MnROADS NGCS LITE Test Strip Evaluation

Transcription

1 2011 MnROADS NGCS LITE Test Strip Evaluation On July 10, 2010 Husqvarna Construction Products and Interstsate Improvement, Inc. constructed a test strip on Cell 37 of the MnROADs Low Volume Road test facility to demonstrate the ability of one of their specialty blades to provide additional texture on the land of the NGCS surface; a process termed NGCS LITE. Testing conducted on July 11 indicated the overall OBSI level was 99.8 dba.. Photo of NGCS LITE Texture 1 ACPA Larry Scofield 1/11/2011

2 Introduction In June of 2007 the industry constructed test strips to field validate the Purdue diamond grinding research. The test strips were constructed on Cell No 37 of the MnROADs Low Volume Road test facility indicated in Figure 1. The field evaluation consisted of constructing three diamond ground test strips, ranging in width from 18 inches to 24 inches as indicated in Figure 2. A fourth strip is also indicated in Figure 2 and this represented the existing random transverse tining that existed on the roadway prior to NGCS construction. The results of that construction set forth the validation of the NGCS texture and subsequent test sections. Cell 37 Figure 1 MnRoads Research Facility with the Location of Cell Number 37 Indicated Figure 2 Test Strips Constructed and Evaluated in Cell 37 of Low Volume Road 2

3 Figure 3 indicates the original NGCS texture constructed in June Although this texture met all the expectations for a low noise surface, it was envisioned that additional texture could be placed upon the lands that may improve the newly developed texture even more in terms of noise and friction. In the 1960s a diamond grinding texture developed by the Christensen Diamond Services Company, see Figure 4, employed serrations on the land area to provide additional friction. At that time noise was not a concern for most roadways. Figure 3 Original NGCS Texture Figure 4 Christensen Diamond Services Company Style 15 Grooving Pattern 1 3

4 During 2009 an effort was underway to develop an NGCS surface with additional texture on the land area; named the NGCS LITE. The NGCS LITE was first attempted in October- November of 2009 by increasing the spacer width from 0.03 (used for the original NGCS surface) to 0.05 inches. Although the texture was successfully constructed on the I-94 MnROADs mainline, it was 1-2 dba louder than the NGCS surface. While the NGCS LITE ribbed tire friction was slightly less than the NGCS friction results, the smooth tire friction was significantly higher than the NGCS surface. A significant advantage of the NGCS LITE surface would be the ability to renew the texture on the land of any NGCS surface. Once constructed the NGCS surface has a wide land area ranging in width from 3/8 to ½ inch wide. This allows a very light re-grind of just the land area which produces an easily renewable surface at a cost-effective price. During the IGGA mid-year meeting in 2009, Mr. Steve Norman indicated that he thought Husqvarna Construction Products had a blade used in architectural applications that could make a surface similar to the desired NGCS LITE or Christensen serrated land area. The V-shaped grooves used in the Christensen design were not necessary as that aspect was a carry-over from the NATO runway era when the V-shape was used to prevent ice formation within the grooving. Although effective, the V-shape is not necessary and complicates blade wear. In the summer of 2010, Husqvarna produced such a blade design for Interstate Improvement, Inc. and they worked with the IGGA and MnDOT to construct a test strip on Cell 37 of the MnROADs low volume road facility. MnDOT agreed to let Interstate grind a two foot wide test strip at the Test Strip No. 4 location indicated in Figure 2. Test strip 4 is located alongside the original NGCS field validation and was the existing transverse tining incorporated in Cell 37 during original construction. NGCS LITE Test Strip Construction On Saturday, June 10, 2010, Interstate Improvement constructed an approximate 500 ft long by two foot wide test strip in Cell 37. Figure 5 indicates the overall view of that test strip in relationship to the three previous test strips constructed for the original NGCS field validation. Figure 6 indicates the Interstate Improvement equipment grinding the test strip. The test strip was successfully constructed and produced the desired texture as indicated in Figure 7. The only problem encountered during construction was the burning of the outside 3-4 inches of the head near the last several hundred feet. Figure 8 indicates the matrix that was deposited on the surface from the burned blades. This was attributed to constructing too soft of a matrix for the section. Husqvarna, however, was not concerned with the ability to produce a more durable blade. The blades were constructed just for the test section in a very short period of time. Appendix 1 has numerous photos of the constructed texture. The groove spacing for this test strip was ¾ c-c as opposed to 1/2: to 5/8 as intended. This was due to the blade widths selected. The existing transverse texture was deep and still evident in a couple of locations on the NGCS LITE test strip. This presumably could increase the overall noise level of the test strip. Appendix 2 has photos of the pavement condition that may affect the overall noise levels 4

5 ranging from existing core holes to existing pavement textures. These effects, if any, should increase the noise level over that produced by just the NGCS texture alone. NGCS LITE CDG Original NGCS Figure 5 NGCS LITE Surface Alongside Original NGCS and CDG Surfaces on MnROADs Cell 37 Figure 6 Interstate Improvement Constructing the NGCS LITE Test Strip 5

6 Figure 7 Photo of NGCS LITE Texture Matrix Deposited by Head Figure 8 Blade Matrix Remaining on Surface After Burning Blades 6

