Long Term Pavement Performance Project Laboratory Materials Testing and Handling Guide

Chapter 5. Section Layering

In the analysis of comparison of different pavement structures, the performance of these structures depends upon many factors. A primary factor is the pavement structure or pavement layering. Information must be readily available to determine the type of layers present (pavement surface and underlying supporting layers), the thickness of these layers, and their material properties.

This chapter provides the steps involved in the process for the determining the pavement structure at each test section. This detailed layering information was considered critical for relating laboratory tests to appropriate layers and for the future access to the laboratory test results in the LTPP PPDB. It should also be noted that this process involved extensive cooperation and coordination between all parties involved in the field sampling and laboratory testing process.

Unlike the GPS, SPS projects consisted of multiple test sections. As illustrated in Chapter 4, all tests were not performed on every layer of every test section of an SPS project due to limitations on budget. Hence, the section layering information was used to provide the analyst with a means of relating test results on similar materials in separate test sections. Therefore, portions of these procedures were specific only to SPS projects and these will be identified in the following sections.

5.1 General Pavement Layering Methodology

Instructions for three forms were provided within this section. These forms were identified in Table 5.1.

Since SPS projects consist of multiple test sections, a "Project Level Layering Structure" was developed to keep track of pavement layering and test results from various test sections. The ultimate purpose of the project level layering was to set up an accounting system to be used to link material tests for a given pavement layer in a particular section to other similar materials, throughout the project.

As the name suggests, in order to complete Form L05, every pavement layer within a SPS project will be listed and assigned a "Project Level Layer Code." This project level layer code was used to extract layer information from the PPDB. Form L05 was input into the PPDB prior to entry of any other materials data (except field material sampling and field testing data).

Form L05A was used on a test section basis for both GPS and SPS test sections to record the field or laboratory determined material classification and measured thicknesses for a given pavement layer. Since testing plans were developed to address specific needs, portions of the form may have been left blank for some layers within the test section. This form was used in concert with other information to develop the "Analysis Section" (Form L05B) for each test section.

Form L05B (Analysis Section) was used to establish the final pavement layer structure for each test section. All information available for the test section was used to derive this layer structure. Therefore, this form may have used data actually derived from the section itself, or if information was not available, data from other test sections in close proximity to the section. The purpose and process for completing this form was identical between SPS and GPS test sections.

The following sections outline the process used in completing the above referenced forms. These directions provide the methods used to define an appropriate project and section level layer structure. Prior to completion of the L05s, the personnel evaluating the test section were required to have at their disposal the following resources:

• Inventory data, if available (Inventory data were not required on new construction SPS projects),
• Field material sampling and testing data, including photographs of cores, test pits, etc. that were taken in the field,
• Materials testing data packet, including any photographs which were taken during core examinations, etc.,
• Construction plans or typical cross sections, when available,
• Appropriate state supplemental documents,
• Any other useful information which the evaluation personnel deem relevant, including falling weight deflectometer (FWD) information and profilometer (i.e., roughness) data.

For SPS projects the following additional information was required as well:

• For SPS test sections, the appropriate SPS Experimental Designs (used to establish the expected layer structure for new construction),
• Project specific material sampling and testing plan,
• Construction data sheets for the experiment including rod and level survey data, if available,
• A draft version of Form L05 Summary of Pavement Layers: Project Level (completed prior to field material sampling and testing).

After the appropriate materials were gathered, the evaluation personnel made an informed decision concerning the final pavement layer structure for each project and/or test section.

5.2 Completion of Form L05 - SPS ONLY

Within the SPS experiments, two main classes of experimental pavements were investigated. Within the first class were the three experiments of newly constructed pavements consisting of:

• SPS-1 Strategic Study of Structural Factors for Flexible Pavements
• SPS-2 Strategic Study of Structural Factors for Rigid Pavements
• SPS-8 Study of Environmental Effects in the Absence of Heavy Loads

Within the second class, a study of the effectiveness of various maintenance and rehabilitation strategies was investigated. These five studies included:

• SPS-3 Preventive Maintenance Effectiveness of Flexible Pavements
• SPS-4 Preventive Maintenance Effectiveness of Rigid Pavements
• SPS-5 Rehabilitation of Asphalt Concrete Pavements
• SPS-6 Rehabilitation of Jointed Portland Cement Concrete Pavements
• SPS-7 Bonded Portland Cement Concrete Overlays

These two classes of experiment inherently had different strategies for pavement layering due to the greater opportunity for sampling and measuring pavement layers for the new construction class of experiment. SPS-9P and SPS-9A projects could fall into either category with some projects consisting of new construction and others involving rehabilitation.

The destructive sampling and testing of an existing pavement to determine its structure and material properties was limited due to both the potential damage that may have occurred and the related costs of sampling. The following instructions present the set of guidelines used to summarize material properties and thicknesses of the various layers for each SPS experiment and test section.

Within the original design of the PPDB, the layer number was designated as a key field from which data could be easily referenced. Form L05 "Summary of Pavement Layers: Project Level" was designed to define the pavement layering throughout the project, to assist in initializing other tables within the PPDB and to provide a key index for the laboratory testing of the sampled materials. This form was completed primarily using the field sampling and laboratory testing data and the following supplemental sources of information:

• SPS experimental designs,
• Project specific material sampling and testing plan,
• All pertinent construction documents,
• Inventory data,
• State supplemental documents,
• Other related documents as available.

This detailed and distinct project layering information was considered critical for relating laboratory tests to appropriate layers for future access to the laboratory test results in the PPDB. The following is an explanation of the data entry items needed to complete Form L05.

LTPP LABORATORY MATERIAL HANDLING AND TESTING
SUMMARY OF PAVEMENT LAYERS: PROJECT LEVEL
LAB DATA SHEET L05

STATE CODE ___ ___

SECTION ID ___ ___ 0 0

5.2.1 Header Information

The L05 form has three general areas for input data. The first area is the project definition information. This area required the following information:

• Sheet ___ of ___ to identify the order within a data packet. This was primarily used as a bookkeeping tool by the Region. All data sheets from the laboratory materials testing work on a particular SPS project were to be assigned sequential numbers starting from 1 for the sample receipt report (Form L01) followed by the sample inspection report (Form L02); preliminary laboratory test assignment (Form L03); laboratory test assignments (Form L04) and so on in increasing order through all of the respective L-type laboratory testing forms and continuing through the T-type laboratory testing forms.

