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CHAPTER 4 EXPERIMENTAL STUDIES A number of experimental field and laboratory studies were necessary In order to provide the data needed to develop the models used In the PAVDRN software. Permeability measurements were obtained in the laboratory for open-graded laboratory and field asphalt mixtures in order to obtain their coefficients of permeability. Mean texture depth measurements were obtained for all of the pavement surfaces tested In the laboratory and field using either the sand patch or a profiling method. Water film thickness measurements were obtained In the laboratory with a color-~ndicat~ng gauge and a point gauge. The color ndicat~g gauge was used exclusively In the field for water film thickness measurements. The Indoor artificial rainfall simulator at Penn State was used in the laboratory to determine ManIiing's n for porous asphalt surfaces and to extend the existing data on Portland cement concrete surfaces to longer flow paths as required for PAVDRN. In the field, full-scale skid testing measurements were needed to extend the hydroplaning model to porous pavement surfaces and to verify the effect of Portland cement concrete grooving on hydroplane g speed. These data were obtained by conducting filll-scale skid test measurements on porous asphalt surfaces installed at the Penn State Pavement Durability Research Facility. Full-scale skid testing was also performed on grooved PCC surfaces at the Wallops Flight Facility. The fulI-scale held skid testing required measurements 69

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at different speeds on the surfaces flooded with water at different fihn thicknesses. The test facilities, test melons, and test results are discussed In this chapter. TEST FACILITIES Indoor Artificial Rain Facility The pavement test surfaces were formed ~ a rectangular channel that was 0.30 m wide and 7~3 m long. The sides of the channel were formed by two BO-mm by 160-mm steel angles that were mounted 0.30 m apart, as shown ~ figure 15. To complete the channel, the steel angles and 20-mm thick sheets of plywood were bolted to the top flange of a 7.3-m wide flange WI2x53 steed beam as shown In figure 16. A jacking system allowed the longitudinal slope of the beam to be adjusted to provide a range of slopes. The porous asphalt concrete and Portland cement concrete were placed In the channel, providing the test surfaces for measuring Mami'ng's n. Artificial rainfall was generated with a series of nozzles placed above the test surface, as shown In figure 17. Extensive evaluations were performed previously to calibrate the rainfall rate and to select appropriate nozzles, spray angles, nozzle distances from the channel pressure settings, etc., to ensure that the rainfall rate was uniform over the entire surface (35). Consequently, the procedures and testing equipment developed previously were used for this study (299. 70

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Plywood base Porous asphalt mixture Steel angle to form sides . Ad. ~ '~-~-~'J-~-~-~-~'~'~-~- - -~'~-~-~'~-~-~'~-~ ke%-%'~'~'~'~'~'%-~-~-~-~-~-~-~-~-~-%'%- - -~-~-~-~-~. '~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~d i..~.~-.~-.~.~-.~.~.~-.~.~-.~-.~-~-.~-.~.~.~-.~-.~-.~-.~-.~-.~-.~-~-~1 Steel"~" section to support base and mixture a, , Note: Elevation of one end of steel beam can be adjusted to change longitudinal slope of drainage surface. Figure 15. Cross-section of pavement used in laboratory rainfall simulator. 71

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Figure 16. Overall view of test channel used with laboratory rainfall simulator. 72

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~ : ~.,~ ~ ~ ~ ~ ~:::::: :~: ~i: :~: :::::::::: ::::::::::::::::::::::::::::::::::::::::::::::::::: ::: ~:~::~: ~:~::~:::~:::::: If: Figure 17. Laboratory rainfall simulator. 73 _ ~

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The channel was limited In length to 7.3 m. With this length and the maximum rainfall rate, the largest Reynold's number that could be generated was approximately 130. However, in this study it was necessary to measure WET values in flow regimes with Reynold's numbers greater than 140. Since the maximum rainfall intensity was 75 mm/in, it was necessary to effectively increase the drainage path lengths to achieve higher Reynold's numbers. This was done by introducing a flow at the top of the channel so that the channel represented the last 7.3-m segment of a longer flow path. For example, to create a 14.6-m long flow path, the flow that would be accumulated over the first 7.3-m segment was introduced at the top of the channel, effectively making the channel act as the last 7.3-m segment of a 14.6-m long flow path. The flow introduced at the top of the channel was commensurate with the rainfalls rate on the channel, adjusted for non-turbulent conditions in the first 0.5 m of flow. A small adjustment in the introduced flow rate, as calculated on the basis of the rainfall rate, was necessary because the turbulence caused by pelting raindrops impede flow. Approximately 0.5 m was required to develop fully turbulent flow, causing the actual flow to be greater than under conditions where the flow on the entire 7.3-m channel length was filly turbulent. This phenomenon has been observed by others when analyzing the short, sudden rise in flow at the end of rainfall-runoff hydrographs (39J . The adjustment was determined experimentally by measuring the flow at the end of the channel for different rainfall rates. The flow was introduced at the top of the channel in a gentle spray applied directly onto the concrete surface in the channel. 74

