Best Practices for Applying Undiluted Emulsified Asphalt Tack Coats

Transcription

The Colorado Asphalt Pavement Association
Presents
Best Practices
for
Applying Undiluted Emulsified
Asphalt Tack Coats
Final Report
Table of Contents
Table of Contents ............................................................................. i
Why Spray Undiluted Emulsions? ................................................. 1
Two Reasons: ....................................................................................................... 1
Here’s Why ........................................................................................................... 1
Why Have Emulsions Been Diluted All These Years? .......................................... 1
Is This Done Anywhere Else? ............................................................................... 2
Why Use a Tack Coat? .................................................................... 2
Here’s How To Do It ........................................................................ 3
Background ........................................................................................................... 3
Getting Ready to Spray Emulsion ......................................................................... 6
Putting the Nozzles in the Spray Bar .......................................................................... 6
Nozzle Sizes .............................................................................................................. 10
Adjusting Bar Height ................................................................................................ 14
Getting the Desired Shot Rate ............................................................................ 16
Measuring the Asphalt Emulsion Application Rate.............................................. 17
‘Dipsticking’ the Tank .............................................................................................. 17
‘How To’ Example ................................................................................................... 20
Emulsion Temperature Prior to Spraying ............................................................ 21
Pavement Condition Prior to Spraying Undiluted Emulsions .............................. 22
Cleaning the Equipment...................................................................................... 23
Troubleshooting ............................................................................ 24
Materials and Methods Used to Produce This Manual ............... 25
Emulsion ............................................................................................................. 25
Temperatures ..................................................................................................... 25
Adjustments and Modifications to Equipment ..................................................... 25
And Finally, a Checklist ................................................................ 26
References ..................................................................................... 28
Appendix A – Examples of Some State Requirements............... 29
Florida DOT ........................................................................................................ 29
i
Louisiana DOT .................................................................................................... 29
North Carolina DOT ............................................................................................ 29
Ohio DOT ........................................................................................................... 30
Texas DOT ......................................................................................................... 30
ii
Why Spray Undiluted Emulsions?
Two Reasons:
o It reduces costs
 the number of times a distributor has to be loaded to apply the same
volume of asphalt to the roadway is cut in half (for 1:1 dilution rates),
reducing costs.
o It improves quality
 more uniform asphalt dispersion in storage tanks or distributors.
Here’s Why
Costs are reduced because there is less travel time required to fill the distributor. If 0.10
gallons per square yard is required for a 1:1 diluted emulsion, only 0.05 gallons per
square yard would be required for the same emulsion undiluted. In this case, for the
same pavement area the distributor would need refilling half as many times.
The second reason is due to the fact that dispersion of the asphalt in the emulsion is
