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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
REPORT |
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Publication Number: FHWA- HRT-17-095 Date: September 2017 |
Publication Number: FHWA- HRT-17-095 Date: September 2017 |
Pavement deflection data are typically collected by State transportation departments at the project level and rarely at the network level. However, most LTPP test sections were subjected to deflection testing on a periodic basis. The deflection data were collected using the most common type of equipment, the FWD. FWD tests are often preferred over laboratory testing for several reasons, including the following:(78,83)
The FWD operates on two basic assumptions: the force of impact of a falling weight is considered a static load, and the roadbed soils act as an elastic body.(83) The deflection data collected from FWD testing are typically used for the following purposes:
At the time of this report, research was exploring methods to increase the efficiency of deflection data collection by using a rolling wheel deflectometer (RWD). The RWD collects pavement deflection data at highway speeds and makes network-level data collection more feasible. It was reported that the results were used to flag structurally deficient pavement sections for further analyses and to estimate the structural number.(83,84) In this study, the LTPP deflection data were analyzed to determine whether the data could be used to estimate the RSP of pavement sections and to determine the critical time for pavement preservation.
The RSP algorithm is primarily based on the measured time-dependent pavement surface condition and distress data and their corresponding threshold values. Hence, the distress (such as cracking) must be visible from the pavement surface. During the development of the RFP and RSP concepts, it was envisioned that the pavement deflection data could be used to indicate impending distress and become a part of the RSP algorithm. Such algorithms would empower State transportation departments to take corrective actions prior to the manifestation of surface defects.
To incorporate deflection into the RSP algorithm, a deflection threshold value must be developed for each pavement section. To investigate the potential for the development of deflection threshold values, the measured FWD deflection data of various LTPP test sections were analyzed as described in the next few subsections.
At the outset, it was envisioned that the rate of change and the magnitude of the measured deflections were related to the measured pavement distresses such as alligator cracking. Because alligator cracks initiate at the bottom of the asphalt layer and propagate upward toward the pavement surface, the pavement system starts to weaken as the cracks initiate and before they reach the pavement surface. Therefore, it was assumed that flexible pavement deflections would start to increase before the appearance of alligator cracking on the pavement surface (i.e., the response of a pavement structure to load would increase as the pavement deteriorated, which could be used as an early warning of impending, surface alligator cracking). Similarly, for rigid pavements, increasing the magnitude of deflection could be a sign of deterioration of the concrete slab support. Such deterioration could lead to distresses such as transverse cracking, corner breaks, and so forth. Again, increasing deflection over time may provide a flag prior to the appearance of the pavement surface distress. Further, LTE across joints or cracks in rigid pavements was typically measured using the differential deflection across joints or cracks. Increasing relative differential deflection implied lower LTE. It was also envisioned that the rate of change of LTE across joints or cracks in rigid pavements could be related to the rate of change of faulting. Joints with a good load transfer mechanism, such as dowel bars, would have almost 100‑percent LTE and little or no faulting, whereas joints without dowel bars or with damaged or sheared dowel bars, or cracks with no aggregate interlock, would have minimal LTE and increased probability of faulting. Therefore, decreasing LTE over time could be used to warn of impending surface defects.
Once again, it was envisioned that an analysis of the time-series deflection data could provide indication of relationships between pavement deflection and pavement condition or distress. To investigate such potential relationships, FWD deflection data from the LTPP SMP test sections were plotted as a function of time following the procedures discussed in the following subsections. A partial record of the inventory data for the SMP test sections are listed in table 108. The deflection data were analyzed to determine trends in the measured deflection over time. Such trends, if they existed, would provide a tool for pavement managers to estimate future pavement conditions and distress before surface defects such as cracking occurred. The SMP test sections were used in this analysis because deflection data were collected on a much more frequent basis than the other LTPP test sections. However, because the FWD tests were performed at various times of the year and at different temperatures, the measured deflection was adjusted to account for the material properties and their relationships to temperature. The details of these adjustments are presented in the following subsections.
Table 108. LTPP SMP partial inventory data.
