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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

2011

ACPA Larry Scofield

1/11/2011

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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.

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

Cell 37

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Figure 3 indicates the original NGCS texture constructed in June 2007. 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 Pattern1

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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

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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.

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

NGCS LITE

Original NGCS

CDG

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Figure 7 Photo of NGCS LITE Texture

Figure 8 Blade Matrix Remaining on Surface After Burning Blades

Matrix Deposited by Head

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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, 10-15 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.

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.

“Gunsite”

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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

Figure 11 Overall A-weighted OBSI Test Results for Husqvarna/Interstate Test

Strip

99.8 99.6 99.599.8 99.9 99.7 99.7 99.9 99.9 100.0

94

96

98

100

102

104

106

108

110

So

un

d I

nte

nsit

y L

evel,

dB

A

Pavement Section

XX & XX OBSIOverall A-wtd Levels

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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.

Figure 13 MnDOT Friction Testing of Cell 37 Test Strips

75

80

85

90

95

100

105

500 630 800 1000 1250 1600 2000 2500 3150 4000 5000

So

un

d In

ten

sit

y L

evel,

dB

A

1/3 Octave Band Center Frequency, Hz

MnROADS Husqavarna NGCS Results

Pass 1

Pass 2

Pass 3

Pass 4

Pass 5

Pass 6

Pass 7

Pass 8

Pass 9

Pass 10

54.4 55.4 55.7 55.6

59.1

53.4

63.7

52.855.2

53.7

0

10

20

30

40

50

60

70

Fric

tio

n N

um

be

r (S

N4

0)

Test Strip Texture

Friction Results for MnROADS Cell 37 Test Strips 9/8/10

NGCST1

NGCST2

CDGT3 Existing

Transverse Tine

NGCSLITET4

Smooth Tire

Ribbed Tire

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Summary

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.

References

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 1969

Appendix 1 Photos of Husqvarna/Interstate NGCS Texture

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Figure 1-1 Close Up of Husqvarna NGCS Texture

Figure 1-2 Close Up of Husqvarna NGCS Texture w/Ruler

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Figure 1-3 Angle View of Husqvarna NGCS Texture

Figure 1-4 Angle View of Husqvarna NGCS Texture

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Figure 1-5 Angle View of Husqvarna NGCS Texture

Figure 1-6 Existing Transverse Texture within NGCS Test Strip

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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

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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

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Figure 1-10 Existing Texture In Pavement Low Spot

Figure 1-11 Existing Texture in NGCS Texture

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Figure 1-12 Close Up of NGCS Texture

Figure 1-13 Close Up of NGCS Texture

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Figure 1-14 NGCS Texture with Ruler

Figure 1-15 Existing Transverse Texture in NGCS Surface

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Figure 1-16 NGCS Texture Just After Grinding

Figure 1-17 NGCS Texture Just After Grinding

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Figure 1-18 NGCS Texture Just After Grinding

Figure 1-19 NGCS Texture Immediately After Grinding

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Figure 1-20 Photo of Original NGCS Surface Constructed in 2007

Appendix 2 Photos of Pavement Issues in Test Strip

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Figure 2-1 Plant Growing From Core Hole in Test Strip

Figure 2-2 Existing Handholes In Test Strip

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Figure 2-3 Hand Hole In Test Strip

Figure 2-4 Hand Hole In Test Strip

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Figure 2-5 Plant Growing in Core Hole Between Test Strips

Figure 2-6 Transverse Joint in Existing Pavement