often not uniform if the emulsion is diluted after manufacture. This can result in several
performance issues resulting from instability of the emulsion. Instability can result in
separation of the asphalt binder within the emulsion. Then, when the emulsion is
sprayed onto the pavement surface, some areas of the pavement may receive higher or
lower concentrations of residue than desired. When too much residue is present the
overlay can debond from the underlying pavement. When too little residue is present
the same debonding can occur.
Why Have Emulsions Been Diluted All These Years?
Slow setting asphalt emulsions are often used as an adhesive binder between new
asphalt overlays and existing pavements. These slow setting emulsions are called tack
coats. They are applied with self-propelled pressure distributors prior to application of
the new overlay. The application rate for such tack coats is generally specified at 0.10 to
0.12 gallons per square yard of diluted emulsion. The dilution rate varies but is usually
one part emulsion to one part water, or 1:1. Dilution of the emulsion has been done in
the past so a higher volume of liquid could be applied to the pavement surface. A
higher volume was necessary to accommodate the ability of pressure distributors that
had difficulty applying uniform quantities of asphalt emulsion under 0.10 gallons per
square yard.
1
However, the technology available in modern pressure distributors allows for very low
volume spray applications today. Therefore, this Best Practices Manual has been
produced to explain how to apply asphalt emulsions without dilution.
Is This Done Anywhere Else?
At least five states currently require asphalt emulsions be undiluted when used as tack
coats. These states are Florida, Louisiana, North Carolina, Ohio, and Texas. Excerpts of
the specifications from these states are included in Appendix A.
Why Use a Tack Coat?
An emulsified asphalt tack coat produces a strong adhesive bond without slippage
between an existing pavement and a new overlay (ASTM 2003; Asphalt Institute MS-19,
Army Corps of Engineers 1991; Oglesby, et al 1982; Texas DOT 2001). The existing
pavement could be either an older pavement surface or a recently placed lift of a multilift asphalt pavement (Asphalt Institute MS-4). Asphalt material used as a tack coat
should be easily sprayable, cured readily prior to subsequent construction and generate
adequate bond between layers. The three essential properties of a tack coat are 1) it
must be a good adhesive, 2) it must be thin, and 2) it must uniformly cover the entire
surface of the area between new and old HMA layers so they act as a monolithic system
(Asphalt Institute MS-4). The handbook states that many tack coats have been placed
too heavy, leaving a surplus of asphalt which flushes into the overlying course, resulting
in a tendency to avoid their use. A thin tack coat was reported to do no harm to the
pavement and would properly bond the pavement layers together (Asphalt Institute
MS-4).
2
Here’s How To Do It
Background
This manual was prepared by evaluating the performance of three brands of asphalt
distributors applying as low as 0.025 gallons per square yard of undiluted CSS-1h asphalt
emulsion. The widest variety of distributors available was included to make sure the
practices described in this manual were generally applicable. Performance was judged
based on the abilities of each piece of equipment to apply the CSS-1h in a uniform
manner. Equipment came from the following manufacturers:
E. D. Etnyre and Company
BearCat Manufacturing
Rosco LeeBoy
Two Etnyre distributors shown in Figures 1 and 2 were provided by Connell Resources,
Inc, and Martin Marietta Materials of Fort Collins, CO.
Figure 1. Connell Etnyre Blacktopper Centennial
3
Figure 2. Martin Marietta Etnyre Blacktopper Centennial
The Bearcat distributor shown in Figure 3 was provided by Rocky Mountain Materials
and Asphalt of Colorado Springs, CO.
Figure 3. Rocky Mountain Materials and Asphalt Bearcat
4
Two Rosco distributors supplied by CDOT Region 4 Maintenance of Loveland, CO and
the City of Fort Collins, CO are shown in Figures 4 and 5.
Figure 4. CDOT Rosco Distributor
Figure 5. Fort Collins Rosco Distributor
5
Getting Ready to Spray Emulsion
Putting the Nozzles in the Spray Bar
Nozzle alignment is particularly important when applying asphalt emulsion in the range
of 0.025 to 0.05 gallons per square yard.
Nozzles need to be installed in the spray bar at the proper angle for the equipment
