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Publication Number: FHWA-RD-03-040
Date: July 2002

Researcher's Guide to The LTPP Layer Thickness Data

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  1. Inventory Layer Thickness Data
  2. Rehabilitation Layer Thickness Data
  3. Laboratory Core Examination Data
  4. Field Elevation Measurements
  5. Field Layer Material Type and Thickness Measurements
  6. Layer Material Type and Thickness Summary Data


Several types of layer thickness data were collected under the LTPP program, and these data reside in different LTPP database modules and tables. This chapter provides detailed discussions about each of these data sources and data tables.

The following lists LTPP tables that contain layer material or thickness information:

Additional information about the LTPP program, field sampling, materials testing, layer structure and layering information, data collection guidelines, and the LTPP database can be found in the following documents:

Note that information presented in this Guide about LTPP table structures, field names and descriptions, and code lists reflect the current LTPP database structure and may be changed in the future. For the updated information, the users should refer to the most recent IMS Quality Control Checks document [19].

Inventory Layer Thickness Data

Inventory or design layer structure data for the existing LTPP pavement sections are collected by LTPP and stored in table INV_LAYER. The data are generally based on highway agency records. Inventory data are historical in nature and exist for all GPS sections. For SPS experiments, only the rehabilitation projects (SPS-5, SPS-6, SPS-7, and SPS-9) and the sections that are linked to a GPS section have records in the INV_LAYER table. [1, 20-25]

The essential fields other than the section and layer identification fields in table INV_LAYER are the following:

Field Name Description
DESCRIPTION Code indicating general type of layer.
MATERIAL_TYPE Code for material type classification. QC applies to GPS; see QC Manual for SPS.
MEAN_THICKNESS Mean thickness of each layer. QC applies to GPS; see QC Manual for SPS
MIN_THICKNESS Minimum thickness of each layer. QC applies to GPS; see QC Manual for SPS.
MAX_THICKNESS Maximum thickness of each layer. QC applies to GPS; see QC Manual for SPS.
STD_DEV_THICKNESS Standard deviation of layer thickness. QC applies to GPS; see QC Manual for SPS.

A list of the codes and their descriptions for the field DESCRIPTION (code name "DESCRIPTION") is given in table 1. The code name for field "MATERIAL_TYPE" is "MAT_TYPE." Table 2 provides the code list and descriptions for the MATERIAL_TYPE field. Up to four numbers were provided to indicate the minimum, maximum, mean, and standard deviation of thickness for each specific layer. If only a single specified design value for thickness was available, it was entered as the mean value. When a number of boreholes were made for sampling materials, thickness measurements may also have been taken. In such cases, the mean thicknesses were then verified or revised and variability information (MIN, MAX, and STD_DEV) added as a result of these field measurements. [2,3]

Table 1. Code list and code descriptions for "DESCRIPTION"

Code Number Code Description for Code "DESCRIPTION"
1 Overlay
2 Seal Coat
3 OriginalSurface Layer
4 AC Layer Below Surface (Binder Course)
5 Base Layer
6 Subbase Layer
7 Subgrade
8 Interlayer
9 Friction Course
10 Surface Treatment
11 Embankment Layer

Table 2. Code list and code descriptions for code "MAT_TYPE", continued.

Code Number Code Description for Code "MAT_TYPE"
1 Hot-Mixed, Hot-Laid Asphalt Concrete, Dense-Graded
2 Hot-Mixed, Hot-Laid Asphalt Concrete, Open-Graded (Porous Friction Course)
3 Sand Asphalt
4 Portland Cement Concrete (Jointed Plain Concrete pavement [JPCP])
5 Portland Cement Concrete (Jointed reinforced Concrete pavement [JRCP])
6 Portland Cement Concrete (Continuously Reinforced Concrete Pavement [CRCP])
7 Portland Cement Concrete (Prestressed)
8 Portland Cement Concrete (Fiber-Reinforced)
9 Plant Mix (Emulsified Asphalt) Material, Cold-Laid
10 Plant Mix (Cutback Asphalt) Material, Cold-Laid
11 Single Surface Treatment
12 Double Surface Treatment
13 Recycled Asphalt Concrete Hot-Laid, Central Plant Mix
14 Recycled Asphalt Concrete Cold-Laid Central Plant Mix
15 Recycled Asphalt Concrete Cold-Laid Mixed-In-Place
16 Recycled Asphalt Concrete Heater Scarification/Recompaction
17 Recycled Portland Cement Concrete (JPCP)
18 Recycled Portland Cement Concrete (JRCP)
19 Recycled Portland Cement Concrete (CRCP)
20 Other
21 No Base(Pavement Placed Directly on Subgrade)
22 Gravel (Uncrushed)
23 Crushed Stone, Gravel or Slag
24 Sand
25 Soil-Aggregate Mixture (Predominantly Fine-Grained Soil)
26 Soil-Aggregate Mixture (Predominantly Coarse-Grained Soil)
27 Soil Cement
28 Dense-Graded, Hot-Laid, Central Plant Mix
29 Dense-Graded, Cold-Laid, Central Plant Mix
30 Dense-Graded,Cold-Laid, Mixed-In-Place
31 Open-Graded,Hot-Laid, Central Plant Mix
32 Open-Graded, Cold-Laid, Central Plant Mix
33 Open-Graded,Cold-Laid, Mixed-In-Place
34 Recycled Asphalt Concrete, Plant Mix, Hot-Laid
35 Recycled Asphalt Concrete, Plant Mix, Cold-Laid
36o Recycled Asphalt Concrete, Mixed-In-Place
37 Cement-Aggregate Mixture
38 Lean Concrete (<3 sacks cement/cy)
39 Recycled Portland Cement Concrete
40 Sand-Shell Mixture
41 Limerock, Caliche (Soft Carbonate Rock)
42 Lime-Treated Subgrade Soil
43 Cement-Treated Subgrade Soil
44 Pozzolanic-Aggregate Mixture
45 Cracked and Seated PCC Layer
46 Sand Asphalt
49 Other
51 Clay (Liquid Limit > 50)
52 Sandy Clay
53 Silty Clay
54 Silt
55 Sandy Silt
56 Clayey Silt
57 Sand
58 Poorly Graded Sand
59 Silty Sand
60 Clayey Sand
61 Gravel
62 Poorly Graded Gravel
63 Clayey Gravel
64 Shale
65 Rock
70 Grout
71 Chip Seal Coat
72 Slurry Seal Coat
73 Fog Seal Coat
74 Woven Geotextile
75 Nonwoven Geotextile
77 Stress Absorbing Membrane Interlayer
78 Dense-Graded Asphalt Concrete Interlayer
79 Aggregate Interlayer
80 Open-Graded Asphalt Concrete Interlayer
81 Chip Seal with Modified Binder (Does Not Include Crumb Rubber)
82 Sand Seal
83 Asphalt-Rubber Seal Coat (Stress Absorbing Membrane
84 Sand Asphalt
85 Other
86 Thin Seals and Interlayers
90 Plain Portland Cement Concrete (only used for SPS-7 overlays of CRCP)

