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Publication Number: FHWA-HRT-01-167
Date: April 2005

Structural Factors of Jointed Plain Concrete Pavements: SPS-2—Initial Evaluation and Analysis

Chapter 2. Evaluation of The SPS-2 Experiment

The first step in the evaluation of the SPS-2 experiment is to assess how much of the original experiment was actually constructed and what effect missing sites will have on obtaining expected findings. The original SPS-2 experiment design, the SPS-2 experimental sites actually constructed, the effects of blank experimental design cells, and potential information available from the SPS-2 supplemental sites are discussed in this chapter.

Original SPS-2 Experiment Design

The complete experiment design factorial, the site classification category, and individual section identification numbers are given in table 1. This design factorial requires a total of 16 SPS-2 sites and 192 core sections be evenly distributed within the factorial matrix of climate and subgrade to satisfy the requirement of the SPS-2 experiment design.

The experiment design for SPS-2 included eight main factors. Three are project site factors, and the remaining five are related to the pavement structure.

Project Site Factors

Three factors describe site conditions at the test site:

  1. Climatic—Temperature - Freeze and no-freeze
  2. Climatic—Precipitation - Wet and dry
  3. Subgrade - Fine-grained and coarse-grained

Traffic loading was incorporated as a covariant. Each of the SPS-2 sites required relatively high rate of traffic of at least 200,000 rigid equivalent single-axle loads (ESALs) per year.

The experiment design factorial at the project site level is provided in table 2. The design factorial calls for a total of 16 SPS-2 sites to be constructed throughout the United States.

Pavement Structure Design Factors

In addition to the three site factors, five experiment design factors were allocated to the pavement structure. Two factors were allocated to the surface layer: one for thickness and one for strength. Two other structural factors were allocated to the base/sub base: one for strength/stability and the other for drainage. The last factor was assigned to the width of the pavement slab. In summary, the SPS-2 experiment incorporates the following pavement structural factors:

  1. Slab thickness - 203 and 279 millimeters (mm)
  2. Concrete flexural strength - 3.8 and 6.2 megapascals (MPa) at 14-days
  3. Base type and drainage - Dense-graded aggregate base (DGAB)
    - Lean concrete base (LCB)
    - Permeable asphalt-treated base (PATB) with edge drains
  4. Slab width - 3.66 and 4.27 meters (m)

 

Table 1. Original SPS-2 experiment design.
Pavement Structure SPS-2 Site Designation
J K L M N O P Q R S T U V W X Y
Edge Drain Base Type PCC Lane Width, m Climate Zones, Subgrade
Wet Dry
Thick mm Strength MPa Freeze No-Freeze Freeze No-Freeze
Fine Coarse Fine Coarse Fine Coarse Fine Coarse
No AGG 203 3.8 3.66 01   01   01   01   01   01   01   01  
4.27   13   13   13   13   13   13   13   13
6.2 3.66   14   14   14   14   14   14   14   14
4.27 02   02   02   02   02   02   02   02  
279 3.8 3.66   15   15   15   15   15   15   15   15
4.27 03   03   03   03   03   03   03   03  
6.2 3.66 04   04   04   04   04   04   04   04  
4.27   16   16   16   16   16   16   16   16
No LCB 203 3.8 3.66 05   05   05   05   05   05   05   05  
4.27   17   17   17   17   17   17   17   17
6.2 3.66   18   18   18   18   18   18   18   18
4.27 06   06   06   06   06   06   06   06  
279 3.8 3.66   19   19   19   19   19   19   19   19
4.27 07   07   07   07   07   07   07   07  
6.2 3.66 08   08   08   08   08   08   08   08  
4.27   20   20   20   20   20   20   20   20
Yes PATB 203 3.8 3.66 09   09   09   09   09   09   09   09  
4.27   21   21   21   21   21   21   21   21
6.2 3.66   22   22   22   22   22   22   22   22
4.27 10   10   10   10   10   10   10   10  
279 3.8 3.66   23   23   23   23   23   23   23   23
4.27 11   11   11   11   11   11   11   11  
6.2 3.66 12   12   12   12   12   12   12   12  
4.27   24   24   24   24   24   24   24   24

Notes: Test section numbers included in cells from 01 to 24 represent a full factorial experiment.

