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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 Concrete Pavements: SPS-2—Initial Evaluation and Analysis

Chapter 6. initial Evaluation of Key Performance Trends

This chapter provides an initial review and evaluation of the key performance trends for the SPS-2 project. Note that this initial evaluation is cursory in nature, because it is not within the scope of this study to conduct a comprehensive evaluation. Furthermore, the long-term performance may be different from short-term performance. The following key performance data are reviewed:

  • Edge joint faulting.
  • Transverse cracking.
  • Longitudinal cracking.
  • Pavement smoothness.

The SPS-2 project sites are relatively young pavements, ranging from 2 years old in Wisconsin to 7.5 years old in Kansas. Therefore, as expected, most SPS-2 sections are showing good performance and low distress levels. Table 52 summarizes the SPS-2 sections showing noticeable distress, along with key pavement design factors. (Noticeable distress is defined as a section that has a mean edge faulting greater than 1.0 mm or that exhibits longitudinal or transverse cracking.) As of January 2000, only 43 out of 155 sections (28 percent) showed any noticeable distress.

Because of the very low distress level of most sections, distress prediction models were not developed at this time. However, an initial evaluation of what affects the distressed sections was conducted. The results of the distress and profile data review and evaluation are presented in the following sections.

Note that these are early performance trends; the long-term performance may be different.

JOINT FAULTING REVIEW AND EVALUATION

The distribution of the mean joint faulting values (the lane at edge) in SPS-2 sections, recorded as of January 2000, is illustrated in figure 13. Note that these values are the maximum mean faulting values recorded over the life of the section to date.

Ninety-five percent of the SPS-2 sections (148 sections) currently have a mean edge faulting less than 1 mm. Of the seven sections having greater than 1-mm faulting, six were constructed with an aggregate base and one was constructed with a lean concrete base. Additionally, three sections are from the heavily trafficked Michigan SPS-2 project site, and two sections are from the Nevada SPS-2 project site.

Table 52. SPS-2 sections with noticeable distress.

Section ID Age as of Jan. 2000 Climate Zone Subgrade Base / Drain Lane Width, m Slab Thick mm 14-day F.S. MPa Maximum Distress Recorded
State SHRP Fault mm Trans. Cracks, % slab cracked Long, Cracks, length, m
4 0213 6.3 DNF Coarse AGG 4.27 201 3.9 0.4 0 5
4 0215 6.3 DNF Coarse AGG 3.66 287 3.9 1.1 0 0
4 0217 6.3 DNF Coarse LCB 4.27 206 3.9 -0.1 15 11
4 0218 6.3 DNF Coarse LCB 3.66 211 5.8 0 24 11
4 0219 6.3 DNF Coarse LCB 3.66 274 3.9 -0.1 0 2
4 0220 6.3 DNF Coarse LCB 4.27 287 5.8 0.8 6 1
4 0221 6.3 DNF Coarse PATB/Drain 4.27 208 3.9 0.8 0 8
4 0222 6.3 DNF Coarse PATB/Drain 3.66 218 5.8 0.5 0 2
8 0217 6.3 DF Coarse LCB 4.27 218 3.6 0.4 30 12
8 0218 6.3 DF Coarse LCB 3.66 196 6.2 1.0 3 0
8 0221 6.3 DF Coarse PATB/Drain 4.27 211 3.6 0.1 0 1
8 0222 6.3 DF Coarse PATB/Drain 3.66 221 6.2 0.1 0 1
10 0205 3.7 WF Coarse LCB 4.27 234 4.5 1.3 30 15
10 0207 3.7 WF Coarse LCB 4.27 287 4.5 0 0 46
19 0213 5.4 WF Fine AGG 4.27 216 3.2 0.4 0 3
19 0217 5.4 WF Fine LCB 3.66 196 3.2 0.4 6 0
19 0218 5.4 WF Fine LCB 3.66 208 5.2 0.3 3 0
20 0201 7.5 WF Fine AGG 4.27 196 4.2 0 21 8
20 0202 7.5 WF Fine AGG 4.27 188 5.8 0 12 11
20 0206 7.5 WF Fine LCB 4.27 201 5.8 0 0 2
26 0213 6.2 WF Fine AGG 3.66 218 4.3 1.2 9 0
26 0214 6.2 WF Fine AGG 3.66 226 6.7 1.4 0 0
26 0215 6.2 WF Fine AGG 4.27 284 4.3 2.6 6 0
26 0217 6.2 WF Fine LCB 3.66 216 4.3 0.3 0 6
26 0218 6.2 WF Fine LCB 3.66 180 6.7 0.9 36 20
32 0201 4.4 DF Coarse AGG 4.27 234 3.6 1.0 100 119
32 0202 4.4 DF Coarse AGG 4.27 208 5.4 1.1 100 170
32 0203 4.4 DF Coarse AGG 3.66 302 3.6 0.8 100 107
32 0204 4.4 DF Coarse AGG 3.66 300 5.4 1.4 70 11
32 0205 4.4 DF Coarse LCB 4.27 216 3.6 0.8 100 216
32 0206 4.4 DF Coarse LCB 4.27 198 5.4 0.3 100 273
32 0207 4.4 DF Coarse LCB 3.66 277 3.6 0.8 6 18
32 0208 4.4 DF Coarse LCB 4.27 279 5.4 0.8 85 18
32 0210 4.4 DF Coarse PATB/Drain 4.27 257 5.4 0.8 94 12
32 0211 4.4 DF Coarse PATB/Drain 3.66 287 3.6 0.8 12 2
37 0201 5.5 WNF Fine AGG 4.27 229   0.9 0 4
37 0210 5.5 WNF Fine PATB/Drain 4.27 213   0.1 6 0.2
38 0217 5.3 WF Fine LCB 4.27 201   0.1 12 26
38 0224 5.3 WF Fine PATB/Drain 3.66 274   0.5 0 9
39 0205 3.3 WF Fine LCB 4.27 203 4.7 0.5 9 0
39 0206 3.3 WF Fine LCB 3.66 201 4.2 0 0 21
53 0205 4.2 DF Coarse LCB 3.66 216 3.3 0.5 3 0
53 0206 4.2 DF Coarse LCB 4.27 218 5.7 0.6 61 53