Rehabilation Layer Thickness Data

Each highway agency is expected to notify the LTPP regional office prior to doing rehabilitation on a highway segment containing an LTPP section [1]. Rehabilitation activities include resurfacing, reconstruction, and the addition of lanes. Rehabilitation sometimes alters the pavement structure. In these cases, layer data are recorded in table RHB_LAYER from information provided by the highway agencies. Table RHB_LAYER contains layer thickness and material type information for sections that were rehabilitated during the LTPP program.

The essential fields other than the section and layer identification fields in table RHB_LAYER are the following:

Field Name Description
DESCRIPTION Code indicating general type of layer.
MATERIAL_TYPE Code for type of material used in the rehabilitation.
MEAN_THICKNESS The average thickness of each material layer.
MIN_THICKNESS The minimum thickness of each material layer.
MAX_THICKNESS Maximum layer thickness.
STD_DEV_THICKNESS Standard deviation of layer thickness.

The code list and descriptions for the following fields were provided previously: DESCRIPTION (table 1) and MATERIAL_TYPE (code MAT_TYPE, table 2). Up to four numbers are provided to indicate the minimum, maximum, mean, and standard deviation of thickness for each rehabilitated layer. If only a single specified design value for thickness was available from project historic records, it was entered as the mean value. For SHRP/LTPP, when a number of boreholes were made for sampling materials, careful thickness measurements may also be made. In such cases, the mean thicknesses were then verified or revised and variability information (MIN, MAX, and STD_DEV) added as a result of these field measurements and measurements of cores in the laboratory. [2,3]

Laboratory Core Examination Data

Field and laboratory tests are conducted to establish material properties and layer characteristics. Characterization of material properties and the variations in these properties between and within the test sections is required to evaluate causes of performance differences between test sections.

Laboratory core examination data are stored in three LTPP tables: TST_AC01 and TST_AC01_LAYER for asphalt bound layers and TST_PC06 for PCC layers

AC Core Examination and Thickness

For the asphalt bound layers, SHRP protocol P01 [17], Visual Examination and Thickness of Asphaltic Concrete Cores, provides detailed procedures for identifying and determining the thickness of individual layers within the AC core. A single asphalt concrete core taken from the field may contain more than one layer. For example, a single AC core identified in the field as AC material may contain hot-mix AC (HMAC) wearing, binder, and base layers.

The test results for an entire AC core are stored in table TST_AC01, and the test results for the individual layers within the AC core are stored in table TST_AC01_LAYER

The essential fields other than the section and layer identification fields in table TST_AC01 are:

CORE_AVG-THICKNESS Avergage thickness of core sample.
VISUAL_EXAM_1 to 6 Code "VISUAL_ACPC" for visual examination comments.
VISUAL_EXAM_OTHER Other visual examination comments.
COMMENTS_1 to 6 Code "COMMENT" for testing comments
COMMENTS_OTHER A note used to record additional observations regarding the test, or test results.
TEST_DATE The date the test was performed.

Since the thickness measurements stored in table TST_AC01 is not keyed to LAYER_NO field and may not be for a single layer, it is difficult to identify which layer the measurement belongs to. The code lists for codes VISUAL_ACPC and COMMENTS are provided in tables 3 and 4 respectively.

Table 3. Code list and code descriptions for code "VISUAL_ACPC"

Code Number Code Description for Code "VISUAL_ACPC"
66 Coarse aggregate along face of core is mix of uncrushed gravel and crushed stone.
67 The exposed aggregates along face of core are lightweight aggregate concrete.
68 More than 10% of core surface area contains soft aggregate particles/clay balls.
69 Cracks are generally across or through the coarse aggregate.
70 Cracks are generally around the periphery of the coarse aggregate.
71 Cracks are associated with embedded steel.
72 Rims are observed on aggregate.
73 Fine aggregate is natural sand.
74 Fine aggregate is manufactured sand.
75 Fine aggregate is a mixture of natural and manufactured sand.
76 Steel is present in the core.
77 Steel is corroded.
78 Core indicates D-cracking.
79 Core indicates deterioration due to freeze-thaw cycles.
80 Core indicates sulfate attack.
81 Core indicates alkali silica reactivity
82 Skewed core.
99 Other comment.

Table 4. Code list and code descriptions for code "COMMENT," continued.

