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376 CHAPTER 7 - ANALYSIS RESULTS FOR THE SPS-8 EXPERIMENT 7.1 INTRODUCTION The purpose of this chapter is to provide a summary of the results of the analyses conducted for the SPS-8 experiment on flexible and rigid pavements. The performance measures used in the analysis include fatigue cracking, rutting, longitudinal cracking (in the wheel path and outside the wheel path), transverse cracking, faulting and IRI. The results are summarized according to individual design and site factors. As mentioned in Chapter 3 under sections 3.5 and 3.6, all the pavement sections (flexible & rigid) in SPS-8 experiment are aged between 3 and 10 years, with an average age of 6 and 7 years for flexible and rigid pavements, respectively. Thus a majority of pavement sections of both pavement types are relatively âyoungâ to exhibit any environment-related distresses. Only a few of SPS-8 pavements have shown some distresses as of Release 17.0. It is to be noted that the current status for SPS-8 experiment for rigid pavements shows that there is no site located in the DNF zone. The extent of various distresses exhibited by the pavements is presented in Chapter 3. Site-wise summaries of inventory data, construction issues and performance of flexible and rigid pavements can be found in Appendix C. Keeping in view the number of sections constructed for SPS-8 experiment (32 flexible pavements in 15 sites and 14 rigid pavements in 6 sites) and the extent distresses at present, statistical analysis as in the case of SPS-1 and SPS-2 experiments may not be applicable. Therefore, simple mean comparisons (only for sections that exhibited distresses) were performed to identify the effects of experimental factors on various performance measures. Some initial trends obtained from these comparisons are reported below. 7.2 EFFECTS OF ENVIRONMENTAL FACTORS IN SPS-8 EXPERIMENT FOR FLEXIBLE PAVEMENTS The objective of the SPS-8 experiment is to develop conclusions concerning environmentally induced serviceability loss and the contribution of environment and subgrade to the distress of pavements. The experiment will also develop conclusions concerning the effects of base and surface thickness variations on retarding environmentally driven distress.
377 7.2.1 Site-Level Analysis The analysis of the data from SPS-8 sections was done based on the concepts of PI and relative performance concepts (see Chapter 4) as in SPS-1 experiment. At the site-level, various performance measures (fatigue cracking, longitudinal cracking (WP and NWP), transverse cracking, raveling, rutting and roughness) were analyzed to investigate the effects of the main site factors (climatic zone and subgrade type) on performance. The summary of results from this analysis is given below: ⢠The results of the available data indicate that WF zones have shown relatively higher potential for fatigue cracking; however as expected, the magnitude of distress is not significant. ⢠Results for longitudinal cracking-NWP were inconclusive. ⢠Transverse cracking occurred mainly in freeze zones. ⢠There was higher amount of raveling observed in WNF zone. ⢠Rutting performance was similar in all environments and for different subgrade types; this is to be expected since rutting is essentially a load-related distress. ⢠The results of roughness in terms of IRI show that sections built in WF zones appear to have higher roughness, followed by those built in WNF zones. 7.2.2 Overall Analysis The overall initial trends which show the effect of SPS-8 experimental factors on various performance measures will be discussed in this section. These comparisons were carried out only for the performance measures which have shown some extent in the SPS-8 flexible pavements. Fatigue Cracking: Fatigue cracking was observed in only 12 out of 32 pavement sections. Among the cracked sections, the area of fatigue cracking varies from 0.2% to about 19% with an average of 3%. Excluding section 36-0801, where 19% of area has fatigue cracking, the average cracking area of cracked sections is about 1% with a range of 0.2% to 4.5%. The average fatigue cracking by experimental factors is shown in Figure 7-1. Pavements located in WF zones have a higher potential for cracking. On average, flexible pavements constructed on active subgrade
