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Rawls, Im, Castorena 1

Tack Lifter for In-Situ Measurement of Effective Emulsion Application Rates 1

2

3

Mary Rawls 4 Graduate Research Assistant 5

Department of Civil, Construction, and Environmental Engineering 6

Campus Box 7908 7

North Carolina State University, Raleigh, NC, 27695-7908 USA 8

Tel: 1-919-515-2331; Fax: 919-515-7908; Email: [email protected] 9

10

Jeong Hyuk Im, PhD 11 Senior Researcher 12

Highway and Transportation Research Institute, 13

Korea Institute of Civil Engineering and Building Technology 14

283, Goyangdae-Ro, Ilsanseo-Gu, Goyang-Si, Gyeonggi-Do, 411-712, South Korea 15

Tel: 82-31-995-0894 Fax: 82-31-910-0374 Email: [email protected] 16

17

Cassie Castorena, PhD (Corresponding Author) 18 Assistant Professor 19

Department of Civil, Construction, and Environmental Engineering 20

Campus Box 7908 21

North Carolina State University, Raleigh, NC, 27695-7908 USA 22

Tel: 1-919-515-6411; Fax: 919-515-7908; Email: [email protected] 23

24

Word count: 4,998 words text + 10 tables/figures x 250 words (each) = 7,498 words 25

26

27

28

29

30

31

Submission Date: 11/05/2015 32


ABSTRACT 1 Emulsion application rates are critically important to the performance of pavement surface 2

treatments and tack coats. In this study, the Tack Lifter is introduced as a means to measure in-3

situ effective emulsion application rates at specific locations along the length of paving. The 4

Tack Lifter is a simple, weighted device that is placed on top of a super-absorbent foam sheet 5

applied to a paving surface. The absorbent sheet soaks up emulsion from the roadway surface in 6

order to get a spot check of the amount of emulsion on the surface. The device measures the 7

effective emulsion application rate on the paving surface, neglecting emulsions absorbed into the 8

paving surface. Laboratory studies of emulsion application onto chip seal and hot-mix asphalt 9

concrete surfaces demonstrate the ability of the Tack Lifter to capture the sensitivity of emulsion 10

absorption to pavement surface texture. In addition, preliminary Tack Lifter field trial results are 11

presented to demonstrate its use as a quality control field test. 12


INTRODUCTION 1 Asphalt emulsions are used as tack coats to bond hot-mix asphalt (HMA) layers and as a bonding 2

agent for aggregates in chip seal surface treatments. The rate of emulsion application is critical in 3

determining the performance of both tack coats (1, 2) and chip seals (3, 10). It has been 4

demonstrated that field emulsion applications rates (EARs) can be highly variable (3, 4). 5

Emulsion distributor nozzle size, nozzle pattern, distributor pressure, tank temperature, and spray 6

bar height can all affect quality control (QC) of emulsion application (5). It is imperative that all 7

of these factors be calibrated regularly to minimize discrepancies between prescribed and actual 8

EARs. However, a survey conducted in 2005 revealed that 25% of agencies in the U.S. do not 9

require calibration (6). Very few measures exist for QC of in-situ emulsion application rates. 10

Mohammad et al. conducted an international survey to identify the methods currently used for 11

QC of EAR (5). The majority of respondents indicated that the change in volume of emulsion in 12

the distributor before and after paving is the only measure used for QC. Additionally, 27% of 13

respondents reported use of the change in tank weight before and after paving as their QC 14

measure and 18% reported that no QC measure is taken. 15

The only standardized procedure which allows for capturing transverse and longitudinal 16

EAR variability is ASTM D 2995: Standard Practice for Estimating Application Rate of 17

Bituminous Distributors (7). However, only 2% of the participants in Mohammad et al.’s survey 18

indicated use of ASTM D 2995 for QC of EAR (5). ASTM 2995 includes provisions for two test 19

methods. The first consists of spot checks, in which the distributer applies emulsion to a standard 20

size tarp placed on the roadway. The tarp is weighed before and after emulsion application to 21

determine EAR. Tarps can be aligned transversely or longitudinally to study the location 22

dependence of emulsion application rate. In the second method, containers are placed directly 23

under each nozzle and distributer releases emulsion for a set amount of time to determine 24

transverse EAR variability. 25

Several studies have noted issues with ASTM D 2995. Mohammad et al. reported that the 26

procedure is a “lengthy process and required multiple calibration runs to ensure accuracy and 27

uniformity of tack coat application” (5). Muench and Moomaw (8) expressed concern that when 28