Code Number Code Description for Code "VISUAL_ACPC"
1 Intact core; excellent condition.
2 Hairline cracks on the surface; no visible vertical crack within 1/3 of length.
3 Cracks and/or voids visible along the side of the core.
4 Badly cracked or damaged core; unsuitable for testing.
5 Ridges on the sides of the cores; condition should be recorded if used.
6 Very rough and uneven bottom surface.
7 Core severely damaged from sampling, handling, etc. Unsuitable for testing.
8 Core was sawed in laboratory for removing it from the underlying bonded layer.
9 Core consisted of 2 or more AC layers. Core to be sawed and assigned layer numbers.
10 Visible separation of one or more layers. Layers to be sawed and assigned numbers.
11 Visible segregation of coarse and fine aggregates over 25% of surface area of core.
12 Voids in the matrix of the AC mixture are observed along the sides of the core.
13 Voids due to loss of coarse and fine aggregate observed along the sides of core.
14 Core missing significant portions, unsuitable for testing.
15 Coarse aggregate along face of core contains 50% or more of crushed materials.
16 Coarse aggregate along face of core is mix of uncrushed gravel and crushed stone.
17 More than 10% of core surface area contains soft aggregate particles/clay balls.
18 Slight stripping.
19 Severe stripping.
20 Slight bleeding.
21 Severe bleeding.
22 Skewed core.
51 Intact core; excellent condition.
52 Hairline cracks on the surface; suitable for testing.
53 Cracks and/or voids visible along the side of the core; suitable for testing.
54 Badly cracked or damaged core; unsuitable for testing.
55 Ridges on the sides of the cores; condition should be recorded if used for test.
56 Very rough and uneven bottom surface.
57 Core severely damaged during handling; unsuitable for testing.
58 Core was sawed in laboratory for removing it from the underlying bonded layer.
59 Core consisted of 2 or more layer. Core was assigned and assigned layer numbers.
60 Visible separation of one or more layers; layers separated and assigned numbers.
61 Segregation of coarse and fine aggregates observed over 25% of core surface area.
62 Voids in the matrix are observed along the sides of the core.
63 Voids due to loss of coarse and fine aggregates observed along sides of core.
64 Core is missing significant portions. Unsuitable for testing.
65 Coarse aggregate are generally crushed stone with predominately fractured faces.
66 Coarse aggregate along face of core is mix of uncrushed gravel and crushed stone.
67 The exposed aggregates along face of core are lightweight aggregate concrete.
68 More than 10% of core surface area contains soft aggregate particles/clay balls.
69 Cracks are generally across or through the coarse aggregate.
70 Cracks are generally around the periphery of the coarse aggregate.
71 Cracks are associated with embedded steel.
72 Rims are observed on aggregate.
73 Fine aggregate is natural sand.
74 Fine aggregate is manufactured sand.
75 Fine aggregate is a mixture of natural and manufactured sand.
76 Steel is present in the core.
77 Steel is corroded.
78 Core indicates D-cracking.
79 Core indicates deterioration due to freeze-thaw cycles.
80 Core indicates sulfate attack.
81 Core indicates alkali silica reactivity
82 Skewed core.
99 Other comment.

The essential fields other than the section and layer identification fields in table TST_AC01_LAYER are as following:

FIELD_LAYER_COMMENT Comment on the field layer.
LAYER_DESCRIPTION Code for the description of the pavement layer.
LAYER-THICKNESS The measured thickness of an individual layer.

The code list and descriptions for field LAYER_DESCRIPTION (code DESCRIPTION, table 1) were provided previously.

Material Sampling Plan for AC Cores

Material sampling for AC cores was performed according to guidelines provided in several LTPP documents and reports, including the SHRP-LTPP Interim Guide for Laboratory Material Handling and Testing and the SPS Guidelines [2,3,5-16]. For GPS experiments, test samples were collected at specific locations outside the monitoring sections of the LTPP test sections. For SPS projects, cores were extracted from designated locations adjacent to the pavement test sections. Core thickness examination and thickness measurements were performed on all cores retrieved. Basically, two types of cores were extracted:

Sampling and testing requirements for AC core examination and thickness testing are presented in tables 5 and 6. The tables show the minimum number of core specimens required for testing for the various LTPP experiments, along with the designated sampling locations.

Table 5. Sampling requirements for visual examination and thickness of AC cores.

Experiment Type Layer Type Min. No. of Tests per Layer Sampling Location [2,3]
GPS-1, -2, -6, and -7 AC16 All 100-mm and 150-mm-diameter cores
SPS-1 ATB134 102-mm OD2 cores: C1-C10, C21-C34, C47-C56
AC surface and binder 60102-mm OD cores: C1-C60
SPS-3 ATB34 102-mm OD cores: C1-C10, C21-C34, C47-C56
AC surface and binder 60102-mm OD cores: C1-C60
SPS-5 (Preconstruction) AC26 All Type-C cores
SPS-5 (Postconstruction) AC40 All cores
SPS-6 AC20 All cores
SPS-8 AC16 All cores
SPS-9 (Preconstruction) AC6 A01A01, A02A01, A01A02
A02A02, A01A03, A02A03
SPS-9 (Postconstruction) AC8

Table 6. Detailed SPS sampling requirements for visual examination and thickness of AC cores.

