Click for next page ( 18


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 17
17 Accelerated Pavement Test Results 0 Accelerated pavement tests were conducted at the APT 5 facility at the Indiana DOT Research Division in West Average Total Rut Depth, mm Lafayette, Indiana. Up to four test lanes can be constructed in 10 this facility at a time using conventional paving equipment. Details of the facility, test section construction, and data col- 15 lection can be found in Appendix D, which is available in NCHRP Web-Only Document 82. 20 25 Rutting Rutting was monitored by recording transverse surface 30 profiles at increments of traffic applied with dual tires and without wander. These profiles were captured with software 35 that automatically reduces and stores the data in a spread- 1 10 100 1000 10000 100000 Number of Wheel Passes, N sheet (7). An initial profile was recorded before traffic appli- CA-1 CA-2 CA-3 CA-4 CA-5b cation and used as the baseline reference for determining rutting from subsequent profiles. Figure 6. Coarse-graded mixture rut Each test lane was trafficked until a total rut depth of 20 depth development. mm was achieved or 20,000 wheel passes were applied, whichever occurred first. Profiles were recorded at nine locations over the length of a given test section; however, to 5 (worst). The mixtures were ranked by four parameters; three consecutive sections nearest the center of the test three of the mixtures were ranked the same by the four section (Sections 4, 5, and 6, see Figure D.8) were averaged parameters; however, the early rut rate inverts 1 and 2, and and used as a single result in the subsequent analyses. 3 and 4. This would seem to indicate that after approxi- These three locations were used because the APT wheel mately 200 wheel passes are applied with the APT, one can carriage travels at a constant speed over this portion of the obtain a good indication of the relative rutting rank of an test lane. HMA mixture. Fine-Graded Mixtures. APT rutting of the fine-graded Performance mixtures is shown in Figure 7. Testing on Mixture FA-1 (Nat- Coarse-Graded Mixtures. Rutting in the APT as a ural Sand A) was terminated at 1,000 wheel passes because of function of wheel passes for the coarse-graded mixtures is excessive total rut depth. Testing on Mixture FA-2 was termi- shown in Figure 6. In addition to total rut depth, the rut rate nated inadvertently at 12,500 wheel passes; however, the trend was also computed. Rut rate is simply the slope of the regres- for this mixture shows that it would have most likely accom- sion line and has units of mm/log(N) where N is the num- modated additional passes with a minimal increase in rutting. ber of wheel passes. Rutting data for mixtures CA-1, CA-2, Rut development curves for fine-graded mixtures also CA-3, and CA-5b exhibited a bilinear trend; these data were appear to be bilinear. As above, the first regression line repre- fitted by two logarithmic functions. The rut rate during the sents early traffic stage rutting and the second later traffic early traffic stage is the slope of the first regression line while the rut rate during later traffic stage is the slope of the sec- ond regression line. The regression equations for all mix- Table 11. Coarse-graded mixture rutting tures are given in Table 11. regression equations. Rutting performance parameters for coarse-graded mix- Mixture ID Regression Equation Condition tures are shown in Table 12. These parameters include total CA-1 Total rut depth = 1.56 log(N) + 0.28 for N < 400 rut depth at 5,000 and 20,000 wheel passes as well as the rut Total rut depth = 2.25 log(N) -1.50 for N > 500 Total rut depth = 1.89 log(N) + 0.17 for N < 200 rate during early and later traffic stages (early and late CA-2 Total rut depth = 3.56 log(N) -3.74 for N > 200 stages are defined by the N break point shown in the table). CA-3 Total rut depth = 4.88 log(N) 1.27 for N < 200 Total rut depth = 14.72 log(N) 26.02 for N > 200 As an example, for mixture CA-2, early traffic is where CA-4 Total rut depth = 1.75 log(N) 0.13 for all N N200, while late traffic is N200. For each of the rutting CA-5b Total rut depth = 2.09 log(N) 0.01 for N < 200 Total rut depth = 3.27 log(N) 2.66 for N > 200 performance parameters, mixtures are ranked from 1 (best)