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For the porous asphalt mixtures, the How through the mixture had to be determined and evaluated e A distribution box with a baffle was placed at the top of the channel to provide a base flow through the porous mixes. The bottom of the channel was sealed to a depth of 12 mm below the top of the surface, effectively forming a dam to prevent ~awdown effects of the flow through the porous asphalt. If the bottom was left completely open, the water surface profile would draw down dramatically at the end of the channel, which would lessen the length of the channel that could be used for experimentation. This arrangement is shown in figure 18. Production and Placement of Porous Mixes Three porous mixes were tested In ache laboratory under artificial rainfall. Each mixture was designed to yield a different mean texture depth and air-void content. Attempts to place hot-mixed asphalt in the channel were not successful, and instead, a slow-setting epoxy was used as the binder for these mixtures by replacing the asphalt binder on a vol~netric basis. The epoxy had a curing tune of six hours, which allowed for an adequate time to place and compact the mixes. A number of trial mixtures were prepared to obtain a range In air void content and MTD. The composition of the resulting three porous asphalt mixtures placed in the laboratory is shown in table 8, and the gradations are presented in figure 19. The mixes were prepared from a blend of two coarse aggregates (PennnOT gradation IB and 2B, bow Innestone, retained on No. 4 sieve) and washed glacial sand (siliceous, passing No. 4 sieve). Norrunal 75

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1 a) ~ - ~ - ~ a) ~ ~ - co o - an al := ce m cats .E ~ 3 ~ O O ~ m .= it' \ \ \ ce a, ma,, oEl ! I; ,1~ x . - Q In In 3 2 o ID 3 Cal o (D- In ~ ~ o CO Figure 18. Cross-section of flow for porous asphalt sections In laboratory 76 .

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1 .~ i 1 1 ; 1 i I , Ad ~ ~ 2 X ~ an Y CD CO ~_ oh an oh : I l : 1 1 ~ m {D 0 ye Cal Q 1 1 Con ~2 o o Q J 1 1 _ Al ~ cry E - _ ~ ~ cad E E _ _ ., E 1~''-~'- 1-..t -ant. ~-.~ -A 1 1 1 1 1 - ~ 4g, f 1 l l =~- 5= 1 1 , .V ~ ~-~ ~. o o o o ~ CO C ~ o o o o 0 ~ ac ~ ~ E 0 0 0 ~ u, 6u!ssed o/O ~ E 1 _ _ _ %, `. . -\, ~: \\ (' \. \\~.t Figure 19. Gradations of laboratory and field porous asphalt mr~tures. 77

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Table 8. Mixture designs for porous asphalt laboratory mixes. Component Mixture (% by total weight of aggregate) A B C 2B Aggregate ~44 IB Aggregate 75 75 34 Washed Sand 19 19 20 Hydrated Lune 6 6 2 Epoxy (%wt. of 7 7 5.5 total mix) maximum size is 9 and IS mm for IB and 2B aggregates, respectively. Hydrated lime was added to thicken the epoxy and prevent drainage of the epoxy from the mixture. Mixture A was designed using the guidelines and design process as outlined for open-graded friction courses as published by NCHRP (109. This mixture was placed by hand, resulting in a very high a~-void content, as illustrated In table 8. Mixtures B and C were placed with a vibratory compactor; the gradations and max~m~,rn aggregate size were selected to account for the increased compaction and to give a range in air voids and MTD. The compactor, developed as part of this study, consisted of a 0.30-m square by 25.4-mm thick steel plate with an air vibrator mounted on top of the plate. The vibrator is used commercially for applications such as vibrating granular materials from storage bins. It is rated at 2,400 cycles per minute with 7.2 kN of applied force per cycle. The entire assembly weighed 580 N. A photograph of the assembly is shown In figure 20. 78

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Figure 20. Photograph of vibratory compactor. 79