Experiment Type Test Section Min. No. of Cores Required
(Surface and binder/ATB1)
Sampling Location [2,3]
SPS-1 0101 (0113) Jun-00 C41-C46
SPS-1 0102 (0114) Apr-00 C57-C60
SPS-1 0103 (0115) 4-Apr C47-C50
SPS-1 0104 (0116) 4-Apr C1-C4
SPS-1 0105 (0117) 6-Jun C51-C56
SPS-1 0106 (0118) 6-Jun C5-C9
SPS-1 0107 (0119) Jun-00 C35-C40
SPS-1 0108 (0120) Jun-00 C15-C20
SPS-1 0109 (0121) Apr-00 C11-C14
SPS-1 0110 (0122) 4-Apr C21-C24
SPS-1 0111 (0123) 4-Apr C31-C34
SPS-1 0112 (0124) 4-Jun C25-C30
SPS-5 (Preconstruction) 501 2 C1,C2
SPS-5 (Preconstruction) 502 4 C3-C6
SPS-5 (Preconstruction) 503 2 C7-C8
SPS-5 (Preconstruction) 504 2 C9-C10
SPS-5 (Preconstruction) 505 2 C11-C12
SPS-5 (Preconstruction) 506 5 C13-C17
SPS-5 (Preconstruction) 507 2 C18-C19
SPS-5 (Preconstruction) 508 5 C20-C24
SPS-5 (Preconstruction) 509 2 C25-C26
SPS-5 (Postconstruction) 501 0 –#
SPS-5 (Postconstruction) 502 4 C27-C30
SPS-5 (Postconstruction) 503 6 C31-C35
SPS-5 (Postconstruction) 504 6 C37-C42
SPS-5 (Postconstruction) 505 4 C43-C46
SPS-5 (Postconstruction) 506 4 C47-C50
SPS-5 (Postconstruction) 507 6 C51-C56
SPS-5 (Postconstruction) 508 6 C57-C62
SPS-5 (Postconstruction) 509 4 C63-C66
SPS-6 (Preconstruction) 601 3 C1-C3
SPS-6 (Preconstruction) 602 3 C3-C6
SPS-6 (Preconstruction) 603 2 C11-C12
SPS-6 (Preconstruction) 604 2 C13-C14
SPS-6 (Preconstruction) 605 4 C7-C10
SPS-6 (Preconstruction) 606 2 C15-C16
SPS-6 (Preconstruction) 607 2 C17-C18
SPS-6 (Preconstruction) 608 2 C19-C20
SPS-6 (Postconstruction) 603 4 C21-C24
SPS-6 (Postconstruction) 604 4 C25-C28
SPS-6 (Postconstruction) 606 4 C29-C32
SPS-6 (Postconstruction) 607 4 C33-C36
SPS-6 (Postconstruction) 608 4 C37-C40
SPS-8 0801, 0803, 0805 8 C1-C8
SPS-8 0802, 0804, 0806 8 C9-C16
SPS-9 0901, 0902, 0903 8 –#

PCC Core Examination and Thickness

Visual examination and length measurement are performed on PCC core specimens as part of the material characterization program for the LTPP study. These basic tests are conducted on all PCC cores before they are subjected to compressive strength, split tensile strength, and static modulus of elasticity testing.

Usually, cores are taken at specified periods after construction (e.g., 14, 28, and 365 days) for newly constructed pavements and several years after construction for in-service pavements adopted into the LTPP program. The number of cores taken from a given location depends on both the pavement test section properties and LTPP experiment type.

Procedures used for measuring core length (layer thickness) and examining the cores are presented in the following SHRP test protocol and AASHTO/ASTM test procedures:

The PCC core specimens are examined visually to determine their general condition, presence of distresses, presence of defects such as cracks, voids, D-cracking, alkali-silica reactivity, and problems with layer separation (for overlaid pavements). The general type and shape of aggregates (e.g., rounded gravel or angular crushed stone) were also documented. The cores were also examined to determine their suitability for length measurements and other testing. Cores with serious defects, such as uneven surfaces and segregated aggregates, were noted and not used for further testing.

The length measurement and visual examination test results are stored in the LTPP database after undergoing quality checks that ensure anomalies (e.g., negative PCC core thickness values) are identified and corrected. Data that are of acceptable quality after the quality control (QC) checks are classified as Level E and are stored in table TST_PC06. The following essential data other than the section and layer identification fields are maintained in table TST_PC06:

Field Name Description
CORE_AVG_THICKNESS Average thickness of core sample
VISUAL_EXAM_1 to 6 Code for visual examination comments
VISUAL_EXAM_OTHER Other Visual examination comment.
COMMENTS_1 to 6 A note used to record additional obsservations regarding the test, or test results.
TEST_DATE The date the test was performed.

The code list and descriptions for the following fields were provided previously: VISUAL_EXAM_1 to VISUAL_EXAM_6 (VISUAL_ACPC, table 3) and COMMENTS_1 to COMMENTS_6 (COMMENT, table 4).

Material Sampling Plan for PCC Cores

PCC core specimens are collected as directed by the SHRP P66 protocol from designated locations within the GPS and SPS experiments (GPS experiments are cored by SHRP contractors; SPS experiments are cored by highway agencies or contractors). Cores are then prepared according to procedures outlined in SHRP P66 [18], AASHTO T148 [26], and ASTM C856 [27] before being shipped to certified laboratories for testing.

For GPS pavements, cores are taken from both the approach and leave ends of the pavement test section. Both core locations are sited some distance from the monitored test section to avoid damaging the actual test section. For SPS experiments, cores are taken at designated locations from various test sections within a given site.

For SPS experiments, sampling can be complicated because these experiments consist of a diverse matrix of test sections, some of which are newly constructed with different PCC target thicknesses and strengths (e.g., SPS-2), and the others are in-service pavements that have been overlaid and, therefore, consist of both in-service and newly constructed layers (e.g., SPS-7).

Table 7 presents a summary of the minimum core specimens required by the LTPP materials testing and sampling program for core length measurements and visual examination for each LTPP experiment [2,5-10]. Although the minimum number of tests per layer indicated in the table directly translates to the required minimum tests per analysis cell for GPS projects, the same is not true for SPS projects. Therefore, a more detailed description of the testing requirements for various SPS experiments is presented in table 8.

Table 7. Summary of the sampling and testing plan for thickness measurement and visual examination of PCC cores.

Experiment Type Layer Type LTPP Protocol Min. No. of Tests per Layer Sampling Location [2,3]
GPS-3, 4, 5, 9 PCC P66-61 2 C2, C8
GPS-7 PCC P66-61 2 C8, C20
GPS-3, 4, 5, 9 PCC P66-62 2 C5, C11
GPS-7 PCC P66-62 2 C11, C23
GPS-3, 4, 5, 9 PCC P66-64 2 C1, C7
GPS-7 PCC P66-64 2 C7, C19
SPS-2 PCC P66 99 per site/project All cores
SPS-2 LCB P66 24 per site/project –#
SPS-6 PCC P66 23 per site/project C1-C20 A1 A2 A3
SPS-7 PCC-overlay (postconstruction)     C10-20 C21-64 C65-108
  99 per site/project
PCC-overlay (preconstruction) P66 47 per site/project C10-20 C21-64 C65-108
SPS-8 PCC P66 26 per site/project C1-C26
SPS-9A PCC P66 6 per site/project –#

Table 8. Detailed SPS sampling requirements for PCC core visual examination and length measurement.