OCR for page 17
18 Table 12. Coarse-graded mixture rutting performance. Total Rut Mixture Total Rut Depth Depth at Total Rut Rate (mm/log(N)) Overall ID at 20,000 Passes 5,000 Passes Early Later Rank mm Rank mm Rank Rank Rank traffic Traffic CA-1 7.1 2 7.6 2 1.6 1 2.3 2 2 CA-2 9.5 4 11.3 4 1.9 3 3.6 4 4 CA-3 29.5 5 --1 --1 4.9 5 14.7 5 5 CA-4 6.3 1 7.2 1 1.8 2 1.8 1 1 CA-5b 9.2 3 11.1 3 2.1 4 3.3 3 3 1 Tested to only 5,000 wheel passes. stage rutting. Regression equations for the data are given in Moisture Susceptibility Table 13. Table 14 lists total rut depths at 1,000; 5,000; and 20,000 Before APT testing, six cores were taken from each of the wheel passes and rutting rates for both early and later traffic moisture susceptibility test lanes. In-place densities and air stages. These rutting parameters were used as the basis for voids of the test lanes were determined from the cores, which ranking mixture performance from 1 (best) to 6 (worst). were then used to test the plant-produced mixtures for mois- Overall rank is the rank appearing the most number of times ture susceptibility in accordance with AASHTO T 283. In for each mixture. Three of the parameters (rut depth at 5,000 addition to moisture conditioning, the conditioned speci- and 20,000, and rut rate at later traffic) rank the mixtures the mens were also subjected to one freeze/thaw cycle before same. The remaining two parameters rank the mixtures the being tested in indirect tension. same, but have 3 and 4 inverted from the previous three The AASHTO T 283 test results are shown in Table 15. Aver- parameters. Again, it appears that a good indication of the rut ages of VTM ranged from 7.1 to 9.9 percent. Degree of satu- resistance can be gained after approximately 200 wheel passes ration for the conditioned specimens varied from 67.4 to 78.2 of the APT. percent. The tensile strength ratio (TSR) [the ratio of the indi- rect tensile strength of conditioned specimens to that of dry (unconditioned) specimens] varied from 1.10 to 0.79. Some specimens were loaded until they cracked. The interior sur- 0 faces were then inspected for stripping and photographs were taken. Visual observation indicated that stripping occurred. 5 Typically, conditioned specimens lost their glossy appearance and the interior surface exhibited a brownish tint (see Figures E.1 to E.5 in Appendix E provided in NCHRP Web-Only Doc- 10 Average Total Rut Depth, mm ument 82). Stripping in terms of lost binder film was also observed in specimens with dolomite coarse aggregate. 15 Performance 20 Rutting accumulation for all test lanes is shown in Figure 8. A 20-mm total rut depth criteria was adopted for traffic ter- 25 mination. Mixture FAM1 (Natural Sand A) was terminated at 1,000 wheel passes, while mixture FAM5 (Natural Sand B) 30 reached the 20-mm total rut depth criteria and was terminated at 7,500 wheel passes. The FAM5 mixture exhibited a signifi- cant increase in rutting between 5,000 and 7,500 wheel passes. 35 1 10 100 1000 10000 100000 There was also an increase in rutting after 3,000 wheel passes Number of Wheel Passes, N on mixture FAM3 (Granite Sand). In general, this type of FA-1 FA-2 FA-3 FA-4 FA-5b FA-6b rutting does not occur in dry rutting tests and may be an indi- cation of stripping. The rutting data for mixtures FAM1, Figure 7. Fine-graded mixture rut depth FAM2, and FAM4 do not show a change in rate of rutting development. accumulation.