ASTM D 2995 is used, water can be lost from the emulsion prior to weighing the tarps, making 29

the measurement inaccurate. 30

The existing pavement surface texture impacts the “effective” quantity of emulsion 31

available for bonding which cannot be captured using ASTM D 2995. The existing paving 32

surface will absorb a fraction of emulsion applied which will be unavailable to act as a bonding 33

agent for aggregate or HMA placed on top of the emulsion. Thus, it is important to differentiate 34

between total EAR and “effective” EAR available for bonding. The importance of surface 35

absorption is considered in many tack coat and chip seal design methods. For instance, the 36

McLeod chip seal design method specifies adjustments in EAR based on surface texture with 37

adjustments of up to 0.06 gal/yd2 (0.272 L/m2) for porous, oxidized surfaces (9). However, 38

specified adjustments to EARs to account for surface absorption are entirely empirical. 39

This study introduces the “Tack Lifter” as a practical means for QC of in-situ effective 40

EARs at specific locations along the length of paving to overcome limitations of the current 41

practice. The ability of the Tack Lifter to capture effective EARs is demonstrated through both 42

laboratory and field testing. 43

44

45

46


OBJECTIVES 1 The objectives of the study are to: 2

1. Develop practical field test method for in-situ determination of effective EARs 3

2. Evaluate the effect of surface texture on effective EAR 4

5

TACK LIFTER 6 The Tack Lifter consists of a simple, weighted device that is placed on top of a super-absorbent, 7

foam sheet applied to a paving surface. The absorbent sheet soaks up emulsion from the 8

pavement. The weight of emulsion absorbed by the sheet, combined with the known sheet area, 9

is used to obtain a local EAR measurement. The device measures the effective EAR on the 10

pavement, neglecting emulsions absorbed into the paving surface. The specific components of 11

the “Tack Lifter” are shown in Figure 1, which include: 12

1. Weighted device with handle: The total weighted device mass is 33 lb (15 kg). The weighted 13

device includes a base and handle (11 lb (5 kg)) plus removable weights (11 lb (5 kg) each). 14

It was determined that 33 lb (15 kg) was the optimal weight because adding weight beyond 15

33 lb (15 kg) did not lead to significant reduction in variability or absorption. The weighted 16

device base foot print is 5”x5” (127mm x 127mm). 17

2. Sheet: A super-absorbent sheet is placed on the paving surface following emulsion 18

application upon which the weighted device is placed. The sheet utilized in Tack Lifter 19

Testing is characterized as “super-absorbent, super-cushioning, polyurethane foam”. The 20

sheet has a density of 1.8 lb/ft3 (28.83 kg/m3), firmness of 0.6 psi (4.13 kPa), and absorbs 21

100% of emulsion applied to a smooth, non-porous surface. The sheet was selected after 22

evaluating a number of candidate sheet materials. Sheet dimensions are 5”x5”x0.5” 23

(127mmx127mmx12.7mm). 24

3. Frame: To prevent absorption of emulsion outside of the sheet area, a frame is applied to the 25

paving surface following emulsion application but before sheet application to seal the 26

surface. The frame is comprised of steel and includes a rubber, pliable gasket along the edges 27

applied to the paving surface. The gasket conforms to the surface texture, sealing the area of 28

interest from intrusion of additional emulsion. The inner dimensions of the gasket are 29

5.25”x5.25” (133mm x133mm) to allow a small gap for placement of the Tack Lifter sheet. 30

31


1 FIGURE 1 Tack Lifter components. 2

3

To conduct the Tack Lifter test following emulsion application, the frame is first placed 4

on the paving surface. Next, a pre-weighed sheet is placed in the center of the frame. The 5

weighted device is placed on top of the sheet for 30 seconds to allow for emulsion absorption. 6

Note that 30 seconds was found to allow sufficient time for maximum emulsion absorption. The 7

sheet is removed from the paving surface and weighed to determine the mass of emulsion 8

absorbed by the Tack Lifter. The mass of emulsion absorbed is converted to EAR using the 9

emulsion density and area of the sheet. 10

11

Verification that the Tack Lifter has the capability to absorb all effective emulsion on a surface 12

was conducted by applying emulsion to a smooth, steel pan surface (assumed to be impervious). 13

Preliminary Tack Lifter trials on a pan were conducted using three emulsion types: CRS-2, 14

