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This report is an archived publication and may contain dated technical, contact, and link information
Publication Number: FHWA-HRT-01-167
Date: April 2005

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

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CHAPTER 4. EXPERIMENTAL DESIGN VERSUS ACTUAL CONSTRUCTION

One of the main objectives of this study is to identify confounding factors introduced into the SPS-2 experiment by virtue of construction deviations or other factors not accounted for in the original experimental design. It is important to evaluate the variables that are considered as key design factors in the SPS-2 experiment and to determine if they meet the parameters established in the design factorial. Additionally, two SPS guideline reports established specific site-selection criteria and key variable construction guidelines.(11,12) The guidelines in both reports were developed to control the quality and integrity of the SPS-2 experiment results and findings, and therefore should be included in the construction adequacy evaluation.

This chapter evaluates the design and the actual construction of key variables identified in the experiment design factorial and the above-mentioned guidelines. This includes the following:

Climate

The experimental design specified that the SPS-2 sites be located in four specific climates:

The main purpose of this requirement was to obtain representative SPS-2 sections in widely varying climates, with a geographic distribution across the continental United States Table 28 shows a summary of the design requirements and actual precipitation data. All of the sites meet the criteria, except two that were supposed to be in dry areas (Kansas and North Dakota). The Kansas site is much wetter than the design limit, and the North Dakota site is just barely wetter than the limit.

What effect will these deviations have on achieving the objectives relative to climate? Analysis of the data will utilize the actual precipitation, not dry or wet variables. The only limitation is that the performance from the Kansas site will represent an area with greater precipitation than desired (819 mm versus 508 mm maximum or dry area); however, this site is still much drier than the corresponding wet sites. Kansas has 819 mm annual precipitation, and the other wet sites range from 865 to 1,380 mm with an average of 1,068 mm.

Table 28. Summary of the SPS-2 designed versus as-constructed sites, annual precipitation.

SPS-2 Project in State

Designated

Actual Precipitation, mm

Designated?

Zone

Precipitation, mm

From General Climatic Information

From AWSs

AZ

Dry

< 508

232.02

198.75

Check

AR

Wet

> 508

1380.55

-

Check

CO

Dry

< 508

369.74

344.00

Check

DE

Wet

> 508

1143.92

-

Check

IA

Wet

> 508

900.46

-

Check

KS

Dry

< 508

819.48

698.00

No

MI

Wet

> 508

865.59

871.00

Check

NV

Dry

< 508

221.51

249.33

Check

NC

Wet

> 508

1,150.78

1,198.50

Check

ND

Dry

< 508

544.61

534.00

No

OH

Wet

> 508

971.56

730.00

Check

WA

Dry

< 508

308.44

355.00

Check

WI

NA

NA

NA

NA

NA

The freezing index data are shown in table 29. As shown, all sites meet the criteria for freeze and non-freeze based on the annual freezing index criteria.

Table 29. Summary of the SPS-2 designed versus constructed sites, annual freezing index.

SPS-2 Project in State

Designated

Freezing Index, oC-days

Same as Designated?

Zone

Freezing Index, oC-days

From General Climatic Information

From AWSs

AZ

No-freeze

< 83.3

0.0

0.0

Check

AR

No-freeze

< 83.3

38.0

-

Check

CO

Freeze

> 83.3

327.4

394.0

Check

DE

Freeze

> 83.3

102.7

-

Check

IA

Freeze

> 83.3

579.7

-

Check

KS

Freeze

> 83.3

259.1

254.0

Check

MI

Freeze

> 83.3

381.9

140.0

Check

NV

Freeze

> 83.3

275.8

180.7

Check

NC

No-freeze

< 83.3

47.2

67.0

Check

ND

Freeze

> 83.3

1,313.1

1,162.0

Check

OH

Freeze

> 83.3

374.5

121.0

Check

WA

Freeze

> 83.3

264.8

138.0

Check

WI

NA

NA

NA

NA

NA


Subgrade

The SPS-2 experimental design called for half of the sites to be constructed on coarse-grained subgrade soils, and the other half to be constructed on fine-grained soils. Furthermore, it was required that all test sections at one site must be constructed on soils classified as same soil type, either fine-grained or coarse-grained.