OCR for page 17
19 Table 13. Fine-graded mixture rutting regression equations. Mix ID Regression Equation Condition Total rut depth = 7.26 log(N) - 2.78 for N < 100 FA-1 Total rut depth = 21.10 log(N) - 33.33 for N > 200 Total rut depth = 3.81 log(N) 0.74 for N < 200 FA-2 Total rut depth = 5.00 log(N) 3.29 for N > 300 Total rut depth = 2.78 log(N) 0.52 for N < 200 FA-3 Total rut depth = 4.02 log(N) 3.56 for N > 300 FA-4 Total rut depth = 1.06 log(N) 0.61 for N < 200 Total rut depth = 1.63 log(N) 1.84 for N > 300 Total rut depth = 2.75 log(N) 0.004 for N < 400 FA-5b Total rut depth = 4.45 log(N) 4.70 for N > 500 Total rut depth = 2.10 log(N) 0.57 for N < 200 FA-6b Total rut depth = 3.31 log(N) 3.54 for N > 300 Table 14. Fine-graded mixture rutting performance. Rut Rut Rut Total Rut Rate (mm/log (N)) Depth Depth Depth Early Later Rank Rank Rank Mix at at at Traffic Traffic ID 1,000 5,000 20,000 Rank Rank Passes Passes Passes Overall (mm) (mm) (mm) Rank FA-1 30.6 6 NA1 NA1 7.3 6 21.1 6 6 FA-2 11.1 5 15.4 5 18.12 5 3.8 5 5.0 5 5 FA-3 8.6 4 11.3 3 15.5 3 2.8 4 4.0 3 3 FA-4 2.8 1 4.3 1 5.4 1 1.1 1 1.6 1 1 FA-5b 8.4 3 11.7 4 16.8 4 2.8 3 4.5 4 4 FA-6b 6.4 2 8.7 2 10.4 2 2.1 2 3.3 2 2 1Testing was terminated at 1,000 wheel passes because total rut depth was more than 20mm 2Testing was inadvertently terminated at 12,500 wheel passes; total rut depth at 20,000 wheel passes was predicted using the regression equation. The rutting data were also plotted as a function of the log stages. These rutting parameters were used in ranking per- of the number of wheel passes (see Figure 9). This plot formance. Among these rutting parameters, only total rut shows that the rutting of mixtures FAM1, FAM2, FAM3, and depth at 1,000 wheel passes and total rutting rate are available FAM5 appears to be bilinear. As a result, data for these mix- for all mixtures. Based on these rutting parameters, the mix- tures were fitted with two logarithmic regression lines. The tures were ranked from 1 (best) to 5 (worst). Overall per- regression equations for all mixtures are shown in Table 16. formance rank from best to worst are FAM2 (Crushed Gravel Table 17 shows total rut depths for 1,000; 5,000; and 20,000 Sand), FAM3 (Granite Sand), FAM4 (Traprock Sand), FAM5 wheel passes and total rutting rates for early and later traffic (Natural Sand B), and FAM1 (Natural Sand A). Table 15. AASHTO T 283 and MBV test results. Mixture ID FAM1 FAM2 FAM3 FAM4 FAM5 Crushed Natural Natural Aggregate Type Gravel Granite Traprock Sand A Sand Sand B Dry Specimens Tensile Strength, kPa 452.3 689.6 837.7 652.8 808.7 Average Air Voids, % 8.4 9.1 8.3 9.9 7.1 Conditioned Specimens Tensile Strength, kPa 499.4 621.2 708.1 537.0 640.2 Average Air Voids, % 9.1 9.2 8.2 9.4 7.5 Degree of Saturation, % 70.9 78.2 67.4 69.2 71.4 TSR 1.10 0.90 0.85 0.82 0.79 Methylene Blue Value 3.3 1.3 8.0 5.1 5.0

OCR for page 17
20 30 Table 16. Regression equations. Mix ID Regression Equation Condition Total rut depth = 6.82 log(N) - 2.40 for N < 200 25 FAM1 Total rut depth = 26.88 log(N) 52.53 for N > 300 Total rut depth = 1.62 log(N) + 0.77 for N < 200 FAM2 Average Total Rut Depth, mm Total rut depth = 2.31 log(N) 0.89 for N > 300 20 Total rut depth = 2.18 log(N) 1.32 for N < 1000 FAM3 Total rut depth = 4.88 log(N) 10.16 for N > 2000 FAM4 Total rut depth = 2.53 log(N) 0.69 for all N 15 FAM5 Total rut depth = 3.31 log(N) 1.14 for N < 400 Total rut depth = 8.03 log(N) 13.94 for N > 500 10 When APT traffic application was complete, cores were 5 collected and split open to determine visually if stripping had occurred. Photographs of the split surfaces are shown in Fig- 0 ures E.6 through E.10 (Appendix E). Visual inspection 0 5000 10000 15000 20000 revealed no stripping of FAM1, FAM2, and FAM4 cores. Number of Wheel Passes, N There was a loss of glossiness on the split surfaces of FAM3 FAM1 Natural Sand A, IN FAM2 Crushed Gravel Sand, IN (Granite Sand) and FAM5 (Natural Sand B). These two mix- FAM3 Granite Sand, NC FAM4 Traprock Sand, VA tures also exhibited signs of stripping in their rutting data. FAM5 Natural Sand B, OH Signs of stripping were observed on the bottom of cores taken from all of the test lanes. Figure 8. Rut depth development. Fatigue Relationships between fatigue cracking and coarse and fine aggregate properties were evaluated through construction and testing of six mixtures in the APT as indicated in Table 18. Fatigue performance was characterized by percentage of fatigue cracking in the wheel path. The experiment is similar 0 to the rutting experiment, with the exception that a conven- tional flexible pavement was installed consisting of 100 mm 5 of HMA and 200 mm of a crushed stone on a subgrade. An attempt was made to control the pavement test temperature Average Total Rut Depth, mm at approximately 10 to 20C. However, because of the unavail- 10 ability of a cooling system, this temperature range was exceeded for the tests conducted in June and July. 15 The six experimental fatigue mixtures listed in Table 18 were selected based on the earlier APT rutting performance and aggregate quality. Mixtures were selected to have as 20 wide a range in both rutting performance and aggregate quality as possible. Of the six mixtures, three were coarse- 25 graded and three were fine-graded. Mixture FA-1 (Natural Sand A) had the poorest aggregate qualities and exhibited the worst rutting performance. The mixture was included, 30 even though such a mixture probably would be replaced 1 10 100 1000 10000 100000 Number of Wheel Passes, N in the field before failing in fatigue. Testing mixtures with the greatest range of aggregate quality, as determined by FAM1 Natural Sand A, IN FAM2 Crushed Gravel Sand, IN the aggregate test methods, were expected to provide the FAM3 Granite Sand, NC FAM4 Traprock Sand, VA most useful information for determining the strength of FAM5 Natural Sand B, OH the relationships between the aggregate properties and Figure 9. Rut depth development. fatigue performance.