AGG = Dense-graded untreated aggregate base.

LCB = Lean concrete base.

PATB = Permeable asphalt-treated base.

 

Table 2. SPS-2 experiment design-project site factorial.
Subgrade Climatic Condition
Wet Dry
Freeze No-Freeze Freeze No-Freeze
Fine J N R V
K O S W
Coarse L P T X
M Q U Y

Note: Two related sites (e.g., J and K, T and U) make up a full factorial of design features.

The total full factorial designs for combination of the study factors result in 24 different experimental pavement structures (2 thickness x 2 strength x 3 base type x 2 lane width = 24). The experiment design was implemented using a one-half fractional factorial approach that permitted construction of 12 test sections at one site and construction of the 12 complementary sections at another site within the same climatic region and with a similar subgrade type. Both of these complementary sites must be available to evaluate the main effects and all interactions of the design factors within a given climate and subgrade type.

Each SPS-2 test section length is 152 m long. As a result, an SPS-2 project may be constructed over a length greater than 3.2 kilometers (km). Other key design features common to all SPS-2 sections include the following:

  • Joint spacing-4.6 m uniform spacing.
  • Joint load transfer-Doweled perpendicular transverse joints, with 32-mm dowel bars for the 203-mm-thick pavements and 38-mm dowel bars for 279-mm-thick pavements. Dowels are to be epoxy coated, 457 mm long, and spaced at 305 mm.
  • Longitudinal joints-Between lanes the joints should be saw cut, preferably using up to an 8-mm-wide blade, to a depth of D/3 (where D equals slab thickness). The sealant reservoir may be formed later using a second saw cut to provide for an 8-mm-wide by 25-mm-deep cut.
  • Joint sealing-All joints shall be sealed before opening to traffic. Joint sealing shall be accomplished using only silicone sealant.
  • Shoulder-Either AC or portland cement concrete (PCC) shoulders. PCC shoulders shall not be tied to the mainline pavement. If the concrete shoulder is placed monolithically with the traffic lanes, then the shoulder joint shall be sawed full depth.

At each SPS-2 site, test sections are numbered sequentially either from 01 to 12 or from 13 to 24, depending on climatic and soil type combinations. The numbering within each site depends on the levels of each design factor. Figure 1 graphically presents the section structure and numbering schematic for SPS-2 sections.

Figure 1. Test section details for a full factorial SPS-2 experiment located at two sites (01 to 12 and 13 to 24). Diagram. This figure presents the following information: For sections with lane widths of 3.66 meters and using 3.8 megapascals PCC:Section Number 1, Using 203-millimeter PCC over 152-millimeter DGA Base.Section Number 15, Using 279-millimeter PCC over 152-millimeter DGA Base.Section Number 5, Using 203-millimeter PCC over 152-millimeter LCB.Section Number 19, Using 279-millimeter PCC over 152-millimeter LCB.Section Number 9, Using 203-millimeter PCC over 102-millimeter PATB and 102-millimeter DGA Base.Section Number 23, Using 279-millimeter PCC over 102-millimeter PATB and 102-millimeter DGA Base. For sections with lane widths of 3.66 meters and using 6.2 megapascals PCC:Section Number 14, Using 203-millimeter PCC over 152-millimeter DGA Base.Section Number 4, Using 279-millimeter PCC over 152-millimeter DGA Base.Section Number 18, Using 203-millimeter PCC over 152-millimeter LCB.Section Number 8, Using 279-millimeter PCC over 152-millimeter LCB.Section Number 22, Using 203-millimeter PCC over 102-millimeter PATB and 102-millimeter DGA Base.Section Number 12, Using 279-millimeter PCC over 102-millimeter PATB and 102-millimeter DGA Base.For sections with lane widths of 4.27 meters and using 3.8 megapascals PCC:Section Number 13, Using 203-millimeter PCC over 152-millimeter DGA Base.Section Number 3, Using 279-millimeter PCC over 152-millimeter DGA Base.Section Number 17, Using 203-millimeter PCC over 152-millimeter LCB.Section Number 7, Using 279-millimeter PCC over 152-millimeter LCB.Section Number 21, Using 203-millimeter PCC over 102-millimeter PATB and 102-millimeter DGA Base.Section Number 11, Using 279-millimeter PCC over 102-millimeter PATB and 102-millimeter DGA Base.For sections with lane widths of 4.27 meters and using 6.2 megapascals PCC:Section Number 2, Using 203-millimeter PCC over 152-millimeter DGA Base.Section Number 16, Using 279-millimeter PCC over 152-millimeter DGA Base.Section Number 6, Using 203-millimeter PCC over 152-millimeter LCB.Section Number 20, Using 279-millimeter PCC over 152-millimeter LCB.Section Number 10, Using 203-millimeter PCC over 102-millimeter PATB and 102-millimeter DGA Base.Section Number 24, Using 279-millimeter PCC over 102-millimeter PATB and 102-millimeter DGA Base.