SHRP ID | AC Thickness (inches) | Base Thickness (inches) | Subbase Thickness (inches) | Roadbed Soil Type | Most Recent Traffic (ESAL/year) | Climatic Region |
---|---|---|---|---|---|---|
010101 | 7.4 | 7.9 | — | — | — | WNF |
010102 | 4.2 | 12.0 | — | — | — | WNF |
040113 | 4.4 | 7.5 | — | — | 337,000 | DNF |
040114 | 6.8 | 12.0 | — | — | 308,000 | DNF |
041024 | 10.8 | 6.3 | — | Coarse-grained soil: clayey sand with gravel | — | DNF |
081053 | 4.6 | 5.4 | 23.5 | Fine-grained soils: lean inorganic clay | 42,000 | DF |
091803 | 7.1 | 12.0 | — | Coarse-grained soils: well-graded sand with silt and gravel | 36,000 | WF |
100102 | 4.1 | 11.8 | 39.0 | Coarse-grained soils: poorly graded sand | — | WNF |
131031 | 10.6 | 8.8 | — | Coarse-grained soil: silty sand | — | WNF |
131005 | 7.6 | 8.8 | — | Coarse-grained soil: clayey sand | — | WNF |
161010 | 10.7 | 5.4 | — | Coarse-grained soil: silty sand | 235,000 | DF |
231026 | 7.2 | 17.6 | — | Coarse-grained soil: silty sand with gravel | — | WF |
241634 | 3.6 | 4.8 | 13.0 | Fine-grained soils: silt | — | WNF |
251002 | 7.8 | 4.0 | 4.9 | Coarse-grained soils: poorly graded sand with silt | — | WF |
271018 | 4.4 | 5.2 | — | Coarse-grained soils: poorly graded sand with silt | — | WF |
271028 | 9.6 | 0.0 | — | Coarse-grained soils: poorly graded sand with silt | 112,000 | WF |
276251 | 7.4 | 10.2 | — | Coarse-grained soils: poorly graded sand with silt | 70,000 | WF |
281802 | 3.1 | 4.9 | 1.6 | Coarse-grained soils: poorly graded sand | 98,000 | WNF |
281016 | 7.6 | 19.3 | — | — | 52,000 | WNF |
308129 | 3.0 | 22.8 | — | Fine-grained soils: gravelly lean clay with sand | 39,000 | DF |
310114 | 6.6 | 12.0 | — | — | 95,000 | WF |
331001 | 8.4 | 19.3 | 14.4 | Coarse-grained soils: poorly graded sand with silt | 61,000 | WF |
351112 | 5.4 | 6.4 | — | — | 51,000 | DNF |
360801 | 5.0 | 8.4 | — | — | 2,000 | WF |
371028 | 1.6 | 8.2 | — | Coarse-grained soils: poorly graded sand with silt | 93,000 | WNF |
404165 | 2.7 | 5.5 | — | — | 151,000 | WNF |
460804 | 6.9 | 12.0 | — | — | 3,000 | DF |
469187 | 5.5 | 6.0 | 3.0 | Fine-grained soils: lean inorganic clay | — | DF |
481077 | 4.9 | 10.4 | — | Fine-grained soils: sandy silt | 132,000 | WNF |
481068 | 10.9 | 6.0 | 8.0 | Fine-grained soils: sandy lean clay | — | WNF |
481122 | 3.0 | 15.6 | 8.4 | Coarse-grained soil: clayey sand | 51,000 | WNF |
481060 | 7.5 | 12.3 | 6.0 | — | 323,000 | WNF |
483739 | 1.5 | 11.4 | 7.4 | Coarse-grained soils: poorly graded sand | 52,000 | WNF |
491001 | 5.1 | 5.8 | — | Coarse-grained soil: silty sand | — | DF |
501002 | 8.5 | 25.8 | — | — | 92,000 | WF |
510113 | 4.0 | 7.9 | 6.0 | — | 265,000 | WNF |
510114 | 7.3 | 11.9 | 6.0 | Fine-grained soils: sandy silty clay with gravel | 253,000 | WNF |
561007 | 2.8 | 6.2 | — | Coarse-grained soil: silty sand with gravel | 5,000 | DF |
831801 | 4.4 | 5.6 | 13.2 | Coarse-grained soil: silty sand | 372,000 | WF |
871622 | 5.7 | 6.7 | 26.3 | Fine-grained soils: sandy silt | 271,000 | WF |
906405 | 2.8 | 9.0 | 2.5 | Coarse-grained soil: silty sand | 90,000 | DF |
— Indicates no data were available. 1 inch = 25.4 mm |
Some researchers have developed correlations between temperature and the measured flexible pavement deflections. At the time of this report, the most publicized temperature correlation model was that of the AI.(85) In this model, the measured pavement deflection basin was adjusted based on the measured pavement temperature and the untreated base thickness. Stated differently, the AI temperature adjustment factor (TAF) was used as a multiplier to adjust the entire measured deflection basin to a standard temperature of 70 ºF (21 ºC). This made the implementation of the AI method at the network level relatively easy. Other models, such as the BELLS, had also been developed and verified based on the LTPP SMP data.(86) These models were developed using the measured air temperatures during the FWD testing, the measured pavement surface temperatures, and the temperatures of the asphalt mat measured at various depths from the pavement surface. The use of these models facilitated the adjustment of the backcalculated layer moduli values to different temperatures. However, the data required to use the models is not readily available in the current or historic deflection records of most State transportation departments and would require additional effort to obtain.
In this study, the main purpose of the analyses of the deflection data was to identify relationships, if any, between the measured pavement deflection and the measured pavement condition data, to determine whether the deflection data could be used to estimate the optimum time for pavement preservation. To conduct the analyses, the measured pavement deflections must be adjusted to the standard temperature of 70 ºF (21 ºC). Therefore, the first step in the analyses was to validate the existing temperature adjustment models using the LTPP measured deflection data along the various SMP test sections. The analyses were based on the measured pavement deflections and surface temperature, the data most commonly collected by State transportation departments. Please note that at the time of this report, most State transportation departments did not collect network level deflection data, however, that may change in the near future as more efficient deflection measuring techniques are developed. Nevertheless, the temperature adjustment analyses were based on network level assessments, in conjunction with the RFP/RSP concepts developed in this study. After the analyses of the temperature adjustment models, backcalculation of layer moduli were performed at the project level.