OCR for page 17
21 Table 17. Moisture susceptibility rutting performance. Total Total Total Overall Rank Rut Rut Rut Total Rut Rate (mm/log(N)) Rank Rank Rank Mix Depth Depth at Depth at ID at 1000 5000 20000 Rank Rank Passes Passes Passes Early Late Traffic Traffic (mm) (mm) (mm) FAM1 28.5 5 --1 --1 6.8 5 26.9 5 5 FAM2 6.1 2 7.6 1 9.2 1 1.6 1 2.3 1 1 FAM3 5.4 1 7.7 2 11.0 2 2.2 2 4.9 3 2 FAM4 7.1 3 8.8 3 9.9 3 2.5 3 2.5 2 3 FAM5 10.1 4 16.1 4 --2 3.3 4 8.0 4 4 1Testing terminated at 1,000 wheel passes; 20 mm rut depth reached. 2Testing terminated at 7,500 wheel passes; 20 mm rut depth reached. Based on rutting performance from best to worst, the fine- grade was so "springy" that construction was made difficult. graded mixtures selected for the fatigue study were FA-4 It was later discovered that the drain for the APT pit was (Granite), FA-3 (Natural Sand B), and FA-1 (Natural Sand A). clogged and that excess moisture could not be drained from Likewise, coarse-graded mixtures were CA-4 (Granite), CA-2 the soil. Once the drain was repaired, the excess moisture (Limestone), and CA-3 (Uncrushed Gravel). drained and the soil became stiffer. After subgrade compaction, a geotextile fabric was placed on the subgrade and an unbound, crushed stone base course Test Section Construction was placed and compacted such that the finished base course The first step in constructing the fatigue test sections was 200 mm in depth. The 100-mm deep HMA test section involved removing the previous rutting test sections. The mixtures were then constructed on the base course using con- underlying Portland concrete cement (PCC) slabs were then ventional HMA construction techniques as described in removed, along with the underlying pea gravel fill. Subse- Appendix D (available in NCHRP Web-Only Document 82). quently, a subgrade soil was installed and compacted to a depth of 1.5 m. Moisture was added to the soil, and the two Fatigue Testing were mixed using two motorized tillers. Compaction was accomplished using vibrating plate compactors. The Proctor Performance data were collected throughout the loading curve for the soil is shown in Figure 10. An attempt was made process, including transverse profiles when needed. Longitu- to compact the soil on the wet side of optimum in order to dinal and fatigue cracking were measured by counting the render the soil more plastic and thereby aid the pavement number of cracks that developed during loading. The fre- fatigue process. The optimum moisture content is approxi- quency of measurement varied with test section and mately 15 percent and the soil was compacted at 18- to 20- depended on how quickly the cracking occurred. From a percent moisture. As can be seen from Figure 11, the fatigue standpoint, the criterion was established that a test California bearing ratio (CBR) value for moisture content in the desired range was approximately 2. The result was a "springy" subgrade that was indeed plastic. In fact, the sub- 1850 1800 Density (kg/m3) Table 18. Fatigue experiment design. 1750 Aggregate Performance Aggregate Type Tests Category Coarse Aggregate Fine Aggregate Coarse Aggregate Test CA-2 (Limestone) 1700 Methods Evaluation CA-3 (Uncrushed Gravel) Natural Sand A (Coarse-Graded Mixtures) CA-4 (Granite) 1650 FA-1 (Natural Sand A) 5 10 15 20 25 Fine Aggregate Test Methods Evaluation Uncrushed Gravel FA-3 (Natural Sand B) Moisture Content (%) (Fine-Graded Mixtures) FA-4 (Granite) Figure 10. Subgrade Proctor curve.