Figure 1. Test section details for a full factorial SPS-2 experiment located at two sites (01 to 12 and 13 to 24).

Current Status of Design Factorial

As of August 1999, 13 SPS-2 sites had been constructed throughout the United States An additional site in California had been nominated and may be constructed in the near future. The distribution of the SPS-2 sites is shown on a map in figure 2. The current status of the site design factorial is provided in table 3,showing which State is filling which design cell. As shown in the table, there are five study sites missing from the experiment factorial, indicating a loss of 5 of the 16 (or 31 percent) of the design cells.

Figure 2. Geographic distribution of the constructed SPS-2 projects. Map. This figure is a map of the United States that shows regular and supplemental sections in the States of Arizona, Arkansas, Colorado, Iowa, Kansas, Michigan, Nevada, New Jersey, North Carolina, North Dakota, Ohio, Washington, and Wisconsin. California is shown as having a site under construction.

Figure 2. Geographic distribution of the constructed SPS-2 projects.

 

Table 3. SPS-2 projects constructed in relation to the project site factorial (note missing cells).
Subgrade Climatic Condition
Wet Dry
Freeze No-Freeze Freeze No-Freeze
Fine Ohio, Kansas1 (J) North Carolina (N) ? (R) ? (V)
Michigan, Iowa (K) Arkansas (O) North Dakota2 (S) ? (W)
Coarse Delaware (L) ? (P) Nevada,
Washington (T)
California3 (X)
Wisconsin (M) ? (Q) Colorado (U) Arizona (Y)

Notes:
1 - Kansas site was planned to fill the dry-freeze zone cell. However, the actual precipitation is quite a bit higher than the specified annual precipitation for this study.
2 - North Dakota site is slightly wetter than the specified annual precipitation.
3 - California site is currently under construction.
? - Represents a missing SPS-2 project.

A list of all the SPS-2 sections, including both core and supplemental sections, is given in table 4. As shown, many SHAs have constructed additional sections at the SPS-2sites. These additional sections are not included in the original SPS-2 experiment factorial and are referred to as State supplemental sections. A total of155 core sections and 40 supplemental sections have been constructed to date. Seven SPS-2 sections are designated as seasonal monitoring program (SMP) sections, where additional sets of climatic and monitoring data are measured.

 

Table 4. List of constructed SPS-2 core and supplemental sections.
State State Code Core Sections Supplemental Sections Seasonal Sections
ID Record Status
AZ 04 0213-0224 E 0260-0268 (9) 0215
AR 05 0213-0224 E - -
CO 08 0213-0224 E 0259 -
DE 10 0201-0212 E 0259-0260 (2) -
IA 19 0213-0224 E 0259 -
KS 20 0201-0212 E 0259 -
MI 26 0213-0224 E 0259 -
NV 32 0201-0211

(0212 was removed)
E 0259 0204
NC 37 0201-0212 E 0259-0260 (2) 0201, 0205, 0208, 0212
ND 38 0213-0224 E 0259-0264 (6) -
OH 39 0201-0212 E 0259-0265 (7) 0204
WA 53 0201-0212 E 0259 -
WI 55 0213-0224 A 0259-0266 (8) -
Total number of sections 155 40 7

Potential Effects of Missing Experimental Sites

The current status of the SPS-2 experiment design, showing constructed sections in relation to the original experiment design, is given in table 5. The following five sites (columns) are missing from the original experiment design:

  • Two sites in the wet no-freeze climate (southeast U.S.)with a coarse-grained subgrade. Each project fills half of the design factorial.
  • One site in the dry freeze climate (northwest U.S.)with a fine-grained subgrade.
  • Two sites in the dry no-freeze climate (southwest U.S.), one with a fine-grained subgrade and the other with a coarse-grained subgrade. Each site fills half of the design factorial.