Figure 13. Distribution of the mean joint faulting values for SPS-2 sections (total 155 sections). Bar and pie chart. In the bar graph, the figure shows Joint Faulting (in millimeters) on the horizontal axis and Number of Sections on the vertical axis. For faulting of less than 0.5, 0.5-1.0, and greater than 1.0, there are 120, 30, and 5 sections, respectively. In the pie chart, the figure shows joint faulting by percent of sections. Faulting of less than 0.5, 0.5-1.0, and greater than 1.0 corresponds to 76 percent, 19 percent, and 5 percent of sections, respectively.

Figure 13. Distribution of the mean joint faulting values for SPS-2 sections (total 155 sections).

Figure 14. Mean edge joint faulting for different categories. Bar chart. This figure shows Design Features or Site Conditions on the horizontal axis and Mean Edge Faulting (in millimeters) on the vertical axis. Design features DNF, WNF, DF, and WF correspond to approximate faultings of 0.4, 0.15, 0.56, and 0.25, respectively. Design features AGG, LCB, and PATB/Drain correspond to approximate faultings of 0.4, 0.29, and 0.28, respectively. Design features "Not widened" and "Widened" correspond to approximate faultings of 0.38 and 0.29, respectively.

Figure 14. Mean edge joint faulting for different categories.

The mean edge faulting for different groups of design features or site conditions is depicted in figure 14. The following conclusions can be drawn from this initial evaluation:

  • Climatic zone-Joint faulting is the most prevalent in the dry freeze zone, followed by the dry no-freeze zone and the wet freeze zone. Sections in the wet no-freeze climate have the least faulting so far.
  • Base type-Sections with an aggregate base have the highest joint faulting level. Sections with an LCB and PATB have the lowest joint faulting.
  • Widened slab-Widened slab sections are showing less faulting than conventional width slabs.

An example of a faulting time history trend using data from the Michigan SPS-2 project site is provided in figure 15. Faulting measurements from different sections were averaged by base types. The aggregate base type shows the highest faulting trend over time.

TRANSVERSE CRACKING REVIEW AND EVALUATION

The distribution of the transverse cracking is depicted in figure 16. As of January 2000, 82 percent of the sections had zero transverse cracks. However, 5 percent (eight sections) of the SPS-2 sections showed more than 50 percent slabs cracked. As shown in table 52, all eight sections are from at the Nevada SPS-2 project site, which was less than 4.5 years old. This excessive early cracking appears to indicate serious construction problems at the site. A review of the field distress maps will be very helpful in explaining these cracking observations.

