4718, Fax: 415-243-9501, email: subrizi@pbworld.com.

990797 "Forced Vibration Testing of A Full Scale Bridge Span"

Abstract: A nine-span three-lane freeway overpass structure was demolished leaving an isolated single span supported by two bents. These concrete bents were subjected to lateral load capacity testing and retrofitting using carbon fiber composite wrapping. This testing provided the opportunity to perform forced vibration dynamic testing between each episode of damage or retrofit. This sequence resulted in a series of seven dynamic tests performed on the same structure in seven different conditions of damage or retrofit. This work focused on horizontal forced vibration utilizing an eccentric mass shaking machine. Frequency sweeps were conducted in each orthogonal horizontal direction. Data was collected with an array of accelerometers. This paper presents the natural frequencies determined for the structure at each of the seven damage states as well as some mode shape data. The natural frequencies correspond to the first three mode shapes for the structure, namely, the two translational modes and a torsional mode. Significant decreases in the natural frequencies occurred in the structure. Since the mass of the structure remained essentially constant throughout the testing, these decreases can be attributed to a significant lowering of the structural stiffness. A slight increase in structural stiffness occurred as a result of the carbon fiber retrofit and bridge repair. Changes in both the amplitude as well as the shapes of the modes were noted in the experimental results. Conclusions: Significant change occurred in the natural frequencies in the seven structural conditions. The substantial changes in the natural frequencies correspond to substantial changes in the structural stiffness. Loss of stiffness (decrease in natural frequencies) is demonstrated as a result of damage to the structure. The natural frequencies changed by 38%, 49%, and 52% for the fundamental, second, and third modes respectively. The inflicted damages and repairs at specific locations on the structure result in larger response for the same loading levels because of structural softening. Changes in mode shapes are currently being investigated and compared with analytical models. The use of epoxy crack repair and the application of carbon fiber composites at columns and beams result in detectable increases in structural stiffness.

Ikhsan Muhammad, Marvin W. Halling, and Kevin C. Womack, Department of Civil and Environmental Engineering, Utah State University, Logan, Utah 84322-4110, Tel. (435)797-3179, Fax. (435)797-1185, Email: halling@lab.cee.usu.edu.

990822 "Comparison of Experimental and Analytical Load Rating Methodologies for a Pony-Truss Bridge"

Abstract: Due to the limited resources of county and district bridge owners, the evaluation and rating of aging structures must be conducted to facilitate suitable bridge maintenance, repair, replacement, and posting strategies. The present study evaluates the effect of increasingly refining rating evaluation parameter inputs to the analysis of a 1937 riveted pony-truss bridge in Pennsylvania. The study considers results of experimental field testing of the bridge, a detailed section loss inspection, and refined analytical modeling using STAAD III to increase the accuracy of the rating analysis. Where a rating indicates an under-capacity, increasing the refinement of the analysis, or even an experimental evaluation of several parameters, may be justified. The present study evaluates the relative effect of utilizing: (1) allowable stress vs. load factor design methodologies; (2) experimentally derived vs. code specified impact and distribution factors; (3) experimental stress measurements vs. manual and computer stress calculations, and (4) member fixity and composite action for both inventory and operating rating with an AASHTO HS20-44 and ML-80 rating vehicle. Results are presented for selected truss members, floor beams, and stringers. Conclusions: The study found that the rating increases with each increasingly refined parameter input of dynamic load allowance, distribution factor, and refined analytical evaluation, with the rating factor increasing as much as 60% over a standard manual rating analysis by utilizing an experimentally based rating analysis. The best analytical computer model agreement with experimental results was obtained using a reduced deck stiffness to model deck deterioration, fully composite action between stringers and deck, pinned stringer-floor-beam connections, and fixed floor beam to truss connections. The procedures described here-in can be generalized and applied to other similar bridge structures.

Timothy S. Schenck, Structural Engineer, HLW International, LLP, 115 5th Ave, New York, NY 10003, Email: tschenck@hlw.com, Tel: (212) 353-4870, Fax: (212) 353-4896; Jeffrey A. Laman, Ph.D., P.E., Assistant Professor of Civil Engineering, Department of Civil and Environmental Engineering, Pennsylvania State University, University Park, PA 16802, Email: jlaman@psu.edu, Tel: (814) 863-0523, Fax: (814) 863-7304; Thomas E. Boothby, Ph.D., P.E., Associate Professor of Architectural Engineering, Department of Architectural Engineering, Pennsylvania State University, University Park, PA 16802, Email: tebarc@engr.psu.edu, Tel: (814) 863-0523, Fax: (814) 863-4789.

990888 "Transverse Cracking in Bridge Decks"

Abstract: The purpose of this study was to determine the dominant parameters that lead to premature transverse cracking in bridge decks and to make recommendations expected to reduce cracking tendency in bridge decks. The project was divided into two main parts: a field study and a parametric study. The objective of the field study was to determine the correlation between the observed cracking and available design, material and construction-related data. Seventy-two bridges located in the Minneapolis-St. Paul area were included in the field study. The objective of the parametric study was to investigate the relative influence of the factors that affect transverse deck cracking through a controlled analytical study. The variables included: end restraint, girder stiffness, shrinkage, supplemental steel bar cutoff, cross frames, splices, deck concrete modulus of elasticity, and temperature history. In addition, four bridges from the companion field study were modeled using the available design, material and construction information to correlate the analytical results with the actual crack patterns. Conclusions: Based on the results of the study and correlation with other research, the following dominant factors affecting transverse cracking were identified: longitudinal restraint, deck thickness, top transverse bar size, cement content, aggregate type and quantity, air content, and ambient air temperature at deck placement. Concrete decks on prestressed girder bridges never cracked in the parametric study and rarely cracked in the field study. The factors that had the greatest influence on the steel bridge deck cracking were end restraint and deck shrinkage. Recommended practical improvements to bridge deck construction include: reducing the shrinkage of the deck concrete through mix design and/or better curing practices, and minimizing continuity over interior supports.

Catherine French, P.E., Professor and Associate Head, Dept. of Civil Engrg., University of Minnesota, 500 Pillsbury Drive S.E., Minneapolis, MN 55455-0220. Phone: (612) 625-3877, Fax: (612) 626-7750, Email: cfrench@tc.umn.edu; Laurice Eppers, TT-CBM Engineers, 5 N. Wabash Ave., Chicago, IL 60602. Phone: (312) 346-0190, Fax (312) 346-0638, Email: Leppers@tt-cbm.com; Quoc Le, Opus Engineers, Minneapolis, MN. Phone: (612) 934-4608, Email: Lexx0051@tc.umn.edu; and Jerome Hajjar, Associate Professor, Dept. of Civil Engrg., University of Minnesota, 500 Pillsbury Drive S.E., Minneapolis, MN 55455-0220. Phone: (612) 626-8225, Fax: (612) 626-7750, Email: hajja001@tc.umn.edu.