The AI method for temperature adjustment of the measured deflection data could be relatively easily applied to network-level deflection data. As stated earlier, the AI method (see figure 67) provided TAFs to be multiplied by the measured deflection basin based on the mean pavement temperature and the thickness of the untreated base layer.
©Asphalt Institute
1 inch = 25.4 mm.
ºF = 1.8 × ºC + 32.
Figure 67. Graph. AI TAF.(85)
To assess the accuracy and applicability of the AI TAFs, the measured LTPP deflection data along several SMP test sections were analyzed to determine the TAFs at each site using the following steps:
Where:
APDi = Average peak pavement deflection at sensor i.
ωi and Ci are regression constants for sensor i.
Figure 69 depicts the measured pavement deflections at sensors 1, 2, 4, and 7 as a linear function of the pavement surface temperature for SHRP test section 010101. The data in the figure indicate that, as it was expected, increases in the pavement temperatures caused increases in the pavement deflections at sensors 1 and 2, while the deflection data at sensors 4 and 7 were minimally affected by temperature. The data also indicate that the rate of change of deflection with respect to temperature (the slope of the lines) decreased as the distance from the load to the sensor increased. Indeed, the slope at sensor 7 was zero.
1 mil = 25.4 microns.
ºF = 1.8 × ºC + 32.
Figure 69. Graph. Peak measured pavement deflection at sensors 1, 2, 4, and 7 versus pavement surface temperature for SHRP test section 010101, F3.
In addition, the measured deflection data at sensor 1 along the outer wheelpath (F3) and mid lane (F1) along SHRP test sections 010101 and 010102 are depicted in figure 70 as a function of the measured pavement temperature. It can be seen from the figure that all the data could be modeled as a function of temperature using the same form as in figure 68.
ºF = 1.8 × ºC + 32.
1 mil = 25.4 micron.
Figure 70. Graph. Average measured peak deflection at sensor 1 versus the measured pavement surface temperature along the outer wheelpath and mid lane of SHRP test sections 010101 and 010102.
Where:
TAFdi = Temperature adjustment factor for sensor di (multiply the measured pavement deflection at temperature T and sensor di by TAFdi to adjust the deflection to 70 ºF (21 ºC)).
di = Deflection sensor at the ith distance from the FWD load.
αi, βi, γi = regression constants (see table 109).
T = Measured pavement surface temperature at the time of FWD testing (ºF).
Table 109. The regression parameters of figure 71 for each deflection sensor.
Deflection Sensor | Distance from FWD load (inches) | Regression Terms and Values | ||
---|---|---|---|---|
αi (E−05) | βi (E−03) | γi | ||
d1 | 0 | 7.09 | −18.24 | 1.930 |
d2 | 8 | 3.72 | −10.62 | 1.562 |
d3 | 12 | 2.45 | −7.33 | 1.394 |
d4 | 18 | 1.59 | −4.44 | 1.233 |
d5 | 24 | 1.37 | −3.00 | 1.143 |
d6 | 36 | 1.65 | −2.04 | 1.062 |
d7 | 60 | 1.83 | −2.18 | 1.062 |
1 inch = 25.4 mm. |
Where:
TAF = Temperature adjustment factor (multiply the measured pavement deflection by this factor to obtain the temperature-adjusted deflection).
A, B, and C = Global regression parameters of the global temperature adjustment model.
T = Pavement surface temperature measured at the time of FWD testing (ºF).
The equations in figure 73 through figure 75 define the global regression parameters in figure 72.
Where:
d = Lateral distance from the center of the load to the sensor (inch).
α1,2,3, β1,2,3, γ1,2,3, δ1,2 = Regression values (see table 110).
Table 110. Regression values for Calculation of Parameters A, B, and C in figure 73 through figure 75.
Regression Parameter | Regression Value | |||
---|---|---|---|---|
A | B | C | ||
α1 | −1.429E−09 | — | — | |
α2 | — | 2.293E−07 | — | |
α3 | — | — | 4.839E−04 | |
β1 | 1.631E−07 | — | — | |
β2 | — | −2.964E−05 | — | |
β3 | — | — | −4.232E−02 | |
γ1 | −5.516E−06 | — | — | |
γ2 | — | 1.221E−03 | — | |
γ3 | — | — | 1.881 | |
δ1 | 7.086E−05 | — | — | |
δ2 | — | −1.831E−02 | — | |
— Indicates not applicable. |
ºF = 1.8 × ºC + 32.
1 mil = 25.4 micron.
1 inch = 25.4 mm.
Figure 76. Graph. Measured deflection basins at three pavement surface temperatures 52, 70, and 86 ºF (11, 21, and 30 ºC) along the mid-lane of the SHRP test section 351112 on April 25, 1995.