Note: All laboratory testing data forms used the test section specific layer number in reporting data results. The Project Level Layer Code was used only on Forms L05, L05A, and L05B as described in this document. In addition, the final version of Forms L05, L05A, and L05B was completed only after all appropriate laboratory characterization tests had been performed.

• State Code: The State Code was assigned using a two-digit code as shown in Table 3.1 of this Guide.
• SHRP Section ID: The first digit (from the left) of this code should either be a 0 (zero), for the first project conducted in a state (except for the SPS-3 and SPS-4 projects that start with the letter A for the first project in a state) or a letter starting with A, B, etc for the second, third, etc. projects of the same SPS experiment constructed in the same state. The second digit corresponds to the SPS experiment number. The last two digits (third and fourth digits) of the SHRP Section ID were always denoted as 00 to indicate "Project Level" information. This was pre-printed on the form for convenience.

5.2.2 Layer Information

The second area of the form defines the Project Level pavement layers. Five data fields were defined. These are:

• Column 1. Project Layer Code
• Column 2. Material Code
• Column 3. Inventory Layer 1
• Column 4. Inventory Layer 2
• Column 5. Comment Field

Project Layer Code

The Project Layer Code was a single character field identifying a unique material layer existing within the Project. The Project Layer Code always started with the subgrade being labeled Layer A. Each subsequent distinct layer was assigned a Project Layer Code in ascending alphabetical order (B, C, etc.) corresponding to its location or placement within the pavement structure. A Project Layer Code was assigned for all possible distinct pavement layers present on the SPS project (including supplemental sections).

Material Code

The Material Code designations were based on the standard LTPP terminology for pavement materials and soils and these three-digit codes were entered in Column 2 on Form L05. This information was obtained from the test results for all pavement layers. The LTPP standard terminology was provided in Chapter 4 of this Guide. Table 5.2 identifies the tables from Chapter 4 that were used for this purpose and should be derived from the laboratory materials testing of the layer.

All treated base and subbase layers were to be described by series 300 material codes.

Inventory Layer Numbers

These columns (3 and 4) addressed the compatibility of Inventory Layer Structures and Project Level Layer Codes identified above. As part of Form L05, a correlation between the layer structure from the laboratory materials testing data and the layer structure from Inventory data was provided. This correlation was necessary to provide analysts with a means to extract data from the inventory portion of the PPDB and match that data to specific layers within the pavement layer structure. This was especially true for thin (= 1.5 inches [38 mm]) asphalt concrete layers which could not be tested under LTPP procedures. This correlation between the inventory layer data and the laboratory/field sampling determined layer data provided the analyst with the missing information. Two columns were used for this cross reference. The first column (3) was intended to list the primary or most likely Inventory Layer Number for a cross reference. An additional column (4) was included if more than one Inventory Layer was associated with a Project Layer. (It should be noted that these fields did not apply to the newly constructed pavements within SPS-1, SPS-2, and SPS-8). If there were no corresponding inventory layers, then both Inventory Layer Numbers were left blank. If there was only one corresponding inventory layer, then only Inventory Layer Number 1 was completed. If two or more corresponding inventory layers were identified, the Inventory Layer 1 was set to the lowest corresponding layer number and Inventory Layer 2 was set to the highest corresponding layer number.

In no case was the inventory layer data changed to conform to Form L05 results. If an error was detected in the inventory data, then this error was revised accordingly. However, inventory layer data and Form L05 data may not have been in exact accordance. If layers were missing or additional layers were identified, then the "Inventory Layer No. 1 and 2" on Form L05 may have been left blank as appropriate. The purpose of these fields on Form L05 was to provide the best estimate of the link between inventory data and Form L05. It was not mandatory that each layer on Form L05 contain a corresponding inventory layer number if no layer in the inventory layer structure matched the material properties of those layers in Form L05.

Comment

This comment field (Column 5) was included to record additional clarifications in the PPDB. Data within this field was not mandatory. A comment of up to 50 characters may have been entered in this field.

5.2.3 Signatory Section

This section was provided to list general remarks relating to the specific project that were considered helpful to either the database managers and/or the analyst. In addition to general remarks, signatory blocks were included for submitting and reviewing personnel.

5.2.4 Completion of Form L05

The proper layering for Form L05 was considered critical to the ability of researchers to extract and effectively utilize material characterization data for each SPS project. In general, the layering system or scheme satisfied the following requirements:

• All project layering started at the subgrade. If the laboratory testing revealed that the Material Code at one location in the project was 145 (Sandy Silt) while at another location the Material Code was 214 (Silty Sand), two distinct layers (for example "A" and "B") must be used as Subgrade Layer Codes.
• Each distinct layer in the pavement structure must have a unique Pavement Layer Code. This coding system included all distinct layers within the SPS project. (Please note that this form initiated the pavement layer structure in the PPDB and it provided an index for the testing program. It was intended to be a concise, all-inclusive list of layers within the experimental project including supplemental sections.)
• Prior to entering data from a project, the engineer compiled a list of all the materials present within the project. Both the primary SPS materials and any additional materials involved within the supplemental sections were compiled.

5.3 Form L05A Summary of Pavement Layers: Measurement Data - GPS & SPS

Similar to the L05 form, this form has three areas for input. The intent of this form was to identify the various pavement layers within the test section that had layer thickness measurements and material characterization data. One form was to be completed for each construction event on each test section. Layer Thicknesses from cores, borings, test pits or survey data and material descriptions (Material Code) from laboratory testing were to be completed where applicable.

After completion of the specified material characterization tests for each layer (excluding resilient modulus testing), the pavement layering information for each section was summarized for each test location within the pavement section containing measurement data using Form L05A.