990935 "Why AASHTO LRFD"

Abstract: The AASHTO LRFD is based on new development in bridge engineering, sound principles and logical approach to assure constructability, safety, serviceability, inspectability, economy and aesthetics. It incorporates the best of Working Stress Design (WSD) and Load Factor Design (LFD), which are familiar to practicing bridge engineers. It is a comprehensive, well organized, and practical specification with commentary to provide explanation and background information. New bridges designed in accordance with LRFD has the inherent advantage of a more uniform level of safety, resulting in low life-cycle cost. LRFD allows the use of advanced methods in design and analysis. It provides flexibility for maintaining good and successful engineering practices or customizing load and resistance factors to meet the demands of a project. There are many good reasons and motivations to use LRFD. College classes, training courses, design examples, workshops and computer softwares are now available to ease the implementation of AASHTO LRFD. Conclusions: The new AASHTO LRFD Bridge Design Specification is the result of continuous improvement since AASHTO adopted the first national bridge code in 1931. The code had changed from Working Stress Design (WSD) in 1931 to Load Factory Design in 1975 and now to the Load and Resistance Factor Design (LRFD). LRFD is a modern and comprehensive bridge specification, which puts U.S. practice at the leading edge of bridge engineering. The AASHTO LRFD is based on technological advances in bridge engineering, sound scientific principles and systematic approach to ensure constructability, safety, serviceability, inspectability, economy and aesthetics. The AASHTO LRFD has the inherent advantage of a more uniform level of safety in new bridges, which means low maintenance and repair and low life-cycle cost. The parallel commentary in the AASHTO LRFD helps the bridge engineers in understanding the rationale and background of the specifications. It takes the "black box" out of the specification requirements. The AASHTO LRFD fulfills the vision to design and build quality bridges for the 21st Century.

Myint Lwin, Washington State Department of Transportation, P.O. Box 47340, Olympia, WA 98504-7340, Phone: 360-705-7207, Fax: 360-705-6814, Email: lwinm@wsdot.wa.gov.

990940 "Field Performance of Integral Abutment Bridges in Tennessee"

Abstract: The use of integral abutments in highway bridges is not new; the pioneering efforts of bridge designers in California, Ohio, Oregon, and South Dakota have demonstrated the efficacy of this design approach because of the elimination of troublesome joints. While not a "pioneer" in the sense of being the first, the Tennessee Department of Transportation (TDOT) has extended the use of integral abutments to longer and longer spans and is currently the national leader in applying this design concept. This paper consists of two sections: (1) current practice and related field experience and (2) research in progress. Consistent with these two sections, the paper has two objectives: (1) to provide specific examples of TDOT’s experience with integral abutment bridges and (2) to describe research designed to investigate the behavior of integral abutments and to provide some preliminary test results. The longest bridges in Tennessee to incorporate integral abutments are recently built bridges of 1,150 feet (350 m) in concrete and 525 feet (160 m) in steel. While these bridges are still too young to provide definitive information regarding potential problems, the current status of the bridges is described in the paper and details of the abutments are given. Experience with other, older bridges are discussed Field tests are currently in progress at The University of Tennessee, Knoxville, to study the effects of lateral movement due to temperature change on the behavior of an integral abutment. Lateral pile displacements of greater than one inch (25 mm) have been introduced with essentially no damage to the concrete abutment. Conclusions: The paper presents the results of a visual inspection of a number of integral abutment bridges in Tennessee and preliminary results of a field research project which is ongoing. The primary conclusion from the visual inspection of bridges in service was that deck cracking is no more of a problem in integral abutment bridges than in other continuous bridges. The trend in Tennessee toward longer jointless bridges has led to no significant problems. The results of the field research also support the trend to longer jointless bridges. Cracking of the test abutments under large lateral displacements has not compromised the structural integrity of the pile - abutment interface.

Edwin G. Burdette, Professor of Civil Engineering, The University of Tennessee, Knoxville, TN 37996, Tel: (423) 974-7704, Fax: (423) 974-2669, Email: eburdett@utk.edu; Edward P. Wasserman, Director of Structures Division, Tennessee Department of Transportation, Nashville, TN 37243-0339, Tel: (615) 741-3351; David W. Goodpasture and J. Harold Deatherage, Professors of Civil Engineering, The University of Tennessee, Knoxville, TN 37996, Tel: (423) 974-7703 and 974-0724, Fax: (423) 974-2669, Email: David-Goodpasture@utk.edu and hdeath@utk.edu.

991027 "Railing Systems for Use on Timber Deck Bridges"

Abstract: Bridge railing systems in the United States have historically been designed based on static load criteria given in the American Association of State Highway and Transportation Officials (AASHTO) Standard Specifications for Highway Bridges. In the past decade, full-scale vehicle crash testing has been recognized as a more appropriate and reliable method of evaluating bridge railing acceptability. In 1989, AASHTO published the Guide Specifications for Bridge Railings which give the recommendations and procedures to evaluate bridge rails by full-scale vehicle crash testing. In 1993, the National Cooperative Highway Research Program (NCHRP) published Report 350, Recommended Procedures for the Safety Performance Evaluation of Highway Features, which provides criteria for evaluating longitudinal barriers. Based on these specifications, a cooperative research program was initiated between the University of Nebraska-Lincoln and the Forest Products Laboratory, and later the Federal Highway Administration, to develop and crash test eleven bridge rails for wood deck bridges. This paper describes the research that resulted in the successful development and testing of eleven bridge railing systems for longitudinally- and transversely-laminated wood bridge decks in accordance with the AASHTO Performance Level 1 and 2 (PL-1 and PL-2) requirements, and the Test Levels 1, 2, and 4 (TL-1, TL-2, and TL-4) requirements of NCHRP Report 350. Conclusions: This program clearly demonstrates that crashworthy railing systems are feasible for both longitudinal and transverse wood decks. Even at high-impact conditions required by AASHTO PL-2 and NCHRP 350 TL-4, the railing systems performed well with no significant damage to the bridge superstructure. With the development of crashworthy railing systems, a significant barrier to the use of longitudinal and transverse wood deck bridges has been overcome. At the onset of this research program, only one crash tested bridge railing was available for use on wood deck bridges. Over the last ten years, this cooperative research program has resulted in the development of eleven crash tested bridge rails for use on both longitudinally- and transversely-laminated timber deck bridges.