ºF = 1.8 × ºC + 32.
1 mil = 25.4 micron.
1 inch = 25.4 mm.
Figure 77. Graph. Error from TAF and AI adjusted deflection basin at two pavement surface temperatures (52 and 86 ºF (11 and 30 ºC)), along the mid-lane of the SHRP test section 351112 on April 25, 1995.
ºF = 1.8 × ºC + 32.
Figure 78. Graph. Percent error of the temperature-adjusted deflection data using the equation in figure 72 and the AI procedure.
Table 111. Averages and overall average of the regression parameters of TAF (figure 72) for each climatic region.
Regression Term | Average Regression Value for Each Climatic Region | Overall Average | |||
---|---|---|---|---|---|
WF | WNF | DF | DNF | ||
α1 | −1.94E−09 | −1.27E−09 | −8.70E−10 | −1.63E−09 | −1.43E−09 |
α2 | 2.82E−07 | 2.18E−07 | 1.62E−07 | 2.49E−07 | 2.29E−07 |
α3 | 6.73E−04 | 4.04E−04 | 3.23E−04 | 5.58E−04 | 4.84E−04 |
β1 | 2.34E−07 | 1.39E−07 | 9.97E−08 | 1.75E−07 | 1.63E−07 |
β2 | −3.88E−05 | −2.67E−05 | −2.05E−05 | −3.21E−05 | −2.96E−05 |
β3 | −5.74E−02 | −3.55E−02 | −3.00E−02 | −4.88E−02 | −4.23E−02 |
γ1 | −8.35E−06 | −4.24E−06 | −3.71E−06 | −5.71E−06 | −5.52E−06 |
γ2 | 1.67E−03 | 1.03E−03 | 8.69E−04 | 1.34E−03 | 1.22E−03 |
γ3 | 2.19 | 1.65 | 1.90 | 1.85 | 1.88 |
δ1 | 1.07E−04 | 4.61E−05 | 6.81E−05 | 6.73E−05 | 7.09E−05 |
δ2 | −2.54E−02 | −1.32E−02 | −1.82E−02 | −1.77E−02 | −1.83E−02 |
The average peak deflections, after applying temperature adjustment, were used to study the changes in deflection over time. It was envisioned that structural distresses, such as fatigue cracking, might be correlated to the pavement deflection. For example, fatigue cracking could propagate toward the pavement surface at a rate proportional to the rate of increase in pavement deflection. The pavement deflection was envisioned to decrease following construction as the pavement was further compacted by traffic, and then eventually began to increase as the pavement began to deteriorate. Note that this relationship was only anticipated for SPS sections, because GPS sections were in service before the commencement of data collection. The relationships between pavement deflection and time were studied using the following steps:
ºF = 1.8 × ºC + 32.
1 mil = 25.4 microns.
Figure 79. Graph. Average measured peak pavement deflection at sensors 1, 2, 4, and 7versus time for SHRP test section 010101, F1.
Table 112. Summary of deflection for sensor 1 versus time trend descriptions.
Trend Description | Measured Data | Temperature-Adjusted Data | ||
---|---|---|---|---|
No. of Test Sections | Percentage | No. of Test Sections | Percentage | |
Consistent | 44 | 56 | 46 | 59 |
Increasing | 24 | 31 | 25 | 32 |
Decreasing | 3 | 4 | 3 | 4 |
Decreasing and then increasing | 7 | 9 | 4 | 5 |
1 mil = 25.4 micron.
Figure 80. Graph. Temperature-adjusted peak deflection at sensors 1, 2, 4, and 7 versus time for SHRP test section 010101, F1.
1 inch/mi = 0.0158 m/km.
1 mil = 25.4 microns.
Figure 81. Graph. Temperature-adjusted peak deflection at sensor 1 versus IRI for SHRP test section 010101, F1.
1 inch = 25.4 mm.
1 mil = 25.4 microns.
Figure 82. Graph. Temperature-adjusted peak deflection at sensor 1 versus rut depth for SHRP test section 010101, F1.
1 ft2 = 0.0929 m2.
1 mil = 25.4 microns.
Figure 83. Graph. Temperature-adjusted peak deflection at sensor 1 versus alligator cracking for SHRP test section 010101, F1.
1 ft = 0.305 m.
1 mil = 25.4 microns.
Figure 84. Graph. Temperature-adjusted peak deflection at sensor 1 versus longitudinal cracking for SHRP test section 010101, F1.
1 ft = 0.305 m.
1 mil = 25.4 microns.
Figure 85. Graph. Temperature-adjusted peak deflection at sensor 1 versus transverse cracking for SHRP test section 010101, F1.
The measured and/or temperature-adjusted pavement deflection data, along with layer thickness and Poisson’s ratio, can be used to backcalculate the pavement layer moduli (MR) values. Such values are useful in the design of pavement rehabilitation treatments. To further develop and verify the temperature adjustment procedures described previously, the deflection data from a few test sections were used to backcalculate the layer MR values. The data used were from SHRP test sections 010101, 081053, 271028, and 351112. A partial record of the inventory data for the test sections used in this analysis are listed in table 108.
