Computer-Based Guidelines for Concrete Pavements Volume I-Project Summary

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CHAPTER 2. PREVIOUS HIPERPAV FEEDBACK AND PROVISIONS FOR FUTURE IMPLEMENTATION

This chapter summarizes feedback collected during previous implementation efforts of HIPERPAV. In addition, provisions for a successful implementation of the final products from this study are discussed, along with the formation of a technical expert group and the recommendations they provided throughout the development of this project.

2.1 User Survey

In the spring of 1996, the HIPERPAV System was first introduced to FHWA. Since that time, HIPERPAV has been presented at numerous meetings and workshops worldwide. During many of these presentations, a number of suggestions for additional features and advancements to the system were made.

2.1.1 Primary Identified Suggestions

A number of suggestions have been identified from a variety of sources and are compiled in this section. From these recommendations, three are the most predominant:

• Mix proportioning.
• Maturity.
• Bridge deck applications.

2.1.1.1 Mix Proportioning

A large percentage of current users believe that the mix design/proportioning element could give HIPERPAV a twofold purpose. The first is to calculate/predict the stresses in the pavement as a function of concrete mix designs. The second would be to design, proportion, and record mix design information in a complete database. The thought here was that if a mix tool is developed, HIPERPAV's utility might double. Eventually, the user would begin to interrelate mix properties with slab properties and stress development. Mix proportioning can also encompass concepts such as the use of fibers, materials compatibility issues, recycled materials, and durability.

2.1.1.2 Maturity

Many practitioners asked that HIPERPAV expand its capabilities to determine and manage strength gain in the slabs for two reasons: opening-to-traffic requirements and mix economics. Opening to traffic in a timely manner can mean a cost savings to the traveling public, and possibly be a financial incentive to the contractor. Maturity is a method that nondestructively predicts the strength gain in a concrete mix. The core of HIPERPAV is based on temperature and maturity prediction. The majority of the early-age properties that HIPERPAV predicts are a function of the maturity. A common suggestion is to improve the maturity prediction in HIPERPAV by giving the user more power to characterize mixes. This can be accomplished by inputs for adiabatic heat signatures as well as improved default properties for the use of mineral and chemical admixtures. In short, maturity is closely tied to traffic management, quality control, and ultimately, cost of the final product.

2.1.1.3 Bridge Deck Application

At nearly every HIPERPAV presentation, someone asks: "Can I use this software for my concrete bridge decks?" The answer at this time is: "Not without proper modification of the models for this application." However, this is certainly an application that has a lot of demand. A bridge deck (or bridge deck overlay) application of HIPERPAV would allow a user to predict the potential for uncontrolled cracking just as it does currently for pavements. In truth, since the majority of the models inherent in the HIPERPAV system are based on structural engineering models for concrete, this application could be achieved with only minimal validation.

2.1.2 Detailed List of Identified Suggestions

A detailed list of the suggestions received from the users of HIPERPAV is given here. This list of suggestions and advancements has been grouped into four main categories:

1. Advancements included in HIPERPAV I.
2. Advancements incorporated during the HIPERPAV II effort.
3. Suggestions that relate to but are beyond the scope of the HIPERPAV II effort.
4. Suggestions requiring new major efforts.

The list is further subcategorized as:

• Pavement design inputs suggestions.
• Mix design inputs suggestions.
• Environmental inputs suggestions.
• Construction inputs suggestions.
• Output suggestions.
• Graphical user interface modification suggestions.
• Model improvement suggestions.
• Suggestions for additional modules.
• Other suggestions.

2.1.3 Advancements Included in HIPERPAV I

Features observed from previous comments were addressed in HIPERPAV I (software version 2.4.1). These additional features and advancements are listed below:

2.1.3.1 Pavement Design Inputs Advancements

• Additional subbase types were included.
• Laboratory 28-day PCC tensile strength was required as an input, rather than the flexural strength.

2.1.3.2 Mix Design Inputs Advancements

• The default values of the aggregate thermal coefficient of expansion are now displayed for the selected coarse aggregate type.
• Class "C" fly ash was incorporated into the mix design.

2.1.3.3 Model Advancements

• The effect of changes in the Poisson's ratio at early age was taken into account.
• The prediction of the creep relaxation model for early age was slightly improved.