An independent evaluation of measured pavement information was one of the vital pieces of information needed for the PPDB. The Form L05A (Summary of Pavement Layers - Measurement Data) was completed using the information on Form T01B, Form T31, Form T47, Form T52, Form T66, Form L04, the Construction Data Sheets (as applicable), and the field exploration logs contained in the field data packet provided by drilling and sampling personnel. For SPS projects, a sketch of the test locations for the project may have been compiled prior to starting this form. This sketch served as a quick reference to identify locations of material thickness measurement and characterization testing.

5.3.1 L05A Header Information

The L05A form has three general areas for input data. The first area or header was the project definition information. This area required the following information.

• Sheet ____ of ____ to identify the order within a data packet.
• State Code
• SHRP Section ID: For SPS test sections the last two digits of this field were related to the test section number, i.e. 01, 02, etc, unlike the L05 form. For GPS test sections this was the four-digit code assigned to distinguish that test section from the others in the state.
• Construction Number: The construction number was referenced to the EXPERIMENT_SECTION table of the PPDB. The Construction Number shown on Form L05A matched the status of the project at that point in time. This number started at 1 for the original pavement construction and was raised by 1 for each change in the pavement layer structure (including maintenance treatments). For the SPS maintenance and rehabilitation experiments (SPS-3, SPS-4, SPS-5, SPS-6, and SPS-7), the Construction Number generally was a "1" prior to the maintenance treatment or rehabilitation and a "2" after the maintenance treatment or rehabilitation was performed. Form L05A was completed for each change in Construction Number.

This header information was used to identify the experiment and the appropriate test section.

LTPP LABORATORY MATERIAL HANDLING AND TESTING
SUMMARY OF PAVEMENT LAYERS - MEASUREMENT DATA
LAB DATA SHEET L05A

STATE CODE ___ ___

SECTION ID ___ ___ ___ ___

CONSTRUCTION NUMBER ___ ___

* See the shoulder auger probe logs (Form S05); circle "UNK" if no refusal was found within 20 feet; enter depth to refusal in feet if found within 20 feet and cross out "UNK".

5.3.2 Layer Information

The second section of Form L05A contains the following information:

• Column 1. Layer Number
• Column 2. Project Layer Code
• Column 3. Layer Description
• Column 4. Layer Type
• Column 5. Layer Thickness (Before Section)
• Column 6. Material Code (Before Section)
• Column 7. Measurement Type (Before Section)
• Column 8. Layer Thickness (Within Section)
• Column 9. Material Code (Within Section)
• Column 10. Measurement Type (Within Section)
• Column 11. Layer Thickness (After Section)
• Column 12. Material Code (After Section)
• Column 13. Measurement Type (After Section)

Layer Number

The Layer Number (Column 1) was a sequential set of two-digit numbers identifying the pavement layers present within a specific test section. The Layer Number (Column 1) was assigned starting with Layer Number 1. Layer Number 1 was always assigned for the subgrade and the highest Layer Number was always the top pavement layer. In general, the overall structure for the test sections was defined prior to completion of the Form L05A by material sampling and laboratory testing procedures. For SPS projects, all of the pavement layers defined within the Project Layering may not have existed within every test section; however, the Layer Numbers were an all-inclusive sequential set. The Layer Number started at 1 and continued without skipping numbers until the largest Layer Number (surface layer) was entered. Please note that even if a layer(s) was not measured or tested, it was included on Form L05A.

Project Layer Code

The Project Layer Code was required for test sections included in SPS projects. On L05A forms completed for GPS test sections, the project layer code was left blank.

The Project Layer Code (Column 2) was a unique single character code identifying each possible layer within the SPS project. These codes were generated and entered within Form L05. This code provided a critical cross reference between the layers within one test section and the layers throughout the project. Correct identification of this code was considered critical to the efficient operation of the PPDB.

The definition of "layer" is as follows: That part of the pavement produced or comprised of uniform materials and placed with similar equipment and techniques. The material within a particular layer was assumed to be homogeneous. In the case of subgrade layers, small variances in the gradation of the material may have changed its material code slightly. This type of difference was acceptable and the most representative material code was used on Form L05. If significant changes in gradation (i.e., fine versus coarse) occurred in a material, the subgrade was considered two different layers and numbered accordingly. Also engineering fabrics were considered layers in the pavement structure and these materials were shown on the L05, L05A and L05B forms. However, tack coats were not to be considered layers in the pavement structure.

Layer Description

The Layer Description Code (column 3) was provided using the codes shown in Table 5.3.

Layer Description Code "11" was used only for SPS-1, SPS-2, and SPS-8 projects (e.g., "new construction"). Apparent embankment materials used in test sections for other experiments were coded using Layer Description Code 6 (Subbase).

Layer Description Code "8" (Interlayer) applied to Stress Absorbing Membrane Interlayers (SAMIs), all types of engineering fabrics and any other type of distinct layer that was used for providing a separation between two "structural" layers. An interlayer was generally a "non-structural" component of the pavement layer system.

Table 5.4 provides a list of valid material codes for each Layer Description Code.

Layer Type

The Layer Type Code (Column 4) was assigned using the two character codes provided in Table 5.5.

Table 5.6 provides a list of valid Layer Type Codes for each Layer Description Code.

Layer Thickness

The Layer Thicknesses (Column 5 - Before Section, Column 8 - Within Section, and Column 11 - After Section) were based on information available from field logs of boreholes, the test pit log, the shoulder auger probe, field survey data, laboratory determination using Protocol P01 and Form T01B for AC layer thicknesses from AC cores (as available) and Form T66 for PCC layer thicknesses, respectively. The layer thickness was recorded in inches for all layers with the exception of the subgrade layer which was to be recorded to the nearest foot based on information obtained from Form S05, "Log of Shoulder Auger Probe," for each test section.

The layer thickness (i.e., depth to refusal of the shoulder auger probe) for the subgrade layer (layer number 1) and underlying strata was recorded only on Form L05A for each test section adjacent to the shoulder boring. For the test sections without a corresponding shoulder boring, this field was left blank.