Exp. Type Test Section Layer Type Min. No. of Specimens Required per Layer Sampling Location [2,3]
SPS-2 0201 (0215) PCC 8 C10-C17
SPS-2 02002 (0216) PCC 8 C59-C66
SPS-2 0203 (0213) PC 9 C34-C42
SPS-2 0204 (0214) PCC 8 C83-C90
SPS-2 0205 (0219) PCC 8 C21-C25, C18-C20, C22-C24
SPS-2 0206 (02020) PCC 8 C73-C74, C67-C72
SPS-2 0207 (0217) PCC 8 C29-C33, C26-C28, C30-C32
SPS-2 0208 (0218) PCC 8 C78, C82, C75-C77, C79-C81
SPS-2 0209 (02023) PCC 9 C1-C9
SPS-2 0210 (02024) PCC 8 C51-C58
SPS-2 0211 (02021) PCC 8 C43-C50
SPS-2 02102 (020202) PCC 9 C91-C99
SPS-2 0205 (0219) LCB 6 C18-C20, C22-C24
SPS-2 0206 (02020) LCB 6 C67-C72
SPS-2 0207 (0217) LCB 6 C26-C28, C30-C32
SPS-2 0208 (0218) LCB 6 C75-C77, C79-C81
SPS-6 601 Original PCC 3 C1-C3
SPS-6 602 Original PCC 4 C4-C6, A1
SPS-6 603 Original PCC 3 C11-C12
SPS-6 604 Original PCC 2 C13-C14
SPS-6 605 Original PCC 4 C7-C10
SPS-6 6006 Original PCC 2 C15-C16
SPS-6 607 Original PCC 3 C17-C18, A3
SPS-6 608 Original PCC 2 C19-C20
SPS-7 701 Original (Overlay) 1 (0) A1
SPS-7 702 Original (Overlay) 1 (8) A2 (C21-C24, C65-C68)
SPS-7 703 Original (Overlay) 3 (9) C1-C3 (C10, C25-C28, C69-C72)
SPS-7 704 Original (Overlay) 1 (8) A3 (C29-C32, C73-C76)
SPS-7 705 Original (Overlay) 4 (8) A4, BA1-BA3 (C33-C36, C77-C80)
SPS-7 706 Original (Overlay) 3 (11) C4-C6 (C11-C13, C37-C40, C81-C84)
SPS-7 707 Original (Overlay) 1 (17) A5 (C14-C16, C44-C50, C88-C94)
SPS-7 708 Original (Overlay) 1 (16) A6 (C17-C18, C51-C57, C95-C101)
SPS-7 709 Original (Overlay) 3 (16) C7-C9 (C19-C20, C58-C64, C102-C108)
SPS-8 0807, 0809, 0811 Overlay 13 C1-C13
SPS-8 0808, 0810, 0812 Overlay 13 C14-C26
SPS-9A 0901, 0902, 0903 Original 2

Field Elevation Measurements

For SPS newly constructed layers, elevation measurements of the final finished surface are conducted throughout the test section. The measurements normally are made at five offset points at every 500 feet along the section. Subsequently, layer thicknesses of these layers were then determined from before and after elevation measurements at each point where elevation measurements were made.

The measured layer thicknesses were recorded for each material layer type instead of for each relevant layer in the section layer structure. These layer thickness results at each measurement point are stored in the following tables:

The layer thickness measurements in the above tables are not keyed to individual layer numbers but are provided for each identified layer types. Aside from the section identification fields and coordination fields (STATION_NO and OFFSET), the following essential fields are contained in each of the above tables:

For SPS1_LAYER_THICKNESS:

Field Name Description
DENSE_GRADE_AGG_BASE Layer thickness measurement for dense graded aggregate base.
PERM_ASPH_TREAT_BASE Layer thickness measurement for permeable asphalt treated aggregate base
DENSE_GRD_ASPH_TREAT_BASE Layer thickness measurement for dense graded asphalt treated base
SURFACE_AND_BINDER Layer thickness measurement for surface coarse and binder course.
SURFACE_FRICTION Thickness of surface friction course layer

For SPS2_LAYER_THICKNESS:

Field Name Description
DENSE_GRADE_AGG_BASE Dense graded aggregate base layer.
PERM_ASPH_TREAT_BASE Permeable asphalt treated base layer.
LEAN_CONCRETE Lean concrete base layer.
PCC_SURFACE PCC surface layer.

For SPS5_LAYER_THICKNESS:

Field Name Description
RUT_LEVEL_UP Thickness of rut level-up layer.
MILL_REPLACE Thickness of mill replacement layer
BINDER_COURSE Thickness of binder course layer
SURFACE_COURSE Thickness of surface course layer.
SURFACE_FRICTION Thickness of surface friction course layer

For SPS6_LAYER_THICKNESS:

Field Name Description
DATE_BEGAN Date which operations began
RUT_LEVEL_UP Measurement of rut level-up layer after placement.
MILL_REPLACE Measurement of mill replacement layer after placement
BINDER_COURSE Measurement of binder course layer after placement.
SURFACE_COURSE Thickness of surface layer
SURFACE_FRICTION Thickness of surface friction course layer
LAYER_NO_RUT Layer number for each layer for which a layer thickness is shown.
LAYER_NO_MILL Layer number for each layer for which a layer thickness is shown.
LAYER_NO_BINDER Layer number for each layer for which a layer thickness is shown.
LAYER_NO_SURFACE Layer number for each layer for which a layer thickness is shown.
LAYER_NO_FRICTION Layer number for each layer for which a layer thickness is shown.

For SPS7_LAYER_THICKNESS

Field Name Description
DATE_BEGAN Date which operations began
SURFACE_COURSE Thickness of surface course layer.