 

Table 5. Current status of SPS-2 experiment.
Pavement Structure Climate Zones, Subgrade, Site
Wet Dry
Base Type/ Edge Drain PCC Lane Width m Freeze No-Freeze Freeze No-Freeze
Thick mm Flexural Strength MPa Fine Coarse Fine Coarse Fine Coarse Fine Coarse
J K L M N O P Q R S T U V W X Y
AGG 203 3.8 3.66 OH, KS   DE   NC           NV, WA       CA1  
4.27   MI, IA   WI   AR       ND   CO       AZ
6.2 3.66   MI, IA   WI   AR       ND   CO       AZ
4.27 OH, KS   DE   NC           NV, WA       CA1  
279 3.8 3.66   MI, IA   WI   AR       ND   CO       AZ
4.27 OH, KS   DE   NC           NV, WA       CA1  
6.2 3.66 OH, KS   DE   NC           NV, WA       CA1  
4.27   MI, IA   WI   AR       ND   CO       AZ
LCB 203 3.8 3.66 OH, KS   DE   NC           NV, WA       CA1  
4.27   MI, IA   WI   AR       ND   CO       AZ
6.2 3.66   MI, IA   WI   AR       ND   CO       AZ
4.27 OH, KS   DE   NC           NV, WA       CA1  
279 3.8 3.66   MI, IA   WI   AR       ND   CO       AZ
4.27 OH, KS   DE   NC           NV, WA       CA1  
6.2 3.66 OH, KS   DE   NC           NV, WA       CA1  
4.27   MI, IA   WI   AR       ND   CO       AZ
PATB w/ Drain 203 3.8 3.66 OH, KS   DE   NC           NV, WA       CA1  
4.27   MI, IA   WI   AR       ND   CO       AZ
6.2 3.66   MI, IA   WI   AR       ND   CO       AZ
4.27 OH, KS   DE   NC           NV, WA       CA1  
279 3.8 3.66   MI, IA   WI   AR       ND   CO       AZ
4.27 OH, KS   DE   NC           NV, WA       CA1  
6.2 3.66 OH, KS   DE   NC           WA       CA1  
4.27   MI, IA   WI   AR       ND   CO       AZ

Notes: 1 - California site is under construction.

Five additional projects (60 sections total) are needed to complete the design factorial. These missing projects will definitely limit the results obtainable from the SPS-2 experiment, although it is impossible to determine the exact effects at this time. These limitations are summarized as follows:

  • There will be no performance data, and thus, no performance findings from the missing sites.
  • The missing section at the Nevada site will reduce the findings for that site and corresponding cell, although there appears to be replication at the Washington site.
  • SPS-2 sites exist in wet-freeze climates, making a full inference space of performance data available. All main effects and interactions should be ascertainable in this climate.
  • SPS-2 sites are deficient in wet and dry no-freeze climates. There will be difficulties in determining the main effects and interactions in these climates.

Some of these deficiencies can be overcome through use of mechanistic analysis of the data. However, there is no mechanistic analysis that considers all factors involved, and the missing cells will always present limitations in the verification and calibration of any performance models.

State Supplemental Sections

In addition to the 12 core sections required by the SPS-2 experiment, SHAs can include additional experimental sections, referred to as State supplemental sections. Although there were provisions in the experimental design to study un doweled JPCP and jointed reinforced concrete pavements (JRCP), no such controlled sections have been constructed other than some uncontrolled supplemental sections. Table 6 lists the design variables selected by SHAs for supplemental sections.

The main value of the supplemental sections will be as direct comparison to the core sections. For example, one supplemental section in Washington did not have dowels;this will provide a direct comparison to a similar design with dowel bars. This comparison is also possible in Arizona and North Dakota. Various other comparisons are also possible, including skewed joints, base types,sub drainage, slab thickness, AC pavement, jointed reinforced concrete, special dowels, and variable slab thickness.