OCR for page 17
22 15 10 CBR Value 5 0 5 10 15 20 25 Moisture Content (%) Figure 11. Soil CBR values. section was considered to have failed when the center one- Figure 12. CA-3 test section after 1,000 wheel passes. third of the test section had exhibited fatigue cracking exceed- ing 10 percent of the area. This center area of the test lane was in the section during application of the last 60,000 wheel chosen because it was expected to have the most uniform passes as shown in Figure 13. Subgrade failure was repaired mixture properties. Random wheel wander was also incorpo- and traffic continued; however, damage at the edge continued rated during testing to help avoid rutting; it was done by a to accumulate and it was necessary to discontinue trafficking random number generator within the APT control program. of the section to avoid damage to the APT equipment. The fatigue results are shown in Table 19. The third mixture to undergo fatigue testing was the FA-1 The first test section to be trafficked in the fatigue experi- mixture produced using Natural Sand A. This test section ment was the CA-3 (Uncrushed Gravel) mixture. Loading proved difficult to compact during construction because of consisted of a 40 kN load on dual wheels with a tire pressure mixture tenderness and the resiliency of the section against of 690 kPa. The section deformed quickly and failed after which it was being compacted. As a result, numerous cracks only 1,000 passes. The failure is shown in Figure 12. Three to occurred during compaction. These "roller"cracks were painted four cracks appear in the center one-third of the test lane; with a lime-water solution so as to appear white to distinguish however, inspection of the failure revealed that the subgrade them from cracks caused by APT loading. The existence of these failed before the fatigue properties of the mixture could be cracks from the outset of the testing most certainly influenced fully tested. the fatigue results of the section. The section before traffic is Testing began on the next test section, CA-2 (Limestone), with a reduced load of 26.7 kN applied to the dual wheels and the tire pressure reduced to 620 kPa. After 8,000 passes, no signs of cracking were observed, so the load was increased to 33.3 kN and an additional 12,000 passes were applied. The load was then increased to 40 kN and the tire pressure increased to 690 kPa. Testing was stopped at 80,000 wheel passes because the section showed signs of subgrade failure near the edge of the test pit. Minor fatigue cracking developed Table 19. Fatigue results. Test Percent Average Total Number of Mixture Cracking Rut Depth (mm) Wheel Passes CA-2 1 None 80,000 CA-3 30 None 1,000 CA-4 None 40.0 20,000 FA-1 25 None 2,000 FA-3 None 33.6 20,000 Figure 13. CA-2 test section after 80,000 FA-4 None 43.8 20,000 wheel passes.

OCR for page 17
23 Figure 14. Initial FA-1 test section. Figure 15. FA-1 test section after 2,000 wheel passes. shown in Figure 14. Trafficking of this test section began with fatigue results of the last three APT test sections. Finally, in an applied load of 31.1 kN and tire pressure of 690 kPa. As August 2003, trafficking was discontinued because 20,000 shown in Figure 15, the section exhibited substantial fatigue passes were applied on each section with no evidence of sig- cracking when the testing was stopped after 2,000 passes. nificant fatigue cracking; however, each section did show rut- Fatigue testing of mixtures CA-2, CA-3, and FA-1 was ting. The FA-3 mixture (Natural Sand B) had an average rut finally completed in June 2003, and subsequently, the test sec- depth of 33.6 mm, while the FA-4 (Granite) and CA-4 (Gran- tions were removed. In July 2003, test sections of mixtures ite) mixtures had average rut depths of 43.8 and 40.0 mm, FA-3 (Natural Sand B), FA-4 (Granite), and CA-4 (Granite) respectively. Recently, cooling capabilities have been installed were placed in the APT facility. Testing immediately began on in the APT building and fatigue tests have been conducted. the FA-3 mixture; rutting began to develop with no sign of These tests indicate that, had the desired temperature range fatigue cracking. Without the ability to control temperature in been maintained during the testing of the FA-3, FA-4, and CA- the APT facility, the test pavement temperatures were well over 4 mixtures, these mixtures probably would have sustained the desired temperature range of 10 to 20C. This affected the 80,000 to 100,000 APT wheel passes before failing in fatigue.