7 The groove depths ranged between 2/32 and 3/32 of an inch, with most of the section at 2/32 inch. The spacing of the grooves was approaching ¾ of an inch although it was suppose to be at 5/8 of an inch. OBSI Testing of NGCS LITE Test Strip On Sunday, July 11, the ACPA conducted OBSI testing of the section using a 2010 Chevy Malibu, the ACPA OBSI dual probe system, and the ACPA 2009 SRTT tire. Since the test strip was only 2 ft wide, special precautions were necessary to ensure the test tire was actually tracking in the test strip. For the original 2007 NGCS test sections, a spotter was used to witness whether the test vehicle remained within the test strip throughout the testing. However, since testing was conducted on a Sunday this was not possible. To alleviate this issue, trial runs were made to verify the adequacy of the driver s skills. A gunsight approach using the windshield washer was used as shown in Figure 9 to provide alignment of the vehicle SRTT tire to the test strip. Gunsite Figure 9 Windshield Washer Used as Gunsight for Aligning Vehicle Path The current arrangement of the test facility provides a significant grade change in the approach to the test section as indicated in Figure 10. This provided a launch pad for the OBSI test vehicle. At first it was not known whether this would interfere with testing as the speed of the test vehicle was hitting 60 mph just after the bump and the car needed to be in the cruise condition shortly thereafter. After numerous practice runs, it did not present a test problem. The original plan was to conduct 10 tests and average the five lowest. This would help offset any passes that could have contacted the edges of the test strip. However, since all ten runs were within ½ dba, all ten runs were used. 7

8 Sound Intensity Level, dba Figure 11 indicates the overall OBSI level for each of the runs. The overall average was 99.8 dba. It is very difficult for concrete pavements to test below 100 dba, so this was a very successful test strip. Figure 12 indicates the one-third octave spectra results for the ten runs. As indicated, very similar results were obtained for all the runs. Figure 10 Launch Pad On test Approach Pavement Section Figure 11 Overall A-weighted OBSI Test Results for Husqvarna/Interstate Test Strip 8

9 Friction Number (SN40) Sound Intensity Level, dba Pass 1 Pass 2 Pass 3 Pass 4 Pass 5 Pass 6 Pass 7 Pass 8 Pass 9 Pass /3 Octave Band Center Frequency, Hz Figure 12 One Third Octave Spectra Results for Husqvarna Test Strip Friction Results On September 8, 2010 MnDOT conducted E274 friction testing using both the ribbed and smooth tires. Figure 13 indicates the results of that testing. As indicated, the NGCS LITE texture had similar friction levels to the original NGCS surfaces so it appears likely that this technique could be used to develop a renewable surface Ribbed Tire Smooth Tire NGCS T1 NGCS T2 CDG T3 Existing Transverse Tine NGCS LITE T Test Strip Texture Figure 13 MnDOT Friction Testing of Cell 37 Test Strips 9

10 Summary References The test strip was successfully placed and resulted in the desired surface texture. The OBSI results were below 100 dba. Friction test results are similar to the original NGCS surface so it appears likely that this texture can be used as a renewable surface. The difference between the original NGCS and the NGCS LITE can be observed by contrasting Figures 3 and 7. Prior to full scale implementation of this texture, there needs to larger test sections of this texture placed under traffic conditions. This will allow evaluation of the blades ability to successfully operate in a production environment. It will also allow time series evaluation of the texture under traffic for both noise and friction. 1. Sherman,G.B.;Skog,J.B.;and Johnson,M.H., Effect of Pavement Grooving on Motorcycle Rideability, California Department of Public Works-Highways Division, November

11 Appendix 1 Photos of Husqvarna/Interstate NGCS Texture Figure 1-1 Close Up of Husqvarna NGCS Texture Figure 1-2 Close Up of Husqvarna NGCS Texture w/ruler 11

12 Figure 1-3 Angle View of Husqvarna NGCS Texture Figure 1-4 Angle View of Husqvarna NGCS Texture 12

13 Figure 1-5 Angle View of Husqvarna NGCS Texture Figure 1-6 Existing Transverse Texture within NGCS Test Strip 13

14 Figure 1-7 Indicating Existing Transverse Tining Still Evident in NGCS Texture Figure 1-8 Overall View of Husqvarna Test Strip Alongside Original NGCS Test Strips 14

15 Figure 1-9 Close Up of Blade Matrix Deposited on Surface From Burning Blades Figure 1-10 Close Up of Blade Matrix Deposited on Surface 15

16 Figure 1-10 Existing Texture In Pavement Low Spot Figure 1-11 Existing Texture in NGCS Texture 16

17 Figure 1-12 Close Up of NGCS Texture Figure 1-13 Close Up of NGCS Texture 17

18 Figure 1-14 NGCS Texture with Ruler Figure 1-15 Existing Transverse Texture in NGCS Surface 18

19 Figure 1-16 NGCS Texture Just After Grinding Figure 1-17 NGCS Texture Just After Grinding 19

20 Figure 1-18 NGCS Texture Just After Grinding Figure 1-19 NGCS Texture Immediately After Grinding 20

21 Figure 1-20 Photo of Original NGCS Surface Constructed in

22 Appendix 2 Photos of Pavement Issues in Test Strip Figure 2-1 Plant Growing From Core Hole in Test Strip Figure 2-2 Existing Handholes In Test Strip 22

23 Figure 2-3 Hand Hole In Test Strip Figure 2-4 Hand Hole In Test Strip 23

24 Figure 2-5 Plant Growing in Core Hole Between Test Strips Figure 2-6 Transverse Joint in Existing Pavement 24