Table 30 provides a comparison of the designated versus constructed subgrade types for all SPS-2 projects. Information from both cores taken from constructed pavements (TST_L05B table) and construction surveys (SPS2_LAYER table) is provided for comparison purposes. As indicated, for 11 of 13 SPS-2 projects, the subgrade soils are approximately uniform for all the core sections within the project. Furthermore, the soil types are now consistent between the designated and the constructed after correcting the subgrade type of the Washington SPS-2 project from fine-grained to coarse-grained. Further evaluation of the site data is needed to assess the significance of this finding.

For the Colorado site, the project was designed as a coarse-grained subgrade soil. However, four sections within the project were found to be constructed on fine-grained sandy clay soil. For the Nevada site, the project was designed as a coarse-grained soil. However, 9 out of the 11 sections were constructed on fine-grained sandy silt soil. Further evaluation is needed of the site data to assess the significance of this finding.

Table 30. Comparison of the SPS-2 designed versus constructed values for subgrade

SPS-2 Project in State

Assigned

From TST_L05B Table

From

Soil Type

Soil Type

No. Sections

Ok?

SPS2_Layer Table

AZ

Coarse

Coarse-grained: clayey sand with gravel or silty sand with gravel

12

Check

Clayey gravel or poorly graded gravel

AR

Fine

Fine-grained: silty clay

12

Check

Silty clay

CO

Coarse

Coarse-grained: clayey sand, poorly graded sand with silt, or well-graded sand with silt

8

Check

Clayey sand or poorly graded sand

Fine-grained: sandy clay or sandy lean clay

4

No

Sandy clay

DE

Coarse

Coarse-grained: clayey sand or silty sand

12

Check

Silty sand

IA

Fine

Fine-gained: clay with gravel

12

Check

Silty clay

KS

Fine

Fine-grained: silty clay

12

Check

Silty clay

MI

Fine

Fine-grained: sandy clay or silty clay

12

Check

Sandy clay

NV

Coarse

Coarse-grained: silty sand with gravel

2

Check

Silt

Coarse

Fine-grained: sandy silt

9

No

Silt

NC

Fine

Fine-grained: clay, clayey slit, sand silt, or sandy silty clay

12

Check

Silty clay

ND

Fine

Fine-grained: clay

12

Check

Silty clay

OH

Fine

Fine-grained: silty clay

12

Check

Silty clay

WA

Coarse

Coarse-grained: poorly graded gravel

12

Check

Poorly graded gravel or sandy silt

WI

Coarse

NA

12

Check

Silty sand

Traffic

In the original SPS-2 experimental design, traffic was incorporated as a covariant. The traffic rate of at least 200,000 ESALs per year was required. The required annual ESAL and actual ESALs per year are compared in table 31. As shown, this requirement was met for most of the sites and years, with exceptions of the annual traffic for Iowa 1997. The annual ESAL data are not completely available at the time of analysis for five SPS-2 sites (38 percent). The wide range of traffic loadings between sites will need to be fully considered in any comparative analysis between sites.

Table 31. Comparison of the designed versus actual values for annual traffic.

SPS-2 Project in State

Required ESALs per Year

Year Recorded

Annual ESALs from IMS Database

TRF_MONITOR_BASIC_INFO

No. of Sections

Avg.

Min

Max

AR

>200,000

-

-

-

-

-

AZ

>200,000

1994

1,343,854

1,333,149

1,352,180

12

AZ

>200,000

1995

725,978

722,887

731,911

12

AZ

>200,000

1996

1,091,263

1,086,667

1,095,274

11

CO

>200,000

1995

477,870

463,068

487,401

24

CO

>200,000

1996

341,187

334,124

346,082

12

CO

>200,000

1997

223,882

220,773

226,004

12

DE

>200,000

-

-

-

-

-

IA

>200,000

1997

56,406

56,125

57,013

12

KS

>200,000

1993

639,131

639,131

639,131

1

MI

>200,000

1993

596,967

588,953

602,291

12

MI

>200,000

1994

1,778,419

1,710,288

1,816,069

12

MI

>200,000

1996

1,495,685

1,445,548

1,524,539

12

MI

>200,000

1997

2,550,760

2,447,282

2,608,271

12

MI

>200,000

1998

1,661,157

1,620,051

1,684,665

12

NV

>200,000

1997

812,944

799,856

819,517

11

NC

>200,000

1994

779,957

738,986

804,407

12

NC

>200,000

1995

716,309

681,993

737,157

12

NC

>200,000

1996

816,174

774,908

841,857

12

NC

>200,000

1997

727,578

697,168

746,904

13

NC

>200,000

1998

792,086

761,745

809,605

12

ND

>200,000

-

-

-

-

-

OH

>200,000

-

-

-

-

-

WA

>200,000

1998

461,759

452,372

470,407

12

WI

>200,000

-

-

-

-

-

Concrete Slab Thickness

The SPS-2 experimental design specifies two levels for concrete slab thickness: 203 mm and 279 mm. The SPS-2 construction guideline requires that the concrete slab thickness should be constructed within "6.4 mm. Many sections did not meet this guideline. Therefore, for practical reasons, "12.7 mm was used as the thickness tolerance or the design range. Table 32 compares designed versus constructed or measured mean PCC thicknesses from table TST_L05B. Thirty-

Table 32. Designed versus mean constructed SPS-2 PCC slab thickness, mm.

