Chapter 5 continued from...
 
  Definition of Lots and Sublots   

It is important for the agency to clearly define lots and sublots when using the prototype PRS. The following definitions are recommended for use.

Definition of a Lot

A lot is defined as a discrete quantity of as-constructed pavement to which an acceptance procedure (and corresponding pay adjustment) is applied. All pavement placed within a lot is assumed to have similar characteristics (e.g., traffic loadings, design properties, mix design, support, and representative as-designed AQC distributions). It is recommended that the lot length always be set equal to one day's production unless a significant within-day change occurs in one of the pavement characteristics (e.g., change in aggregate source or stoppage of the paving operations for a significant amount of time). If such a change does occur, it is recommended that a new lot be started at that point in the paving. The lot width is defined as the total width of pavement (one or more traffic lanes) being placed at one time in the mainline paving process. This paving width is also defined as a construction pass since it describes the total width of pavement being placed in one pass of the paving train. (Note: The width of a construction pass can change within a project depending on the number of lanes being paved at one time.) Shoulders are not included in the width of a lot; however, when applicable, the entire width of a widened traffic lane is to be considered as part of the mainline paving.

Definition of a Sublot

A sublot is simply defined as a portion of a lot. Each lot is divided into sublots of approximately equal surface area, based on the total linear amount of paving expected in the lot. More specifically, within the prototype PRS, sublots represent the smallest unit of pavement for which pavement performance is predicted (from distress indicators). Therefore, sublot lengths are defined so that all AQC's can be independently sampled from each defined sublot.

Selecting an Appropriate Target Sublot Length

Under the PRS approach, the sublot size is defined in terms of the linear length of longitudinal paving. The minimum sublot length should not be less than 0.16 km; this limit is required to accommodate the measurement of initial smoothness with a California profilograph. Although a maximum sublot length need not be defined, it is recommended that the agency try to select a sublot length that will result in a minimum of three sublots per lot. An appropriate maximum sublot length could then be defined as one-third of the total linear length of longitudinal paving expected for a typical pavement lot (one day of paving). An appropriate sublot length range for a given project can, therefore, be represented by the relationship presented as equation 10.

0.16 km £ PAVINGSUBLOT £ PAVINGSUBLOT-MAX                 10

  where

PAVINGSUBLOT  = Chosen target sublot length for the project (expressed in km).

PAVINGSUBLOT-MAX  = Recommended maximum sublot length (based on the recommended minimum of three sublots per lot). This value is calculated as PAVINGLOT/3 and expressed in km.

PAVINGLOT  = Estimated total linear length of longitudinal paving expected for a typical pavement lot (expressed in km).

If the maximum sublot length (PAVINGSUBLOT-MAX) is calculated to be less than the chosen minimum sublot length (0.16 km), it is recommended that the chosen sublot length be set to the minimum of 0.16 km. Otherwise, it is recommended that the chosen sublot length be subjectively selected from the computed range (the range shown in equation 10) based on knowledge about the chosen acceptance sampling and testing plan. The agency must determine how many AQC samples and tests are to be taken from each sublot in the field. It is believed that the costs of conducting the required acceptance sampling and testing will greatly influence the selected sublot length. A discussion of the selection of an appropriate acceptance sampling and testing plan is contained in this chapter in the section titled Selecting an AQC Acceptance Sampling and Testing Plan.

Determining the Target Number of Sublots Per Lot

The target number of sublots per lot is estimated based on the agency-chosen target sublot length (PAVINGSUBLOT) and the estimated total linear length of longitudinal paving for a typical pavement lot (PAVINGLOT). This relationship is shown in equation 11.

NUMSUBSTARGET  = PAVINGLOT / PAVINGSUBLOT                (11)

  where

NUMSUBSTARGET  = Estimated target number of sublots per lot (based on the chosen target sublot length).

PAVINGLOT  = Estimated total linear length of longitudinal paving expected for a typical pavement lot (expressed in km).

PAVINGSUBLOT  = Chosen target sublot length (expressed in km).

As an example, if it were estimated that a contractor would pave 1.2 km per day (PAVINGLOT = 1.2 km) with a target sublot length of 0.32 km (PAVINGSUBLOT = 0.32 km), the target number of sublots per lot (NUMSUBSTARGET) would be calculated as the following (using equation 11).

NUMSUBSTARGET  = PAVINGLOT / PAVINGSUBLOT

                              =   1.2 km / 0.32 km

                              =   3.75 sublots per lot

For this example, the typical number of sublots per lot would then be three or four. Therefore, the agency should develop preconstruction output for the cases of three and four sublots (as a minimum). More information on choosing appropriate ranges of numbers of sublots per lot is provided in the section titled Selecting Simulation Parameters.

Determining Actual Sublot Lengths in the Field

Since the amount of paving varies from lot to lot, a method for dividing the as-constructed pavement lot into sublots is required. The following defines this procedure.

  1. The first sublot of a lot is typically defined as that amount of pavement that starts at the lot's identified starting station and has a linear length of longitudinal paving equal to the chosen target sublot length (PAVINGSUBLOT). If a significant problem occurs in the field (requiring the start of a new lot) while the length of the first sublot is less than the chosen target sublot length, the sublot will be assumed to represent the entire lot and will be accepted by another method approved by both the agency and contractor.

  2. Additional sublots (each with a length equal to the chosen target sublot length) are defined consecutively until paving operations are complete for the given lot. Using this approach, all sublots will be equal to the chosen target sublot length except for the last sublot in the lot. The length of the final sublot in a lot is determined using the following rules.

    1. If the length of the last sublot in a lot is less than the chosen minimum sublot length (recommended to be 0.16 km), the material is assumed to be included as part of the previous sublot. It is recommended that at least one additional sample location (for each AQC) be selected to represent the additional material. (Note: The tests for initial smoothness will be extended to include the new material.)

    2. If the length of the last sublot in a lot is greater than the chosen minimum sublot length (recommended to be 0.16 km), but less than the chosen sublot length, then the actual measured final sublot length will be used.

    Overall, it is recommended that the agency decide on a target sublot length that is practical for the amount and type of sampling and testing being conducted. This chosen target sublot length should then be used to lay out all the sublots prior to the paving of each lot. This can be done on a day-by-day (lot-by-lot) basis. Therefore, only the final sublot of each lot should differ from the chosen target sublot length.

    Chapter 5 continues...