Ronald Faller, Midwest Roadside Safety Facility, University of Nebraska-Lincoln,1901 Y St., Building C, Lincoln, Nebraska 68588-0601, Phone: (402) 472-6864, Fax: (402) 472-0506, Email: rfaller@unlinfo.unl.edu; Barry Rosson, Civil Engineering Department, University of Nebraska-Lincoln, W348 Nebraska Hall, Lincoln, Nebraska 68588-0531, Phone: (402) 472-8773, Fax: (402) 472-8934, Email: brosson@unlinfo.unl.edu; Michael Ritter, Forest Products Laboratory, USDA - Forest Service, One Gifford Pinchot Drive, Madison, Wisconsin 53705, Phone: (608) 231-9229, Fax: (608) 231-9303, Email: mritter@facstaff.wisc.edu; Sheila Duwadi, Turner-Fairbank Highway Research Center, Federal Highway Administration, 6300 Georgetown Pike, McLean, Virginia 22101-2296, Phone: (703) 285-2472, Fax: (703) 285-2766, Email: sheila.duwadi@fhwa.dot.gov.

991065 "Effects of Horizontal Web Reinforcement on Shear Capacity, Shear Ductility and Strand Anchorage"

Abstract: Simple truss models demonstrate that the inclusion of horizontal reinforcement can improve shear capacity in end regions of pretensioned girders where the prestressing strands may not be fully effective. The same truss models can demonstrate that the inclusion of horizontal reinforcement within the web could increase shear capacity within the web, and could limit propagation of shear cracking that occurs in the end regions of pretensioned girders. Previous experimental evidence has indicated that beam failures result when shear cracking propagates through the anchorage zones of pretensioned strands, thus destroying the capacity of the strands to develop the tensioned required to support shear forces. An experimental program was performed to investigate the effectiveness of horizontal shear reinforcement in improving shear capacity, improving shear ductility and preventing strand anchorage failures near end regions of pretensioned concrete bridge girders. Four pretensioned I-shaped girders were cast with varying shear reinforcement details in the end regions. The results of the experiments are studied and compared to the shear provisions in current ACI and LRFD bridge codes. The results from two of the beams are presented in this paper. Conclusions: Test results demonstrate that the inclusion of horizontal steel in the end regions of pretensioned concrete girders improved both shear capacity and shear ductility. In beam ends without horizontal steel, shear failure coupled with strand anchorage failure occurred almost immediately after the formation of the first web shear crack. Conversely, in the beam ends containing horizontal shear, web shear cracking was limited in size, strand anchorage was less affected and the beams were able to develop flexural capacity.

Bruce W. Russell, Assistant Professor, University of Oklahoma, 202 W. Boyd St., Norman, OK 73019, Tel:(405)325-1416, Fax:(405)325-6826; John Jacob, Graduate Research Assistant, University of Washington.

991191 "Proposed Revisions to AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals"

Abstract: The 1985 AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals has been revised in its entirety with significant additions made to its content and scope. The main objective of the study was to update the previous edition of the Supports Specifications. From a design safety standpoint, all materials for structural supports were treated on an equitable basis. While safety, aesthetics, and economy were three main guidelines in developing the provisions of the Supports Specifications, manufacturing practices and experiences were also taken into consideration. The purpose of this paper is to present highlights of the proposed revisions to the specification. The supporting information, scope, and basis for the proposed changes are also discussed. Conclusions: The proposed specification is the result of an extensive research study performed under NCHRP Project 17-10. Considerable effort was made to specify the best practice, realizing the characteristics and limitations of each material. The document is presented in a specification/commentary side-by-side format that will enable the engineer to review with ease the basis of specification’s provisions. References are updated to provide a resource for research studies related to the structural behavior and performance of structural supports. Overall, the proposed specification represents a vast improvement over the previous editions. It is hoped that the revised specification and the comprehensive information it contains would result in enhancing the design and use of structural supports for highway signs, luminaires, and traffic signals.

Fouad H. Fouad, Ph.D., P.E., Professor and Chairman, Department of Civil and Environmental Engineering, University of Alabama at Birmingham, 1075 13th Street South, Birmingham, AL, 35294, Phone: (205) 934-8430, Fax: (205) 934-9855, Email: ffouad@eng.uab.edu.

991238 "Fatigue Design of Modular Bridge Expansion Joints"

Abstract: The results of NCHRP Project 12-40, Fatigue Design of Modular Bridge Expansion Joints, are described in this paper. This research included experimental and analytical research to develop performance-based specifications and commentary for the fatigue design of modular bridge expansion joints (MBEJ). Field testing was conducted to measure static strain distribution and dynamic response of MBEJ subjected to truck loads. In addition, static load and strain distributions were also measured in the laboratory by applying loads through a truck axle and tires. The proposed fatigue design and test specifications are intended to be integrated with the present LRFD bridge design code. In order to be consistent with these bridge design specifications, the proposed MBEJ fatigue-design specifications used the same fatigue-design truck as the present AASHTO bridge specifications. One important modification of the AASHTO truck loading for MBEJ however, is the explicit recognition that the rear axles of the HS series trucks actually represent tandem axles. A simplified method to estimate the distribution factor, i.e. the fraction of the design wheel load range assigned to a single centerbeam, was recommended. Suggested fatigue test acceptance methods are also included. MBEJ designed in accordance with the proposed specifications should not be susceptible to fatigue cracking and will not cost significantly more than currently designed systems. Conclusions: The proposed specification provides an established fatigue design procedure and a procedure for carrying out the required fatigue tests. The proposed specifications are reasonably easy to use but are sophisticated enough to account for the complex dynamic behavior of the MBEJ as a system. In addition, the specifications are sufficiently general so that innovative new designs for MBEJ are not excluded from consideration. A higher level of confidence in long-term joint performance and possible decreased life-cycle costs will be realized.

Robert J. Connor, Graduate Research Assistant, ATLSS Engineering Research Center, Lehigh University, 117 ATLSS Drive, Bethlehem, PA, 18015; Tel: (610)758-6103 Fax: (610)758-5553 Email: rjc3@lehigh.edu; Robert J. Dexter, Associate Professor Civil Engineering, University of Minnesota, 122 CivE 500 Pillsbury Drive S.E. Minneapolis, MN 55455-0116, Tel: (612) 624-0063 Fax: (612) 626-7750 Email: dexter@tc.umn.edu

991370 "Long-Term Performance of Elastomeric Bridge Bearings"