State

Sections NOT Within Limit?

Section Number

0201, 0213

0202, 0214

0205, 0217

0206, 0218

0209, 0221

0210, 0222

0203, 0215

0204, 0216

0207, 0219

0208, 0220

0211, 0223

0212, 0224

Design Value: 203 (190 to 216), mm

279 (267 to 292), mm

AZ (0213-0224)

1

201

211

206

211

208

218

287

284

274

287

282

272

AR (0213-0224)

2 (all below)

188

211

191

188

208

213

284

277

282

272

277

277

CO (0213-0224)

6

221

213

218

196

211

221

290

300

282

282

300

297

DE (0201-0212)

7

211

224

234

226

208

211

297

279

287

307

300

315

IA (0213-0224)

5

216

213

196

208

239

211

300

295

284

290

297

295

KS (0201-0212)

1 (below)

196

188

198

201

216

211

282

287

287

279

282

277

MI (0213-0224)

3 (1 below)

218

226

216

180

208

213

284

290

277

282

279

284

NV (0201-0212)

5

234

208

216

198

226

257

302

300

277

279

287

-

NC (0201-0212)

4

229

259

203

213

218

213

284

284

295

284

290

277

ND (0213-0224)

0

208

201

201

201

206

208

279

284

277

277

282

274

OH (0201-0212)

0

201

211

203

201

206

203

277

282

282

279

290

269

WA (0201-0212)

4

221

211

216

218

229

211

282

284

282

284

300

287

WI (0213-0224)

NA

-

-

-

-

-

-

-

-

-

-

-

-

Summary

38 out of 143 sections (27%) are outside the design range, with 4 below and 34 above the limits.

Note: Bolded numbers are outside the design required range.

Table 33. Designed versus mean constructed SPS-2 PCC slab flexural strength, MPa.

State

Section Number

0201, 0203, 0205, 0207, 0209, 0211, or

0213, 0215, 0217, 0219, 0221, 0223

0202, 0204, 0206, 0208, 0210, 0212, or

0214, 0216, 0218, 0220, 0222, 0224

Design Value: 3.8 MPa

6.2 MPa

 

No. of Samples

Avg

StD

% Deviation

Average within 10%?

Average within 20%?

No. of Samples

Avg

StD

% Deviation

Average within 10%?

Average within 20%?

AZ (0213-0224)

3

3.94

0.07

3.73

Check

Check

6

5.77

0.40

-6.95

Check

Check

AR (0213-0224)

5

3.76

0.20

-1.04

Check

Check

2

4.59

1.56

-25.99

-

-

CO (0213-0224)

9

3.63

0.31

-4.54

Check

Check

9

6.25

0.40

0.77

Check

Check

DE (0201-0212)

3

4.53

0.69

19.15

-

Check

3

5.22

1.05

-15.85

-

Check

IA (0213-0224)

3

3.22

0.21

-15.32

-

Check

3

5.19

0.33

-16.22

-

Check

KS (0201-0212)

7

4.23

0.33

11.25

-

Check

6

5.81

0.34

-6.21

Check

Check

MI (0213-0224)

1

4.27

 

12.50

-

Check

2

6.71

0.02

8.15

Check

Check

NV (0201-0212)

3

3.60

0.22

-5.34

Check

Check

3

5.41

0.60

-12.70

-

Check

NC (0201-0212)

-

-

-

-

-

-

-

-

-

-

-

-

ND (0213-0224)

-

-

-

-

-

-

-

-

-

-

-

-

OH (0201-0212)

3

4.72

0.39

24.17

-

-

3

4.23

1.05

-31.75

   

WA (0201-0212)

4

3.34

0.38

-12.00

-

Check

3

5.73

0.24

-7.55

Check

Check

WI (0213-0224)

3

4.37

0.20

14.92

-

Check

4

6.09

0.36

-1.72

Check

Check

Summary

7 sites over 10% and 1 site over 20% deviation, with 2 sites below and 5 sites above the design value.