The thicknesses obtained from field survey data (rod and level) on SPS projects were to be used for unbound or potentially unbound base layers on new construction projects. Field determinations of the layer thickness of the Permeable Asphalt Treated Base layers on SPS-1 and SPS-2 projects may have been included in the determination of layer thicknesses, since laboratory testing of these cores (if available) was minimal.

Material Code

The Material Code designation was based on the LTPP standard terminology for pavement materials and soils and these codes were entered in Column 6 (Before Section), Column 9 (Within Section) and/or Column 12 (After Section) on Form L05A. This field was completed in a similar manner as explained for Form L05.

Similar to layer thickness, the laboratory only completed the Material Code of the underlying structure for test section locations that had material characterization tests performed.

Measurement Type

The measurement type was entered in Column 7 (Before Section), Column 10 (Within Section) and Column 13 (After Section) and was used to enter the code(s) on which the thickness measurements were based. Space was provided for up to three one-digit codes in each corresponding column on Form L05A. The codes are presented in Table 5.7.

5.3.3 Signatory Section

This section was provided to list general remarks relating to the specific project that were considered helpful to either the database manager(s) and/or the analyst. In addition to general remarks, signatory blocks were included for submitting and reviewing personnel.

5.3.4 Completion of Form L05A

In addition to the above explanation, the following general guidelines were used to check Form L05A after completion.

• For an original surface (Layer Description = 3), the layer type (Column 4), AC or PC in Form L05A, was expected to correspond to the original surface as listed in the inventory layer data (This does not apply to new construction SPS experiments).
• For an overlay (Layer Description = 1), the layer type (Column 4), AC or PC in Form L05A, was expected to correspond to the overlay surface as listed in the inventory layer data (if the overlay surface was present in the inventory data).
• A comparison was made between Form T01B (AC Core Examination and Thickness) and Form L05A. For a given layer number, the Layer Description on Form T01B was required to equal the Layer Description on Form L05A. Additionally, the layer thickness on Form L05A was required to be close to the average of all of the cores tested on Form T01B for a given end of the test section.
• Layer thickness values on Form L05A were compared with the field data sheets as a check to ensure that the proper layer thickness was assigned, and to resolve significant differences.
• Layer thickness values on Form L05A were checked for reasonableness. A list of suggested checks for reasonableness is presented in Table 5.8.
• If the values were out of range, then a check was made of the field and laboratory data, as appropriate, to determine if the layer thickness reported on Form L05A was valid.
• Each layer was to be included on the Form even if no measurements or testing was conducted on the layer. Measurement Type number 8 (no measurements conducted on this layer) was to be used to document this case. All fields, except Measurement Type were to be left blank if Measurement Type 8 was used.

• For base/subbase layers, the Material Code descriptions as entered in columns 6 and 9 or 12 of Form L05A were the "Classification and Description of Unbound Granular Base and Subbase" codes as obtained from Table 4.29. These codes were based on laboratory test data and on visual examinations.
• For subgrade and embankment layers, the Material Code descriptions as entered in Columns 6, 9, and 12 of Form L05A were the "Soil Classification and Description" codes as obtained from Table 4.26 of Chapter 4, based on the laboratory test data and on visual examinations.

After the rudimentary QC/QA checks were completed and all discrepancies resolved, Form L05B, Analysis Section was completed. This form defined a single set of layer material codes and layer thicknesses which best represented that pavement structure layering beneath each LTPP pavement study section.

5.4 Form L05B Summary of Pavement Layers: Analysis Section - GPS & SPS

Form L05B was used to establish the final "analysis section" for each construction event on each pavement test section. The most representative pavement structure and material characterization for the pavement structure of each test section was determined from the field, laboratory and measured project layering information (Form L05A).

5.4.1 L05B Header Information

The L05B form has three general areas for input data. The first area or header was the project definition information. This area required the following information:

LTPP LABORATORY MATERIAL HANDLING AND TESTING
SUMMARY OF PAVEMENT LAYERS - ANALYSIS
LAB DATA SHEET L05B

STATE CODE ___ ___

SECTION ID ___ ___ ___ ___

CONSTRUCTION NUMBER ___ ___

*See the shoulder auger probe logs (Form S05); circle "UNK" if no refusal was found within 20 feet at the nearest adjacent probe; enter depth to refusal in feet if found within 20 feet and cross out "UNK".

• Sheet ___ of ___ to identify the order within a data packet.
• State Code
• SHRP Section ID: For SPS test sections the last two digits of this field were related to the test section number, i.e. 01, 02, etc, unlike the L05 form. For GPS test sections this was the four-digit code assigned to distinguish that test section from the others in the state.
• Construction Number: The construction number was referenced to the EXPERIMENT_SECTION table of the PPDB. The construction number shown on Form L05B matched the status of the project at the point in time represented by the L05B. This number started at 1 for the original pavement construction and was raised by 1 for each change in the pavement layer structure (including maintenance treatments). For the SPS maintenance and rehabilitation experiments (SPS-3, SPS-4, SPS-5, SPS-6, and SPS-7), the Construction Number generally was a "1" prior to the maintenance treatment or rehabilitation and a "2" after the maintenance treatment or rehabilitation was performed. Form L05B was completed for each change in Construction Number.

This header information was used to identify the experiment and the appropriate test section.

5.4.2 Layer Information

The second section of Form L05B contains the following information:

• Column 1. Layer Number
• Column 2. Project Layer Code
• Column 3. Layer Description
• Column 4. Layer Type
• Column 5. Layer Thickness
• Column 6. Material Code
• Column 7. Comment Code
• Column 8. Comment Note

Layer Number

The Layer Number (Column 1) was a sequential set of two-digit numbers identifying the pavement layers present within a specific test section. The Layer Number (Column 1) was assigned starting with Layer Number 1. Layer Number 1 was always assigned for the subgrade and the highest Layer Number was always the pavement surface layer. The overall structure for the test sections was generally defined by material sampling and laboratory testing procedures. It is important to note that all of the pavement layers defined within the Project Layering may not have existed within each test section; however, the Layer Numbers were required to be an all-inclusive sequential set. The Layer Number started at 1 and continued without skipping numbers until the largest Layer Number (top layer) was entered.