2.1.3.4 Additional Modules Incorporated

• A joint sawing module was incorporated based on a FHWA study (but disabled until validated).
• An earliest traffic loading module was incorporated based on a FHWA study (but disabled until validated).

2.1.3.5 Other Advancements

• An autoscale feature of the output screen was included.
• Icons related to each one of the modules were included in the control panel.
• A warning note was added to explain the need for laboratory-measured values of strength and modulus of elasticity.
• A warning note was included in the maturity data box to explain the maturity method used in HIPERPAV.
• Online help for chemical and mineral admixtures, cement chemistry, and different curing methods was provided.

2.1.4 Advancements Incorporated During the HIPERPAV II Effort

Each recommendation is categorized with a high (H), moderate (M), or low (L) rank based on the level of user desirability.

2.1.4.1 Pavement Design Inputs Advancements

• Improve the stress prediction accuracy by adding paving width as an input, adjusting the models accordingly. (H)

2.1.4.2 Mix Design and PCC Properties Inputs Advancements

• Allow the user to enter the coefficient of thermal expansion (CTE) of the mix or the aggregate. (M)
• Add a conversion calculator to estimate splitting tensile strength from other strength types (i.e. compressive, flexural). (M)
• Add graphical representation of maturity input data. (H)
• Add an input option for Arrhenius maturity data in addition to Nurse-Saul. (H)
• Add an input for cement fineness and adjust the models accordingly. (H)
• Allow the user to enter drying shrinkage test results. (M)

2.1.4.3 Environmental Inputs Advancements

• Allow for solar radiation, windspeed, and humidity to be user-defined over the 72-hour period. (H)
• Add a grid control for the air temperature input data to allow the user to manually enter it in a gridline (as numbers) instead of only graphically (point dragging). (H)
• Use a simplified geographic information system (GIS) for climatic inputs. This data is stored on a CD-ROM along with the software. (H)

2.1.4.4 Construction Inputs Advancements

• Add a "no sawing" input option instead of setting saw time to 72. (H)
• Add a "green sawing" input option instead of setting saw time to 0. (H)
• Add a skip saw option. Add an input for the time of the intermediate cuts. (H)

2.1.4.5 Output Advancements

• Save output in Microsoft® Excel format. (H)
• Improve the print dialog; add zoom, printer configuration, and multiple pages. (M)
• Allow the user to change the scale of output plots (autoscale). (H)
• Show stress and strength when the mouse is hovered over them. (H)

2.1.4.6 Graphical User Interface Modification Advancements

• Add input bounds checks. (H)
• Add a multiple document interface (allowing multiple analysis files to be opened simultaneously.) (H)
• Change to a Microsoft Outlook®-style (document object model) graphical user interface. (H)
• Add better tool tips. (M)
• Add pulldown menu to change units but not value. (M)
• Add more units-e.g., millimeters (mm) for thickness. (M)
• Add a most recently used file list under the file menu option. (M)
• Add default option to reset the variables back to default values. (H)

2.1.4.7 Model Advancements

• Make efforts to improve and/or validate the creep relaxation model. (H)
• Improve materials characterization for mineral and chemical admixtures. (H)
• Add autogenous shrinkage model. (H)

2.1.4.8 Additional Modules Incorporated

• Add a JPCP long-term performance module. (H)
• Add a CRCP early-age behavior module. (H)

2.1.4.9 Other Advancements

• Add warning/guidance screens with the "do's" and don'ts" on the use and interpretation of HIPERPAV. (H)
• Add online documentation by digitizing the final report and user's manual. (H)
• Develop a technology transfer package for implementing HIPERPAV. (H)

2.1.5 Suggestions Related to, but Beyond the Scope of the HIPERPAV II Effort

2.1.5.1 Pavement Design Inputs Suggestions

• Add a database for the customization of subbase types. (L)
• Add more cementitious subbase types with better descriptions to account for large variance in different types. (L)

2.1.5.2 Mix Design Inputs Suggestions

• Add a mix-design and proportioning module. (H)
• Add an option for aggregate blending. (H)
• Add volumetric flags for unbalanced (incorrect) total volumes of PCC. (H)
• Add a mix proportions pie chart feature "by volume." (M)
• Add import/export feature for maturity data. (H)
• Add a cements database that can be customized to a specific location. (H)
• Add mix design database that can be customized to a specific location. (H)
• Add type IV cement as a default cement type. (L)