CRS2-L, and CRS-1H. Testing was conducted using an EAR of 0.25 gal/yd2 (1.132 L/m2) for 15

CRS-2 and CRS-2L emulsions to represent a typical chip seal EAR, whereas an EAR of 0.06 16

gal/yd2 (0.272 L/m2) was used for testing the CRS-1H emulsion, representative of a typical tack 17

coat EAR. Testing was conducted at 25°C (77°F). The weight of emulsion on the surface was 18

monitored during application in order to control the EAR. EARs measured using the Tack Lifter 19

are presented in Figure 2(a). Results demonstrate close agreement between the applied and 20

measured EARs, especially considering there could be minor non-uniformity in actual emulsion 21

application. Thus, it is concluded that the Tack Lifter absorbs 100% of emulsion applied to a 22

smooth surface. This conclusion is supported by the photograph in Figure 2(b), which shows a 23

steel plate after emulsion application and subsequent Tack Lifter testing. These results suggest 24

that the difference between applied and measured EARs on actual paving surfaces can be 25

attributed to emulsion absorption into the paving surface. 26


1 FIGURE 2 (a) Tack lifter measured EARs on pan (b) Photo of pan after Tack Lifter test. 2

3

LABORATORY STUDY 4

5

Experimental Plan 6 To evaluate the ability of the Tack Lifter to capture effective EARs, a laboratory study was 7

conducted including various surface types, EARs, and emulsions. Conditions considered are 8

detailed in Table 1. A CSS-1H emulsion was used for tack coat EARs whereas CRS-2 and CRS-9

2L were used for chip seal EARs. Two types of HMA surfaces and three types of chip seal 10

surfaces were considered. HMA samples were laboratory fabricated using a slab compactor. The 11

smooth HMA surfaces had negligible visible surface pores. Rough HMA samples displayed a 12

rougher, more porous texture. Chip seal samples were laboratory fabricated in past research 13

projects at North Carolina State University (NCSU) (10). A portion of chip seal samples were left 14

un-trafficked, to represent extreme rough texture. Other samples were subjected to wheel loading 15

in the MMLS3, which is a one-third scale mobile load simulator (10). A portion of the trafficked 16

chip seal samples were characterized as bled (Figure 4(c)) and the remaining samples were 17

raveled but un-bled (Figure 4(b)). For each test condition, two to six replicates were conducted. 18

All tests were conducted at 25°C (77°F). 19

20

TABLE 1 Laboratory Experimental Plan 21

Surface

Type

HMA

Smooth

HMA

(Rough) Chip Seal

(trafficked bled)

Chip Seal

(trafficked,

unbled)

Chip Seal

(Un-

trafficked)

Target

EARs

0.08 gal/yd2

(0.362 L/m2) (CSS-1H)

0.04 gal/yd2

(0.181 L/m2) (CSS-1H)

0.25 gal/yd2

(1.132 L/m2)

(CRS-2L)

0.25 gal/yd2

(1.132 L/m2)

(CRS-2L)

0.25 gal/yd2

(1.132 L/m2)

(CRS-2L &

CRS-2) 0.08 gal/yd2

(0.362 L/m2) (CSS-1H)

0.25 gal/yd2

(1.132 L/m2)

(CRS-2L)

0.25 gal/yd2

(1.132 L/m2)

(CRS-2L)

0.35 gal/yd2

(1.585 L/m2)

(CRS-2L)

0.35 gal/yd2

(1.585 L/m2) (CRS-2L)

22

0

0.05

0.1

0.15

0.2

0.25

0.3

Eff

ec

tive

EA

R (

ga

l/yd

2)

CRS-2

CRS-2L

CRS-1H

(a)

(b)


Surface Texture Characterization 1 Surface texture measurements were obtained through the sand patch method (11) and a 2

stationary laser profilometer developed by NCSU. The sand patch method is conducted by 3

pouring a known volume (V) of sand onto a surface, spreading it using a circular motion with a 4

flat disk, and measuring the diameter at four different radial locations. Higher roughness leads to 5

a lower measured diameter, as a greater quantity of sand will be trapped in the surface 6

irregularities. Four replicates are conducted on each surface. The average of all measurements of 7

the diameter (D) is used to calculate Mean Texture Depth (MTD) shown in Equation 1. 8