5 sites over 10% and 2 sites over 20% deviation, all below the design value.

8 of 143 SPS-2 sections (27 percent) fall outside of the design ranges (design value ±12.7 mm), with 4 sections having below-range values and 34 sections having above-range values. Twelve sections, all at the Wisconsin SPS-2 site, do not have thickness information in TST_L05B table at the time of analysis.

The frequency distributions of the tested slab thickness from table TST_L05B are provided in figure 4 for 203-mm design cells, and figure 5 for 279-mm design cells. As shown, 203-mm cell design sections have more scatter slab thickness distribution. Both the 203-mm and 279-mm mean thickness distribution shows a skew toward higher-than-designed thicknesses.

PCC Flexural Strength

The SPS-2 experimental design specifies two levels for concrete flexural strength at 14 days: 3.8 MPa and 6.2 MPa. Table TST_PC09 was examined to compare the designed and constructed flexural strength values. The 14-day concrete flexural strength data were found for 11 SPS-2 sites; North Carolina and North Dakota sites' flexural strength information was not available at the time of analysis.

The design versus constructed SPS-2 PCC slab flexural strength comparison results are given in table 33. For the 3.8 MPa design cells, 7 of the 11 sites (64 percent) have average tested flexural strength values 10 percent outside of the design range, and 1 site's values were 20 percent outside of the design range. For the seven sites that are 10 percent outside of the design range, two sites are below the design range (3.8 MPa) and five are above. For the 6.2 MPa design cells, 5 of the 11 sites (45 percent) have average tested flexural strength 10 percent outside of the design range, and 3 sites' data were 20 percent outside of the design range. All of these five sites fall below the design value of 6.2 MPa.

The frequency distributions of the tested flexural strength values are provided in figure 6 for 3.8 MPa design cells, and in figure 7 for 6.2 MPa design cells. As shown, the distribution of the 3.8 MPa design cells is closer to a normal distribution, while the distribution of the 6.2 MPa design cells is very skewed to the right.

Field studies have shown that PCC continues to gain strength over many years. The 1 year strength data may be more indicative of the actual strength over the 20-year pavement evaluation period than the 20-day data. The differences in strength levels at 1 year are very important. Time-series plots were generated for concrete strength, as shown in figures 8 to 10. For most sites, the time-series plot of the concrete strength remains more or less parallel between 3.8 MPa and 6.2 MPa cells. The frequency distributions of the 1-year modulus of rupture values are shown in figures 11 and 12. They remain two distinct distributions with some overlay.

Statistical t-tests were performed on both the 14-day concrete strength and 1-year concrete strength, and the results are presented in table 34. Even though the mean difference of the strength measurements decreases from 1.71 MPa at 14 days to 1.24 MPa at 1 year, the strength differences between the lower and higher strength concrete were still very significant at 1 year specimen age. This finding indicates that overall concrete strength values of the 6.2 MPa cells are still significantly higher than those of the 3.8 MPa cells at 1 year of pavement age.

 

Figure 4. Frequency distribution of the mean PCC slab thickness for SPS-2 203-millimeter cells. Bar graph. This figure shows PCC Slab Thickness (in millimeters) on the horizontal axis; Number of Sections on the left, vertical axis; and Percent of Sections on the right, vertical axis. The graphs shows about 4 sections (about 12 percent) for thicknesses between 180-190 millimeters, about 13 (40 percent) for 190-203 millimeters, about 32 (90 percent) for 203-216, about 17 (50 percent) for 216-228, about 5 (13 percent) for 228-241, and about 2 (6 percent) for 241-254. The frequency distribution graph (standard deviation plus/minus 12.7 millimeters) shows a skew toward higher-than-designed thicknesses slab thickness for SPS-2 203-millimeter cells.

Figure 4. Frequency distribution of the mean PCC slab thickness for SPS-2 203-mm cells.

Figure 5. Frequency distribution of the mean PCC slab thickness for SPS-2 279-millimeter cells. Bar graph.  This figure shows PCC Slab Thickness (in millimeters) on the horizontal axis; Number of Sections on the left, vertical axis; and Percent of Sections on the right, vertical axis. The graph shows about 15 sections (about 35 percent) for thicknesses between 267-279 millimeters, about 41 (90 percent) for 279-292 millimeters, about 14 (30 percent) for 292-305, about 2 (4 percent) for 305-318. The frequency distribution graph (standard deviation plus/minus 12.7 millimeters) shows a skew toward higher-than-designed thicknesses.