Abstract: This report summarizes effects of long-term service on steel laminated elastomeric bearings placed on twin structures carrying the Aurora Expressway (New York State Route 400) over Conrail and NY 16, Erie County. Expansion-joint bearings replaced as part of rehabilitation project on these bridges were recovered for evaluation. Generally, the bearings were found to be in good condition, with only a few test values out of specification. NYSDOT's current accelerated-test procedures were were evaluated by comparing mean ratings of 1969 acceptance testing for these bearings after simulated aging, with results of the same tests in 1996 on the as-received samples after their removal from thses bridges. The Materials Bureau's acceptance tests (as used for the recovered samples) were validated by the comparison with results for the original, artifically aged bearings in 1969. Lastly, acceptance tests were done on the recovered bearings to evaluate performance on current specification tests. Included in this study is an analysis of mean ratings of acceptance test results from 1969 compared to mean ratings of the same tests to judge the effect of the years in service. The bearings used in the project had problems in design, construction, and materials properties, yet performed very well in service and are relatively insensitive to deficiencies in these areas. Conclusions: Neoprene's resistance to shear, weather aging, and compression set ensures a long service life and no maintenance in bridge bearing applications. This is borne out by the performance of the bearings on acceptance tests after 22 years' service. The value of NYSDOT's rigorous material specification and aging-test process of elastomeric properties is verified by the bearings' performance in the testing after service compared to initial aged-test results. The initial compressive deflection the bearings were subjected to, and subsequent performance, reinforces the need for proper design of the bearing (shape factor) to maintain effective rubber thickness to deflect shear stresses, as well as properly specified material properties.

Michael E. Doody, New York State Department of Transportation, 84 Holland Ave., Albany, NY 12208, Tel:(518) 474-6377 Fax: (518) 474-9963.

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II. CONSTRUCTION: GENERAL

990072 "Analysis of the Impacts of Freeway Re-Construction Closures in Urban Areas"

Abstract: The intent of this paper is to evaluate the traffic- and business-related impacts of a weekend closure of a major urban freeway. Data were gathered from a 9-km section of Interstate 405 (I-405) in Seattle that was closed to traffic in a single direction for two consecutive weekends, August 15-17 and August 22-24, 1997 for repaving operations. In evaluating this approach to highway reconstruction (i.e., total directional closure), we estimate the impact on the vehicle travel time and total emissions including carbon monoxide, oxides of nitrogen, and volatile organic compounds. Also, a survey was conducted asking travelers how their travel patterns changed in response to the weekend closure of this section of I-405. In addition to asking questions about changes in travel patterns, questions relating to the traveler's overall impressions were asked. Limited dependent analysis techniques including ordered probit and binary logit models were used in the survey analyses. Finally, a small sample of businesses was interviewed to get a quick sense of their impressions of the closure. Conclusions: The findings show that the impacts of total directional weekend closures are not excessive. From a traffic impact perspective, computer-generated simulations suggest travel-time impacts for the Seattle closure to be on the order of an 11-13% increase in system-wide travel time, which is quite reasonable when compared to other closure options (i.e., partial closure). The user survey indicated that only 12.7% of the users surveyed thought the closure had a major impact on their travel plans and 88.7% indicated a preference for total closures over partial closures. The statistical analyses showed that socioeconomics and geographic location affected the extent to which individual users were impacted but that few consistently adverse impacts were detected. The survey of local businesses also indicated only minor impacts.

Doohee Nam, Jinsun Lee, Phillip Dunston and Fred Mannering, Department of Civil and Environmental Engineering, University of Washington, Box 352700, Seattle, WA 98195-2700, Tel: (206) 517-3139, Fax: (206) 543-8935, Email: flm@u.washington.edu.

990516 "Current Use of Warranties in Highway Construction"

Abstract: The transportation industry is investigating non-traditional and innovative contracting practices that can lead to improvement in the areas of quality, safety, and the reduction of State Highway Agency (SHA) resources. Warranty contracting, best value, and A+B+I/D are some examples of the non-traditional and innovative practices currently being investigated by the highway construction industry. Warranty contracting has several advantages, including potential for reduced delivery costs, lower total construction costs, focus on performance outcomes rather then material outputs, improved quality, and an opportunity to provide SHAs with another contracting option. This paper reviews the history of warranty contracting in the United States, offers an assessment of the current status of SHA warranty contracting, presents issues to consider in drafting a model specification, and develops a framework for implementation of warranty contracting. Conclusions: Despite its advantages, warranty contracting is not appropriate for all situations. Therefore, an in-depth study should be conducted to determine what project, SHA, and contractor characteristics are necessary to have a successful warranty project. Data must also be collected and analyzed on on-going and future projects in order to determine the best practices regarding warranty contracting. SHAs will continue to increase the number of projects warranted and length of the warranty, tighten thresholds on performance indicators, and warrant more end products. Cooperation is very important in the development of a warranty program. The goals, risks and new responsibilities of all the parties involved need to be clearly defined and understood. With open communication between the SHA, the contracting community, and the surety companies, the warranty program can be successful.

Jeffrey S. Russell, Assoc. Professor, University of Wisconsin- Madison, Department of Civil and Environmental Engineering Room 2304 1415 Engineering Dr. Madison, WI 53706 Phone: 608-262-7244, Fax: 608-262-5199, russell@engr.wisc.edu; Awad S. Hanna, Assoc. Professor, University of Wisconsin- Madison, Department of Civil and Environmental Engineering Room 2260 1415 Engineering Dr. Madison, WI 53706 Phone: 608-262-0614, Fax: 608-262-5199, ashanna@facstaff.wisc.edu; Stuart D. Anderson, Assoc. Professor, Texas A&M University, Department of Civil Engineering CE/TTI Building Spence Street College Station, TX 77843-3136 Phone: 409-845-4414, Fax: 409-845-6554, sda4823@acs.tamu.edu; Patrick W. Wiseley, Project Engineer, EMCS Design Group, 205 W. Highland Ave. #501, Milwaukee, WI 53201 Phone: 414-347-1617; and Robert J. Smith, Attorney, Wickwire Gavin, Suite 300, 2 East Gilman St. P.O. Box 1683, Madison, WI 53701-1683 Phone: 608-257-5335, Fax: 608-257-2029, rsmith@wi.wickwire.com.

990579 "Use of Best Value Selection"

Abstract: Carter and Burgess, Inc., was selected by the Utah Department of Transportation (UDOT) to evaluate several aspects of the I-15 Design/Build Reconstruction project under construction in Salt Lake City. The evaluations are being completed in part to fulfill commitments made to the Federal Highway Administration as they granted a Special Experimental Project 14 (SEP-14) status to the I-15 project permitting design/build contracting methods. This report presents information about the selection process used by UDOT to hire a design/build team to work on this project. UDOT decided to use a "best value" selection process rather than low cost to select a contractor. The report discusses comparison between design-bid-build and design/build processes. It describes the "best value" selection process used by UDOT to evaluate and select a contractor, using the detailed selection process. A description of the organizational structure required to prepare and review the proposals is presented. Unique features of the UDOT process are discussed, including use of stipend, risk sharing, ISO 9000 certification, design life, performance specifications, "best and final offer" (BAFO), award fees and use of CD-ROM’s used to distribute the proposal information. Lessons learned in the process are also presented.