9

2

4VMTD

D (1) 10

11

The laser profilometer quantifies surface texture by measuring the distance between a 12

laser sensor and the pavement surface at varying longitudinal and transverse locations (12). The 13

stationary profilometer includes a point laser with adjustable resolution. For this study, a laser 14

scan area of 100 mm (3.9 in) by 100 mm (3.9 in) was utilized for all surfaces with 0.5 mm (0.02 15

in) resolution (13). Scanning time was approximately six minutes. Surface texture is quantified 16

from laser results using Mean Profile Depth (MPD) defined in Equation 2 as specified in ASTM 17

E1845-09: Standard Practice for Calculating Pavement Macrotexture Mean Profile Depth (14). 18

MPD was calculated along each line of scanning and then averaged. 19

20 (Peak Level 1st) (Peak Level 2nd)

Average Level2

MPD

(2) 21

22

A strong correlation was found between the laser and sand patch results as shown in 23

Figure 3. Therefore, only the laser results are presented in proceeding discussions. Note the laser 24

is not subject to operator variability concerns associated with the sand patch method. 25

26

27 Figure 3 Correlation between sand patch and laser results. 28

Tack Lifter Testing 29 30

y = 1.0782xR² = 0.8891

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 1 2 3 4 5

Sa

nd

Pa

tch

MT

D (

mm

)

Laser MPD (mm)


Prior to emulsion application, specimen areas were measured and the corresponding mass of 1

emulsion required to reach the target EAR was calculated. Emulsion was applied as uniformly as 2

possible. For tack coat EARs, a paint sprayer (Figure 4(a)) was used to apply emulsion 3

uniformly. For chip seal EARs, emulsion was spread as evenly as possible with the aid of a 4

brush. Following emulsion application, Tack Lifter testing was conducted as quickly as possible. 5

Tack lifter sheets were weighed immediately after removal from the application surface to 6

minimize the possibility for water loss. The Tack Lifter sheet is pliable and thus conforms to the 7

large, outward macro-texture of surfaces, but not penetrate surface pores as evident by samples 8

photographs following testing in Figure 4(d) and (e). 9

10

11

12

(a)

(b) (c)


1 Figure 4 (a) Paint sprayer emulsion application, (b) Trafficked, un-bled chip seal sample 2

prior to testing, (c) Trafficked, bled chip seal sample prior to testing, (d) Chip seal surface 3

after testing, and (e) HMA surface after testing. 4

5

Results 6

7 Effect of Surface Texture on Tack Lifter Results 8

To evaluate the effect of surface texture on “effective” EARs measured by the Tack Lifter, tests 9

were conducted on varying surfaces using typical EARs for tack coats and chip seals. To reflect 10

typical chip seal emulsion application, a CRS-2L was applied on HMA and chip seal surfaces at 11

a target EAR of 0.25 gal/yd2 (1.132 L/m2). To reflect typical tack coat application, a CSS-1H 12

emulsion was applied to HMA surfaces at a target EAR of 0.08 gal/yd2 (0.362 L/m2). 13

Figure 5(a) and (b) show results of CRS-2L emulsion applied to surfaces of varying 14

texture at a target application EAR of 0.25 gal/yd2 (1.132 L/m2). Figure 5(a) shows the 15

comparison between surface texture and the percentage of applied emulsion absorbed by the 16

Tack Lifter sheet (i.e., percentage of emulsion not absorbed by the surface). Error bars are 17

included to indicate variability of surface texture among samples in a given category and in 18

measured Tack Lifter emulsion absorption. The error bars displayed are the standard error. 19

Standard error is calculated by dividing the standard deviation by the square root of the number 20

of samples. It should be noted that in some cases emulsion absorbed by the Tack Lifter exceeds 21

100%, which can be attributed to slight non-uniformity in emulsion application. Figure 5(b) 22

shows the comparison between “effective” EAR measured by the Tack Lifter and the actual 23

applied EAR for CRS-2L at 0.25 gal/yd2 (1.132 L/m2) EAR. Error bars are included to 24

demonstrate inherent variability in the applied EARs and Tack Lifter effective EARs. Trends in 25

Tack Lifter results amongst chip seal surface types match intuition: a higher MPD (i.e., rougher 26

texture) leads to greater emulsion absorbed by the surface. Smaller differences between applied 27

and Tack Lifter effective EARs exist for bled surfaces than un-bled trafficked or un-trafficked 28

surfaces, which matches expected trends as bled surfaces contain few bare aggregate surfaces 29

and surface pores and thus, are not anticipated to absorb a significant amount of emulsion. 30