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texture depths of mixtures A, B. and C are visibly different and fall within the expected range of ~ mm (0.04 in) to 3 mm (0. 12 Ins. Profile traces were used to calculate estimated texture depth (ETD) according to ASTM E IS45-96, "Standard Method for Measuring Surface Macrotexture Depth Using a Volumetric Technique," ISO standard as described In figure 29 (421. The results are presented in table ~ ~ . The sand patch measurements on the original surface are suspect, especially for mixture A. The profile measurements were difficult to obtain because the probe constantly stalled In the deep voids. Based on these facts, sand patch measurements on replicates of the surface are the recommended technique for making texture measurements even though it may not be convenient for field testing, particularly on highly trafficked pavements. Texture measurements made at the Penn State Pavement Durability Research Facility are found in table 12. Table 11. Texture Kept measurements on laboratory porous asphalt sections. Distance MTD Values (mm) along channel (m) Mix A Mix B MLX C 0.3 1.45 1.04 2.34 1.5 1.60 -- - 3.2 2.13 1.07 2.24 3.6 1.57 1.45 - 4.8 - 1.24 1.98 6.3 1.47 1.93 Average 1.70 1.24 2.13 Sand patch directly on 5.1 1.9 2.3 surface, Average (mm) MTD estimated from profile measurements 2.54 2.26 2.92 directly on surface (see figure 29) 106

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Table 12. Sand patch data obtained at the Penn State Pavement Durability Research Facility. _ Mean Texture Depth Sand Patch Diameter (rnm) (in) MixStation ~2 3 4 Average Station Section Average Average 1105 149.2 136.5 139.7 139.7 1411.55 75 139.7 139.7 146.1 136.5 1401.60 45 146.1 146.1 146.1 139.7 1441.55 15 152.4 158.8 158.8 158.8 157 145 1.27 1.5 2 105 88.9 95.3 88.9 88.9 90 3.66 75 95.3 95.3 88.9 88.9 92 3.66 101.6 101.6 101.6 88.9 98 3.12 15 88.9 88.9 82.6 82.6 85 91 4.11 3 105 133.4 133.4 133.4 136.5 134 1.73 75 136.5 139.7 133.4 139.7 137 1.65 45 146.1 146.1 139.7 139.7 142 1.55 15 146.1 127.0 139.7 146.1 139 138 1.60 1.6 4 105 165.1 165.1 158.8 168.3 164 1.14 75 177.8 165.1 171.5 177.8 173 1.04 177.8 165.1 177.8 177.8 174 1.02 15 171.5 158.8 165 166 169 1.12 1.1 Full-Scale Skid Testing Full-scale skid testing was done at the Penn State Pavement Durability Research Facility and at the Wallops Flight Facility. The results of the testing performed at the Penn 107

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State Durability Research Facility are presented In figures 33 through 36 for the four test sections. A great effort was required to obtain these results. The sections were dammed along their side and flooded (one section at a tune) as described previously In this chapter. The skid trailer was driven at different speeds down the track, and the tire, a bald ASTM E 524-88 ("Standard Specification for Standard Smooth Tire for pavement Skid-Resistance Tests") tire, was locked over the flooded middle portion of the section. Water film Sickness measurements were taken with the color-~ndicat~ng gauge at intervals along the section immediately before each test as described previously. This resulted in nearly 50 sets of skid resistance-water film thickness data. In general, relatively uniform water film measurements were obtained, and only a few of the data sets were discarded. Analog traces of wheel friction recorded by the tester were examined for anomalous data. In order to obtain a zero thickness value of skid resistance, the wheel of the trailer was locked on each section with no flooding but with a damp surface. In general, replicate runs were made at each water film thickness and speed. Although there is considerable variability In the data, several conclusions can be drawn from the test results. For the water film thicknesses that were tested, the skid resistance values were less than the "zero thickness" values. For each section, the skid resistance decreased as the water film thickness Increased. However, the skid resistance typically reached a minimum and then unexpectedly increased with increasing water film thickness. After some thought, this was considered reasonable, explained by the "plough~ng" effect of the wave of water pushed by the locked tire. Minim~:nn skid resistance values were in the range of four to ten depending on the test section. Hydroplaning occurred on all of the test sections at 60 and 90 Inch when the water film thickness became high. 108

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1 Flooded pavement, 30 km/in Flooded pavement, 60 km/in Flooded pavement, 90 km/in 0 Wet pavement, 60 km/in 1l 0 Flooded pavement, ribbed tire, 60 km/in I 60 50 Z~n a) Q ~ 30 ~5 z ~ 20 In 40 10 l 3 km/in | \ ~ ~60 km/in l \ 4~ |9o km/in | ~ - . . i 0.0 5.0 1 0.0 1 5.0 Water film thickness, mm Figure 33. Skid resistance measurements at ache Penn State Pavement Durability Research Facility, mixture I. 109