 

Table 6. List of the constructed SPS-2 State supplemental sections and designs.
State SHRP ID Pavement Design Description
AZ 0260 216 mm dense-graded AC on 102 mm DGAB.
0261 216 mm dense-graded AC on 102 mm DGAB.
0262 203 mm undoweled JPC (3.8 MPa Resilient Modulus (MR)) on DGAB and 4.27 m lane.
0263 203 mm undoweled JPC (3.8 MPa MR) on PATB and DGAB and 4.27 m lane.
0264 279 mm undoweled JPC (3.8 MPa MR) on PATB and DGAB and 3.66 m lane.
0265 279 mm undoweled JPC (3.8 MPa MR) on DGAB and 3.66 m lane.
0266 318 mm doweled JPC (3.8 MPa MR) on bituminous treated base (BTB) and 4.27 m lane.
0267 279 mm doweled JPC (3.8 MPa MR) on BTB and 4.27 m lane.
0268 203 mm doweled JPC (3.8 MPa MR) on BTB and 4.27 m lane.
CO 0259 279 mm JPC (4.5 MPa) on subgrade and 3.66 m lanes.
DE 0259 254 mm JPC (20.7 MPa f'c) on 203 mm DGAB; 3.66 m lane; steel dowels.
0260 254 mm JPC (20.7 MPa f'c) on 203 mm DGAB; 3.66 m lane; plastic dowels.
IA 0259 279 mm JPC; 4.27 m wide lane.
KS 0259 305 mm doweled JPC (4.1-MPa mix) on 152 mm stabilized subbase on 152 mm modified fly ash subgrade and 3.66 m lane.
MI 0259 267 mm JRC on 102 mm open-graded base course (OGBC) on 76 mm aggregate base.
NV 0259 267 mm JPC on 38 mm leveling course, 27.6 MPa +- 20% 14-day compressive strength.
NC 0259 254 mm JPC on 102 mm PATB on 25.4 mm AC on 203-mm lime-stabilized subgrade.
0260 279 mm JPC on 25.4 mm AC on 127 mm BTB on 203-mm cement-treated subgrade.
ND 0259 254 mm doweled JPC (ND mix) on 203 mm salve with skewed joints and 3.66 m lanes.
0260 279 mm doweled JPC (ND mix) on DGAB with skewed joints and 4.27 m lanes.
0261 279 mm undoweled JPC (3.8 MPa MR) on DGAB with skewed joints and 3.66 m lanes.
0262 279 mm undoweled JPC on LCB with skewed joints (various lengths) and 4.27 m lanes.
0263 279 mm undoweled JPC on PATB with random skewed joints and 3.66 m lanes.
0264 279 mm undoweled JPC on PATB with skewed joints and 4.27 m lanes.
OH 0259 279 mm JPC (3.8 MPa MR) on 152 mm DGAB.
0260 279 mm JPC (3.8 MPa MR) on 102 mm PATB on 102 mm DGAB.
0261 279 mm JPC (3.8 MPa MR) on 102 mm CTPB on 102 mm DGAB.
0262 279 mm JPC on 102 mm CTPB on 102 mm DGAB.
0263 279 mm JPC on 152 mm DGAB.
0264 279 mm JPC on 152 mm DGAB.
0265 279 mm JPC (3.8 MPa MR) on 102 mm PATB on 102 mm DGAB.
WA 0259 Undoweled 254 mm JPC (4.5 MPa MR) on 76 mm ATB on 51 mm crushed surfacing base course; 4.27 m lane.
WI 0259 279 mm JPC (3.8 MPa MR) on 152 mm DGAB.
0260 279 mm JPC (3.8 MPa MR) on 152 mm DGAB, with alternate dowel bar placement.
0261 203 mm JPC (3.8 MPa MR) on 102 mm OGBC on 102 mm DGAB.
0262 203 mm JPC (6.3 MPa MR) on 152 mm DGAB, with tied concrete shoulder.
0263 203-279 mm JPC (3.8 MPa MR) on 152 mm DGAB, variable pavement thickness.
0264 279 mm JPC (3.8 MPa MR) on 152 mm DGAB, with composite dowels.
0265 279 mm JPC (3.8 MPa MR) on 152 mm DGAB, with stainless steel dowels.
0266 Unknown

Note: The Arkansas SPS-2 project site does not contain any supplemental sections.

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