Stanley S. Postma, Carter & Burgess, Inc., 420 E. South Temple, Suite 345, Salt Lake City, UT 84040, email: postmass@c-b.com; Frank Carlisle, Carter & Burgess, Inc., 420 E. South Temple, Suite 345, Salt Lake City, UT 84040; James E. Roberts, CALTRANS, 1801 30th Street, 5th Floor, P.O. Box 942874, Bin #9, Sacramento, CA 94274, Tel: 916-227-8808, Fax: 916-227-8251, email: jroberts@trmx2.dot.ca.gov; and David Downs, Utah Department of Transportation.

991403 "In-House versus Consultant Design Costs in State Departments of Transportation"

Abstract: The use of consultants in providing pre-construction engineering designs services for state Department’s of Transportation has increased over the last 20 years. This has resulted in several investigations into the cost-effectiveness of this trend. This paper reviews past studies, examines their methodology, suggests improvements to certain parts of the commonly-used investigative process, and demonstrates their use in an application to the Louisiana Department of Transportation and Development. The suggested improvements include using the same project to compare in-house and consultant design costs (rather than the use of similar projects, as in most studies), performing a detailed analysis of overhead rates that are comparable between state and consultants, and measuring comparative design costs as the ratio of in-house to consultant design costs rather than as the ratio of design to construction cost commonly used in past studies. Conclusions: Most studies in the past have concluded that consultant design costs are higher than in-house costs or that there is not a significant difference in cost between the two. The Louisiana study found that consultants are approximately 20 percent more expensive than in-house staff in producing road and bridge designs but that the difference was almost entirely due to the extra cost of contract preparation and in-house supervision required for consultant designs. The study also identified factors other than cost that are used in decision-making to employ consultants.

Chester G. Wilmot, Department of Civil and Environmental Engineering, Louisiana State University, Baton Rouge, Louisiana 70803, Tel: (225) 388 4697 Fax: (225) 388 8652 Email:

cewilm@eng.lsu.edu.

Donald R. Deis, Department of Accounting, E.J. Ourso School of Business, Louisiana State University, Baton Rouge, Louisiana 70803, Tel: (225) 388 6214 Fax: (225) 388 5256 Email:

acdeis@unix1.sncc.lsu.edu.

Helmut Schneider, Director, Information Services and Decision Sciences, E.J. Ourso School of Business, Louisiana State University, Baton Rouge, Louisiana 70803, Tel: (225) 388 2126 Fax: (225) 388 2511 Email:

hschnei@lsu.edu.

Charles H. Coates, Jr., Consulting Civil Engineer, 2730 Tall Timbers Road, Baton Rouge, Louisiana 70816, Tel: (225) 292 8337.

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III. CONSTRUCTION: PAVEMENTS

990031 "The Development Of Smoothness Specifications For Flexible Pavements In The State Of Florida"

Abstract: Initial pavement smoothness has been shown to improve the overall pavement performance. This combined with the importance of providing a comfortable ride for the driving public justifies the importance of achieving high initial pavement smoothness. FDOT has recently developed smoothness specifications for asphalt pavements. These smoothness specifications will be used on high-speed facilities and they will be based on measurements obtained with laser road profilers. The ultimate goal is to include incentive/disincentive specifications aimed at rewarding the contractor for a high quality ride and simultaneously providing a financial deterrent to providing a poor quality ride. Conclusions: Ride Numbers measured with a laser profiler can be used to rank the level of rideability on rural projects with some limitations. The sections evaluated should be at least 0.100 mile in length. Roadway sections at bridges, railroad crossings, intersections, etc. will need to be tested using a rolling straightedge. Acceleration and deceleration lanes will also need to be tested with a rolling straightedge. Limitations that affect the use of the laser profiler for collecting ride data are stop and go driving due to traffic lights, traffic flow, etc. The laser profiler must operate at fairly constant speeds above 15 miles per hour. The laser profiler also must be operated at constant speed when it enters and leaves the test section. About twenty five percent of the new sections tested will have ride numbers less than 4.30. These sections are targeted for improvement with the newly developed specifications.

Khaled Ksaibati, University of Wyoming, PO Box 3295, Laramie, WY 82071-3295, 307-766-6230, Fax: 307-766-2221, khaled@uwyo.edu.

990229 "Summary of the 1996 PCC Performance-Related Specification Shadow Field Trial—Iowa State Route 23"

Abstract: This paper summarizes the results of a "shadow" field trial (actual contractor pay was not affected) conducted to demonstrate a "Level 1" prototype performance-related specification (PRS) for jointed plain concrete pavement (JPCP) construction. The Level 1 PRS (the most practical PRS method at this time) is believed to be immediately implementable because it uses currently practiced sampling and testing procedures. The future pavement performance is represented by distress indicators that are predicted based on measured quality characteristic (QAC) values. Pay factors are determined independently for each QAC from simulated pay factor vs. QAC curves and corresponding equations. The overall lot pay factor is determined from a simple mathematical manipulation of the individual QAC pay factors. The specific objectives of the field trial were to verify/confirm the draft specification's effectiveness, identify potential problem areas, and determine its reasonableness. This paper discusses all aspects of the field trial including the relevant definitions, selection of lots and sublots, sampling and testing plan, calculation of "shadow" PRS pay adjustments, problems encountered, and a summary of lessons learned. Conclusions: The successful completion of this first shadow field trial demonstrated that the current Level 1 PRS approach is both a reasonable and practical PRS method. It is believed that the current Level 1 PRS approach could be implemented by most State Highway Agencies (SHAs) with little change to an SHA's current QAC sampling and testing procedures. Valuable experience was obtained at the Iowa field trial, specifically in the area of developing practical QAC sampling and testing plans. The current PRS demonstration software (PaveSpec 2.0) was also revised to reflect the lessons learned at the Iowa field trial.

Todd Hoerner, and Michael Darter, ERES Consultants, Inc., 505 W. University Ave., Champaign, Illinois 61820, Tel: (217) 356-4500 Fax: (217) 356-3088. Email: thoerner@eresnet.com; mdarter@eresnet.com.