For SPS8_LAYER_THICKNESS

Field Name Description
DATE_BEGAN Date which operations began
DENSE_GRADE_AGG_BASE Surface elevation for the dense graded agrregate base.
PORT_CEMENT_CONCRETE_SURFACE Surface elevation for the Portland Ccement Concrete surface.
ASPH_SURFACE_AND_BINDER Surface elevation for the asphalt surface and binder.
SURFACE_COURSE Thickness of surface friction course layer.

In addition to being provided at individual elevation measurement points, the summary layer thickness values (mean, minimum, maximum, and standard deviation) derived from elevation measurements are also stored in the LTPP database for individual layers for each section. These summaries are maintained in the following tables:

The following essential fields other than the section and layer identification fields are present in all the above tables:

Field Name Description
DESCRIPTION Code indicating general type of layer
MATERIAL_TYPE Code identifying type of material in each layer.
MEAN_THICKNESS The average thickness of each material layer.
MIN_THICKNESS The minimum thickness of each material layer.
MAX_THICKNESS Maximum thickness measurement
STD_DEV_THICKNESS Standard deviation of the thickness measurements.

The code list and descriptions for the "DESCRIPTION" field were previously given in table 1, while the code list and descriptions for field "MATERIAL_TYPE" (code name "MAT_TYPE") were previously provided in table 2.

Field Layer Material Type and Thickness Measurements

Material types and depths to strata top and strata bottom are identified or measured in the field from holes, test pits, and probes. Table TST_SAMPLE_LOG stores information about the samples taken from holes, pits, and probes, and is a good raw data source for unbound layers. However, records in this table are not keyed to the layer numbers as stored in TST_L05B and TST_L05A tables (field LAYER_NO). The thickness measurement from this table can only be manually matched to the layers established in the TST_L05B table. Nevertheless, this table can be used as raw layer thickness related data source and be consulted for unbound layer material type and thickness on a case-by-case basis.

The following essential fields other than the section and layer identification fields are present in table TST_SAMPLE_LOG:

Field Name Description
FIELD_SET Sequential number indicating the field sampling event. Assigned 1 for first sample event and incremented by 1 for subsequent events.
LOC_NO Unique code number assigned to each sampling location indicating the sample type. The single character prefix indicates the sample type. The numeric suffix is the unique project location for the sample type.
STRATA_LEVEL The sequential number of a stratum layer.
SAMPLE_NO Unique code number assigned to each material sample indicating the sample type and material type. The fist character indicates the sample type. The second character indicates the material type. The numeric suffix is the unique sample number for the sample type and material type.
MATERIAL_DESC Description of the material comprising the sample.
MATERIAL_CODE Code used to identify the material comprising the sample.
DEPTH_TOP_STRATA Depth to top of a stratum, measured from the surface.
DEPTH_BOT_ TRATA The depth to the bottom of a stratum, measured from the surface.
NO_BLOWS_1 Number of blows per 6 inches of penetration of the splitspoon sampler
NO_BLOWS_2 Number of blows per 6 inches of penetration of the splitspoon sampler.
NO_BLOWS_3 Number of blows per 6 inches of penetration of the splitspoon sampler.
REFUSAL Was splitspoon refused? [REFUSAL_S].
DLR Depth to refusal of a splitspoon sample.
IOP Inches of penetration of the splitspoon sampler.
DIAMETER Diameter of the sample.
MOIST_NO Sample number assigned to a sample to be used for moisture content testing.
BULK_NO The identification number assigned to the bulk sample.

The code list and descriptions for the field "MATERIAL_CODE" (code name "MATERIAL") are provided in table 9.

Table 9. Code list and code descriptions for code "MATERIAL".