(d) (e)


Furthermore, un-trafficked samples show evidence of higher surface absorption compared to un-1

bled trafficked samples which matches expectations. Un-trafficked surfaces contain a significant 2

amount of bare aggregate surfaces and pores between aggregate particles which are not 3

significantly embedded into the existing emulsion residue and thus, give significant opportunity 4

for the applied emulsion to be absorbed and consequently unavailable for bonding to materials 5

applied on top of the emulsion (e.g., additional layer of aggregate). 6

Trends in Tack Lifter results among rough and smooth HMA surfaces in Figure 5(a) and 7

(b) also match expected trends with rougher texture leading to higher differences between 8

applied and Tack Lifter measured effective EARs. It should also be noted that it is not possible to 9

directly compare trends in surface absorption among chip seals and HMA surfaces. Results 10

indicate that the MPDs of the HMA surfaces are significantly lower those of chip seal surfaces 11

(i.e., HMA surfaces are smoother). However, the amount of emulsion absorbed by HMA is 12

comparable to chip seals. Inherent differences between the mechanisms of emulsion absorption 13

in chip seal an HMA surfaces preclude direct comparison between surface texture and Tack 14

Lifter results of the two surface types. Chip seal surfaces consist of a single layer of aggregate 15

embedded in emulsion residue. Emulsion can be absorbed into the surface of bare aggregate 16

surfaces or into voids between embedded aggregate. In contrast, HMA is a mixture of aggregate 17

and asphalt with air voids. While HMA surfaces are smooth compared to chip seals, surface 18

porosity offers significant opportunity for emulsion absorption compared to chip seals which do 19

not contain surface pores. 20

The results of CSS-1H emulsion applied to HMA surfaces of varying texture at a target 21

applied EAR of 0.08 gal/yd2 (0.362 L/m2) are shown in Figure 5(c) and (d). Figure 5(c) shows 22

the comparison between surface texture and the percentage of applied emulsion absorbed by the 23

Tack Lifter. Figure 5(d) shows the comparison between “effective” EAR measured by the Tack 24

Lifter and the actual applied EAR. Error bars are included to demonstrate variability in surface 25

textures amongst specimens, applied EARs, and measured effective EARs. Note that precise 26

application of low EARs, such as 0.08 gal/yd2 (0.362 L/m2), is very difficult in the laboratory. 27

Correspondingly, it can be noted that applied EAR results for a target EAR of 0.08 gal/yd2 28

(0.362 L/m2) are closer to 0.09 gal/yd2 (0.407 L/m2) on average. Results demonstrate rougher 29

HMA surface texture leads to a lower effective EAR. These results indicate the Tack Lifter could 30

be used as a tool to identify how applied EARs should be adjusted to account for surface 31

absorption. 32

33


1 2

FIGURE 5 Effect of surface texture on Tack Lifter results for 0.25 gal/yd2 EAR: (a) 3

comparison between surface texture and Tack Lifter emulsion absorption, (b) comparison 4

between applied and effective EARs, and for 0.08 gal/yd2 EAR: (c) comparison between 5

surface texture and Tack Lifter emulsion absorption, (d) comparison between applied and 6

effective EARs. 7 8

Effect of Emulsion Application Rate on Tack Lifter Results 9

To allow for assessment of the sensitivity of Tack Lifter results to EAR, a series of Tack Lifter 10

tests with varying applied EARs were conducted on rough HMA surfaces, un-bled trafficked and 11

un-trafficked chip seal samples, which represent conditions of the two surface types that offer 12

greatest opportunity for emulsion absorption. Both tack coat and chip seal applications are 13

common on HMA surfaces. Hence, typical conditions for both applications were considered. 14

Target applied EARs of 0.04 gal/yd2 (0.181 L/m2) and 0.08 gal/yd2 (0.362 L/m2) reflect typical 15

tack coat EARs, whereas 0.25 gal/yd2 (1.131 L/m2) reflects a typical chip seal EAR. CSS-1H 16

emulsion was used for tack coat EARs, whereas CRS-2L was used for the chip seal EAR. A 17

comparison between applied and Tack Lifter measured effective EARs for varying EARs applied 18

to rough HMA surfaces are presented in Figure 6(a). Results indicate the difference between 19

applied and effective EARs decreases as applied EAR increases, which matches expected trends. 20