Figure 5. Frequency distribution of the mean PCC slab thickness for SPS-2 279-mm cells.

Figure 6. Frequency distribution of the 14-day modulus of rupture for SPS-2 3.8-megapascal cells. Bar graph.  This figure shows 14-Day Modulus of Rupture (in megapascals) on the horizontal axis; Number of Sections on the left, vertical axis; and Percent of Sections on the right, vertical axis. The graphs shows about 2 sections (about 10 percent) for 14-day modulus of rupture between 2.8-3.0 megapascals, about 5 (25 percent) for 3.0-3.4 megapascals, about 10 (50 percent) for 3.4-3.8, about 12 (60 percent) for 3.8-4.2 megapascals, about 6 (30 percent) for 4.2-4.6 megapascals, about 3 (15 percent) for 4.6-4.9 megapascals, and about 2 (10 percent) for 4.9-5.2 megapascals. The frequency distribution graph for 3.8 megapascals design cells (standard deviation plus/minus 10 percent) shows a closer to normal distribution.

Figure 6. Frequency distribution of the 14-day modulus of rupture for SPS-2 3.8-MPa cells.

Figure 7. Frequency distribution of the 14-day modulus of rupture for SPS-2 6.2-megapascal cells. Bar graph.  This figure shows 14-Day Modulus of Rupture (in megapascals) on the horizontal axis; Number of Sections on the left, vertical axis; and Percent of Sections on the right, vertical axis. The graphs shows about 2 sections (about 10 percent) for 14-day modulus of rupture between 3.0-3.7 megapascals, about 1 (5 percent) for 3.7-4.4 megapascals, about 3 (15 percent) for 4.4-5.0 megapascals, about 10 (50 percent) for 5.0-5.6 megapascals, about 15 (75 percent) for 5.6-6.2 megapascals, and about 10 (50 percent) for 6.2-6.8 megapascals. The frequency distribution graph for 6.2-megapascal design cells (standard deviation plus/minus 10 percent) is very skewed to the right.

Figure 7. Frequency distribution of the 14-day modulus of rupture for SPS-2 6.2-MPa cells.


Figure 8. Time-series plot of modulus of rupture for SPS projects in Arizona, Arkansas, and Colorado.  Graphs.  The figure contains three graphs showing Specimen Age (in days) on the horizontal axis and Modulus of Rupture (in megapascals) on the vertical axis. For the Arizona SPS-2: at a 14-day-strength of 3.8 megapascals, the modulus of rupture goes from 4-4.5 megapascals between 0-50 days and up to 6 megapascals at about 350 days; at a strength of 6.2 megapascals it is just under 6 megapascals from 0-50 days to just under 7 megapascals at about 350 days. For the Arkansas SPS-2: at a 14-day-strength of 3.8 megapascals, the modulus of rupture dips from nearly 4 to just over 3 megapascals between 0-50 days and goes up to 4.5 megapascals at about 350 days; at a strength of 6.2 megapascals it is around 4.5 megapascals from 0-50 days to about 6 megapascals at about 350 days. For the Colorado SPS-2: at a 14-day-strength of 3.8 megapascals, the modulus goes from 3.5-4 megapascals between 0-50 days and up to 4.5 megapascals at about 350 days; at a strength of 6.2 megapascals it stays around 6-6.5 megapascals during the time series.

Figure 8. Time-series plot of modulus of rupture for SPS projects in Arizona, Arkansas, and Colorado.


Figure 9. Time-series plot of modulus of rupture for SPS projects in Delaware, Iowa, and Kansas. Graphs.  The figure contains three graphs showing Specimen Age (in days) on the horizontal axis and Modulus of Rupture (in megapascals) on the vertical axis. For the Delaware SPS-2: at a 14-day-strength of 3.8 megapascals, the modulus of rupture goes from 4.5-5 megapascals between 0-50 days and up to 5.5 megapascals at about 350 days; at a strength of 6.2 megapascals it stays around 6 megapascals for the time series. For the Iowa SPS-2: at a strength of 3.8 megapascals, the modulus of rupture goes from 3-4 megapascals between 0-50 days to just over 4 megapascals at about 350 days; at a strength of 6.2 megapascals the modulus of rupture goes from 5 megapascals between 0-50 days to 6 megapascals at about 350 days. For the Kansas SPS-2: at a strength of 3.8 megapascals, the modulus goes from 4 megapascals between 0-50 days up to 5 megapascals at about 350 days; at a strength of 6.2 megapascals it stays around 6 megapascals during the time series.