378 (frost susceptible or expansive) soils and pavements with thin [102 mm (4-inch)] asphalt layer have exhibited more cracking on average than those built on other subgrade types and with thick [178 mm (7-inch)] HMA surface layer. In order to show the effect of active subgrade within fine and coarse soil types, the average performance is presented in Figure 7-2. It was observed that flexible pavements constructed on the active coarse-grained subgrade soils have shown higher potential for fatigue cracking. Longitudinal Cracking (WP and NWP): Longitudinal cracking-WP was observed in only 13 out of 32 pavement sections, while longitudinal cracking-NWP occurred in 20 pavement sections. Among the cracked sections, longitudinal cracking-WP length varies from 1 to 97 m with an average of 18 m, while longitudinal cracking-NWP length varies from 1 to 305 m with an average of 115 m. Excluding both sections from MT (30) site, where 78 m and 97 m of longitudinal cracking-WP occurred in sections 0805 and 0806, among cracked sections, the average crack length is 5 m with a range of 1 to 22 m. The average longitudinal cracking in the wheel path (WP) and non-wheel path (NWP) by experimental factors are shown in Figure 7-3 and Figure 7-5. More longitudinal cracking-WP was observed on sections located in DF zone. This cracking is mainly contributed by sections in site MT (30), which are constructed on coarse subgrade type. More cracking-NWP was observed in all pavements constructed on active subgrade soils and located in WF zone. Also more cracking-NWP was observed in sections located in DNF, which is contributed by sections in NM (35) site only, these sections were constructed on fine-grained subgrade soils. The flexible pavements constructed on active fine- grained soils have shown slightly more cracking-WP; the opposite trend was observed for pavements constructed on coarse-grained soil due to contribution of only sections at site MT (30) (see Figure 7-4). More cracking-NWP is observed for flexible pavements constructed on active soils (see Figure 7-6). Transverse Cracking: Transverse cracking was observed in only 10 out of 32 pavement sections. Among the cracked sections, transverse cracking length varies from 1 to 44 m with an average of 11 m. On average, pavements located in âfreezeâ climate and constructed on active soils have exhibit more transverse cracking. The average transverse cracking by experimental factors is shown in Figure 7-7. Pavements with âthickâ [178 mm (7-inch)] HMA surface layer
379 have shown less transverse cracking than those with âthinâ [102 mm (4-inch)] HMA surface layer. On an average more transverse cracking was exhibited by flexible pavements constructed on active soils and pavements located in âfreezeâ climates. The pavements with thicker asphalt layer have shown lower transverse cracking than pavements with thinner asphalt surface layer. The flexible pavements constructed on active subgrade have exhibited more transverse cracking than those constructed on non-active subgrade soils especially within fine subgrades (see Figure 7-7). Roughness: The average roughness, in terms of IRI, by experimental factors is presented in Figure 7-9. The average initial IRI of the SPS-8 flexible pavement sections is 1.1 m/km, with a range of 0.8 to 3.2 m/km. The average change in IRI (IRI) for pavements is 0.32 m/km with a range of 0.0 to 2.4 m/km. Excluding both sections from OH (39) site, where 2.2 m/km and 1.7 m/km of IRI occurred in sections 0803 and 0804, the average IRI is 0.2 m/km with a range of 0 to 1 m/km. On average, pavements located in âwetâ climate have higher change in IRI than those in âdryâ climate. Furthermore, pavements located in WF zone and those built on active soils have the higher changes in IRI. Also pavements constructed on active subgrade soils have exhibited more roughness than other pavements (see Figure 7-10). Rut Depth: The average rut depth for flexible pavements by experimental factors is shown in Figure 7-11. The average latest rut depth of the sections is 5 mm with a range of 1 to 24 mm. Excluding section 39-0803, where 24 mm of rut depth was observed, the average rutting is about 4 mm with a range of 1 to 9 mm. On average, the magnitude of rutting observed is âlowâ for the sections. Slightly higher average rut depths were observed for the pavements located in WF zone. Also pavement sections with âthinâ [102 mm (4-inch)] HMA surface layer have exhibited higher rutting than pavements with âthickâ [178 mm (7-inch)] HMA surface layer. Furthermore, active subgrade seems to contribute towards more rutting (Figure 7-12). The magnitude of rutting was observed to be âlowâ for all sections in the experiment, which is expected since rutting is essentially a load-related distress.