Figure 15. Sample faulting time history plot-heavily trafficked Michigan SPS-2 sections by base types. Graph. In a line graph, the figure shows Survey Date on the horizontal axis and Joint Faulting (in millimeters) on the vertical axis. Faulting was graphed between the dates January 31, 1992 to April 19, 2001 for three types of sections: Average for sections with AGG base; Average for sections with LCB; and Average for sections with PATB/Drain. Faulting for all three averages tracked about the same, starting at zero before June 15, 1994, rising to around 0.3-0.4 around June 15, 1994, falling to zero around March 11, 1997, rising to about 0.2 around July 24, 1998, and falling to zero or slightly negative on December 6, 1999. The only exception is that the AGG base sections jumped from zero on March 11, 1997, to about 1.3 on July 24, 1998 and then falling to about 0.8 on December 6, 1999.

Figure 15. Sample faulting time history plot-heavily trafficked Michigan SPS-2 sections by base types.

Due to the excessive cracking at the Nevada site, the cracking data from that site were not included in the following evaluation. The mean percentage of slabs cracked transversely, grouped by design features or site conditions, is given in figure 17. The following preliminary conclusions can be drawn from these mean value comparisons:

  • Climatic zone-The percentage of slabs cracked transversely is highest in the dry no-freeze zone, followed by the wet freeze and dry freeze zones. The smallest percentage is in sections in the wet no-freeze zone.
  • Base type-Sections with PATB show the lowest percentage of slabs cracked transversely, while the sections with an LCB show the highest transverse cracking.
  • Slab thickness-Thinner (203-mm) slabs show more transverse cracks than thick slabs.

A sample time history for transverse cracking, using data from the Michigan SPS-2 project site, is shown in figure 18. Section 260218, which has a very thin slab and LCB, shows the highest level of cracking. Nine of 12 sections (75 percent) show no transverse cracking.

LONGITUDINAL CRACKING REVIEW AND EVALUATION

The distribution of longitudinal cracking is shown in figure 19. As of January 2000, 78 percent of the sections have no longitudinal cracks, whereas 4 percent (6 sections) have more than 50 m longitudinal cracking. Five of these six sections are at the Nevada SPS-2 project site, which was less than 4.5 years old at that time. Again, this excessive early cracking indicates serious construction problems at the site, and a review of the field distress maps will be very helpful in explaining these cracking observations. The Nevada site data were not included in the following plots and analyses.

Figure 16. Distribution of the transverse cracking for SPS-2 sections (total 155 sections). Bar and pie chart. In the bar chart, the figure shows Percent Slabs Cracked on the horizontal axis and Number of Sections on the vertical axis. There were about 125 sections that showed 0 percent cracked, 20 slabs showed between 0-50 percent cracked, and less than 10 sections with greater than 50 percent cracked. In a pie chart, the percent slabs cracked and percent of sections is shown, with percent slabs cracked of 0, 0-50, and greater than 50 corresponding to 8 percent, 13 percent, and 5 percent of sections, respectively.

Figure 16. Distribution of the transverse cracking for SPS-2 sections (total 155 sections)

Figure 17. SPS-2 mean percentage of slabs cracked transversely for different categories. Bar chart. This figure shows Design Features or Site Conditions on the horizontal axis and Mean Percent of Slabs Cracked Transversely. Design features AGG, LCB, and PATB/Drain correspond to approximate percent slabs of 1.0, 3.9, and 0.2, respectively. Design features WF, DF, WNF, and DNF correspond to percent slabs of 1.6, 1.7, and 3.8, respectively. Design features 203-millimeter slab and 279-millimeter slab correspond to 3.2 and 0.2 percent slabs, respectively.

Figure 17. SPS-2 mean percentage of slabs cracked transversely for different categories.

Figure 18. Sample time history plot for transverse cracking-Michigan SPS-2 project. In a line graph, Survey Date is shown on the horizontal axis and Percent Slabs Cracked Transversely is shown on the vertical axis. Slabs cracked was graphed for sections 0213, 0214, 0215, 0216, 0217, 0218, 0219, 0220, 0221, 0222, 0223, and 0224. All sections showed no cracking transversely except for the following: Section 0218, which is a 180-millimeter slab (very thin) on LCB, went from 0 to about 34 to about 37 percent cracking over a 2-year period; section 0213, which is a widened 218-millimeter slab on AGG base, had 10 percent cracked over a 1-year period; and section 0215, which is a 284-millimeter slab on AGG base, showed around 6 percent cracked in about a 1-year period.

Figure 18. Sample time history plot for transverse cracking, Michigan SPS-2 project site.

The average total longitudinal crack length per section for different groups of design features or site conditions is given in figure 20. The conclusions drawn from these comparisons are very similar to those for transverse cracking.