Figure 9. Time-series plot of modulus of rupture for SPS projects in Delaware, Iowa, and Kansas.

Figure 10. Time-series plot of modulus of rupture for SPS projects in Nevada, Ohio, and Washington. Graphs.  The figure contains three graphs showing Specimen Age (in days) on the horizontal axis and Modulus of Rupture on the vertical axis (in megapascals). For the Nevada SPS-2: at a 14-day-strength of 3.8 megapascals, the modulus of rupture goes from 3.5-4 megapascals between 0-50 days to 4.25 megapascals at about 350 days; at a strength of 6.2 megapascals, it goes from 5.5-5.8 megapascals between 0-50 days to 6 megapascals at about 350 days. For the Ohio SPS-2: at a strength of 3.8 megapascals, the modulus of rupture goes from about 4.5 to 5.5 megapascals between 0-50 days and then to 6.25 megapascals at about 350 days; at a strength of 6.2 megapascals it goes from 4-5.8 megapascals between 0-50 days and up to 6.5 megapascals at about 350 days. For the Washington SPS-2: at a strength of 3.8 megapascals, the modulus goes from 3.3-4.3 megapascals between 0-50 days up to 4.8 megapascals at about 350 days; at a strength of 6.2 megapascals it goes from 5.8 to 6.8 at 0-50 days at down to 5.5 megapascals at about 350 days.

Figure 10. Time-series plot of modulus of rupture for SPS projects in Nevada, Ohio, and Washington.

Figure 11. Frequency distribution of the 1-year modulus of rupture for 3.8-megapascal cells. Graph.  The figure shows 1-year Modulus of Rupture (in megapascals) on the horizontal axis and Number of Sections on the vertical axis. For a modulus of rupture of 4.0-4.4, 4.4-4.8, 4.8-5.2, 5.2-5.6, 5.6-6.0, 6.0-6.4, 6.4-6.8, 6.8-7.2, 7.2-7.6, and 7.6-8.0, the number of sections are 8, 9, 10, 6, 4, 0, and 6 sections, respectively. The frequency distribution climbs steadily from 4-20 for modulus of rupture from 4.0-6.8 megapascals, except at 5.6-6.4 megapascals where the curve is flat.

Figure 11. Frequency distribution of the 1-year modulus of rupture for 3.8-MPa cells.

Figure 12. Frequency distribution of the 1-year modulus of rupture for 6.2-megapascal cells. Graph.  The figure shows 1-year Modulus of Rupture (in megapascals) on the horizontal axis and Number of Sections on the vertical axis. For a modulus of rupture of 4.0-4.4, 4.4-4.8, 4.8-5.2, 5.2-5.6, 5.6-6.0, 6.0-6.4, 6.4-6.8, 6.8-7.2, 7.2-7.6, and 7.6-8.0, the number of sections are 0, 0, 4, 1, 6, 8, 15, 6, 2, and 1 sections, respectively. The frequency distribution has an S-shape, going from zero to 20.

Figure 12. Frequency distribution of the 1-year modulus of rupture for 6.2-MPa cells.

 

The concrete strength factor should be examined in the future analysis to determine if it affects pavement performance. The actual strength measurements (instead of the target strength levels) should be used in any analysis due to the variation in strength of any given section.

Table 34. Summary statistics and t-test results for flexural strength data from all SPS-2 sites.

14-day Target

Strength

Summary Statistics

Specimen Age

14-day

365-day

3.8 MPa

Mean

3.91

5.11

Std. Dev

0.54

0.76

No. specimens

40

43

6.2 MPa

Mean

5.62

6.34

Std. Dev

0.79

0.68

No. specimens

41

43

Mean difference

1.71

1.24

t-Stat

11.4

8.4

P(T<=t)

<0.0001

<0.0001

Base Layer

The following base types and thicknesses are specified in SPS-2 experiment design:

IMS table TST_L05B was used to compare the designed versus constructed base types and thicknesses. The base types were confirmed to be constructed as designed for all the sections with base type information. For the base thicknesses, "13-mm tolerance was used for the design ranges. The comparison results are provided in table 35. Twenty out of 131 SPS-2 sections (15 percent) have representative base thicknesses outside the design range, with 3 sections having base thicknesses below the design range and 17 above the design range.