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Flooded pavement, 30 km/in Flooded pavement, 60 km/in Flooded pavement, 90 km/in 0 Wet pavement, 60 km/in ll l 50 45 40 z 35 ; 30 Q z co 1 5 25 20 10 5 O \ \/|30km/h| / .~ ~ 1 ~ \ / L \ ~. \ ~160 km/in| '~ . ~ ~ 0.0 5.0 1 0.0 1 5.0 20.0 Water film thickness, mm ,~ Figure 34. Skid resistance measurements at the Penn State Pavement Durability Research Facility, mixture 2. ~0

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60 50 Z 40 Q 30 ~ 20 cn 10 O 0.0 l Flooded pavement, 30 km/in Floodecl pavement, 60 km/in Flooded pavement, 90 km/in o Wet pavement, 60 km/in \~ / - ~ 130 km/in 1 60 km/in I 1 / 90 km/in ~ - - . ! l l - 5.0 1 0.0 1 5.0 20.0 Water film thickness, mm Figure 35. Skid resistance measurements at the Penn State Pavement Durability Research Facility, mixture 3 .

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Flooded pavement, 30 km/in Flooded pavement, 60 km/in Flooded pavement, 90 km/in o Wet pavement, 60 km/in 70 60 z 50 ~n - ~ 40 ~ Q z 30 ~5 ._ C'' 20 10 o /13 km/in| ~ ~ my, ,/~k ~ ~ : ! . . ~I 1 0-0 5.0 1 0.0 1 5.0 20.0 Water film thickness, mm Figure 36. Skid resistance measurements at the Penn State Pavement Durability Research Facility, mixture 4. ~2

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The results from the testing In the grooved and plain Portland cement concrete at the Wallops Flight Facility are shown in table 13 arid figures 37 and 38. Quite surprisingly, the skid resistance versus water film thickness relationship for the grooved versus the plain Portland cement concrete surface was very similar when the mew texture depth is calculated using the surface at the top of the grooves as the Datsun. Thus, although the grooves are a definite aid ~ removing water from the pavement surface, they do little to relieve the water film from beneath the tire. This effect is not apparent ~ the standard ASTM E 274 test as illustrated In figures 34 and 35. ~ the opinion of the researchers, this is also the case with porous asphalt surfaces. In other words, We main contribution offered by porous asphalt pavement surfaces to the lowering of hydroplaning speed, even though it is a very significant contribution, is ache Increase In the mean texture depth that these surfaces offer. These findings do not agree with maIly practitioners who fee! that the grooving and large texture ~ porous mixtures allows the water to drain from beneath the tire. Of course, Me findings here are for the locked bald tire according to ASTM E 274, and the findings may be different for more heavily loaded truck tires or grooved passenger tires. ~3

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Table 13. Skid resistance test data obtained at the Wallops Flight Facility . Pavement Water Film (skp~ ehd) Skid Number Average Brushed Concrete 12.5~' 60 14.8 14.8 12.5 75 9.6 9.6 12.5 90 6.1 6.1 12.5 82 7.1 7.1 12.5 100 4.6 4.6 Grooved Concrete 12.5 60 17.3 17.3 12.5 80 12.7 12.7 12.5 90 6.0 6.0 Brushed Concrete ASTM`2' 30 26.9 ASTM 30 31.5 ASTM 30 31.8 30.1 ASTM 60 18.6 ASTM 60 20.3 ASTM 60 24.2 23.2 ASTM 90 13.8 ASTM 90 15.3 ASTM 90 17.0 15.4 Grooved Concrete ASTM 30 30.9 ASTM 30 32.9 31.9 ASTM 60 22.4 ASTM 60 22.6 ASTM 60 46.2 30.4 ASTM 90 30.1 30.1 (')Flooded with water prior to testing. (~'Water applied in front of tire in accordance with ASTM E 274. ~4

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II A S Tag Standennj T est L B' Flood ed to ~ 2 m m 3 5 3 0 2 5 e 2 0 , 1 5 ._ 1 0 5 o n 3 0 6 0 7 5 82 90 1 00 S peed k m/h Ft ore 37. lest res ^ far pi ^ ccdlcretc sections at the TVillcqps Il1~1~ Facility 115

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MASTS Standard Test ~ Flooded to 12 mm 35 30 25 20 - z ~ 15 ._ oh 10 5 a KEgg 1 ~ 1 9 30 1 60 80 Speed, km/in 90 Figure 38. Test results for grooved concrete sections at the Wallops Flight Facility 116 .