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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 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.
  • Subgrade.
  • Traffic.
  • Concrete slab thickness.
  • PCC flexural strength.
  • Base layer.
  • Drainage (edge drains).
  • Lane width.

Climate

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

  • Wet freeze.
  • Wet no-freeze.
  • Dry freeze.
  • Dry no-freeze.

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:

  • DGAB-152 mm.
  • LCB-152 mm.
  • PATB-102 mm (on 102 mm DGAB).

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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