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0

20

40

60

80

100

120

HMASmooth

HMA Rough Bled ChipSeal

TraffickedChip Seal

UntraffickedChip Seal

Me

an

Pro

file

De

pth

(m

m)

Ta

ck

Lif

ter

Ab

so

rpti

on

(%

)Surface Texture

Tack Lifter Absorption

(a)

0

0.05

0.1

0.15

0.2

0.25

0.3

HMASmooth

HMA Rough Bled ChipSeal

TraffickedChip Seal

UntraffickedChip Seal

EA

R (

ga

l/yd

2)

Applied EAR

Effective EAR

(b)(b)

0

0.01

0.02

0.03

0.04

0.05

0.06

0

20

40

60

80

100

120

HMA Smooth HMA Rough

Me

an

Pro

file

De

pth

(m

m)

Ta

ck

Lif

ter

Ab

so

rpti

on

(%

)

Surface Texture

Tack Lifter Absorption

(c)

0

0.02

0.04

0.06

0.08

0.1

0.12

HMA Smooth HMA Rough

EA

R (

ga

l/yd

2)

Applied EAR

Effective EAR

(d)


Use of a lower EAR will allow a greater percentage of the total emulsion applied to be absorbed 1

into the surface. It should be noted at the lower EARs of 0.08 and 0.04 gal/yd2 (0.181 L/m2 and 2

0.362 L/m2) of the applied EAR differs somewhat from the target. Precise application of low 3

EARs in the laboratory is difficult due to the small quantity of emulsion applied. 4

To evaluate the effect of applied EAR on effective EAR on chip seal surfaces, Tack 5

Lifter tests were conducted using CRS-2L emulsion applied to both un-bled trafficked and un-6

trafficked chip seal samples at two rates: 0.25 gal/yd2 (1.131 L/m2) and 0.35 gal/yd2 (1.585 7

L/m2). A comparison between applied and Tack Lifter effective EARs is shown in Figure 6(b). 8

Results indicate that an applied EAR of 0.35 gal/yd2 (1.585 L/m2) leads to a lower difference 9

between measured and effective EAR for a given chip seal surface condition than an applied 10

EAR of 0.25 gal/yd2 (1.131 L/m2). Results match intuitions as the surface absorption is fixed. 11

Thus, a surface will become saturated at a lower percentage of the applied emulsion as the 12

applied EAR increases. 13

14

15 FIGURE 6 (a) Effect of EAR on the difference between applied and effective EARs for 16

rough HMA surfaces, and (b) Effect of EAR on the difference between applied and effective 17

EARs for typical chip seal surfaces. 18 19

Effect of Emulsion Type on Tack Lifter Results 20

To evaluate the effect of emulsion type on surface absorption, a comparison was made between 21

Tack Lifter results of CRS-2L and CRS-2 applied to un-trafficked chip seal samples at a target 22

applied EAR of 0.25 gal/yd2 (1.131 L/m2). Emulsion viscosity may affect the amount of 23

emulsion absorbed by a surface. Higher viscosity emulsions are less likely to penetrate surface 24

pores. Results are presented in Figure 7. Results indicate little difference between the 25

percentages of applied emulsion absorbed by the Tack Lifter for the two emulsion types. 26

However, future research should more rigorously evaluate the effect of emulsion type on surface 27

absorption. 28

29

0

0.05

0.1

0.15

0.2

0.25

0.3

0.04 0.08 0.25

Me

as

ure

d E

AR

(g

al/

yd

2)

Target EAR (gal/yd2)

Applied EAR

Effective EAR

(a)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Trafficked Chip Seal Untrafficked Chip Seal

EA

R (

ga

l/yd

2)

0.25 Applied EAR

0.25 Effective EAR

0.35 Applied EAR

0.35 Effecitve EAR

(b)


1 FIGURE 7 Effect of emulsion type on tack lifter absorption. 2

3

FIELD TRIAL 4

5

Experimental Plan 6 In addition to laboratory experiments, a field trial was conducted. The field trial consisted of 7

applying a CRS-2L emulsion at a target rate of 0.30 gal/yd2 (1.358 L/m2) to an existing HMA 8

pavement in Warren County, NC. The pavement included alligator cracking and a rougher 9

texture in the wheel paths with relatively smooth texture in the lane center which was not in the 10

wheel path. The field trial included several experiments: (1) ASTM D2995, (2) Tack Lifter tests 11

applied to the paving surface, and (3) Tack Lifter tests conducted on a pan placed on the paving 12

surface prior to emulsion application. The latter allows for measurement of the total applied EAR 13

as the Tack Lifter absorbs 100% of emulsion applied to a steel pan (Figure 2). Testing was 14

conducted at three locations along the length of emulsion application, numbered one through 15

three. For Location 1, EAR was only measured in the wheel path. For Locations 2 and 3, testing 16

was conducted in both the (a) wheel path and (b) lane center, which displayed significantly 17

different surface texture. The experimental layout used for each location is depicted in Figure 8. 18