NOTE: The correspondence of the Section Layer Number (Form L05B) with the Project Layer code (Form L05) was required to accurately identify the appropriate materials data for a given SPS project in the PPDB. Columns 1 and 2 were completed with care for the proper link between all of the forms to be identified.

Project Layer Code

The Project Layer Code was only required for test sections included in SPS projects. This field was left blank for L05B forms on GPS test sections.

The Project Layer Code (Column 2) was a unique single character code identifying each possible layer within the project. These codes were generated and entered within Form L05. This code provided a critical cross reference from the layers within one test section to the layers throughout the project. Correct identification of this code was considered critical to the efficient operation of the PPDB.

Layer Description

The Layer Description Code (Column 3) was provided using the same procedures and codes as used for Form L05A.

Layer Type

The Layer Type Code (Column 4) was assigned using the same procedures and codes as used for Form L05A.

Layer Thickness

The depth to the rigid layer of the subgrade was determined using Form S05, Log of Shoulder Auger Probe, for the nearest adjacent test probe. The thickness for the subsequent layers was determined from Form L05A, Construction Data Sheets or field boring logs for the nearest adjacent test boring or measurement location. In the event of two locations being equidistant to the test section, selection of layer thickness was based upon the most "reasonable" measurement. Similarly, if a layer was milled or decreased in thickness by some means, the survey data was used to determine this reduction. This reduction was then subtracted from the original thickness of the layer and recorded in Column 5.

Material Code

The Material Code designation was based on the LTPP standard terminology for pavement materials and soils and these codes were entered in Column 6 on Form L05B. This field was completed in a similar manner as explained for Form L05 and the material code shown on Form L05B was the same code as used for Form L05.

Comment Code

This code provides a clarification of the selected thickness and material codes selected. Column 7 is completed by including any pertinent comment codes (A-Z) associated with the determination of layer structure, layer thickness determination, etc. Comment codes used for column 7 are presented in Table 5.9.

A total of three comment codes may have been entered in Column 7 of Form L05B to describe the decisions made to determine the analysis layer structure.

Comment Note

Comment Note (Column 8) was completed if code Z, "other", was used to describe the decision made in defining a layer. This note also may have been used to record any other pertinent information concerning the definition of the test section layer structure. Up to 50 characters may have been entered into this column.

5.4.3 Signatory Section

This section was provided to list general remarks relating to the specific project that were considered helpful to either the database managers and/or the analyst. In addition to general remarks, signatory blocks have been included for submitting and reviewing personnel.

5.4.4 Completion of Form L05B

The Form L05B was completed in the following order:

1. Establish the layer structure,
2. Establish layer thicknesses, and
3. Establish material codes for each layer.

The complete layer structure for the test section was established by analyzing Form L05A, inventory data and construction records and determining the appropriate layer structure. For many of the GPS test sections and SPS projects, this procedure was relatively straightforward for bound pavement layers (AC, PCC, ATB, LCB) since these layers were generally measured for thickness at each test section. The main difficulty in the completion of Form L05B was that of classifying and determining the thickness of unbound layers for each test section in a given SPS project. Generally, the unbound layers were not classified nor did they have thickness measurements performed at each test section.

This process involved a substantial amount of engineering judgment by the Regions. The following discussion relating to the completion of the L05B form and guidelines for the engineering judgement used by the Regions was separated into four distinct sections according to type of experiment as follows:

1. GPS Experiments
2. New Construction SPS Experiments: SPS-1, SPS-2, and SPS-8
3. Rehabilitation Experiments: SPS-5, SPS-6, and SPS-7
4. Maintenance Effectiveness Experiments: SPS-3 and SPS-4

Each type of experiment had its own special circumstances that are discussed in detail in the following sections. Since SPS-9P and SPS-9A projects may have been either new construction or rehabilitation experiments, the section pertaining to new construction SPS experiments or the section pertaining to rehabilitation experiments were used as appropriate to the construction of the individual project.

GPS Experiments

The complete layer structure for the test section was established by first analyzing Form L05A and determining the appropriate layer structure. In most cases, this was a fairly straightforward procedure. In some cases, layers may have been missing from one end of the test section when compared with the other, and in others the subgrade materials may have been considerably different from end to end.

In the event of a missing layer at one end, it was up to the Region to devise a layering scheme that accommodated both "within section" layering under one layer structure. This case may have involved any number of circumstances, and resolution of this case was completed using a consistent procedure. The following guidelines were followed when assigning layer structures to LTPP pavement test sections.

Layers Consistent Between Ends of the Test Section: The pavement layer structure on Form L05B was assigned using the layer structure as shown on Form L05A.

Layer(s) Missing from One End to Another: For unbound base or subbase layers, the inventory and construction records and typical cross-sections were to be consulted to determine if the layer was planned as part of the layer structure. If the layer was in the original design, then serious consideration was given to using this layer in the analysis pavement section. If the layer was not part of the original design, the as-built construction records and other state records were reviewed to determine if there was some special circumstance associated with the test section. For example, the LTPP sampling area may have been located in a transition area between two older construction projects and/or pavement designs, or two different materials sources may have been used to construct portions of a single specified layer. FWD and profilometer data may also have been used to determine test section homogeneity.

Additionally, the laboratory materials testing data for a layer present only at one end (gradation, Atterberg limits, description and classification, etc.) were reviewed to assure that the layer was not part of another layer either above or below the sampled layer. If for example, the layer structure provided in Table 5.10 was encountered. The material properties of layer 2 (GS - granular subbase) were examined to determine if these were similar to the material properties of layer 3 (GB - unbound base) of the approach end. In this case, the field personnel may have inadvertently sampled this layer (layer 3, approach end) as two independent layers instead of one homogeneous layer. The solution was to combine layer 2 with layer 3 on the approach end for thickness averaging, and to average the lab test data to obtain the properties of the combined layers.

If none of the previous solutions were effective in providing an obvious choice, the layering from the test pit location may have been used as the representative structure for this section, and an appropriate comment provided to document this decision. If a test pit was not conducted on the section, the Region was expected to choose between the available sampling locations in resolving this layering situation, and again document the basis of the decision in the comments.

