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| FHWA > Engineering > Pavements > Concrete > FHWA-RD-01-169 > Chapter 5 |
Rehabilitation of Jointed Portland Cement Concrete Pavements: SPS-6, Initial Evaluation and AnalysisCHAPTER 5. DESIGN VERSUS ACTUAL CONSTRUCTIONOne of the main objectives of this report is to identify factors introduced into the SPS-6 experiment by virtue of construction deviation or other factors not accounted for in the original experimental design. It is important to evaluate the design variables that are considered key design factors in the SPS-6 experiment and to determine if the as-constructed sections meet the design parameters established in the design factorial. Therefore, this section of the report evaluates the design construction versus the actual construction of key variables as defined by the guidelines for the experiment. The major guidelines established in these documents are described below: The first report, Guidelines for Nomination and Evaluation of Candidate Projects for Experiment SPS-6 Rehabilitation of Jointed Portland Cement Concrete Pavements, was used to nominate potential candidates for the SPS-6 experiment.(17) According to this report, several key guidelines were listed as follows:
The second report, Specific Pavement Studies Construction Guidelines for Experiment SPS-6, Rehabilitation of Jointed Portland Cement Concrete Pavements, establishes the rehabilitation guidelines for each of the SPS-6 sections.(18) This includes the following guidelines:
This report also defines the rehabilitation treatments to be applied for each experiment section type. This includes all mandatory and optional rehabilitation treatments, and specific rehabilitation treatments that should not be performed. This chapter evaluates the design construction versus the actual construction of key variables identified from the experimental design factorial and the experiment guidelines mentioned above. This includes:
SITE CLIMATIC CONDITIONAll sections in the LTPP program are classified by climatic region based on annual precipitation and the annual freezing index. It was determined that pavements that receive less than 508 mm (20 inches) of precipitation are located in a "dry" region, while precipitation greater than this amount indicates a "wet" region. Pavements located in areas where the annual freezing index is less than 83.3 degree-days (degrees Celsius (°C)) are classified as "no freeze" regions, while a value greater than this indicates a "freeze" region. These climatic zones were used to develop the original SPS-6 design matrix. Based on this classification system, each of the SPS-6 sites was selected to fill part of the original design matrix. The designated precipitation and freezing index zones are listed in tables 30 and 31, respectively. The actual annual precipitation and freezing index values for each site were obtained from the IMS tables CLM_VWS_PRECIP_ANNUAL and CLM_VWS_TEMP_ANNUAL, respectively, with the exception of the California site. The climatic information was not included in the database received from IMS. Therefore, the climatic information for California was obtained from the DataPave, version 2.0, software program. The average annual precipitation and freezing index values were then compared to those of the designated zone for each SPS-6 site. Tables 30 and 31 summarize the design versus constructed climatic results. As shown in these tables, most of the sections were constructed in the anticipated climatic zones. However, a few sections did not quite meet the criteria. According to the limits established by the LTPP program, the Arizona, California, and South Dakota sites should be classified as "wet" climatic zones. In addition, the Oklahoma and Tennessee sites should be classified as "freeze" climatic zones and the California sites should be classified as "no freeze" climatic zones. These changes in the designated climatic zones will alter the original experimental design matrix. This will result in more sites located in the wet-freeze zone and, consequently, fewer sites located in the wet-no freeze and dry-freeze zones.
1 mm= .039 inch *Information obtained from DataPave.
°F=1.8*°C+32 *Information obtained from DataPave. SITE TRAFFICTable 32 lists the average annual ESALs for each SPS-6 site. Alabama, Arkansas, Missouri (A), and Tennessee do not have any ESAL information in the IMS database. Arizona and California have negative ESAL values in the IMS database. These values are in error and should be corrected before further analysis is conducted. Of the remaining sites, only South Dakota does not meet the ESAL requirement of more than 200,000 rigid ESALs per year. However, based on the location of the site in South Dakota, the ESAL values appear to be correct even though they are lower than that required for the SPS-6 experiment.
N/A= not available Because of the existing condition of the calculated ESAL values, a brief review of the single- and tandem-axle distributions and the vehicle classification trends was conducted. In general, the traffic trends appear to be reasonable from year to year. Occasionally, it appears that 1 or 2 years of traffic data were not consistent with the rest of the years. These data should be reviewed and adjusted or corrected as required. CONSTRUCTION AGE OF ORIGINAL PCC AND REHABILITATED PAVEMENT SECTIONSAccording to the design guidelines, the original PCC pavement must have been constructed between 1965 and 1979. Most of the data obtained for this comparison were extracted from the INV_AGE table of the IMS database. Additional dates were obtained from the SPS construction forms/construction reports as noted. The ages of the original PCC pavements (constructed and opened to traffic) for each site are listed in table 33. Based on these results, most of the sites meet the design guidelines. It should be noted that, of the sites that do not meet the age criteria, Alabama, Illinois, Michigan, and Oklahoma are older than the construction age desired for the project. This should pose no significant problem in the analysis.