990230 "Nuclear Density Readings and Core Densities: A Comparative Study"

Abstract: This paper presents the findings of an investigation performed to identify possible correlations between nuclear density gauge readings and core density results. The nuclear density data was collected on a Superpave section of Interstate Highway I-95 in Brevard County. Core samples were also obtained from this section for laboratory density determination. Five gauge units (Troxler models 3401, 3440 (2 units), 3450, and 4640) and three core density methods (Florida test method FM 1-T 166, ASTM D 1188 using parafilm, and dimensional analysis) were considered. The relationships among the core density results were first analyzed. Then an investigation of the correlation among the different gauges used in this study was evaluated. Finally, the performance of each of the units with respect to the core density results was assessed. Conclusions: The findings of this study indicated that the five nuclear gauge density units did not always produce similar results and did not consistently correlate with the core densities. The nuclear density testing variability did not only differ from gauge to gauge but also from location to location within each gauge. In addition, a higher degree of correlation existed between core density methods than between the core and nuclear readings (an indication of a higher variability in nuclear density data as compared to that in core densities). The findings also suggest a need to correct the readings of all nuclear gauges, including the thin lift gauges, for the density of the underlying materials.

Bouzid Choubane, Patrick Upshaw, Gregory Sholar, Gale Page and James Musselman, Florida Dept. of Transportation, State Materials Office, 2006 N.E. Waldo Road, Gainesville, FL 32609, Tel: (352) 337-3100, Fax: (352) 334-1649, Email: bouzid.choubane@dot.state.fl.us.

990990 "Application Of Fiber Reinforced Concrete For Thin And Ultra-Thin Whitetopping On I-20 In Mississippi"

Abstract: A thin, portland cement concrete whitetopping project was constructed on Interstate 20 near Jackson, Mississippi in August 1997, as a test of this technology on a high traffic, high speed roadway. The primary objective of this project was to evaluate the potential of the 3M fibers to expand thin whitetopping (TW) applications to compete economically on routine roadways by extending slab length, since sawing and sealing joints is a significant part of the cost of constructing a TW. This project contained sections utilizing plain concrete, concrete containing 3M polyolefin fibers (50/63 fiber), and concrete containing fibrillated polypropylene fibers. Joint spacing for the 50/63 fiber section ranged from 1.82 m to 12.2 m. Joint spacings for the plain and fibrillated fiber sections were 3.65 m and 1.82 m, respectively. The whitetopping was done as an inlay in the truck lane of a hot mix asphalt pavement with a history of rutting despite 4 rehabilitations since 1983. Total project size was 1220 m long and 3.65 m wide and involved thicknesses of 100 mm, 150 mm, and 200 mm. This project involved partnering with industry and various branches of government. Monitoring data includes distress surveys, deflection surveys, and skid measurements. At 11 months of age, there are several corner cracks in the fibrillated fiber and 50/63 fiber sections. Some of the corner crack areas in the 50/63 section are deteriorating while those in the fibrillated fiber section appear stable. Conclusions: The plain and fibrillated fiber sections will perform well if proper sawing is done. It is obvious the 50/63 fiber sections, for all slab lengths, will require patching of many of the slab corners.

Alfred Crawley, Mississippi Department of Transportation, P. O. Box 1850, Jackson, MS 39215-1850, Tel: (601) 359-7650 Fax: (601) 359-7634, Email: acrawley@mdot.state.ms.us.

991118 "Analysis of Paving Construction Quality for Urban Highway Weekend Closures"

Abstract: This paper presents the results of an analysis of paving quality that was achieved through the implementation of a full weekend closure strategy for constructing an asphalt overlay. The pilot project was an approximately 8.87-km (5.5-mi) section of Interstate 405 (I-405) in Seattle that was closed to traffic in a single direction on two consecutive weekends, planned for August 15-18 and August 22-25, 1997, so that overlay construction could be performed. The Washington State Department of Transportation (WSDOT) used this approach as an alternative to frequent partial closures during nighttime hours. Quality parameters that were quantitatively examined for the mainline paving in this study were surface smoothness (rideability), in-place density, and gradation. Other factors such as the presence of "cyclic" segregation, the condition of longitudinal joints were assessed by observation. Since project-to-project comparisons are difficult to validate, the primary question of the analysis was whether consistent quality could be achieved between the night and day cycles of the paving operations. Comparisons with historical data were used to establish benchmarks for assessing quality in the general sense. The major findings were that consistent quality through the night and day cycles may be achieved with the weekend closure strategy, and the level of quality achieved on this project exceeds average reported quality levels in the parameters examined. It is noted that these results were achieved with high paving production rates.

Phillip S. Dunston, Bonnie M. Savage, and Fred L. Mannering, Department of Civil and Evironmental Engineering, University of Washington, Box 352700, Seattle, WA 98195-2700, Tel: 206-685-1795, Fax: 206-543-1543, Email: pdunston@u.washington.edu, bonmae@u.washington.edu, flm@u.washington.edu.

991160 "Development of A Method For Early Prediction Of The Asphalt Content Of Hot Mix Asphalt (HMA) By Ignition Test"

Abstract: The ignition test, developed by the National Center for Asphalt Technology (NCAT), has proved to be a fast, pollution free, automated and inexpensive method of determining the asphalt content of a hot mix asphalt (HMA) sample. The time required to perform this test is about 30 to 40 minutes, which is significantly less than the time required to perform a solvent extraction test procedure. However, having the ability to determine asphalt content in 10-15 minutes would allow the technician to identify any problem in mix production much earlier, and thus save a significant amount of time and money. This paper presents the results of a study carried out to develop a method for estimating the asphalt content of hot mix asphalt (HMA) sample within 10to 15 minutes after testing begins. The method consists of determining the prediction factor on the basis of test results from two samples and then predicting the asphalt content of additional samples on the basis of the prediction factor and the asphalt content loss at 10-15 minutes of test. Use of this method is expected to provide a good estimate of the measured asphalt content in less than half the test time. This short cut method should be used for quality control only and should not be used for acceptance or rejection of the mixtures. Conclusions: A simple practical method has been developed to predict the asphalt content of a HMA sample after 10-15 minutes. The method consists of determining the prediction factor on the basis of test results from two samples and predicting the asphalt content of additional samples on the basis of the prediction factor and the asphalt loss after 10 to 15 minutes of test. Use of this method is expected to cut down the testing time by 15 to 30 minutes for quality control testing. This means that with the use of proper prediction factors, the user will be able to determine any change in asphalt content within 10 to 15 minutes of starting the ignition test. The substantial savings in time will translate to early detection of any change in asphalt content and hence significant monetary savings. It should be understood that this procedure is meant for quality control (QC) only, and is not recommended as a tool for quality assurance (QA).Rajib Mallick, CEE Department, Worcester Polytechnic Institute, 100 Institute Road, Worcester, MA 01609, Tel: (508) 831 5289, Fax: (508) 831 5808, Email: rajib@wpi.edu; Elton Ray Brown, National Center for Asphalt Technology, 211 Ramsay Hall, Auburn University, AL 36849, Tel: (334) 844 6244, Fax: (334) 844 6248, Email: rbrown@eng.auburn.edu.