being used. Distributor manufacturers supply a wrench with the equipment that is
intended specifically for this purpose as shown in Figure 6. When the wrench is inserted
over the nozzle and turned parallel to the bar, the nozzle angle is set correctly. Figure 7
shows nozzles installed incorrectly in the bar. In this case, the nozzles are all parallel to
the bar or perpendicular to the centerline of the truck. However, when the wrench is
used to turn the nozzles as shown in Figure 8, the correct nozzle configuration is
obtained as shown in Figure 9.
6
Figure 6. Nozzle Wrench on Nozzle Parallel to Bar
7
Figure 7. Incorrect Nozzle Alignment
8
Figure 8. Correcting Nozzle Alignment
9
15-30 deg
Figure 9. Correct Nozzle Alignment
Nozzle Sizes
A 1/16-inch width nozzle is recommended when spraying 0.025 to 0.05 gallons per
square yard. This worked well for both Rosco distributors. This 1/16-inch wide nozzle is
shown on the far left in the photo in Figure 10 next to the 1/8-inch and 3/16-inch
10
Figure 10. Nozzles for CDOT Rosco Distributor
nozzles which were used in the CDOT distributor and in Figure 11 for the Fort Collins
distributor.
Figure 11. Nozzle from Fort Collins Rosco Distributor
11
For Etnyre equipment these are the 1/16” Coin Slot nozzles shown on the Etnyre Spray
bar Nozzles chart on page 51 of the owner’s manual and reproduced below in Figure 12.
Similar information was found on a placard mounted in the cab of the Fort Collins
distributor as shown in Figure 13.
Figure 12. Etnyre Nozzle Selection Chart
Similar sizes of nozzles should be used in the BearCat distributor, as well. However,
when these small nozzles are not available, we obtained reasonable results with the
next larger No. 2 nozzles shown in Figures 14 and 15.
12
Figure 13. Rosco Nozzle Selection Chart
Figure 14. BearCat No. 2 Nozzle with 1/8-inch Slot (Orifice) Width
13
Figure 15. BearCat No. 2 Nozzle with 1/4-inch Long Orifice
Spray Bar Height
It is very important to adjust the spray bar height, Figure 16, so that improper overlap
does not produce streaking as shown in Figure 17. The example shown was done with
every other nozzle removed so streaks could more easily be seen if the spray bar was
not at the correct height.
Adjusting Bar Height
If the spray bar is not at the correct height from the surface to be sprayed, ridges, or
streaking, or ‘roping’ can occur. This is a non-uniform application and must be avoided.
To adjust the bar height, remove every other nozzle from the bar and spray a short
section. There should not be any overlap in the applied emulsion as appears in Figure
16. In this case the bar should be raised so that no overlap occurs. Then, when all the
nozzles are installed in the bar, an exact double lap of emulsion will be applied with no
extra overlapping to create streaks, or ‘roping’.
14
Overlap
Creates Streaks
Figure 16. Spray bar Too Low for Double Lap Application
Figure 17. Streaking From Nozzles Too High
15
After the correct nozzles are installed in the bar at the proper angle and the bar height is
adjusted to provide one double overlap of material across the substrate as shown in
Figure 18, you are ready for calibration of the distributor. This must be done to be sure
the shot rate applied is the shot rate desired.
Figure 18. Streaking Reduced with Lower Bar Height
Getting the Desired Shot Rate
Modern Etnyre and BearCat distributors are equipped with on-board computer controls
that allow operators to enter the desired shot rate (BearCat) into the cab control panel
or the distributor speed and pump discharge to obtain the desired application rate
(Etnyre). In the case of the Etnyre, a ‘Computator’ is supplied with each truck that
allows the operator to enter application rate and spray bar length to determine what
settings for truck speed and pump discharge will provide the desired result. For
example in Figure 19 the Computator is set at 0.025 gal/yd2 and a 16 foot bar length.
This gives the operator various options regarding how fast to drive the truck for various
pump discharge rates. In this case, 400 feet per minute would require 18 gallons per
minute pump discharge.
16
Figure 19. Etnyre Computator
The BearCat distributor provides the operator the ability to enter the desired shot rate
and the computer selects a flow rate and speed. In addition, the BearCat can be run
manually so the operator can control pump pressures and speeds. It was discovered
during trials for this manual that with the No. 2 BearCat nozzles previously shown in