Code Number Code Description for Code "MATERIAL"
1 Hot Mixed, Hot Laid AC, Dense Graded
2 Hot Mixed, Hot Laid AC, Open Graded
3 Sand Asphalt
4 Portland Cement Concrete (JPCP)
5 Portland Cement Concrete (JRCP)
6 Portland Cement Concrete (CRCP)
7 Portland Cement Concrete (Prestressed)
8 Portland Cement Concrete (Fiber Reinforced)
9 Plant Mix (Emulsified Asphalt) Material, Cold Laid
10 Plant Mix (Cutback Asphalt) Material, Cold Laid
11 Single Surface Treatment
12 Double Surface Treatment
13 Recycled AC, Hot Laid, Central Plant Mix
14 Recycled AC, Cold Laid, Central Plant Mix
15 Recycled AC, Cold Laid Mixed-In-Place
16 Recycled AC, Heater Scarification/Recompaction
17 Recycled Portland Cement Concrete, JPCP
18 Recycled Portland Cement Concrete, JRCP
19 Recycled Portland Cement Concrete, CRCP
20 Other
70 Grout
71 Chip Seal
72 Slurry Seal
73 Fog Seal
74 Woven Geotextile
75 Nonwoven Geotextile
77 Stress Absorbing Membrane Interlayer
78 Dense Graded Asphalt Concrete Interlayer
79 Aggregate Interlayer
80 Open Graded Asphalt Concrete Interlayer
81 Chip Seal with Modified Binder (Does not include crumb rubber)
82 Sand Seal
83 Asphalt-rubber Seal Coat
84 Sand Asphalt
85 Other
90 Plain Portland Cement Concrete (only used for SPS-7 overlays of CRCP)
100 Fine-Grained Soils: General
101 Fine-Grained Soils: Clay
102 Fine-Grained Soils: Lean Inorganic Clay
103 Fine-Grained Soils: Fat Inorganic Clay
104 Fine-Grained Soils: Clay with Gravel
105 Fine-Grained Soils: Lean Clay with Gravel
106 Fine-Grained Soils: Fat Clay with Gravel
107 Fine-Grained Soils: Clay with Sand
108 Fine-Grained Soils: Lean Clay with Sand
109 Fine-Grained Soils: Fat Clay with Sand
110 Fine-Grained Soils: Gravelly Clay
111 Fine-Grained Soils: Gravelly Lean Clay
112 Fine-Grained Soils: Gravelly Fat Clay
113 Fine-Grained Soils: Sandy Clay
114 Fine-Grained Soils: Sandy Lean Clay
115 Fine-Grained Soils: Sandy Fat Clay
116 Fine-Grained Soils: Gravelly Clay with Sand
117 Fine-Grained Soils: Gravelly Lean Clay with Sand
118 Fine-Grained Soils: Gravelly Fat Clay with Sand
119 Fine-Grained Soils: Sandy Clay with Gravel
120 Fine-Grained Soils: Sandy Lean Clay with Gravel
121 Fine-Grained Soils: Sandy Fat Clay with Gravel
131 Fine-Grained Soils: Silty Clay
132 Fine-Grained Soils: Silty Clay with Gravel
133 Fine-Grained Soils: Silty Clay with Sand
134 Fine-Grained Soils: Gravelly Silty Clay
135 Fine-Grained Soils: Sandy Silty Clay
136 Fine-Grained Soils: Gravelly Silty Clay with Sand
137 Fine-Grained Soils: Sandy Silty Clay with Gravel
141 Fine-Grained Soils: Silt
142 Fine-Grained Soils: Silt with Gravel
143 Fine-Grained Soils: Silt with Sand
144 Fine-Grained Soils: Gravelly Silt
145 Fine-Grained Soils: Sandy Silt
146 Fine-Grained Soils: Gravelly Silt with Sand
147 Fine-Grained Soils: Sandy Silt with Gravel
148 Fine-Grained Soils: Clayey Silt
151 Fine-Grained Soils: Peat
160 Fine-Grained Soils: Organic Soil
161 Fine-Grained Soils: Organic Soil with Gravel
162 Fine-Grained Soils: Organic Soil with Sand
163 Fine-Grained Soils: Gravelly Organic Soil
164 Fine-Grained Soils: Sandy Organic Soil
165 Fine-Grained Soils: Gravelly Organic Soil with Sand
166 Fine-Grained Soils: Sandy Organic Soil with Gravel
171 Fine-Grained Soils: Organic Clay
172 Fine-Grained Soils: Organic Clay (OL)
173 Fine-Grained Soils: Organic Clay (OH)
176 Fine-Grained Soils: Organic Silt
177 Fine-Grained Soils: Organic Silt (OL)
178 Fine-Grained Soils: Organic Silt (OH)
180 Treated Subgrade Soil
181 Fine-Grained Soils: Lime-Treated Soil
182 Fine-Grained Soils: Cement-Treated Soil
183 Bituminous Treated Subgrade Soil
200 Coarse-Grained Soils: General
201 Coarse-Grained Soils: Sand
202 Coarse-Grained Soils: Poorly Graded Sand
203 Coarse-Grained Soils: Poorly Graded Sand with Gravel
204 Coarse-Grained Soils: Poorly Graded Sand with Silt
205 Coarse-Grained Soils: Poorly Graded Sand with Silt and Gravel
206 Coarse-Grained Soils: Poorly Graded Sand with Clay
207 Coarse-Grained Soils: Poorly Graded Sand with Clay and Gravel
208 Coarse-Grained Soils: Well-Graded Sand
209 Coarse-Grained Soils: Well-Graded Sand with Gravel
210 Coarse-Grained Soils: Well-Graded Sand with Silt
211 Coarse-Grained Soils: Well-Graded Sand with Silt and Gravel
212 Coarse-Grained Soils: Well-Graded Sand with Clay
213 Coarse-grained soils: well-graded sand with clay and gravel
214 Coarse-grained soil: silty sand
215 Coarse-grained soil: silty sand with gravel
216 Coarse-grained soil: clayey sand
217 Coarse-grained soil: clayey sand with gravel
251 Coarse-grained soil: gravel
252 Coarse-grained soil: poorly graded gravel
253 Coarse-grained soil: poorly graded gravel with sand
254 Coarse-grained soil: poorly graded gravel with silt
255 Coarse-grained soil: poorly graded gravel with silt and sand
256 Coarse-grained soil: poorly graded gravel with clay
257 Coarse-grained soil: poorly graded gravel with clay and sand
258 Coarse-grained soil: well-graded gravel
259 Coarse-grained soil: well-graded gravel with sand
260 Coarse-grained soil: well-graded gravel with silt
261 Coarse-grained soil: well-graded gravel with silt and sand\
262 Coarse-grained soil: well-graded gravel with clay
263 Coarse-grained soil: well-graded gravel with clay and sand
264 Coarse-grained soil: silty gravel
265 Coarse-grained soil: silty gravel with sand
266 Coarse-grained soil: clayey gravel
267 Coarse-grained soil: clayey gravel with sand
280 Rock and stone
281 Shale
282 Rock
283 Cobbles
284 Boulders
285 Claystone \ Mudstone
286 Siltstone
287 Sandstone
288 Slag
289 Shale Chunk
290 Crushed sandstone

Once layer structure information was collected from different sources, the FHWA RSC's summarize these layer structure data into the following three LTPP tables:

Layer Material Type and Thickness Summary Data

Prior to completion of the L05 tables, the FHWA RSC evaluation personnel are required to review the following information:

Table TST_L05

The TST_L05 table contains layer material information for SPS projects only. Unlike the GPS studies, SPS projects consist of multiple test sections. To keep track of pavement layering and test results from various test sections, a "Project-Level Layering Structure" was developed and stored in table TST_L05. The ultimate purpose of the Project-Level Layering is 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. This project layering information in table TST_L05 is important to researchers interested in the material properties at the project level. The following is a list of the essential fields other than the SPS project identification fields in table TST_L05:

Field Name Description
PROJECT_LAYER_CODE A sequential alphabetic code assigned to identify group project wide layers
MATL_CODE INV_LAYER_NO_1 A code corresponding to the material type classification.
INV_LAYER_NO_2 The last layer in inventory to which the testing layer corresponds.
COMMENT_NOTE A comment providing additional information.

The code name for field "MATL_CODE" is "MATERIAL," and its code list and descriptions were previously given in table 9.