991222 "Rehabilitation Of Ellaville Weigh Station With Ultra-Thin Whitetopping"

Abstract: The Florida DOT constructed the first Ultra-Thin Whitetopping (UTW) to rehabilitate the Ellaville Truck Weigh Station on I-10 in Northwest Florida. This rehabilitation project included the placement of UTW on the existing asphalt pavement which had severe rutting and cracking problems. Nominal layer thicknesses for the UTW were 80 mm and 100 mm. The joint spacings for the UTW panels were 1.2 m and 1.6 m. High early strength concrete was used in this project. Polypropylene fibers were included in the concrete for the sections on the west side of the weighing platform and plain concrete was used on the east sections. Panel joints on the east sections were sealed with silicone sealant while the joints in the west sections were left unsealed. This paper discusses the implementation of the UTW in Florida which includes design, specification and construction. Also addressed is the performance the Ellaville Weigh Station after one year of truck loading, and the predicted life of the UTW. Conclusions: Primary emphasis should be placed on ensuring maximum bond between the UTW and asphalt. Specifying compressive strength, shearing strength at UTW/asphalt interface and rideability as acceptance criteria can produce better performance and ensure smoother ride. UTW panels with 1.2 m and 1.6 m joint spacing seem to provide equal performance. Placing UTW on a 32 mm thick asphalt layer did not show any premature cracking. A preconstruction conference with the contractor is essential to discuss the specific details of UTW. The effect of fibers on performance of the UTW could not be determined. Sealing the joints did not make any difference in the performance of the UTW sections. A one year service life of the UTW at the weigh station is equivalent to 4.8 years of service life on an intersection with medium traffic.

Jamshid Armaghani, and Diep Tu, Florida Department of Transportation, 2006 Northeast Waldo Road, Gainesville, Florida 32609, Tel: (352) 337-3200, Fax: (352) 334-1648, jamshid.armaghani@dot.state.fl.us.

991357 "A Contractor's Experience with Polymer Modified Asphalt in Alabama"

Abstract: The use of polymer modified asphalt binder has increased in the state of Alabama with the requirement for higher Performance Graded (PG) asphalt on high-volume roadways. In 1997, four types of polymer modified asphalt binders (PMAB) were available from suppliers in Alabama: one modified with plastomer wax (EE2), one modified with a reactive elastic plastomer (GEA), and two modified with an elastomer polymer (SBS). A laboratory investigation was undertaken to compare three of the polymer modified asphalts (only one elastomer modified asphalt binder was tested) in terms of: force ductility at 4*C, separation of polymer and asphalt, and laboratory rutting performance of hot mix asphalt (HMA) prepared with each asphalt. Performance testing was also performed on the elastomer polymer (SBS) and the GEA during asphalt production for two roadways in Alabama. Conclusions: Laboratory testing indicates that the use of PMAB in hot mix asphalt can greatly enhance performance of the HMA in comparison to the use of PG 64-22. However, proper production and storage procedures must be followed when using PMAB to prevent separation. Daily separation testing by the PMAB suppliers should be required by the DOT due to the fact that when separation of the PMAB occurs it is a problem for everyone involved. Unforeseen expenses, equipment damage, and possible asphalt pavement failure can occur. The testing results have shown that some PMAB's are more prone to separation than others but that the final product "Hot Mix Asphalt" should benefit from the use of PMAB if the PMAB is handled and produced properly.

Paul Messersmith, Chris Jones and Chris Wells, Superfos Construction (U.S.), Inc. 715 Twitchell Road, Dothan, AL 36303, Tel: (334) 794-2631 Fax: (334) 794-2631 Ext. 310 Email: paulm@Superfos-usa.com.

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IV. CONSTRUCTION: STRUCTURES

991422 "Epoxy Jointing of Precast Prestressed Concrete Segments"

Abstract: Epoxy is normally used between precast segments to fill voids, to keep water from seeping in the joint, to prevent grout from bleeding into the joint from the post tensioning ducts, and to act as a lubricant between the segments. Better and more efficient means of ensuring a good seal between ducts are needed for enhanced protection against rain water, de-icing salts and cross grouting, which may lead to corrosion of prestressing steel. Two new experimental epoxy applications were tested in this study: a top strip recess at the joint that was formed into the concrete during the precast process, and a recessed annulur groove around the duct which provides a distinct guide for the proper amount of epoxy application. The joints were tested with water tanks placed above the joints to measure the seepage of water. Pressurized water was subsequently applied through the ducts, and the amount of pressure loss was measured. The joints were inspected for water that may have escaped from the ducts. Conclusions: Results showed that the current practice of one face epoxy application performed well when properly applied. The epoxy filled annuli provided good protection against grout penetration, coupling between segments, and automatic epoxy clearance around ducts. The epoxy filled top strip was very effective in resisting water penetration, and provided a convenient way to correct alignment and handling damage at the edges. It is recommended that the use of the one face epoxy application should be continued, with the annulus feature added. The top strip feature may not be practical because of maintenance and grinding problems.

Nur Yazdani, Professor of Civil Engineering, Florida A&M University – Florida State University, 2525 Pottsdamer Road, Room 129, Tallahassee, Florida 32310, Phone: (850) 410-6125, Fax: (850) 410-6142, Email: yazdani@eng.fsu.edu.

V. BITUMINOUS MATERIALS

990080 "An Evaluation Of Stripping In Virginia’s Pavements"

Abstract: Virginia has struggled with stripping of asphalt mixes since the 1970’s. Initially, chemical antistripping additives were used; eventually, hydrated lime was required, under certain conditions, when it proved to be effective in a limited set of field tests. The specifications were then changed to require hydrated lime or a chemical additive that could produce a tensile strength ratio (TSR) equivalent to that obtained by using hydrated lime. Because of this change, it was believed that chemical additive manufacturers made improvements to produce a new generation of additives that were superior to those previously available. In 1991, a small field study was initiated in Virginia to determine the performance of the new-generation additives and hydrated lime. The pavements showed significant stripping; therefore, a follow-up survey including 74 sites scattered throughout the state was conducted to verify these findings. Conclusions: The follow-up survey indicated that stripping of asphalt mixes continues to be a problem in Virginia. A high degree of stripping was observed in 30 to 50 percent of the pavements surveyed. Although the initial small field study indicated that hydrated lime was more beneficial than chemical additives the follow-up survey that included a large number of sites did not verify this finding. Also, there was no significant difference in stripping between different types of mixes. The air voids level of the pavements was higher than desirable which might have contributed to some of the excessive stripping.

George W. Maupin, maupingw@vdot.state.va.us.

