The following frequently asked questions have come from users of PAVEXpress and from webinars conducted. If you can not find an answer to your question please feel free to contact us.
Please see the VERIFIED page for a couple of third-party reports verifying that PAVEXpress meets the design criteria of the AASHTO Guide for Design of Pavement Structures 1993 for flexible pavements and AASHTO Guide for Design of Pavement Structures 1998 Supplement for rigid pavements. In addition, Washington State DOT also allows for use of PAVEXpress (WSDOT, p.11).
Rigid Pavement design is based on unreinforced, jointed-plain slabs. If fibers are used in the concrete, then the properties of the concrete such as modulus of rupture and elastic modulus can be adjusted by the user.
For Flexible Pavements, iteration is done two different ways. If only the total AC thickness is needed, then the user inputs a minimum AC thickness and a set thickness for each base layer. Once these are entered by the user, then PAVEXpress determines the total asphalt thickness to the nearest ½” based on the traffic loadings and subgrade strength. If the user wants to select the multiple lift approach for the asphalt layers, then the asphalt surface and intermediate/binder thickness is entered and PAVEXpress iterates on the bases asphalt layer thickness to the nearest ½” based on the traffic loadings and subgrade strength. For Rigid Pavements, the only approach is iterating on the final concrete slab thickness to the nearest ½” based on traffic loadings and subgrade strength.
Version 1 of PAVEXpress uses set values for lane distribution and directional percentages. Allowing the user to customize or input these values will be considered with future versions of the application.
PAVEXpress has multiple tools to performance various sensitivity analysis. However, PAVEXpress does not currently have the capability to perform a sensitivity analysis on ESALs to failure by changing sub-base strengths or materials. This suggestion will be considered by the Task Group responsible for the development and enhancements of PAVEXpress.
PAVEXpress is a web-based application and not a standalone application that can be downloaded. As long as the user has access to the internet, PAVEXpress is available.
There are no plans to add the capability. The vast majority of pavements contain no more than three asphalt layers – surface, intermediate/binder, and base. To incorporate a layer such as a friction course, then then user can combine the surface and intermediate/binder layers into a single layer with a set thickness (i.e., 3, 4 or 5 inches) and layer coefficient (i.e., 0.45). The application will use this information to calculate the required base asphalt thickness to meet the predicted traffic and subgrade soil strength.
Version 1 of PAVEXpress does not contain tools to assess pavements for rehabilitation. However, the next version of PAVEXpress will allow for pavement overlay design based on predicted traffic and existing structural condition of the pavement.
The Old Darwin has a tool to calculate the Mr- and k-effective, will PAVEXpress have the same capability?
For the initial version of PAVEXpress, the design team decided to reference conversion tables. The next versions of PAVEXpress may include automating the conversion tables for estimating subgrade resilient modulus from CBR and R-values. For the calculation of modulus of subgrade reaction or k-value based on the subgrade Mr, that may be provided in future versions of PAVEXpress as well.
When will the overlay design tool be added and can the current tool be used to approximate overlay design?
The anticipated schedule for incorporating the 1993 AASHTO Overlay design procedure is the second quarter of 2015. Once the capability has been developed and tested, registered PAVEXpress users will get a notification email and the new version will be available on the website.
PAVEXpress was designed to accommodate up to three unique layers in the sub-structure design. Each layer must be identified and design parameters input such as layer thickness and layer coefficient.
PAVEXpress does not accommodate varying growth rates for ESALs over the pavement’s design life. PAVEXpress uses a constant growth rate over time that is defined by the user. Future versions of the application may include this functionality.
All data contained within PAVEXpress is securely and confidentially stored in a database based on your credentials. It can only be accessed with your email and password as credentials. All data and information contained within the database is routinely backed up to avoid loss of data or information.
Two-wheeler and other traffic can be entered using the “other” category. The user must enter the percentage of two wheeler traffic and load equivalency factor.
At the moment, PAVEXpress only uses English units. Based on the feedback by users, a future version of PAVEXpress may be available in Metric units.
For Rigid Pavement design, only the 1998 Supplement is available.
Can we export the project information to keep on our local system? Is there a way to retrieve your project information offline?
PAVEXpress does not allow the download of the project reports to an Excel, Access or other format file. The Task Group responsible for developing and enhancing PAVEXpress will consider the request for an export feature.
PAVEXpress’ mechanistic design module is in the scoping phase. The plan is to incorporate Per Road into PAVEXpress. Per Road was developed for NAPA in the early 2000’s and it has been used extensively around the country.
The average daily traffic (ADT) or average annual daily traffic (AADT) is an input used for ESAL calculation. Once the AADT is input by the user, the user can specify the percentage of vehicles in 5 different categories under the Load Equivalency Factor window (Calculate LEF). In this window, the percentages of each type of vehicle using the road can be set. However, PAVEXpress does not allow these percentages to vary over the life of the pavement analysis period.
How do you differentiate design for pavement overlay vs grind and overlay. The amount of cracks or type of cracks are being considered?
For the overlay module of PAVEXpress under development, the user will be able to specify a mill/grind depth for the existing pavement. The amount of material removed will be used to adjust the in-place structural number. This adjusted structural number will be used with the required structural number for the overlaid pavement to determine an overlay thickness. PAVEXpress will provide guidance is determining mill depth and procedures to adjust the existing structural number if cracks exist and the pavement will not be milled.
How to can a user incorporate different surface types in flexible pavement design using PAVEXpress?
PAVEXpress follows 1993 AASHTO Pavement Design and allows up to three different asphalt layers. Each material used in a layer is defined by the layer coefficient. Therefore, if a new surface material is used, then a different layer coefficient is entered. Unless a non-standard layer coefficient is used, then PAVEXpress does not differientate between materials.
Subgrade strength changes during the year, how does PAVEXpress adjust subgrade strength for seasonal climate?
PAVEXpress does not adjust subgrade strength based on seasonality. The application uses only one subgrade strength value for calculation purposes. To account for seasonality in the design, the adjusted subgrade modulus must be calculated outside the program. If the demand from users for the ability to adjust for seasonality exists, then the future versions of PAVEXpress may incorporate that ability.
The application uses subgrade resilient modulus for design purposes. If the user has a CBR value, it must be converted to modulus. The program does not prompt or provide this information. In the future versions of PAVEXpress, suggested values may be provided based on subgrade soil classification.
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