380 7.2.3 Comparison between Similar Designs of SPS-8 and SPS-1 Experiments To investigate the effect of traffic loading, similar designs in SPS-8 and SPS-1 experiments can be compared for various performance measures. This comparison may help in identifying load-related and environment-related distresses. Median comparisons (non-parametric) were performed on similar sections in both experiments. From the experiment design matrix for SPS-1, sections 113 & 114 in all sites were identified to be similar to the structural design of SPS-8 flexible pavement sections. To investigate the median difference between the performances of these sections, the sections were analyzed in two groups [102 mm (4-inch) and 178 mm (7-inch) HMA thickness]. It was found that fatigue cracking is essentially a load-related distress whereas; transverse cracking and longitudinal cracking-NWP may be attributed to environment. However, because of the apparent differences in the traffic levels between SPS-8 and SPS-1 experiment, the project panel recommended that such comparisons should not be considered. 7.3 EFFECTS OF ENVIRONMENTAL FACTORS IN SPS-8 EXPERIMENT FOR RIGID PAVEMENTS The objective of the SPS-8 experiment is to develop conclusions concerning environmentally induced serviceability loss and the contribution of environment and subgrade to the distress of pavements. The experiment will also develop conclusions concerning the effects of base and surface thickness variations on retarding environmentally driven distress. 7.3.1 Site-Level Analysis The analysis of the SPS-8 rigid pavements was done based on the PI and the relative performance concepts (see Chapter 4) similar to SPS-2 experiment. At the site-level, roughness and transverse joint sealant damage were analyzed to investigate the effects of the main site factors (climatic zone and subgrade type) on performance. The summary of results from this analysis is given below: ⢠The ride quality for sections constructed in the Dry Freeze zone was better than those constructed in the Wet zones. Furthermore, it can be concluded that the sections in the Wet Freeze zone exhibit a better ride than the ones in the Wet No Freeze zone. ⢠Transverse joint sealant damage appeared to be more prevalent in the Wet zones as compared to the Dry Freeze zone.
381 0 5 10 15 20 25 30 35 40 WF WNF DF DNF A C F Thin Thick Experimental Factors A v g . f a t i g u e c r a c k i n g , s q - m Figure 7-1 Average fatigue cracking by experimental factorsâ SPS-8 flexible pavements 0 10 20 30 40 50 60 70 F C Subgrade Type A v g . f a t i g u e c r a c k i n g ( s q - m ) Non-Active Active Figure 7-2 Average fatigue cracking by subgrade typeâ SPS-8 flexible pavements 0 10 20 30 40 50 60 70 WF WNF DF DNF A C F Thin Thick Experimental Factors A v e r a g e L C - W P ( m ) Figure 7-3 Average LC-WP by experimental factorsâ SPS-8 flexible pavements 0 10 20 30 40 50 60 70 F C Subgrade Type A v e r a g e L C - W P ( m ) Non-Active Active Figure 7-4 Average LC-WP by subgrade typeâ SPS-8 flexible pavements
382 0 50 100 150 200 250 300 WF WNF DF DNF A C F Thin Thick Experimental Factors A v e r a g e L C - N W P ( m ) Figure 7-5 Average LC-NWP by experimental factorsâ SPS-8 flexible pavements 0 50 100 150 200 250 300 F C Subgrade Type A v e r a g e L C - N W P ( m ) Non-Active Active Figure 7-6 Average LC-NWP by subgrade typeâ SPS-8 flexible pavements 0 2 4 6 8 10 12 14 16 WF WNF DF DNF A C F Thin Thick Experimental Factors A v g . t r a n s v e r s e c r a c k i n g ( m ) Figure 7-7 Average transverse cracking by experimental factorsâ SPS-8 flexible pavements 0 5 10 15 20 25 F C Subgrade Type A v g . T r a n s v e r s e C r a c k i n g ( m ) Non-Active Active Figure 7-8 Average transverse cracking by subgrade typeâ SPS-8 flexible pavements
383 0.0 0.5 1.0 1.5 2.0 WF WNF DF DNF A C F Thin Thick Experimental Factors A v e r a g e I R I , m / k m Figure 7-9 Average roughness by experimental factorsâ SPS-8 flexible pavements 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 F C Subgrade Type A v e r a g e I R I ( m / k m ) Non-Active Active Figure 7-10 Average roughness by subgrade typeâ SPS-8 flexible pavements 0.0 1.0 2.0 3.0 4.0 5.0 6.0 WF WNF DF DNF A C F Thin Thick Experimental Factors A v e r a g e R u t d e p t h , m m Figure 7-11 Average rut depth by experimental factorsâ SPS-8 flexible pavements 0.0 1.0 2.0 3.0 4.0 5.0 6.0 F C Subgrade Type A v e r a g e R u t d e p t h ( m m ) Non-Active Active Figure 7-12 Average rut depth by subgrade typeâ SPS-8 flexible pavements