Figures 14 and 15, the machine had to be run manually as the computer controls did not
provide enough pump pressure to get an even distribution of emulsion.
Measuring the Asphalt Emulsion Application Rate
Although the computer controls on the Etnyre and BearCat distributors should provide
an accurate application of emulsion it is always best to be sure by manually checking
periodically. This is a very important aspect of asphalt emulsion spray applications.
And, the best way to determine how much material is actually being applied to the
substrate pavement surface is to apply some and measure the results.
‘Dipsticking’ the Tank
The best way to manually check the spray rate is to measure the volume of emulsion in
the tank before spraying, spray, and then recheck the volume in the tank. Most asphalt
distributors have a pointer gauge on the rear of the tank which indicates the volume of
emulsion in the tank. Do not use this pointer. It is not precise enough. It is intended by
the manufacturer to provide the operator with a visual indication of the volume of the
tank to determine when refilling is necessary. Instead, the tank volume must be
checked using the dipstick supplied with the truck by the manufacturer.
This tool is usually stored on top of the tank. Readings must be taken with the truck on
level ground, or as close as can be done within reason as shown in Figure 20.
17
Figure 20. Measuring Tank Volume Before Spraying
Two types of dipsticks are available depending on the manufacturer.
The Etnyre dipstick is marked so that the 0 gallons mark is at the top of the dipstick as
shown in Figure 21. This dipstick is not intended to be submerged in the emulsion, but
instead, it is intended to be lowered into the tank until it just touches the top of the
emulsion surface. The operator then reads the volume in the tank by lining up the top
of the inspection manhole with the mark on the dipstick.
BearCat and Rosco distributors are marked with the 0 gallon mark at the bottom of the
dipstick. These dipsticks are intended to be lowered into the emulsion and the level of
emulsion determined by how far up the dipstick the emulsion rises when the dipstick is
fully inserted into the tank.
18
0 gallon
mark
Figure 21. Etnyre Dipstick With 0 Gallon Mark on Top
Application rate can be measured by shooting the emulsion over pre-weighed ‘coupons’
placed on the pavement in front of the distributor following ASTM D2995, “Standard
Practice for Estimating Application Rate of Bituminous Distributors”. Although this is
acceptable practice, we believe this method can lead to misleading results due to the
relatively small sample size of the ‘coupons’ utilized to measure the shot rate. As an
alternative, we recommend determining shot rate by spraying a known area of the
19
pavement and measuring the volume of emulsion applied. We recommend a minimum
of 100 gallons and no more than 75 percent of the volume of emulsion in the truck be
sprayed using this method.
‘How To’ Example
An example of how truck spray rate is measured using this procedure follows:
Given an 1800 gallon distributor applying emulsion 12 feet wide.
1) Initial dip stick reading, Ri = 1650 gallons
2) Dip stick reading after applying emulsion, Ra = 1350
3) Distance travelled while spraying, D = 4500 feet
4) Spray width, W = 12 feet
So, the application rate is:
9 * (Ri - Ra)
D*W
Or,
Ri – Ra = 1650 – 1350
= 300 gallons sprayed
D * W = 4500 x 12
= 54,000 sf
and,
= 0.05 gallons per square yard
9 * (300 gallons)
54,000 sf
This check should be accomplished at least two times and the results compared. Check
by spraying a small quantity as illustrated above to determine if the onboard computer
(if so equipped) is providing accurate information, then spray a larger quantity and
compare the results. The two measurements should be within 10 percent of each other.
20
Emulsion Temperature Prior to Spraying
The temperature of the emulsion affects viscosity, the ability of the emulsion to flow.
Temperature is especially important when applying undiluted emulsions since they will
be thicker or more viscous than the same diluted products at a given temperature.
Therefore, the spray temperature should be increased for undiluted emulsions to obtain
the same flow properties as diluted emulsions when spraying with the smaller nozzles
required. Figure 22 shows the temperature of an undiluted emulsion during a recent
field trial used to produce this manual. The dial indicator reads 113F. This may be an