N/A= not available *Dates obtained from the SPS construction report or LTPP coordinating offices. PAVEMENT STRUCTURESeveral key parameters were developed for the pavement structure, including the subgrade, base, PCC, and AC overlay layers. Within each of these layers, there are key design components that will affect the overall quality of the SPS-6 experiment. Each key design component was evaluated and discussed as follows for each section within the experiment. This information was extracted from the TST_L05B table (levels A through E) unless specified otherwise. SubgradeThe initial guidelines established for this experiment identify the subgrade material type as a key design variable. Material TypeThe factorial design for this experiment identifies the fine-grained subgrade soils, such as silty clay materials (A-4, A-5, A-6, and A-7), as influencing factors; however, sections with coarse- grained subgrade soils will also be considered. Table 34 lists the subgrade material codes that were used in the SPS-6 experiment. Most of these codes refer to fine-grained subgrade materials. A few sections have subgrade materials classified as coarse-grained. Even though coarse-grained materials are not recommended for inclusion in this experiment, they are tolerated and, therefore, are included in the study. Table 35 shows the subgrade material codes for each core and supplemental section included in the experiment. As shown in the table, each section within the experiment has uniform subgrade materials. In addition, most of the sites generally have similar subgrade materials within the entire site. Only Arizona and California were constructed on coarse-grained subgrades. In addition, a couple of sections in Tennessee were also built on coarse-grained subgrade materials.
Base LayerThe initial guidelines established for this experiment identify the thickness of the existing base layer as a key variable in this experiment. ThicknessAs part of the selection criteria for the SPS-6 factorial design, all of the core sections should have a base thickness of at least 76 mm (3 inches). This thickness includes all stabilized or unstabilized base and subbase materials. Table 36 shows the average base thickness for each core and supplemental section included in the experiment. All of the core and State supplemental sections have thicknesses of at least 76 mm (3 inches) and, therefore, meet this criterion.
1 mm= 039 inch *Values listed are the "as-designed" values. PCC PavementThe initial guidelines established for this experiment identify the thickness of the existing PCC pavement to be rehabilitated as a key variable in this experiment. In addition, it was specified that the type, extent, and severity of distress should be relatively uniform over the entire project. It is nearly impossible to determine the uniformity of these distresses without the distress maps, which are not currently available. Therefore, at this time, this parameter could not be evaluated. ThicknessAs part of the selection criteria for the SPS-6 factorial design, all of the core sections should have a PCC thickness between 203 and 254 mm (8 and 10 inches). Table 37 shows the average PCC thicknesses for all core and supplemental sections included in the experiment. Because the State supplemental sections are not part of the design factorial established by the experiment, no PCC thickness limits were established for the supplemental sections. Figure 12 visually illustrates the ranges of constructed PCC thicknesses for the core experiment sections. This figure shows that 9 percent (8 sections) were less than, 89 percent (77 sections) were within, and 2 percent (2 sections) exceeded the proposed design thickness range of 203 to 254 mm (8 to 10 inches). Figure 12. Frequency of PCC thickness.
1 mm= 039 inch *Values listed are the "as-designed" values. AC Overlay ThicknessBased on the data stored in IMS for the SPS-6 experimental design plan, sections ***603, ***604, ***606, and ***607 were designed to have 102-mm (4-inch) AC overlays and section ***608 was designed with a 203-mm (8-inch) AC overlay. The allowable construction design thickness ranges from 95 to 108 mm (3.7 inches to 4.3 inches) for the 102-mm (4-inch) overlays and 190 to 216 mm (7.5 inches to 8.5 inches) for the 203-mm (8-inch) overlays. Table 38 shows the average AC overlay thicknesses as constructed for all core and supplemental sections included in the SPS-6 experiment. Because the State supplemental sections are not part of the design factorial established by the experiment, no AC overlay thickness limits were established. This information is visually illustrated in figures 13 and 14 for the core experiment sections with 102-mm (4-inch) and 203-mm (8-inch) AC overlays, respectively. Figure 13 shows that 16 percent (7 sections) were less than, 48 percent (21 sections) were within, and 36 percent (16 sections) exceeded the design thickness of 102 mm (4 inches). Likewise, figure 14 shows that 27 percent (three sections) were less than, 55 percent (six sections) were within, and 18 percent (two sections) exceeded the proposed design thickness of 203 mm (8 inches). INITIAL AC OVERLAY SMOOTHNESSThe initial smoothness of the AC overlays has also been identified as a key issue. It is important that the surface of an AC overlay be constructed to a sufficient smoothness. A high degree of variability in the pavement smoothness will result in a very rough riding surface. This constructed roughness may lead to early deterioration of the pavement because of vehicular response and dynamic loading. The smoothness of each AC overlay will be evaluated using the initial PI. Initial Profile IndexThe construction guidelines have noted the importance of AC surface smoothness on the finished surface of the overlay immediately after construction.(18) It is desirable that each AC overlay is smooth and provides an excellent level of ride; each overlay shall be evaluated using the prorated PI. A PI of less than 0.16 m/km (10 inches/mi) (5-mm (0.2-inch) blanking band) as measured by a California-type profilograph will achieve this goal.