384 7.3.2 Overall Analysis The overall initial trends which show the effect of SPS-8 experimental factors on various performance measures will be discussed in this section. These comparisons were carried out only for those performance measures that were exhibited to some extent in the rigid pavements sections. Transverse Cracking: Figure 7-13 shows the average transverse cracking length by experimental factors, for rigid pavements. Only three of the fourteen sections have transverse cracking, ranging from 1 to 5 cracks. Cracking was not observed in any of the pavements constructed with thicker PCC slab and in any of the pavements constructed on coarse-grained subgrade soil. Average transverse cracking was found to be higher on section located in DF zone, which was contributed by section 0811 of site CO (8). This site is the oldest (10 years) in the experiment and âvery poorâ climatic conditions prevailed during the construction that caused construction to happen at faster rate. Among the pavements built on fine-grained soils, those built on active soils have exhibited slightly lesser cracking than those built on non-active subgrades (see Figure 7-14). Longitudinal Spalling: Figure 7-15 shows the average longitudinal spalling length by experimental factors, for rigid pavements. Six of the fourteen sections have longitudinal spalling ranging from 1 to 79 m with an average of 34 m. Spalling was not observed in any of the pavements located in the DF zone and in any of the pavements constructed on coarse-grained subgrade soil. Average spalling was found to be higher on section located in WNF zone. Also pavements with thicker PCC slab have shown slightly higher spalling than those with thinner PCC slab. Among the pavements built on fine-grained soils, those built on active soils have exhibited slightly higher spalling than those built on non-active subgrades (see Figure 7-16). Wheel Path Joint Faulting: Average percent of joints that faulted more than 1 mm, by experimental factors, is shown in Figure 7-17. Seven sections have faulting of more than 1.0 mm at one or more joints. Among these sections, on average, 8% of the joints faulted more than 1 mm, with a range of 3 to 21% of joints. Average percentage of joints that faulted more than 1 mm was found to be higher on sections located in WNF zone. Also pavements constructed on active subgrade soil have shown slightly higher faulting than those constructed on others. Among the
385 pavements built on coarse-grained soils, those built on active soils have exhibited higher faulting than those built on non-active subgrades (see Figure 7-18). Roughness: Average roughness by experimental factors, is shown in Figure 7-19. The average initial IRI of the SPS-8 rigid pavement sections is 1.8 m/km, with a range of 1.0 to 3.6 m/km. The average change in IRI for rigid pavements is 0.1 m/km with a range of 0.0 to 0.7 m/km. Average roughness was found to be higher on sections located in WNF zone. Also pavements constructed on active subgrade soil have shown slightly higher IRI than those constructed on others. Among the pavements built on coarse-grained soils, those built on active soils have exhibited higher IRI than those built on non-active subgrades (see Figure 7-20). It may be noted that similar trends were observed for faulting and roughness, which may suggest a cause-effect relation among these performance measure. 7.3.3 Comparison between Similar Designs of SPS-8 and SPS-2 Experiments As in the case of analysis of flexible pavements of the experiment, comparisons were performed between the similar designs of SPS-8 and SPS-2 experiments. SPS-8 rigid pavements exhibited insignificant amount of distresses, whereas the companion SPS-2 states exhibit a wide variety of distresses (see Chapter 3). These distresses may be attributed to traffic-loading.