Table 35. Designed versus mean constructed base thickness, mm.

State

Sections NOT Within Limit?

Section Number

0201, 0213

0202, 0214

0203, 0215

0204, 0216

0205, 0217

0206, 0218

0207, 0219

0208, 0220

0209, 0221

0210, 0222

0211, 0223

0212, 0224

Design Value: 152 (140 to 165) mm

102 (89 to 114) mm

   

Base Type: DGAB

LCB

PATB

AZ (0213-0224)

0

150

155

155

157

155

157

158

155

104

97

107

112

AR (0213-0224)

NA

-

-

-

-

-

-

-

-

-

-

-

-

CO (0213-0224)

1

150

150

152

147

160

157

155

160

94

114

107

117

DE (0201-0212)

2

158

165

155

160

140

155

175

152

119

97

94

94

IA (0213-0224)

4 (1 below)

155

160

147

150

165

163

173

175

99

86

89

124

KS (0201-0212)

1 (below)

155

150

144

139

152

152

150

152

99

94

107

112

MI (0213-0224)

1

155

147

157

149

157

175

160

147

107

107

104

109

NV (0201-0212)

4

150

147

145

157

173

168

173

190

102

94

104

-

NC (0201-0212)

5 (1 below)

168

152

142

137

165

170

142

150

142

135

91

109

ND (0213-0224)

2

145

158

163

155

165

168

165

170

112

97

104

102

OH (0201-0212)

0

155

147

157

147

157

150

160

160

102

104

99

112

WA (0201-0212)

1

147

165

175

150

155

157

155

165

99

97

99

89

WI (0213-0224)

NA

-

-

-

-

-

-

-

-

-

-

-

 

Summary

21 out of 131 sections (16%) are outside the design range, with 3 below and 18 above the limits.

Note: Bolded numbers are outside the design required range.


Table 36. Designed versus mean constructed lane width, m.

State

Sections NOT Within Limit?

Section Number

0201, 0214

0204, 0215

0205, 0218

0208, 0219

0209, 0222

0212, 0223

0202, 0213

0203, 0216

0206, 0217

0207, 0220

0210, 0221

0211, 0224

Design Value: 3.66 m

4.27 m

AZ (0213-0224)

-

3.66

3.66

3.66

3.66

3.66

3.66

4.27

4.27

4.27

4.27

4.27

4.27

AR (0213-0224)

-

3.66

3.66

3.66

3.66

3.66

3.66

4.27

4.27

4.27

4.27

4.27

4.27

CO (0213-0224)

-

3.66

3.66

3.66

3.66

3.66

3.66

4.27

4.27

4.27

4.27

4.27

4.27

DE (0201-0212)

-

3.66

3.66

3.66

3.66

3.66

3.66

4.27

4.27

4.27

4.27

4.27

4.27

IA (0213-0224)

2

3.66

3.66

3.66

4.27

3.66

3.66

4.27

3.66

4.27

4.27

4.27

4.27

KS (0201-0212)

N/A

-

-

-

-

-

-

-

-

-

-

-

-

MI (0213-0224)

1

3.66

3.66

3.66

3.66

3.66

3.66

4.27

4.27

4.27

3.66

4.27

4.27

NV (0201-0212)

-

3.66

3.66

3.66

3.66

3.66

-

4.27

4.27

4.27

4.27

4.27

4.27

NC (0201-0212)

-

3.66

3.66

3.66

3.66

3.66

3.66

4.27

4.27

4.27

4.27

4.27

4.27

ND (0213-0224)

-

3.66

3.66

3.66

3.66

3.66

3.66

4.27

4.27

4.27

4.27

4.27

4.27

OH (0201-0212)

-

-

3.66

3.66

3.66

3.66

3.66

4.27

4.27

4.27

4.27

4.27

4.27

WA (0201-0212)

-

3.66

3.66

3.66

3.66

3.66

3.66

4.27

4.27

4.27

4.27

4.27

4.27

WI (0213-0224)

N/A

-

-

-

-

-

-

-

-

-

-

-

-

Summary

3 (of 131) sections are not as designated.

Note: Bolded numbers are outside the design required range.

Drainage (Edge Drains)

Edge drains were required for SPS-2 sections with PATBs. IMS table SPS_GENERAL contains drainage information for SPS-2 sections. Records were found for 130 SPS-2 sections in this table, and drainage designations were found to be as designed for all the sections.