The MICHBACK software package, developed at Michigan State University, was used in the analyses to backcalculate pavement layer MR values. MICHBACK uses the Chevronx computer program (a five-layer elastic program) as the forward engine to calculate the pavement deflections for a given set of layer moduli, Poisson ratios, layer thicknesses, and load magnitude. The MICHBACK program uses a modified Newtonian algorithm to calculate a gradient matrix by incrementing the estimated layer modulus values and calculating the differences between the measured and the calculated pavement deflection in three consecutive cycles. When the convergence criteria (specified by the program user) are satisfied, the iteration process stops, and the final set of backcalculated layer moduli are recorded.(83) In this study, the following convergence criteria were used:
The pavement layers were assigned the following Poisson’s ratio values:
Note that the aggregate base and sand subbase layers were combined into a singular base layer. This was done to improve the accuracy of the backcalculation.
The results of the backcalculation are listed in table 113. Note that for each location, three or four tests were performed during a 1-day period. Also note that the first set of four tests was conducted at point location 114.3, the next four at point location 91.4, and the third four was the average for the entire test section. The first set of three tests was conducted at point location 30.5, the next three at point location 7.6, and the final three at point location 7.6. The pavement surface temperature varied throughout each day of testing by as much as 82 ºF (28 ºC). Hence, the AC layer MR value varied throughout the day. Higher temperature corresponded to softer asphalt binder and lower MR. There were also some changes in the base layer MR values and minimal changes in the roadbed soil MR values. The changes in AC layer MR are shown as a function of pavement surface temperature for the analysis using both the measured and temperature-adjusted deflection data in figure 86 through figure 89. The data in the figures indicate that in general the AC layer MR values decreased with increasing temperature based on the measured deflection, while the values based on the temperature-adjusted deflection were opposite. Note that the two curves generally cross near the reference temperature of 70 °F (21ºC). This finding supports the use of the equation in figure 72 and indicates that the AC layer modulus values could be determined from the model of the backcalculated moduli values based on the measured or temperature-adjusted data by selecting the value at 70 °F (21 ºC).
Table 113. Backcalculated resilient modulus values.
State Code | SHRP ID | FWD Test Date | FWD Test Time | Pavement Surface Temperature (°F) | Backcalculated Layer Resilient Modulus—Measured Deflection (psi) | Backcalculated Layer Resilient Modulus—Adjusted Deflection (psi) | ||||
---|---|---|---|---|---|---|---|---|---|---|
Asphalt | Base | Roadbed Soil | Asphalt | Base | Roadbed Soil | |||||
1 | 0101 | 4/16/96 | 0832 | 52 | 1,162,303 | 9,176 | 19,771 | 674,661 | 16,317 | 18,823 |
1 | 0101 | 4/16/96 | 1121 | 77 | 718,996 | 9,819 | 18,931 | 844,193 | 8,525 | 19,248 |
1 | 0101 | 4/16/96 | 1402 | 102 | 487,634 | 11,556 | 18,635 | 941,488 | 7,592 | 19,340 |
1 | 0101 | 4/16/96 | 1639 | 97 | 466,884 | 12,809 | 19,059 | 812,734 | 9,834 | 19,532 |
1 | 0101 | 4/16/96 | 0821 | 50 | 1,191,564 | 53,493 | 22,261 | 656,820 | 56,902 | 22,102 |
1 | 0101 | 4/16/96 | 1112 | 79 | 641,012 | 65,940 | 20,930 | 906,343 | 54,878 | 21,040 |
1 | 0101 | 4/16/96 | 1350 | 104 | 455,836 | 58,919 | 21,264 | 1,132,931 | 49,501 | 21,107 |
1 | 0101 | 4/16/96 | 1630 | 99 | 379,298 | 82,785 | 21,602 | 895,810 | 78,689 | 21,423 |
1 | 0101 | 4/16/96 | 0836 | 53 | 1,098,468 | 22,168 | 19,160 | 639,126 | 30,920 | 18,815 |
1 | 0101 | 4/16/96 | 1126 | 78 | 698,266 | 21,903 | 18,821 | 889,003 | 17,587 | 19,068 |
1 | 0101 | 4/16/96 | 1407 | 102 | 439,646 | 27,870 | 18,610 | 954,010 | 19,785 | 18,789 |
1 | 0101 | 4/16/96 | 1643 | 96 | 407,830 | 32,042 | 18,916 | 811,745 | 24,301 | 19,119 |
8 | 1053 | 3/7/97 | 0954 | 43 | 809,038 | 25,551 | 20,518 | 457,612 | 21,733 | 20,496 |
8 | 1053 | 3/7/97 | 1121 | 64 | 656,069 | 25,579 | 21,976 | 619,150 | 24,196 | 22,198 |
8 | 1053 | 3/7/97 | 1246 | 84 | 506,896 | 26,722 | 22,196 | 709,939 | 28,053 | 22,219 |
27 | 1028 | 10/8/96 | 0822 | 50 | 2,092,102 | — | 25,441 | 1,343,882 | — | 25,956 |
27 | 1028 | 10/8/96 | 1031 | 64 | 1,908,807 | — | 25,231 | 1,689,933 | — | 25,415 |
27 | 1028 | 10/8/96 | 1219 | 73 | 1,862,257 | — | 25,621 | 1,984,829 | — | 25,539 |
35 | 1112 | 4/25/95 | 0754 | 52 | 2,626,520 | 102,303 | 42,397 | 1,668,134 | 84,612 | 42,021 |
35 | 1112 | 4/25/95 | 1017 | 70 | 2,045,288 | 81,978 | 40,578 | 2,266,073 | 63,815 | 40,914 |
35 | 1112 | 4/25/95 | 1219 | 86 | 1,647,345 | 47,891 | 40,152 | 2,571,180 | 38,301 | 40,846 |
— Indicates not applicable. ºF = 1.8 × ºC + 32. 1 psi = 6.895 kPa. |
ºF = 1.8 × ºC + 32.