For bound layers of base/subbase or surface courses, a similar process as that discussed for the unbound layers was followed in the following priority:

1. Inventory, construction records and other state records were checked to identify the intended layer structure or the presence of special circumstances in the sampling location.
2. Laboratory materials testing data were checked to verify measured material properties which may have provided some indication of the appropriate layering.

If the pavement was found to have distinctly different layer/material configurations at each end, additional field drilling and sampling on the section or a more detailed analysis may have been required. As a final resort, if none of these options was viable, the test section may have been discarded. Discarding a test section was considered to be a very serious and expensive decision because of the considerable time and effort spent on each section. On the other hand, this decision may have resulted in the avoidance of future expenses and erroneous interpretations.

After establishing the layer structure, the appropriate layer thicknesses for each layer were determined using the following methods.

Layer Thickness Consistency Between Both Ends. If the thickness of a particular layer was consistent between both ends of the pavement section, then an average pavement layer thickness was established by taking an average layer thickness using the information from both ends. Table 5.11 was used as a guide to determine whether a layer thickness was consistent between section ends and the appropriate action to be taken in each circumstance.

For example, Table 5.12 provides information from Form L05A for a given pavement section that may have been encountered. This test section could be considered consistent between ends (i.e., layer thickness ratios were within tolerable limits). Therefore, the layer thickness from one end to another could be averaged and summarized on Form L05B as presented in Table 5.13.

This example represents the simplest case for determination of layer thicknesses. In some cases, layer thickness ratios between ends of a pavement section were less than the tolerable limits. In these cases, a more detailed investigation of pavement layer thickness was warranted.

Layer Thickness Inconsistent Between Both Ends: If the layer thickness was not consistent between section ends or a layer had a zero thickness on one end, then the section was more closely evaluated to determine the appropriate layer thickness in the following priority:

1. Inventory, construction records and other state records were checked to identify the intended layer structure or the presence of special circumstances in the sampling location. Also the FWD, pavement condition, and profilometer data were checked to ascertain section homogeneity. Through this review, the sampling site at one end of a section was found to be more representative than the other, then the data from the more representative end of the section was used on Form L05B.

Note: ¹For layer of interest, the absolute value of the difference between thicknesses at station 0- and 5+.

²For layer of interest, the greatest thickness for either end appearing on form L05A, designated as "A".

³A thickness of 999.9 was only used after a complete investigation of the layer thickness discrepancy and as a last resort when everything else, including engineering judgment, failed to produce a compromise.

1. Laboratory materials testing data and field material sampling data were checked to verify the measured material properties which may have provided some indication of the appropriate layer thickness or establishe if a layer thickness entry was errant. Also, the shoulder auger probe log (Form S05) was examined to see if this yields additional information on the layer structure. This was especially prudent for subgrade layers.
2. If the above examinations failed to yield an adequate solution and to provide an obvious choice where a layer was present at both ends, but the layer thickness varied by more than the tolerable limits, between section ends, the situation was reviewed with the SHA. If this also failed to resolve the question, additional sampling of the pavement structure may have been considered. As an interim measure to complete form L05B's for pavement and treated base layers, a thickness of 999.9 was used on Form L05B column 4 along with a comment which indicated that the thickness variation was excessive for analysis purposes. A thickness of 999.9 was only to be used as a last resort when everything else, including engineering judgment, had failed to produce a compromise. To resolve thickness differences on untreated base and subbase layers where no obvious choice existed, the two end thicknesses may have been averaged and an appropriate comment added in column 6 to make the data analyst aware that differences existed.
3. For cases where a layer was not found at one end of the section, leading to a zero thickness entry on Form L05A, and again the above mentioned examinations of FWD, profile and pavement condition data provided no obvious solutions; additional sampling was considered for resolving the structure question. In lieu of added sampling, the weaker of the two pavement structures, as judged by calculating the pavement Structural Number using the AASHTO Guide method and data from Form L05A for both ends of the section, may have been chosen for insertion on Form L05B as the representative pavement structure.

After establishing the layer thicknesses, the appropriate material code for each layer was established using the following method. This may already have been established during the QC/QA of Form L05A.

Material Codes were Consistent from One End to Another: If the material codes were consistent between ends of the test section, then the material code was assigned to the layer in Form L05B.

Material Codes Differed from One End to Another: For subgrade and also for subbase soils, due to the large number of codes available with which to identify the material, there was a greater possibility for discrepancies between the two ends of a test section. The following procedure was used to evaluate and resolve these coding conflicts:

1. The laboratory materials testing data (Form T52, Table 4.27) were checked to ensure that the appropriate materials code was assigned to the layer for the end of the test section. Finally, the soil gradation test data on the critical sieves (No. 10 [2.00-mm], No. 40 [0.425-mm], No. 200 [0.075-mm]) and the Atterberg limit test data for the two opposing samples from each layer were examined. Because a change of only 1% on a critical sieve can change a sample from one material code to another, this examination served to eliminate some apparent code conflicts. Where differences in test data were minor the most appropriate code was chosen, and an appropriate comment inserted in column 6.
2. The gradation data were checked: if ratios between individual sieve sizes or Atterberg limits for the two samples of a given layer taken from the opposite ends of the section were higher than 0.7 (lower percentage/higher percentage), the gradation and Atterberg results were averaged and Table 4.26 was used to assign the subgrade material code.

For example, if the percent passing the No. 200 (0.075-mm) sieve has the following values: Lab Test No. 1 = 14.2% and Lab Test No. 2 = 12.1%, the ratio (12.1/14.2) = 0.85; therefore, it was acceptable to average these two sieve sizes to determine an "average" material classification code.