acceptable temperature for a diluted CSS-1h, but when the undiluted CSS-1h was shot
at this temperature the result was a non-uniform spray application.
Figure 22. Undiluted Emulsion Temperature Too Low
In addition to uniform application a higher spray temperature allows the emulsion to
penetrate the substrate pavement surface and not just lie on top. If the emulsion
residue does not penetrate the pavement surface adequately, it will be subject to
picking up on the tires of equipment traversing the surface.
21
Pavement Condition Prior to Spraying Undiluted Emulsions
Temperature
Pavement temperature must be high enough when spraying undiluted emulsions so that
adequate bonding occurs between the emulsion residue and the substrate pavement. A
higher substrate temperature in combination with higher emulsion temperatures should
prevent the residue from picking up on the tires of equipment driving on the emulsion
residue. The photo in Figure 23 shows emulsion residue almost completely removed
from the substrate surface in the wheel paths where tandems delivering hot mix to the
paver. The substrate pavement temperature was measured at 45F and the emulsion
temperature was 113F.
Figure 23. Undiluted Emulsion Temperature Too Low
Cleanliness
Sweeping the substrate is always good practice prior to tack coating. However, when
tack coat is undiluted sweeping is critical. Dust or debris on the surface will prevent the
undiluted emulsion from bonding to the substrate pavement even more than when the
emulsion is diluted.
22
Cleaning the Equipment
The nozzles should be cleaned thoroughly after each use. This is especially true when
spraying undiluted emulsions because undiluted emulsions are thicker liquids than
diluted emulsions and will clog the smaller nozzles being used faster than diluted
emulsions. Cleaning is best done when the bar and nozzles are still warm from spraying
the heated emulsion. Each distributor manufacturer provides information on the best
method to use for cleaning the bar and nozzles. Although petroleum solvents such as
kerosene or diesel fuel are often the most efficient liquids for cleaning residual asphalt
from nozzles, these materials must not be used if local environmental laws prohibit their
use. Instead, the best practice is to follow the manufacturer’s recommendations.
23
Troubleshooting
When producing this manual we assumed the reader would possess a significant level of
expertise regarding how to spray asphalt emulsions. Therefore, every problem that
could arise when applying asphalt emulsions has not been addressed. Instead, the two
issues that could arise when applying undiluted emulsions are covered in Table 2 below.
Table 2. Possible Problems When Shooting Undiluted Emulsions
Problem
Solution
Streaking or ‘Roping’ of Emulsion on Surface
Being Sprayed
Spray bar not at correct height
Nozzles not at correct angle
Nozzles plugged
Nozzle Size Too Large
Spray Temperature Too Low
Spray Pattern Uneven
Nozzles not at correct angle
Nozzles plugged
Nozzle Size Too Large
Pick up on Tires
Substrate Pavement Too Cold
Dusty Substrate
24
Materials and Methods Used to Produce This Manual
Emulsion
All of the emulsions used to assemble this Best Practices Manual were cationic slow
setting type 1h (CSS-1h) materials obtained from Cobitco in Denver, CO. Properties of
the emulsion are as shown in Table 1.
Table 1. Asphalt Emulsion Properties
Property
CDOT
Connell
RMM
MMM
AASHTO
M208
Viscosity, Saybolt
Furol, 77F (25C), s
35
34
39
34
20-100
Storage Stability,
24h, %
0.6
0.5
0.5
0.2
1, max
Particle Charge Test
Positive
Positive
Positive
Positive
Positive
Sieve Test, %
0
0
0
0
0.10, max
Cement Mixing Test,
max %
Nr
Nr
Nr
Nr
Nr
Residue, %
61.7
63.0
62.2
63.4
57, min
Residue Penetration,
25C, 100g, 5 s
74
64
64
64
40-90
Residue Solubility in
TCE, min %
Nr
Nr
Nr
Nr
97.5
Nr = Not reported
Temperatures
All of the trials conducted for this manual were accomplished with the CSS-1h sprayed
between 113F and 160F. The 113F temperature was too low.
Adjustments and Modifications to Equipment
As stated previously in the manual, no special adjustments were needed to any of the
equipment used with the exception of inserting the smallest size nozzles available in the
spray bar. In the case of the BearCat distributor, the next larger size No. 2 nozzle was
used with acceptable results but the pump pressure had to be adjusted manually to
obtain a uniform application.
25
And Finally, a Checklist
Highpoints to remember are:

Use nozzles with 1/16” wide slot for shot rates between 0.025 and 0.05
gallons/square yard

Install nozzles in spray bar at 15-30 degrees using manufacturer’s nozzle wrench

Adjust spray bar height so at least a double lap of the emulsion occurs

Measure shot rate using ‘dipstick’ to get tank volume before and after shot

Make sure emulsion temperature is high enough for spraying undiluted tack

Sweeping the substrate pavement is more important for undiluted tack to
prevent pick up on equipment tires and assuring the tack sticks

Nozzles are usually smaller for undiluted tack. Make sure they are clean or they
will plug up and streaking or roping will occur in the application
26
Any questions or comments about this manual are welcomed by:
The Colorado Asphalt Pavement Association
6880 South Yosemite Court, Suite 110
Centennial, Colorado 80112
(303) 741-6150
www.co-asphalt.com
27
References
A Basic Asphalt Emulsion Manual. Manual Series No. 19 (MS-19), Third Edition, The
Asphalt Institute, Lexington, KY.
The Asphalt Handbook. Manual Series No. 4 (MS-4), 1989 Edition, The Asphalt
Institute, Lexington, KY.
“ASTM D 8-02 Standard Terminology Relating to Materials for Roads and
Pavements.”Annual Book of ASTM Standards 2003, Section 4: Construction, Volume
04.03, American Society for Testing and Materials, West Conshohocken, PA, 2003.
Guide Specifications for Military Construction. CEGS-02556, U.S. Army Corps of
Engineers, Washington, DC, June 1991.
Oglesby, Clarkson H. and R. Gary Hicks. Highway Engineering, 4th edition. John Wiley &
Sons, New York, NY, 1982.
“Proper Use of Tack Coat.” Technical Advisory 2001-1, Construction and Bridge
Divisions, Texas Department of Transportation, Austin, TX, June 29, 2001.
28
Appendix A – Examples of Some State Requirements
Florida DOT
300-2.3 Tack Coat: Unless the Contract Documents call for a specific type or grade of
tack coat, use PG 52-28 meeting the requirements of 916-1, heated to a temperature of
250 to 300ºF or undiluted Emulsified Asphalt Grades RS-1h, RS-2, CRS-1h, or NTSS-1hm
meeting the requirements of 916-3. Heat RS-1h, RS-2, CRS-1h, and NTSS-1hm to a
temperature of 150 to 180ºF. The Contractor may use RS-1h modified to include up to
3% naphtha to improve handling of the material during the winter months of December,
January and February or at any other time, as approved by the Engineer.
For night paving, use PG 52-28 tack coat. The Engineer may approve RS-1h,
RS-2, CRS-1h, or NTSS-1hm for night paving if the Contractor demonstrates, at the time
of use, that the emulsion will break and not affect the progress of the paving operation.
Louisiana DOT
Section 504 Asphalt Tack Coat
504.02 ASPHALT MATERIALS. Tack coat shall be an undiluted modified asphalt
emulsion Grade CRS-2P, CSS-1, SS-1, SS-1P, or SS-1L complying with Section 1002.
North Carolina DOT
SECTION 605 ASPHALT TACK COAT
605-2 MATERIALS
Item
Asphalt Binder, Grade PG 64-22
Emulsified Asphalt, Grade CRS-1
Emulsified Asphalt, Grade CRS-1H
Emulsified Asphalt, Grade CRS-2
Emulsified Asphalt, Grade HFMS-1
Emulsified Asphalt, Grade RS-1H
Section
1020-2
1020-3
1020-3
1020-3
1020-3
1020-3
29
Do not dilute or mix the tack coat material with water, solvents or other materials
before application. Unless otherwise specified in the contract, use any of the grades of
tack coat material specified in this article.
Ohio DOT
Item 407 Tack Coat
407.06 Application of Asphalt Material. Uniformly apply the asphalt material with a
distributor having clean nozzles functioning properly. Obtain the Engineer’s approval for
dilution with water, if desired to achieve a more uniform application. The Department
will not pay for diluted tack used without approval. Ensure any diluted asphalt material
used for tack has a minimum viscosity of 20 seconds Saybolt Furol.
Texas DOT
Seven items in the Texas DOT Standard Specifications for Road and Bridge Construction
refer to tack coats. These are listed below with the description of the tack coat material
shown at the end.
ITEM 292
ASPHALT TREATMENT (PLANT-MIXED)
ITEM 318
HOT ASPHALT-RUBBER SURFACE TREATMENTS
ITEM 330
LIMESTONE ROCK ASPHALT PAVEMENT
ITEM 334
HOT-MIX COLD-LAID ASPHALT CONCRETE PAVEMENT
ITEM 340
DENSE-GRADED HOT-MIX ASPHALT (METHOD)
ITEM 344
PERFORMANCE-DESIGNED MIXTURES
30
ITEM 346
STONE-MATRIX ASPHALT
XX. Tack Coat. Unless otherwise shown on the plans or approved, furnish
CSS-1H, SS-1H, or a PG binder with a minimum high temperature
grade of PG 58 for tack coat binder in accordance with Item 300,
“Asphalts, Oils, and Emulsions.” Do not dilute emulsified asphalts at the terminal, in the
field, or at any other location before use. If required, verify that emulsified asphalt
proposed for use meets the minimum residual asphalt percentage specified in Item 300,
“Asphalts, Oils, and Emulsions.”
31

Best Practices for Applying Undiluted Emulsified Asphalt Tack Coats

Transcription

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