Lane Width

The SPS-2 experimental design specifies two levels for lane width: standard lane width of 3.66 m, and widened lane width of 4.27 m. The lane width information contained in IMS table SPS-GENERAL was examined for the designed versus constructed data, as shown in table 36. Three of the 131 SPS-2 sections (2 percent) have different lane width values from the design specifications (sections 19-0216 and 19-0219 in Iowa, and 26-0220 in Michigan).

Summary

The experimental design specifications and the actual construction data of the key experimental factors for the SPS-2 project sites are summarized in table 37. As shown in the table, most SPS-2 sections meet the experimental design criteria for the large majority of the design factors. Most deviations from the experimental design are found for the concrete slab thickness and 14-day flexural strength.

A summary of experimental specifications versus as-constructed data for each SPS-2 project is provided in table 38.

Of the 13 SPS-2 projects, only the Wisconsin SPS-2 project does not have enough data in the IMS database to be evaluated. Eight projects can be characterized as good to excellent when comparing designed versus constructed data, while the remaining four projects are considered poor to fair.

Table 37. Designed versus constructed data summary for SPS-2 experiment.

Evaluation Element

Information Available (Total 13 sites, 155 sections)

Sites or Sections Not as Designed or Not Within Design Range

Climate

Annual precipitation

Freezing index

12 sites (missing WI)

12 sites (missing WI)

2 sites (KS and ND), both designated as in dry region but with over 508 mm annual precipitation.

Check (All okay)

Traffic

8 sites

(no data for AR, DE, ND, OH, WI)

2 sites (IA and WA). IA has annual ESAL of 56,406 in 1997. WA has annual ESAL of 819 in 1997.

14-day concrete flexural strength

11 sites

(no 14-day flexural strength data for NC and ND)

For the 3.8-MPa design cells, 7 of the 11 sites (64%) have average flexural strength falling 10% outside of the design value (1 site 20% outside of the design value).

For the 6.2-MPa design cells, 5 of the 11 sites (45%) have average flexural strength 10% outside of the design value (3 sites 20% outside).

Subgrade

13 sites

(WI site information comes from SPS-2 layer table)

2 sites (CO and NV). CO site has 4 sections not as designed. NV site has 9 sections not as designed.

Slab thickness

13 sections (missing all 12 sections from WI site)

38 sections are outside the design ranges (design ±12.7 mm), with 4 sections below and 34 above the design range.

Base types and thickness

131 sections

(missing all sections from KS and WI sites)

Base types are as designed. For base thickness, 21 sections are outside the design ranges (design ±12.7 mm), with 3 sections below and 18 above the design range.

Drainage

130 sections (missing all sections from KS and WI sites and 39-0201 in OH)

Check (All okay)

Lane width

131 sections (missing all sections from KS and WI sites).

3 sections: 19-0216 and 19-0219 in Iowa, and 26-0220 in Michigan.


Table 38. Designed versus constructed SPS-2 PCC.

SPS-2 Sites

Climatic Zone

Traffic

Subg. Type

Flexural Strength, MPa

Average cell Slab Thick. mm

Base/ Long. Drain.

Lane Width

Comments

3.8

6.2

203

279

AZ

Check

Check

Check

Check

Check

Check

Check

Check

Check

Excellent

AR

Check

-

Check

Check

No

(4.6)

Check

Check

Check

Check

Good

CO

Check

Check

No 4 sections

Check

Check

Check

Check

Check

Check

Good

DE

Check

Check

Check

No

(4.5)

No

(5.2)

No

No

Check

Check

Fair

IA

Check

No

Check

No

(3.2)

No

(5.2)

Check

No

Check

No- 2 sections

Poor

KS

Not Precip.

Check

Check

No

(4.2)

Check

Check

Check

-

Check

Good

MI

Check

Check

Check

No

(4.3)

Check

Check

Check

Check

No- 1 section

Good

NV

Check

Check

No 9 sections

Check

No

(5.4)

No

Check

Check

Check

Fair

NC

Check

Check

Check

-

-

No

Check

Check

Check

Good-missing data

ND

Not Precip.

-

Check

-

-

Check

Check

Check

Check

Good-missing data

OH

Check

-

Check

No

(4.7)

No

(4.2)

Check

Check

Check

Check

Good-missing data

WA

Check

Not 1997

Check

No

(3.3)

Check

No

Check

Check

Check

Fair

WI

-

-

-

No

(4.4)

Check

-

-

-

-

Not enough data

Check = Indicates as-constructed value meets as-designed criteria.

- = No data

 

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