(Note that for the first location, the lane center testing (b) was omitted). To avoid the possible 19

influence of transverse variability in comparing measurements of applied and effective EAR, 20

measurements with each method were made at the same transverse location, with close spacing 21

longitudinally. Surface texture measurements were made using the laser prior to emulsion 22

application. Tack lifter tests were conducted within two minutes of emulsion application. 23

Weights of the Tack Lifter and ASTM D 2995 sheets were obtained within three minutes of 24

removal from the paving surface to minimize water loss. 25

0

10

20

30

40

50

60

70

80

90

100

Untrafficked Chip Seal

Ta

ck

Lif

ter

Ab

so

rpti

on

(%

)

CRS-2

CRS-2L


1 FIGURE 8 Testing layout of the field trial, with (a) marking the wheel path and (b) 2

marking the center of the lane 3 4

Results 5 The field trial results of Tack Lifter testing are displayed in Figure 9. Note that ASTM D 2995 6

results are omitted as measurements were compromised due to difficulties in implementing the 7

procedure. The sheets placed in the wheel path often adhered to the emulsion distributor wheels 8

which precluded measurement of the applied EAR. The results that were obtained from ASTM D 9

2995 consistently indicated an applied EAR of 0.25 gal/yd2, which is significantly lower than 10

both the target EAR and Tack Lifter results. The large size of the ASTM D 2995 (12”x12” 11

(304.8mm x 304.8mm)) made them difficult to handle and emulsion dripped from the edges of 12

the sheets during transit to the scale, which explains the erroneous low EAR measurements. 13

Figure 9(a) shows the comparison between surface texture at the different spots of Tack 14

Lifter testing and the percentage of applied emulsion absorbed by the Tack Lifter tests applied to 15

the paving surface. Note that the percentage of emulsion absorbed by the Tack Lifter was 16

determined through comparison to Tack Lifter results conducted on the steel plans placed on the 17

paving surface prior to emulsion application. Results in Figure 9(a) demonstrate an inverse trend 18

between MPD and the percentage of applied emulsion absorbed by the Tack Lifter as expected. 19

The only exception to this trend is the last spot, denoted “3B,” which shows low roughness and 20

low absorption. It is speculated this outlier reflects water loss from the Tack Lifter sheet prior to 21

weighing. This was the last spot of testing was conducted and experienced the greatest delay in 22

sheet removal from surface to weighing. In addition, the ambient temperature exceeded 35°C 23

(95°F) at the time of this last measurement and thus, conditions were severe. Future research is 24

needed to determine the allowable time delay between emulsion application and Tack Lifter 25

testing and subsequent delay to weighing to avoid water loss. 26

Figure 9(b) shows the comparison between Tack Lifter results applied to the surface (i.e., 27

effective EAR measurements) and those applied to the pan placed on the paving surface prior to 28

emulsion application (i.e., applied EAR measurements). Results indicate negligible differences 29

between pan and paving surface Tack Lifter measurements for locations of low texture (with the 30

(a) (b)


exception of the last spot). For cracking locations of higher MPD, results indicate approximately 1

0.06 gal/yd2 (0.272 L/m2) of emulsion is absorbed by the surface, indicating significant 2

adjustment in applied EAR is needed for cracked locations of emulsion application to overcome 3

surface absorption. 4

5

6 FIGURE 9 (a) Field Trial comparison of surface texture and Tack Lifter emulsion 7

absorption (b) Field trial comparison between applied and effective EARs. 8

9

CONCLUSIONS 10 The following conclusions can be drawn from this study: 11


1. The Tack Lifter is a simple, practical device for measurement of effective Emulsion 1

Application Rates (EAR) in the laboratory and field. 2

2. The Tack Lifter can be used to guide adjustment of EARs to account for emulsion absorption 3

into a paving surface. 4

3. While the Tack Lifter results presented demonstrate its potential to capture effective EARs, 5

testing frequency in the field remains to be established. At a minimum, testing should be 6

conducted prior to paving to allow for adjustment of the target EAR to account for emulsion 7

absorption by the surface and at locations of paving where surface texture changes 8

appreciably to subsequently allow for target EAR adjustments along the length of paving. 9