  • Climatic zone-The total longitudinal crack length is largest in the dry no-freeze zone, followed by the dry freeze and wet freeze zones. The smallest crack length is found in sections in the wet no-freeze zone.
  • Base type-Sections with PATB show the lowest total longitudinal cracking levels, while the sections with an LCB show the highest longitudinal cracking.
  • Slab thickness and widened slab-Thinner (203-mm) slabs show more longitudinal cracks. Sections with a thinner slab and widened slab show by far the highest level of longitudinal cracking by far.

A sample time history for the longitudinal cracking, using data from the Michigan SPS-2 project site, is provided in figure 21. Again, section 260218 shows the highest level of cracking. Ten out of 12 sections (83 percent) show no longitudinal cracking.

PAVEMENT SMOOTHNESS REVIEW AND EVALUATION

Pavement smoothness affects ride quality, and therefore is a very important performance indicator. In this study, the initial IRI and the IRI over time were both evaluated.

Figure 19. Distribution of the longitudinal cracking for SPS-2 sections (total 155 sections). Bar and pie chart. In a bar graph, the figure shows Total Crack Length (in meters) on the horizontal axis and Number of Sections on the vertical axis. There were about 120 sections that showed no cracks, about 30 showed 0 to 50-meter cracks, and fewer than 5 showed greater than 50-meter crack lengths. In a pie chart, Total Crack Length (in meters) and Percent of Sections was graphed. 78 percent of total sections had 0-meter crack lengths, 18 percent of sections had 0 to 50-meter crack lengths, and only 4 percent of sections showed crack lengths greater than 50 meters.

Figure 19. Distribution of the longitudinal cracking for SPS-2 sections (total 155 sections).

Figure 20. SPS-2 mean total longitudinal cracking for different categories. Bar Graph. The figure shows Design Features or Site Conditions on the horizontal axis and Mean Longitudinal Crack Length in meters on the vertical axis. The Mean Longitudinal Crack Length are as follow for the Design Feature/Site Conditions: AGG is about 0.6 m, LCB is about 4.6 m, PATB/Drain is about 0.4 m, 203-mmnot widened is about 1.7 m, 203-mm widened is about 4.4 m, 279-mm not widened is about 0.1 m, 279-mm widened is about 1.6 m, WF is about 2 m, DR is about 2.8 m, WNF is about 0.2 m, and DNF is about3.3 m.

Figure 20. SPS-2 mean total longitudinal cracking for different categories.

Figure 21. Sample time history plot for longitudinal cracking-heavily trafficked Michigan SPS-2 project. Graph. In a line graph, the figure shows Survey Date on the horizontal axis and Total Longitudinal Crack Length (in meters) on the vertical axis. Crack length was graphed between the dates January 31, 1993 and April 19, 2001 for sections 0213-0224. Only two sections had crack lengths greater than zero. Section 0218 (180-millimeter slab, very thin, on LCB) had lengths of about 16 meters, and then 20 meters on surveys over about a 1-year period. Section 0217 (widened 216-millimeter slab on LCB) had crack lengths of about 6 meters over a 2-year period.

Figure 21. Sample time history plot for longitudinal cracking-heavily trafficked Michigan SPS-2 project.

Initial IRI Measurements

The initial IRI measurements represent the smoothness of the pavement soon after construction. Previous studies showed that initial smoothness significantly affects future smoothness of the pavements. For SPS-2 sections, the distribution of the initial IRI is shown in figure 22. The mean initial IRI was 1.30 m/km, and ranged from 0.76 to 2.19 m/km.

The effects of the key design features on initial IRI were analyzed statistically. An analysis of variance (ANOVA) was conducted that showed the following factors as significant:

  • JPCP constructed on coarse-grained subgrades were smoother than those constructed on fine-grained subgrade soil. This could be due to a stiffer foundation upon which to build the pavement.
  • Permeable base with edge drain or aggregate base (versus lean concrete base) was found to be smoother. It has commonly been thought that it is more difficult to build a smooth pavement on a permeable base than on a treated base, but these results show this to not be the case for SPS-2 sites.
  • Widened slab sections were smoother than conventional slab sections.
  • Thinner slabs and lower 14-day strength concrete slabs were constructed smoother than thicker and higher 14-day strength slabs.

The mean initial IRI values for different design features and site conditions are shown in figure 23.

No. of Sections
Figure 22. Distribution of the initial IRI for SPS-2 sections (total 155 sections, mean equals 1.30 meters per kilometer). Bar chart. This figure shows Initial IRI (in meters per kilometer) on the horizontal axis and Number of Sections on the vertical axis, with a line of distribution charted over the bar graph. The distribution shows that the mean initial IRI was 1.30 meters per kilometer and ranged from 0.76 to 2.19 Initial IRI.

Figure 22. Distribution of the initial IRI for SPS-2 sections (total 155 sections, mean = 1.30 m/km).