1 psi = 6.895 kPa.
Figure 86. Graph. AC layer MR values versus pavement surface temperature for SHRP test section 010101.
ºF = 1.8 × ºC + 32.
1 psi = 6.895 kPa
Figure 87. Graph. AC layer MR values versus pavement surface temperature for SHRP test section 081053.
ºF = 1.8 × ºC + 32.
1 psi = 6.895 kPa.
Figure 88. Graph. AC layer MR values versus pavement surface temperature for SHRP test section 271028.
ºF = 1.8 × ºC + 32.
1 psi = 6.895 kPa.
Figure 89. Graph. AC layer MR values versus pavement surface temperature for SHRP test section 351112.
The backcalculated MR values were further evaluated by plotting the results based on measured data versus those based on temperature-adjusted data, as shown in figure 90 and figure 91. The data in the figures indicate that minimal bias existed in the procedure for temperature adjustment across the various testing temperatures. Some data were reduced, and some data were increased following adjustment based on temperature (i.e., temperature adjustment did not consistently lead to increases or decreases in backcalculated MR values).
ºF = 1.8 × ºC + 32.
1 psi = 6.895 kPa.
Figure 90. Graph. AC layer MR values from measured and temperature-adjusted deflection data.
1 psi = 6.895 kPa.
Figure 91. Graph. Base and roadbed soil layer MR values from measured and temperature-adjusted deflection data.
Although the backcalculation of pavement layer MR values using temperature-adjusted pavement deflection was shown to work, many pavement engineers recommend performing backcalculation on measured data and then adjusting the results. This is because temperature adjustment in general is not exact, and it can introduce error. Such error can be magnified when the backcalculation routine is performed. Hence, making the adjustment at the end is preferred by many.
The measured rigid pavement deflections were evaluated over time using the following steps:
The data were sorted based on the applied load and the various test locations within the lane. Drop height 2 simulated the application of a 9,000-lbf (40-kN) half single axle load and was selected for analyses. The tests performed at the middle lane at mid-panel location (J1) were selected for individual analyses. All data from other test loads and locations were not included in the analyses.
Table 114. LTPP SPS-2 partial inventory data.
SHRP ID | PCC Thickness (Inches) | Base Thickness (Inches) | Subbase Thickness (Inches) | Roadbed Soil Type | Most Recent Traffic (ESAL/Year) | Climatic Region | ||||
---|---|---|---|---|---|---|---|---|---|---|
040213 | 7.9 | 5.8 | — | Coarse grained soil: silty sand with gravel | 1,444,000 | DNF | ||||
040214 | 8.3 | 6.1 | — | Coarse grained soil: silty sand with gravel | 1,444,000 | DNF | ||||
040215 | 11.0 | 6.3 | — | Coarse grained soil: silty sand with gravel | 1,454,000 | DNF | ||||
040216 | 11.2 | 6.3 | — | Coarse grained soil: silty sand with gravel | 1,454,000 | DNF | ||||
040217 | 8.1 | 6.1† | — | Coarse grained soil: silty sand with gravel | 1,444,000 | DNF | ||||
040218 | 8.3 | 6.2† | — | Coarse grained soil: clayey sand with gravel | 1,444,000 | DNF | ||||
040219 | 10.8 | 6.2† | — | Coarse grained soil: silty sand with gravel | 1,453,000 | DNF | ||||
040220 | 11.2 | 6.2† | — | Coarse grained soil: clayey sand with gravel | 1,454,000 | DNF | ||||
040221 | 8.1 | 8.4* | — | Coarse grained soil: silty sand with gravel | 1,444,000 | DNF | ||||
040222 | 8.6 | 8.2* | — | Coarse grained soil: clayey sand with gravel | 1,445,000 | DNF | ||||
040223 | 11.1 | 7.6* | — | Coarse grained soil: silty sand with gravel | 1,453,000 | DNF | ||||
040224 | 10.6 | 8.2* | — | Coarse grained soil: clayey sand with gravel | 1,452,000 | DNF | ||||
040262 | 8.1 | 6.1 | — | Coarse grained soil: silty sand with gravel | 1,444,000 | DNF | ||||
040263 | 8.2 | 8.3* | — | Coarse grained soil: clayey sand with gravel | 1,444,000 | DNF | ||||
040264 | 11.5 | 8.2* | — | Coarse grained soil: clayey sand with gravel | 1,454,000 | DNF | ||||