2.1.5.3 Environmental Inputs Suggestions

• Add (as an advanced input) the latitude to estimate solar radiation. (M)
• Add a feature to save/load ambient air temperature distributions to disk, and provide default files for various climatological events. (M)
• Include the ability to account for the effects of rainfall on the early-age slab temperature. (M)
• For clarity, make the mouse cursor shape a function of the selected environment tool (e.g., cold front). (L)
• Add an air temperature "spline" tool to allow the user to define maxima and minima at any time. (L)

2.1.5.4 Construction Inputs Suggestions

• Add application rates for curing method, and perhaps brand names. (H)
• Add a mix temperature calculator that will calculate the estimated initial PCC temperature (a HIPERPAV input) as a function of the aggregate, cement, and water temperatures. (M)
• Add an option to automatically calculate the base temperature before placement, instead of making it a user input only. (M)

2.1.5.5 Output Suggestions

• Add a feature to show all of the stresses in the pavement (top, mid, bottom). (H)
• Make a three-dimensional plot of stress and strength for different placement times of day-color code surface for closeness to failure-green, yellow, and red. (M)
• Make analysis period variable (e.g., anywhere from 24 to 96 hours). (M)
• Add animations for stresses and displacements (in post-processor). (M)
• Separate the curling, shrinkage, and axial stresses on plot. (M)
• Show evaporation rate, air temperature, concrete temperature, relative humidity, and windspeed for points on the evaporation rate output curves as the mouse is hovered over them. (M)
• Add a feature for user-defined plot color schemes. (M)
• Add a toggle to show the compressive stresses in the pavement (instead of just zero stress). (L)
• Add a button to switch between absolute (megapascals (MPa)) and relative (percent) stress vs. strength. (M)
• Add tool tip showing absolute (MPa) and relative (percent) stress vs. strength. (M)

2.1.5.6 Graphical User Interface Modification Suggestions

• Color code the inputs for specific applications of the software (planner, designer, construction, etc.), or use a wizard interface to step through inputs that can be tailored to the user. (L)

2.1.5.7 Model Improvement Suggestions

• Add combined curling-axial restraint model. (H)
• Include consolidation/density impacts on stress/strength development model input. (M)
• Add effects of alkali content on the heat of hydration. (M)
• Add a longitudinal early-age cracking prediction. (M)
• Investigate edge restraint due to multipass paving. (L)
• Improve characterization of moisture state with respect to strength and other behaviors. (H)

2.1.5.8 Other Suggestions

• Include help screens with measurement guidelines for base temperature, slab-base friction, and other nonstandardized inputs. (H)
• Add additional help screens to describe curing application, moisture loss, and heat retention. (H)
• Add more detailed Microsoft Windows® help files to help the user execute the program. (H)
• Add warning/guidance screens with the "do's" and "don'ts" on the use and interpretation of HIPERPAV. (H)
• Add advanced input screens for inputs like k-value, latitude, and finite-element method (FEM) mesh size, etc. (M)
• Add a smart update feature for easy software updates via the Internet. (M)
• Add command line options for batch processing of input files. (L)

2.1.6 Suggestions Requiring New Major Efforts

The following advancements suggested by the customers would require relatively significant effort:

2.1.6.1 Mix Design Inputs Suggestions

• Add the use of synthetic or steel fibers as an input, and adjust the models accordingly. (H)

2.1.6.2 Other Suggestions

• Develop a construction (real-time) version of HIPERPAV using a weather station and digital satellite weather forecasting. (H)
• Develop a version to model bridge slab decks or deck overlays. (H)
• Add sensitivity analysis options that would run several simulations and compare the results of the runs via plots and tables. (H)
• Convert to a Web-based application. (H)
• Add plot-predicted pavement temperatures vs. time and space. (H)

2.1.6.3 Model Improvement Suggestions

• Develop a version for bridge decks and bridge deck overlays. (H)
• Add a mechanistic moisture model to better predict moisture-related behavior. (H)
• Add fracture mechanics theory to better predict uncontrolled cracking and/or joint popping. (H)
• Conduct a validation study of the effects of chemical and mineral admixtures on the heat of hydration. (H)
• Include early-age PCC durability models as a parallel simulation. (H)
• Develop materials for a National Highway Institute (or other) short course. (H)

2.2 Technical Expert Panel (TEP)

In recent years, FHWA has begun to specify forming technical expert groups as part of its various research endeavors. The importance of such groups cannot be overstated-this is especially true for projects that require the end result to be ready to implement.