Table TST_L05A

TST_L05A includes field or laboratory determined material classification and measured thicknesses for a given pavement layer on a test section basis. TST_L05A is a final laboratory summary of pavement layering material and thickness information at each end of the pavement section, as well as within a section. The following essential information other than the section and layer identification fields is contained in this table:

Field Name Description
PROJECT_LAYER_CODE A sequential alphabetic code assigned to identify group project wide layers.
DESCRIPTION Code indicating general type of layer
LAYER_THICK_STATION 0 Thickness of layer at beginning of section (station 0-).
MATL_CODE_STATION 0 Material code at the beginning of a section (station 0-).
MEASURE_TYPE_1_STATION 0 Method used to take measurements at station 0-.
MEASURE_TYPE_2_STATION 0 Method used to take measurements at station 0-.
MEASURE_TYPE_3_STATION 0 Method used to take measurements at station 0-.
LAYER_THICK_WITHIN Thickness of layer within section.
MATL_CODE_WITHIN Material code within the section.
MEASURE_TYPE_1_WITHIN Method used to take measurements within the section
MEASURE_TYPE_2_WITHIN Method used to take measurements within the section.
MEASURE_TYPE_3_WITHIN Method used to take measurements within the section.
LAYER_THICK_STATION 5 Thickness of layer at end of section (station 5+).
MATL_CODE_STATION 5 Material code at the end of the SHRP section (station 5+).
MEASURE_TYPE_1_STATION 5 Method used to take measurements at station 5+.

 

Field Name Description
PROJECT_LAYER_CODE A sequential alphabetic code assigned to identify group project wide layers.
DESCRIPTION Code indicating general type of layer

 

Field Name Description
MEASURE_TYPE_2_STATION 5 Method used to take measurements at station  5+.
MEASURE_TYPE_3_STATION 5 Method used to take measurements at station 5+.

The code list and descriptions for the following fields were provided previously: DESCRIPTION (table 1), MATL_CODE_STATION0, MATL_CODE_ WITHIN, and MATL_CODE_STATION5 (code MATERIAL, table 9). The code list and descriptions for field LAYER_TYPE are provided in table 10. The code name for the following fields is "MEASURE_TYPE":

Table 10. Code list and code descriptions for code "LAYER_TYPE".

Code Item Code Description for Code "LAYER_TYPE"
AC Asphalt concrete layer
PC Portland cement concrete layer
TB Bound (treated) base
TS Bound (treated) subbase
GB Unbound (granular) base
GS Unbound (granular) subbase
SS Subgrade (untreated)
RB Rigid Layer used for backcalculation

The code list and descriptions for code "MEASURE_TYPE" are provided in table 11.

Table 11. Code list and code descriptions for code "MEASURE_TYPE"

Code Item Code Description for Code "MEASURE_TYPE"
1 Pavement Core (laboratory measurement)
2 Pavement Core (field core logs)
3 Core of Bound Base/Subbase
4 Borehole logs for BA1, BA2, BA3, and A1, A2, type boreholes
5 Shoulder Auger Probe Log
6 Shoulder Auger Probe Log
7 Other
8 No measurements conducted on this layer
9 Ground Penetrating Radar

Table TST_L05B

TST_L05B establishes the final pavement layer structure for each test section. All information available for the test section is used to derive this layer structure. Therefore, this table can potentially use data actually derived from the section itself, or if information is not available, data from other test sections in close proximity to the section. Table TST_L05B contains the following essential fields other than the section and layer identification fields:

Field Name Description
PROJECT_LAYER_CODE A sequential alphabetic code assigned to identify group project wide layers.
DESCRIPTION Code indicating general type of layer.
LAYER_TYPE A character code indicating the type of layer
REPR_THICKNESS The representative thickness for a layer in a section.
MATL_CODE Material code for the layer.
LAYER_COMMENT 1 Codes to describe any additional information concerning layer.
LAYER_COMMENT 2 Codes to describe any additional information concerning layer.
LAYER_COMMENT 3 Codes to describe any additional information concerning layer.
INV_LAYER_NO The first corresponding layer in INV_LAYER.
INV_LAYER_NO_2 The last layer in inventory to which the testing layer corresponds.

The code list and descriptions for the following fields were provided previously: DESCRIPTION (table 1), LAYER_TYPE (table 10) and MATL_CODE (code MATERIAL, table 9). The code name for field LAYER_COMENT 1, LAYER_COMENT 2, and LAYER_COMENT 3 is "L05B_COMMENT_CODES," and its code list and descriptions are provided in table 12.

Table 12. Code list and code descriptions for code "L05B_COMMENT_CODES".

Code Item Code description for Code "L05B_COMMENT_CODES"
A FWD data on section agree best with approach end sample location.
B FWD data agree best with leave end sample location.
C Profile and condition data agree best with approach end sample location.
D Profile and condition data agree best with leave end sample location.
E Gradations similar at section ends and averaged to determine material code.
F Gradations different at section ends, material code from approach end used.
G Gradations different at section ends, material code from leave end used.
H Atterberg limits similar at both section ends and average to determine material code.
I Atterberg limits different at both section ends. Material code from approach used.
J Atterberg limits different at both section ends. Material code from leave used.
K This layer absent at approach end.
L This layer absent at leave end.
M Layer inadvertently not stamped during drill and sample, but layer does exist.
N Information from the state DOT indicates that beginning end is more representative.
O Information from the state DOT indicates that leave end is more representative.
P Material code for layer derived from lab. Testing of adjacent test section
Q Layer thickness derived by measuring same material fro adjacent test section.
R Layer was partially removed by milling.
S Layer was completely removed by milling.
T Sampling only occurred at approach end.
U Sampling only occurred at leave end.
V No sampling at either end
Z Other (use column 8 to describe the action taken.)

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The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT).
The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT). Provide leadership and technology for the delivery of long life pavements that meet our customers needs and are safe, cost effective, and can be effectively maintained. Federal Highway Administration's (FHWA) R&T Web site portal, which provides access to or information about the Agency’s R&T program, projects, partnerships, publications, and results.
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