4. Tack Lifter results indicate the amount of emulsion absorbed by a paving surface is 10

influenced by surface texture. Rougher surface texture leads to lower tack lifter emulsion 11

absorption. The effect of surface texture on emulsion differs between chip seal and HMA 12

surfaces as a result of different mechanisms of surface absorption. Future work should 13

include the effects of emulsion absorption on the surface of the pavement. 14

5. Preliminary Tack Lifter results indicate little sensitivity to emulsion type. However, emulsion 15

viscosity could influence absorption into a paving surface. Thus, the effect of emulsion on 16

surface absorption merits further consideration in future research. 17

6. Preliminary Tack Lifter field trials suggest extreme heat may require efficient testing to 18

avoid water loss. Future research should establish the maximum allowable delay between 19

emulsion application and Tack Lifter measurement to avoid potential water loss. 20

7. Future work should validate findings of this study with a broader set of emulsion and surface 21

types. 22

23

ACKNOWLEDGEMENTS 24 The authors would like to acknowledge the financial support from the North Carolina 25

Department of Transportation under project NCDOT HWY-2014-03. The authors would like to 26

acknowledge Instrotek, Inc. for fabricating the Tack Lifter. 27

28

REFERENCES 29 1. Mohammad, L. N., A. Bae, M. A. Elseifi, J. Button, and N. Pate. “Effects of Pavement 30

Surface Type and Sample Preparation Method on Tack Coat Interface Shear Strength,” 31

Transportation Research Record, No. 2180, 2010, pp. 93-101. 32

2. Hakimzadeh, S., W. Buttlar, and R. Santarromana. “Shear- and Tension- Type Tests to 33

Evaluate Bonding of Hot-Mix Asphalt Layers with Different Tack Application Rates,” 34

Transportation Research Record, No. 2295, Transportation Research Board, National 35

Research Council, Washington, D.C., 2012, pp. 54-62. 36

3. Gurer, C., M. Karas. C. Sedat, and B. Bekir Aktas. “Effects of construction-related factors on 37

chip seal performance,” Construction and Building Materials, Vol. 35, 2012, pp. 605–613. 38

4. West, R.C., J. Zhang, and J. Moore. Evaluation of Bond Strength Between Pavement Layers, 39

NCAT Report 05-08, 2005. 40

5. Gransberg, D. and D.M.B. James. Chip Seal Best Practices, NCHRP Synthesis 342, 2005. 41

6. Mohammad, L.N., M. Elseifi, A. Bae, N. Patel, J. Button, and J.A. Scherocman. Optimization 42

of Tack Coat for HMA Placement, NCHRP Report 712, 2012. 43

7. ASTM D2995. “Standard Practice for Estimating Application Rate of Bituminous 44

Distributors,” ASTM, 2009. 45


8. Muench, S. T. and T. Moomaw. De-bonding of hot mix asphalt pavements in Washington 1

State: an initial investigation, Washington State Department of Transportation, Report WA-2

RD 712.1, 2008. 3

9. McLeod, N. W. “A General Method of Design for Seal Coats and Surface Treatments,” 4

Proceedings of the Association of Asphalt Paving Technologists, Vol. 38. 1969. pp. 537-630. 5

10. Kim, Y.R., Adams, J. Development of a New Chip Seal Mix Design Method, NCDOT Final 6

Report, HWY-2008-04, 2011. 7

11. ASTM E965-96. “Standard Test Measurement for Measuring Pavement Macrotexture Depth 8

Using a Volumetric Technique,” ASTM, 2006. 9

12. Adams, J. M., and Y. Richard Kim. Mean Profile Depth Analysis of Field and Laboratory 10

Traffic-Loaded Chip Seal Surface Treatments. International Journal of Pavement 11

Engineering, Vol. 15, No. 7, 2014, pp. 645-656. 12

13. Im, J. H. Performance Evaluation of Chip Seals for High Volume Roads using Polymer-13

Modified Emulsions and Optimized Construction Procedures. North Carolina State 14

University, 2013. 15

14. ASTM E1845-09. “Standard Practice for Calculating Pavement Macrotexture Mean Profile 16

Depth,” ASTM 2009. 17

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