990110 "Use of RAP in Superpave HMA Applications"

Abstract: This research program evaluated the possibility of splitting RAP stockpiles then using the coarser RAP fraction in a typical 12.5 mm below the restricted zone Superpave gradation. The finer RAP fraction was used in an above the restricted zone 12.5 mm Superpave gradation. Two sources of RAP (Georgia and Minnesota) were used so that a wide range of asphalt and aggregate properties would be represented. Screening the RAP allowed up to 40 percent of the coarse RAP fraction to be used and still meet below-the-restricted zone Superpave gradation and volumetric requirements. This was mainly due to the significant reduction in the finer aggregate fractions, especially the minus 0.075 mm material. The use of RAP in these mixtures resulted a savings in the required neat asphalt of between 18 to 25 percent. A noticeable increase in mixture tensile strength with as little as 15 percent RAP was seen. This change in mixture properties suggested that a softer grade of neat binder might be needed. A maximum of 15 percent of the fine RAP fraction was used to produce an acceptable above-the-restricted zone Superpave gradation. The net savings in neat asphalt content was 25 percent. Little change was seen in tensile strengths due to the addition of this RAP fraction. However, there was a substantial increase in mixture stiffness at intermediate to warm temperatures. This increase was also seen as a 20 percent reduction in the APA rut depth when RAP was used. The indirect tensile creep compliance decreased when RAP was added. While there was little difference in compliance at -20oC, there was a decrease of about 30 and 50 percent at -10 and 0oC test temperatures, respectively. Conclusions: Using RAP in mixtures, even at low percentages, require an evaluation of the composite mixture properties in order to accurately assess the need for a change in neat asphalt grade.

Mary Stroup-Gardiner, and Chris Wagner, National Center for Asphalt Technology, 211 Ramsay, Auburn University, Alabama 36849; Phone (344) 844-6280, Email: marysg@eng.auburn.edu.

990163 "Blending Charts Based on the Performance-Graded (PG) Asphalt Binder Specification"

Abstract: In this study, one binder was laboratory aged with the RTFO and PAV to simulate the aged binder in the RAP. The aged binder was blended with two soft binders and two rejuvenated materials. Ten blended and rejuvenated binders were characterized with the PG binder parameters such as G* (complex shear modulus), d (phase angle), S (stiffness), and m-value (creep rate). The relationship of the PG binder criteria (G*/sin d, G*.sin d, S, and m-value) versus amount of soft binders and rejuvenators in the blends was studied. Conclusions: A linear relationship was found sufficient accurate for prediction of the PG parameters and criteria of blended and rejuvenated binders versus proportion of new binder/recycling agents in blends. Two type of blending charts can be used for selection of proper type or amount of soft binder/recycling agents in the design of mixtures containing RAP. The first method is based on a linear relationship for PG performance criteria (G*/sin d, G*.sin d, S and m-value) versus proportion of soft binder/recycling agents. The second method is based on linear relationship for change in temperatures that PG criteria were satisfied versus proportion of soft binder/recycling agents in blends. In prediction of the PG testing parameters for blended binders, the interaction criteria a lower coefficient of correlation (R2) and higher standard error of mean were found for binders blended with recycling agents than binders blended with soft binders. This can be attribute to blending two materials with high viscosity differences.

Hamid R. Soleymani, North Central Superpave Center, Purdue University West Lafayette, IN. 47906 Tel # 765 463-2317 Email: soleyman@ecn.purdue.edu; Hussain U. Bahia, University of Wisconsin-Madison, Email: bahia@engr.wisc.edu Arthur T. Bergan, University of Saskatchewan, Saskatoon, Canada.

990498 "Collaborative Evaluations of Low Temperature Superpave PG Asphalt Binders"

Abstract: Superpave developed the specifications and selection of Performance Graded Asphalt Binders to address performance in the field. To facilitate the implementation of Superpave, highway agencies are sharing information and working with industry. Wisconsin, Iowa, and Minnesota have collaborated to develop a joint certification program to streamline the process and promote partnering with suppliers. The low temperature grading of the Superpave asphalt binders is of special interest in very severe climates. This paper looks at several projects which have incorporated Superpave asphalt binders, including new construction, reconstruction, overlays on rehabilitated highways and overlays on existing highways. The projects vary from low volume highways to high volume interstates to an airport in an extremely severe climate. The projects, which have been in place several years, have been evaluated for their field performance, especially for behavior at low temperature. The new asphalt binders have been found to increase the resistance to thermal cracking on newly constructed roads and to inhibit reflective cracking on overlays. Conclusions: Of specific interest in the severe climates, the low temperature performance of the Superpave Performance Graded Asphalt Binders has shown significant reduction in thermal cracking on both new construction and reconstruction. 1) On overlays over rehabilitated pavement applications such as pulverized base, the PG asphalt binders have shown value by reduction in thermal cracking. 2) Similarly, PG asphalt binders have shown value by retarding reflective cracking for up to three years on overlays such as the International Falls Airport, CSAH 30 in Blue Earth County, Minnesota, and TH 63 in Lake County, Wisconsin. It is important to use this information in comparison with newer asphalt binder selection guidelines adopted with the new low temperature algorithm.

Dan Wegman, Koch Materials Company, P.O. Box 64596 St. Paul, MN 55164-0596; Jack Weigel, Payne and Dolan, P.O. Box 781, Waukesha, WI 53187; and Alan Forsberg, Blue Earth County Engineer, 35 Map Drive, Mankato MN 56001.

990512 "The Difficult Nature of Minimum VMA: A Historical Perspective"

Abstract: Several researchers have recently discussed problems achieving the minimum voids in the mineral aggregate (VMA) requirements specified in Superpave volumetric mix design. The minimum VMA requirements are often difficult to achieve; they can "fail" mixes that have acceptable performance records, and they may require a higher asphalt content leading to higher project costs. To address these issues the background and logic behind the minimum VMA requirement are re-examined. A review of asphalt mix design methods shows that a minimum VMA requirement was not used until the 1950s, when Dr. Norman W. McLeod almost single-handedly advanced VMA to a critical design parameter. In 1962, The Asphalt Institute specified VMA as a Marshall mix design requirement, but as late as 1985 it was still misused by many highway agencies. Only through the Strategic Highway Research Program (SHRP) and the implementation of Superpave has the minimum VMA requirement become a design standard. The literature review uncovered several problems with specifying minimum VMA: (1) The field data from which the minimum VMA requirements were established could not be found in the literature, (2) The original VMA requirements were based on Marshall compaction, and (3) The precision of the testing necessary for measuring VMA is not good enough for rigid enforcement of VMA specifications. In light of the information presented, it seems clear that the minimum VMA requirements need to be re-examined in light of Superpave and validated with field data