1. The shoulder borehole log was reviewed to determine if it provided useful information on the soil types beneath the study section and agreed with sample data from one end or the other.
2. Inventory, construction records and other state records were checked to identify the in situ subgrade soil or embankment soil placed at this location of the project. Using the construction plans (if available), sampling area locations were evaluated to determine areas of cut and fill in or around the test section. The state highway department may also have been consulted during this process which was highly recommended. The material code which appeared to be more logical was assigned.
3. If nothing could be established from the review of pertinent records, then the FWDCHECK plots were reviewed. FWDCHECK data from the outermost sensors (6 & 7) were used to establish if there were consistent results between ends. If the results from within the test section were more similar to the FWD readings at one of the ends, then this was used as the representative layer for material codes. If the FWDCHECK data were not consistent with either end of the test section, then the reviewer used a special material code designation (code 999) to indicate to the analyst that two different subgrade types may underlie the section. A code of 999 was only used as a last resort when everything else, including engineering judgment, had failed to produce a compromise.

For unbound base and subbase layers, the following procedure was followed:

1. The laboratory materials testing data (Form T47, Table 4.29) were checked to assure that the appropriate materials code had been assigned to the layer on Form L05A for each end of the test section.
2. The gradation and Atterberg Limit test data were checked as noted in comment 2 above, and the test data was averaged if test results differed by no more than the 0.7:1 ratio as noted for the subgrade layers. Then the material code for the averaged test data was used.
3. Inventory, construction records and other state records were checked to identify the unbound base and/or subbase layers specified for the pavement. This information was evaluated and the pavement material code was used which was most logical for Form L05B.
4. If the above review did not yield an appropriate resolution to this discrepancy, then the Code 999 was used as the material code for this layer, which was to indicate the significant materials differences to the analyst. A code of 999 was only used as a last resort when everything else, including engineering judgment, had failed to produce a compromise.

For bound base and subbase layers, the following procedure was used:

1. The field materials sampling and laboratory materials testing data were checked to ensure that the appropriate materials code had been assigned to the layers for both ends of the test section. This check involved an extensive review of Form T31, Table 4.29, and a review of the photographs and field logs taken during the field drilling and sampling operations.
2. If this review did not reveal a single logical code, the inventory, construction records and other SHA records were checked to identify the type of bound base and/or subbase layers specified for the pavement. This information was evaluated and the pavement material code was used which was most logical for Form L05B.

For surface layers, the following procedure was followed to resolve discrepancies between material codes:

1. The field materials sampling and laboratory materials testing data were checked to ensure that the appropriate materials testing code had been assigned to the layer. A check was made of Forms T01A, T01B, T02, T03, T04, and T14 forms to determine the appropriate material code. Special care was taken to ensure that different lifts of the same material were not designated as separate layers. Layers were combined where there was no clear reason to list them separately. Cases where a single layer was described, sampled, and tested as two layers at only one end of the section were to be resolved by combining the thicknesses and averaging the test data for the two layers.
2. If this did not resolve the discrepancy, then the inventory, construction records and other state records were checked to identify the surface layer specified for the pavement. This information was evaluated and the pavement material code was used which was most logical.
3. If the layer retained an obvious difference at the opposite section ends in spite of the above checks, the material code 999 was entered to indicate this fact to the analyst. A code of 999 was only used as a last resort when everything else, including engineering judgment, failed to produce a compromise.

Compatibility of Inventory Layer Structures and Laboratory Materials Testing Layer Structures (column 8 - Form L05B): During the completion of Form L05B, it was necessary to provide a correlation between the layer structure from the laboratory materials testing data and layer structure from inventory data. This correlation was needed to provide analysts with a means to extract data from the inventory portion of the PPDB which were not determined in the LTPP contract laboratory. This was especially true for thin (= 1.5 inches [38 mm]) asphalt concrete layers which could not be tested under LTPP procedures. This correlation between the inventory layer data and the laboratory/field sampling determined layer data provided a means of providing the analyst with the missing information.

As an example, "Analysis Section" (Form L05B) contained the information provided in Table 5.14 and inventory layer information contained the data provided in Table 5.15.

Using these data, it was very easy to make the correlation between the inventory data and the Analysis Section (L05B) data. It was also obvious from these data, that layer 6, (HMAC overlay, 0.8 inches [20 mm]) would not contain laboratory materials testing data since it did not meet the minimum thickness of 1.5 inch (38 mm) criteria. However, the analyst would be able to extract the inventory layer data for layer 6 using the Form L05B layer data and the inventory correlated layer data. This correlation provided a critical link between laboratory materials testing data and inventory data which was useful to researchers.

As another example, the L05B form contained the structure provided in Table 5.16. The inventory layer data are provided in Table 5.17 for another section that may have been encountered. In this example, layers 1, 2, and 3 from Form L05B correlate well with layers 1, 2, and 3, respectively, from the inventory data. However, layers 4, 5, and 6 (HMAC layers) did not correlate exactly. The analysis section contains 3 HMAC layers while the inventory contains 2 HMAC layers. In this case, the laboratory materials testing data and the construction records were reviewed to determine if layers 4 and 5 shown on Form L05B were indeed two distinct AC layers and not lifts of similar material placed under the same construction contract and specifications. If they were lifts of the same asphalt layer then both layer 4 and layer 5 were correlated with layer 4 of the inventory data. If they (layers 4 and 5) were indeed different layers of AC, then a decision was made on which L05B layer to use to correlate with the inventory data. In this case, it was recommended that both layer 4 and layer 5 be correlated with layer 4 of the inventory data even though from the laboratory testing data they appear as different layers. From the thickness given in the inventory data for layer 4 (3.0 inches) and a review of the combined thickness for layer 4 and 5 (2.8 inches [71 mm]) for Form L05B, it was assumed that layers 4 and 5 were specified and placed as one layer and some other factor, such as differing aggregate color or particle sizes, influenced their designation as two separate layers. Thus, the final L05B was completed as shown in Table 5.18.

In no case were the inventory layer data changed to conform to Form L05B results. If an error was detected in the inventory data, then this error was revised accordingly. However, inventory layer data and Form L05B data were not expected to be in exact accordance. If layers were missing or additional layers were identified, then the Inventory Layer No. on Form L05B may have been left blank for certain layers. The purpose of this field on Form L05B was to provide the best estimate between the inventory data and Form L05B. It was not mandatory that each Form L05B layer contain a corresponding inventory layer number if no layer in the inventory layer structure could adequately be estimated to have the same material properties as those layers in Form L05B.