2.2.1 TEP Members Selection Criteria

For the HIPERPAV II project, the following criteria were used to select TEP members:

• The TEP members should be stakeholders in the concrete paving industry.
• The TEP members should have the ability to contribute constructively to help the project team accomplish the objectives of the project.
• The TEP members should be representative of their respective areas of expertise.
• The TEP members should be leaders in their respective areas of expertise.

2.2.2 TEP Members Selected

For this project, a TEP consisting of seven members was formed. The final selection process of the TEP was done in cooperation with FHWA.

2.2.3 Initial Meeting

The initial TEP meeting for this project was held on June 28-29, 2000 at the Turner-Fairbank Highway Research Center in McLean, VA. The primary objectives of this meeting were to:

• Familiarize the TEP members with HIPERPAV.
• Discuss the overall project objectives.
• Discuss the proposed technical approach to the current project.

During this initial meeting, issues were identified and key recommendations to address potential problems during the implementation phase of the project were made. The primary recommendations from the TEP members and key highlights from this initial meeting included:

• Concentrate efforts on strengthening HIPERPAV in its prediction of early-age pavement behavior.
• Keep HIPERPAV user-friendly by ensuring simplicity of the input screens and by possibly creating unique user profiles.
• Optimize the mix design module for materials selection and proportioning, giving the users another reason to open the software.
• Address long-term performance modeling as a means of further optimizing early-age pavement design, materials selection, and construction procedures; looking at relative performance of the aforementioned factors, but not as an independent tool.

2.2.4 Second TEP Meeting

After a draft version of the written guidelines, interim report, and software prototype were developed, a second meeting was held on January 29-30, 2001. The primary objectives for this meeting were to:

• Review project deliverables to date, including software prototype, written guidelines, and modeling.
• Discuss future software development work plan and validation work plan.

The primary recommendations and highlights from this meeting included:

• The draft written guidelines presented to date are clear and understandable.
• Long-term performance models in HIPERPAV II will depend highly on the load transfer efficiency (LTE) model.
• Regarding the field sites, start contacting departments of transportation (DOT) now, if possible, during the bidding process. Involve the American Concrete Pavement Association chapter executives.
• It is important to incorporate the mix design module to attract additional users and to facilitate the use of HIPERPAV's stress analyses techniques.
• FHWA should eventually consider the development of two versions of HIPERPAV-a research grade and a practical grade. In the research grade, include provisions for inputs that are the most sensitive in the models. During the development of this project, the project team should concentrate more on the development of the practical grade version of HIPERPAV.
• The outputs of the models should be evaluated carefully-different scenarios need to be generated, and the results need to be examined from both the absolute and the relative perspective. The TEP should assist in this determination.
• The measurement and inclusion of adiabatic calorimetry for concrete mixes should be a high priority. As a result, HIPERPAV can become a real-time construction tool for quality control.
• If States are interested, additional sites for validation can be funded via a pooled fund project.

2.2.5 Third TEP Meeting

On May 14 and 15, 2002, after the beta version of the computer guidelines was developed, a third TEP meeting was held with the following objectives:

• Present project deliverables to date.
• Discuss specifics of the work plans as executed thus far.
• Understand fully the software layout, menus, and options.
• Accept the technical premise behind the software.
• Develop the ability to work the software and provide advice as to its functionality and ease of operation.

The primary recommendations and highlights from this meeting included:

• HIPERPAV could be seen as a day-to-day quality control tool as well as an analysis tool.
• Recent University of Texas findings on hydration modeling and characterization of admixtures have been incorporated in HIPERPAV II, and should form part of the fundamental training of the software.
• The Total Environmental Management for Pavements (TEMP) System, currently under development, will be a version of HIPERPAV in-place.
• The main focus of the software should still be on early-age behavior of JPCP. The long-term module can be used to reinforce good paving practices.
• The future of HIPERPAV should include mix-related calorimetry for use with specific project materials.

The feedback received from the TEP members during the three meetings held for this project were considered carefully during development of HIPERPAV II, and an extensive number of them were incorporated to ensure a successful implementation.