1 mm= 039 inch *Values listed are the "as-designed" values. Figure 13. Frequency of 102-mm (4-inch) AC overlays.
Figure 14. Frequency of 203-mm (8 inch) AC overlays.
The PI values immediately after construction are listed in IMS table SPS6_QC_MEASUREMENTS. These results are listed in table 39. Unfortunately, this table only contains PI values for three States, and only a small percentage of these PI values meet the design criteria. In addition, the PI values for Missouri are significantly different than the Indiana and Iowa sites, indicating that Missouri data may, in fact, be another measure of roughness and should not be included in this IMS table. Therefore, it is not possible to accurately assess the PI value directly for each of the SPS-6 sites. However, a correlation exists between the PI and the International Roughness Index (IRI). Therefore, it can be determined whether these sections were approximately below the specified PI values immediately after construction based on the corresponding IRI values. This correlation is based on a study by Kalevela, Kombe, and Scofield(19) and is shown as follows (in English units of inches/mi): (1)AVG IRI= 52.9 + 6.1 * PI Based on a PI value of 0.16 m/km (10 inches/mi), the estimated average IRI is approximately 1.82 m/km (114 inches/mi). Table 40 lists the average IRI values for each section using the first average IRI rating available immediately after the AC overlay was placed. All average IRI data for these sections were collected between 2 and 13 months after placement of the AC overlay. All of the pavement sections listed meet this criterion. REHABILITATION TREATMENTSThe appropriate rehabilitation treatments for each section of the SPS-6 experiment are listed in table 41. A comparison of the designed rehabilitation treatments and the treatments applied to each section is summarized in tables 42 through 49. These tables provide an overview of the rehabilitation treatments applied at each section. More detailed information about the rehabilitation conducted is available in appendix A or in the construction reports. In general, the sections in poor condition received more treatments than the pavement sections in fair condition. From these tables, it can be noted that most of the SHAs completed the required rehabilitation treatments as designated for each section. In addition, most of the SHAs conducted some optional rehabilitation alternatives based on their pavement experience and the initial pavement condition prior to rehabilitation. A few of the SHAs also performed rehabilitation treatments that were specifically identified as treatments not to be performed. The required and optional treatments, and the treatments that were not to be performed, will have some effect on the performance of each pavement section and should be monitored closely.
1 inch/mi= 15.8 mm/km
1 m/km= 63.36 inches
1Optional treatment
1Optional treatment
1Optional treatment
1Required treatment
1Required treatment
1Required treatment
1Required treatment
1Required treatment IMPACT ON EXPERIMENTAL FACTORIAL DESIGNBased on the data available at the time of the IMS data request for each of these sites, the actual traffic and climatic information was used to reorganize the sites within the original design matrix. The climatic location of the Alabama site could not be verified at this time. In addition, the traffic levels for Alabama, Arizona, Arkansas, California, Missouri (A), and Tennessee could not be verified either. Additional information is needed in the IMS database to further verify the location of these sites within the design matrix. According to the climatic specifications of less than 508 mm (20 inches) of precipitation signifying a "dry" climatic zone and a freezing index of less than 83.3 degree-days signifying a "no freeze" climatic zone, the SPS-6 sites should be placed in the cells shown in table 50. Actual climatic data were used to relocate each site into the appropriate location within the design matrix. Bolded sites indicate that the site was designed and nominated for a different climatic zone than that supported by the as-built climatic data. In addition, the South Dakota site does not meet the minimum traffic requirement of more than 200,000 ESALs per year. As noted in table 50, many sites are now located in the wet-freeze climatic region. This will allow for a complete analysis of the wet-freeze climatic region. Unfortunately, many sites are now missing from the wet-no freeze, dry-freeze, and dry-no freeze zones. As mentioned earlier, each asterisk indicates that an additional site is needed to complete that portion of the design matrix. The impact of changing the climatic zones of the sites is only important in that it limits the range of climatic site conditions for which performance results are available for each climatic region. In other words, there is excellent coverage in the wet-freeze areas for both JPCP and JRCP, and excellent coverage for JPCP in wet-no freeze areas. There is no coverage of either JPCP or JRCP in dry areas.
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This page last modified on 06/08/06 |
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