Figure 23. SPS-2 mean initial IRI for different site conditions and design features. Bar chart. This figure shows Design Features or Site Conditions on the horizontal axis and Mean Initial IRI (in meters per kilometer) on the vertical axis. IRI were as follows for each of the Design Features/Site Conditions: Coarse, about 1.20; Fine, about 1.38; AGG, about 1.28, LCB, about 1.38; PABT/Drain, about 1.25; Not widened, about 1.33; Widened, about 1.25.

Figure 23. SPS-2 mean initial IRI for different site conditions and design features.

IRI Evaluation

The IRI of each SPS-2 section was measured over time. The maximum value over time was determined and analyzed (typically, this occurred at the latest survey date). Distribution of the maximum IRI of all SPS-2 sections as of January 2000 is shown in figure 24. A majority of the SPS-2 sections (66 percent) are still very smooth, with an IRI less than 1.5 m/km. However, three sections are very rough, with an IRI greater than 2.5 m/km. These three sections are all in Michigan (sections 260214, 260217, and 260218).

It is a common belief that smoothness or IRI over time is a function of the initial IRI, cumulative traffic, and surface distresses. A multiple regression analysis was conducted on the maximum IRI, and the following regression model was developed:

(1)IRI = 0.08777 + 0.993 * Init_IRI + 0.1630 Fault (1)
+ 0.006045 * KESAL* Survey_Age

R2 = 72% SEE = 0.192 N = 56
Where: IRI=IRI value at SPS-2 sections over time, m/km. Init_IRI=Initial IRI measurements, m/km. KESAL=Average annual KESAL (1,000 equivalent single axle loads). Survey_Age=Age when IRI was measured, year. Fault=Mean joint faulting, mm.

This model shows that the initial IRI, joint faulting, and total KESALs (Age * annual KESALs) affect future IRI values. Transverse cracking and longitudinal cracking did not show significant effects on future IRI. This may be due to the low severity levels of these cracks at SPS-2 sections.

SUMMARY

The SPS-2 sections are relatively young, and a large majority show little distress. As of January 2000, only 43 of 155 sections (28 percent) are showing any noticeable distresses. Ninety-five percent of the SPS-2 sections have less than 1 mm of edge joint faulting. Eighty-seven percent of the SPS-2 sections show zero transverse cracking, and 78 percent of the sections have zero longitudinal cracking.

Based on the preliminary statistical analyses and comparisons, the following preliminary and early performance trends are observed (note that long-term performance may be different from short-term performance):

  • The initial IRI of SPS-2 sections ranged from 0.76 to 2.19 m/km with a mean of 1.30 m/km. JPCP constructed on coarse-grained soil were smoother (lower IRI) than those constructed on fine-grained soils. JPCP constructed on PATB were smoother than those constructed on other base types.
  • The IRI over time (up to 7.5 years) depended heavily on the initial IRI, the traffic loadings, and the extent of joint faulting.
  • Sections with PATB show the lowest total longitudinal cracking levels, while the sections with LCB show the highest longitudinal cracking.
  • Thinner (203 mm) slabs show more longitudinal cracks. Sections with a thinner slab and widened slab show the highest level of longitudinal cracking.
  • Sections with PATB are showing the lowest percentage of slabs cracked transversely, while the sections with LCB show the highest transverse cracking.
  • Thinner (203 mm) slabs show more transverse cracks than thicker slabs. Sections with a thinner slab and a widened slab show the highest level of transverse cracking.
  • Sections with aggregate base show the highest joint faulting level. Sections with an LCB and PATB have the lowest joint faulting.
  • Widened slab sections show less faulting than conventional width slabs.
  • The Nevada SPS-2 site sections showed excessive cracking after only 4 years, most of which occurred during construction. These sections will need special care in analysis of the data.

Figure 24. Distribution of the IRI for SPS-2 sections (January 2000) (total 155 sections). Bar and pie chart. In the bar graph, the figure shows IRI (in meters per kilometer) on the horizontal axis and Number of Sections on the vertical axis. Following are the number of sections for each IRI: 0.5-1.0, about 8 sections; 1.0-1.5, about 95 sections; 1.5-2.0, 40 sections; 2.0-2.5, about 10 sections; greater than 2.0, about 2 sections. In the pie chart, IRI (in meters per kilometer) and Percent of Sections were graphed as follows: less than 1.5, 66 percent, 1.5-2.0, 26 percent, 2.0-2.5, 6 percent, greater than 2.5, 2 percent.

Figure 24. Distribution of the IRI for SPS-2 sections (January 2000) (total 155 sections).

 

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