040265 | 10.8 | 6.8 | — | Coarse grained soil: clayey sand with gravel | 1,453,000 | DNF | ||||
040266 | 12.3 | 3.9† | — | Coarse grained soil: clayey sand with gravel | 1,455,000 | DNF | ||||
040267 | 11.3 | 3.9† | — | Coarse grained soil: clayey sand with gravel | 1,454,000 | DNF | ||||
040268 | 8.5 | 3.8† | — | Coarse grained soil: clayey sand with gravel | 1,445,000 | DNF | ||||
080213 | 8.6 | 5.9 | — | Fine-grained soil: clay with sand | 463,000 | DF | ||||
080214 | 8.4 | 5.9 | — | Coarse-grained soil: clayey sand with gravel | 462,000 | DF | ||||
080215 | 11.5 | 6.0 | — | Fine-grained soil: sandy clay | 470,000 | DF | ||||
080216 | 11.9 | 5.9 | — | Coarse-grained soil: poorly graded sand with silt | Not reported | DF | ||||
080217 | 8.6 | 6.7 | — | Fine-grained soil: sandy lean clay | 463,000 | DF | ||||
080218 | 7.6 | 6.2† | — | Fine-grained soil: clay | 459,000 | DF | ||||
080219 | 9.9 | 6.1† | — | Coarse-grained soil: clayey sand with gravel | 467,000 | DF | ||||
080220 | 11.2 | 6.2† | — | Fine-grained soil: clay | 469,000 | DF | ||||
080221 | 8.3 | 8.0* | — | Fine-grained soil: sandy lean clay | 461,000 | DF | ||||
080222 | 8.5 | 8.5* | — | Fine-grained soil: sandy clay | 462,000 | DF | ||||
080223 | 11.7 | 8.9* | — | Coarse-grained soil: well graded sand with silt | 470,000 | DF | ||||
080224 | 11.6 | 7.7* | — | Coarse-grained soil: clayey sand | 470,000 | DF | ||||
080259 | 11.9 | — | — | Coarse-grained soil: clayey sand | 470,000 | DF | ||||
100201 | 8.3 | 6.2 | 34.0 | Coarse-grained soil: silty sand | 368,000 | WNF | ||||
100202 | 8.8 | 6.2 | 22.0 | Coarse-grained soil: well graded sand with silt | 374,000 | WNF | ||||
100203 | 11.7 | 6.1 | 14.0 | Coarse-grained soil: silty sand | 396,000 | WNF | ||||
100204 | 11.0 | 6.3 | 12.0 | Coarse-grained soil: well graded sand with silt | 392,000 | WNF | ||||
100205 | 9.2 | 5.5† | 30.0 | Coarse-grained soil: silty sand | 378,000 | WNF | ||||
100206 | 8.9 | 6.1† | 42.0 | Coarse-grained soil: well graded sand with silt | 375,000 | WNF | ||||
100207 | 11.3 | 6.9† | 14.1 | Coarse-grained soil: silty sand | 394,000 | WNF | ||||
100208 | 12.1 | 6.0† | 30.0 | Coarse-grained soil: sand | 397,000 | WNF | ||||
100209 | 8.2 | 8.0* | 24.0 | Coarse grained soil: clayey sand | 367,000 | WNF | ||||
100210 | 8.3 | 8.2* | 36.0 | Coarse-grained soil: silty sand | 368,000 | WNF | ||||
100211 | 11.8 | 7.5* | 30.0 | Coarse-grained soil: clayey sand | 396,000 | WNF | ||||
100212 | 12.4 | 7.4 | 30.0 | Coarse-grained soil: silty sand | 398,000 | WNF | ||||
100259 | 10.2 | 7.9 | 42.0 | Coarse-grained soil: well graded sand with silt | 387,000 | WNF | ||||
100260 | 10.2 | 7.8 | 42.0 | Coarse-grained soil: silty sand | 387,000 | WNF | ||||
260213 | 8.3 | 6.1 | 18.5 | Fine-grained soil: silty clay | 2,042,000 | WF | ||||
260214 | 8.8 | 5.8 | 18.5 | Fine-grained soil: silty clay | 1,481,000 | WF | ||||
260215 | 11.1 | 6.2 | 15.5 | Fine-grained soil: silty clay | 2,129,000 | WF | ||||
260216 | 11.3 | 5.9 | 15.5 | Fine-grained soil: silty clay | 1,550,000 | WF | ||||
260217 | 8.4 | 6.1† | 18.5 | Fine-grained soil: silty clay | 2,047,000 | WF | ||||
260218 | 7.3 | 6.3† | 18.5 | Fine-grained soil: silty clay | 1,895,000 | WF | ||||
260219 | 11.3 | 5.9† | 15.5 | Fine-grained soil: silty clay | 1,550,000 | WF | ||||
260220 | 11.2 | 5.8† | 15.5 | Fine-grained soil: silty clay | 1,549,000 | WF | ||||
260221 | 8.1 | 8.6* | 16.5 | Fine-grained soil: silty clay | 1,513,000 | WF | ||||
260222 | 8.3 | 8.4* | 16.5 | Fine-grained soil: silty clay | 1,615,000 | WF | ||||
260223 | 11.0 | 8.4* | 13.5 | Fine-grained soil: sandy clay | 1,548,000 | WF | ||||
260224 | 11.1 | 8.3* | 13.5 | Fine-grained soil: sandy clay | 1,549,000 | WF | ||||
260259 | 11.3 | 8.0* | 18.0 | Fine-grained soil: silty clay | 1,550,000 | WF | ||||
— Indicates no base layer was present. *Upper portion of base was treated. †Treated base. 1 inch = 25.4 mm. |
1 mil = 25.4 microns.