386 0 2 4 6 8 10 12 14 16 WF WNF DF A C F Thin Thick Experimental Factors A v g . t r a n s v e r s e c r a c k i n g , m Figure 7-13 Average transverse cracking by experimental factorsâ SPS-8 rigid pavements 0 1 2 3 4 5 6 7 8 9 10 F C Subgrade Type A v g . t r a n s v e r s e c r a c k i n g ( m ) Non-Active Active Figure 7-14 Average transverse cracking by subgrade typeâ SPS-8 rigid pavements 0 5 10 15 20 25 30 35 40 45 WF WNF DF A C F Thin Thick Experimental Factors A v g . L o n g . S p a l l i n g , m Figure 7-15 Average long. spalling by experimental factorsâ SPS-8 rigid pavements 0 5 10 15 20 25 30 35 40 45 F C Subgrade Type A v g . L o n g . S p a l l i n g ( m ) Non-Active Active Figure 7-16 Average long. spalling by subgrade typeâ SPS-8 rigid pavements
387 0 1 2 3 4 5 6 7 8 9 10 WF WNF DF A C F Thin Thick Experimental Factors A v g . % o f J o i n t s w i t h f a u l t > 1 m m Figure 7-17 Average no. of joints having faulting > 2% by experimental factorsâ SPS-8 rigid pavements 0 2 4 6 8 10 12 14 16 18 20 F C Subgrade Type A v g . % o f J o i n t s w i t h f a u l t > 1 m m Non-Active Active Figure 7-18 No. of joints having faulting > 2% by subgrade typeâ SPS-8 rigid pavements 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 WF WNF DF A C F Thin Thick Experimental Factors A v g . I R I ( m / k m ) . Figure 7-19 Average IRI by experimental factorsâ SPS-8 rigid pavements 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 F C Subgrade Type A v g . I R I ( m / k m ) Non-Active Active Figure 7-20 Average IRI by subgrade typeâ SPS-8 rigid pavements
388 7.4 SUMMARY OF RESULTS The SPS-8 experiment is entitled Strategic Study of Environmental Effects in Absence of Heavy Loads for Flexible and Rigid Pavements. The study examines the effect of climate and subgrade type (active, fine, and coarse) on pavement sections incorporating different flexible and rigid pavements, which are subjected to very limited traffic as measured by ESAL accumulation. The effects of the experimental factors on flexible and rigid pavements, based on the initial trends, are summarized below. 7.4.1 Effect of SPS-8 Experimental Factors on Performance of Flexible Pavements Currently a total of 32 flexible pavement sections, in 15 sites, are present in the experiment. There are 14, 8, 6 and 4 pavement sections in WF, WNF, DF and DNF climatic zones, respectively. A total of 14 pavement sections were constructed on coarse-grained soils among which 4 sections are on âactiveâ soils and 10 sections are on ânon-activeâ soils. Also, 18 pavement sections were built on fine-grained soils, among which 12 sections are on âactiveâ soils and 6 sections are on ânon-activeâ soils. These test sections have an average age of about 6 years with a range of 3 to 10 years. The effects of the design and site factors based on initial trends, as of Release 17.0, on key performance measures are presented below: On average, pavements in WF zone have more fatigue cracking, longitudinal cracking- NWP, and roughness than pavements in other climates. Also, in general, pavements constructed on âactiveâ subgrade (frost susceptible or expansive) soils have higher longitudinal cracking-NWP, transverse cracking, and fatigue cracking than pavements on ânon-activeâ soils. Pavements located in âwetâ climate, on average, have higher change in IRI than those in âdryâ climate. Furthermore, pavements located in WF zone and those built on active soils have the higher changes in IRI.
389 7.4.2 Effect of SPS-8 Experimental Factors on Performance of Rigid Pavements Currently a total of 14 rigid pavement sections, in 5 sites, are present in the experiment. There are 8, 4 and 2 pavement sections in WF, WNF, and DF climatic zones, respectively. Three pavement sections were constructed on coarse-grained soils among which 2 sections are on âactiveâ and one section is on ânon-activeâ soil. Also, 11 pavement sections were built on fine-grained soil, among which 4 sections are on âactiveâ soils and 7 sections are on ânon-activeâ soils. These test sections have an average age of about 6.5 years with a range of 4 to 10 years. The distresses are too âlowâ for any meaningful conclusions to be made, at this point in time. Some observations based on initial trends, as of Release 17.0, on key performance measures are presented below: Longitudinal spalling, on average, was higher in sections located in âwetâ climate. Spalling was not observed in any of the pavements located in the DF zone and in any of the pavements constructed on coarse-grained subgrade soil. Transverse cracking was not observed in any of the pavements constructed with thicker PCC slabs and in any of the pavements constructed on coarse- grained subgrade soils.