New Construction Experiments

Establishing the layer structure for the SPS-1, SPS-2, and SPS-8 experiments was a relatively straightforward process. For each test section, a review was conducted of Form L05A. For these projects, every test section had an entry on Form L05A along with thickness measurements from either field survey measurements (rod and level) or core examination and thickness measurements. The layer structure on Form L05A was used to establish the layer structure for each test section. Also, the layer thickness measurements could be obtained from Form L05A as well.

For test sections that had material characterization tests performed on the unbound layers (including subgrade), the material classification code derived from this testing on Form L05A could be used directly on Form L05B. For those test sections that did not have material characterization tests performed from areas within or near the test section, the material classification for the same material from an adjacent section was used. Engineering judgment was required in this case based on the notes from the field during construction and other information that the personnel may have possessed. An underlying assumption in this discussion is that a particular material placed on the project (e.g., Dense Graded Aggregate Base) remained fairly homogeneous throughout the project unless the material was obtained from more than one source. Therefore, material placed on one test section was the same material as placed on an adjacent test section. The appropriate code was placed in the Comment Code section of Form L05B to indicate that a material classification from another test section was used for the test section under evaluation.

Rehabilitation Experiments

The procedures for completion of Form L05B for the SPS-5, SPS-6, and SPS-7 experiments are very similar to that of the GPS program. However, similar to the rest of the SPS experiments, the process was complicated due to limited amount of sampling and testing performed on each test section.

Generally, the thickness measurements and layer material codes recorded on Form L05A could be used directly to complete the L05B. The remaining missing layer thickness and material code (classification data) was to be interpreted from other test sections using engineering judgment. Like the new construction experiments, a critical assumption in this process was that the SPS project as a whole was comprised of homogeneous layers with a relatively constant layer thickness. Therefore, layer thickness and classification information for one section could be used for adjacent test sections.

The complete layer structure for each test section was established first on Form L05B by analyzing Form L05A and determining the appropriate layer structure. During this evaluation, the inventory, construction records and typical cross-sections were consulted to determine if the layers sampled matched consistently with those that were originally planned for the project. If they did not match, the as-built construction records and other state records were reviewed to determine if there was some special circumstance associated with the test section or SPS project. For example, the SPS project could be located between two construction projects and/or pavement designs or two different material sources may have been used to construct portions of a single specified layer. FWD data and possibly profilometer data could be used to obtain some sense of project homogeneity. Overall, however, it was expected that the as-sampled layers match fairly consistently with those proposed for the project.

After establishing the layer structure, the appropriate layer thicknesses for each layer were determined. For bound pavement layers, the layer thickness values were extracted directly from Form L05A. Because layer thickness measurements for bound layers were usually established from opposite ends of the pavement test section, an average thickness from these measurements was reported on Form L05B. This was only performed however, if the layer thicknesses were considered consistent between the ends of the test section. Table 5.11 was used as a guide to determine if a layer thickness was consistent between section ends and the appropriate action to be taken in each circumstance. This table applies to both bound and unbound layers when layer thickness measurements were taken at opposite ends of a particular test section.

If thickness measurements were taken within the test section by rod and level survey, etc., for the overlay layers, the laboratory measurements from cores were compared with the rod and level survey data using the same criteria as shown in Table 5.11 (i.e., the difference between the rod and level data and the laboratory measured thicknesses) to determine the homogeneity of the overlay surface throughout the test section.

If the layer thickness was not consistent between section ends or a layer had a zero thickness on one end, then the section was more closely evaluated to determine the appropriate layer thickness using the same steps outlined for the GPS experiments.

After establishing the layer thicknesses, the appropriate material code for each layer was established using Form L05A and all other available information.

For test sections that had material characterization tests performed on the unbound layers including subgrade (i.e., test pit locations, BA-type locations, etc.), the material classification code derived from this could be used directly on Form L05B. For those test sections that did not have material characterization tests performed from areas within or near the test section, the material classification for the same material from an adjacent section was used. Engineering judgment was required in this case based on the notes from the field during construction and other information that the personnel may possess. An underlying assumption in this discussion was that a particular material placed on the project (e.g., Dense Graded Aggregate Base) will remain fairly homogenous throughout the project unless the material was obtained from more than one source. Therefore, material placed on one test section was the same material as placed on an adjacent test section. The appropriate code was placed in the Comment Code section of Form L05B to indicate that a material classification from another test section was used for the test section under evaluation.

In the (probably rare) case where the test section had testing performed on both ends of the section or in sampling areas equally adjacent to the test section, the procedure outlined for the GPS experiments was followed.

Maintenance Effectiveness Experiments

The SPS-3 and SPS-4 experiments also required a significant amount of engineering judgment in order to establish the pavement analysis section. Generally, it was expected that the only detailed layer information available would be from the associated GPS test section located adjacent to the SPS-3 or SPS-4 project. Also, it was generally expected that one 6-inch (152-mm) borehole was retrieved from each test section. The materials were supposed to be characterized (visually) for this six-inch corehole for all layers through to the subgrade. For the purposes of the completion of the L05B form, the information obtained from this six inch core and auger was of limited value. Therefore, for each section included in the SPS-3 and SPS-4 program, the layer structure for the GPS test section was used to complete the layer structure. The layer thicknesses and material types for each SPS-3 and SPS-4 section obtained from the 6-inch (152-mm) core and auger were compared to the GPS test section structure to ensure that the layer structures were fairly consistent. The thickness of the maintenance treatment was generally fairly easy to establish from construction records.

If significant variations existed between the GPS test section layering and the 6-inch (152-mm) core and auger location, the as-built construction records and other state records were reviewed to determine if there was some special circumstance associated with the test section or SPS project. For example, the SPS project may have been located between two construction projects and/or pavement designs or two different material sources may have been used to construct portions of a single specified layer. FWD data and possibly profilometer data were used to obtain some sense of project homogeneity.

Prior to completing the layer structure for the SPS-3 and SPS-4 projects, the GPS test section layering and all QC/QA associated with the GPS Form L05B were to have been completed.