Figure 92. Graph. Measured peak deflection at sensor 1 versus time for SHRP test section 100201, J1.
Table 115. Summary of deflection for sensor 1 versus time trend descriptions for LTPPSPS-2.
State | Trend Description | |||||
---|---|---|---|---|---|---|
Increasing | Consistent | Decreasing | ||||
No. of Test Sections | Percentage | No. of Test Sections | Percentage | No. of Test Sections | Percentage | |
Arizona | 10 | 53 | 5 | 26 | 4 | 21 |
Colorado | 2 | 15 | 6 | 46 | 5 | 38 |
Delaware | 5 | 42 | 5 | 42 | 2 | 17 |
Michigan | 8 | 57 | 2 | 14 | 4 | 29 |
Total sections and average percent | 25 | 45 | 15 | 27 | 15 | 27 |
1 inch/mi = 0.0158 m/km.
1 mil = 25.4 microns.
Figure 93. Graph. Measured peak deflection at sensor 1 versus IRI for SHRP test section 100201, J1.
1 inch = 25.4 mm.
1 mil = 25.4 microns.
Figure 94. Graph. Measured peak deflection at sensor 1 versus faulting for SHRP test section 100201, J1.
1 ft = 0.305 m.
1 mil = 25.4 microns.
Figure 95. Graph. Measured peak deflection at sensor 1 versus longitudinal cracking for SHRP test section 100201, J1.
1 ft = 0.305 m.
1 mil = 25.4 microns.
Figure 96. Graph. Measured peak deflection at sensor 1 versus transverse cracking for SHRP test section 100201, J1.
The pavement deflection data could be used to estimate the pavement response to load and for the design of pavement treatments, etc. The LTPP rigid pavement deflection data did not support the use of deflection as an indicator of impending surface distress. Therefore, deflection could not be used in this study as a component of RFP or RSP.
The LTEs calculated based on FWD testing were evaluated over time using the following steps:
Figure 97. Graph. LTE versus time for SHRP test section 100201, J4.
Table 116. Summary of LTE versus time trend descriptions.
State | Trend Description | |||||
---|---|---|---|---|---|---|
Increasing | Consistent | Decreasing | ||||
No. of Test Sections | Percentage | No. of Test Sections | Percentage | No. of Test Sections | Percentage | |
Arizona | 2 | 11 | 3 | 17 | 13 | 72 |
Colorado | 3 | 23 | 7 | 54 | 3 | 23 |
Delaware | 3 | 25 | 4 | 33 | 5 | 42 |
Michigan | 4 | 31 | 3 | 23 | 6 | 46 |
Total sections and average percent | 12 | 21 | 17 | 30 | 27 | 48 |
1 inch/mi = 0.0158 m/km.
Figure 98. Graph. LTE versus IRI for SHRP test section 100201, J4.
1 inch = 25.4 mm.
Figure 99. Graph. LTE versus faulting for SHRP test section 100201, J4.
1 ft = 0.305 m.
Figure 100. Graph. LTE versus longitudinal cracking for SHRP test section 100201, J4.
1 ft = 0.305 m.
Figure 101. Graph. LTE versus transverse cracking for SHRP test section 100201, J4.
This chapter presented the results of the analyses of the measured flexible and rigid pavement deflections and the LTE data. The main objective of the analyses was to determine whether pavement deflections and LTE data could be incorporated into the RFP and RSP algorithms.
It was envisioned that measured pavement deflections and/or LTE data would be correlated with pavement condition or distress, and hence, they could be used as an early warning of pending deterioration before it became visible on the pavement surface.
For flexible pavements, the measured pavement deflections were a function of the pavement temperatures. Therefore, the accuracy of the existing temperature adjustment methods were reviewed and scrutinized using the measured LTPP deflection data. Based on the results, a new global temperature adjustment methodology was developed that could be applied to all deflection sensors and all climatic regions.
Based on the results of the analyses, the following conclusions and recommendations were drawn: