HomeMy Public PortalAbout110_033_Jones Paving Exhibit - Open Graded Interlayer Millen ga May2010 DEPARTMENT OF TRANSPORTATION
STATE OF GEORGIA
INTERDEPARTMENT CORRESPONDENCE
FILE: PRC10-5007-00(629)C1 OFFICE: Materials and Research
Jenkins County Forest Park, Georgia
DATE: May 13, 2010
FROM: Tony J. Felix, Assistant State Bituminous Construction Engineer
TO: Sheila Hines, State Bituminous Construction Engineer
SUBJECT: Open Graded Crack Relief/Leveling Interlayer
As you are aware, GDOT currently uses a single layer surface treatment interlayer directly over the existing
pavement surface to retard reflective fatigue/block cracking. Although, this process is proven to be effective,
several limitations apply to the use of this crack relief method in some circumstances. Since this process is
directly influenced by an acceptable use and application of emulsion and number seven stone, a traditional
milled surface cannot be directly overlaid. Most projects included in the maintenance rehabilitation program
consist of rural routes typically including a short section within curb and gutter through small towns. These
sections are milled and inlayed to the surface mix typical depth. Once these sections are milled, the final surface
prior to inlay normally is observed to have the most severe cracking within the project limits. These cracks are
usually wider and more frequent than the out of town sections. It is not unusual for the cracks to reflect up
through the new pavement surface within the curb and gutter areas within 6 months to a year after completion.
Since the tack for the aggregate will fill the troughs in the milled surface leaving nothing to bond the aggregate,
single layer surface treatment in not useful in these conditions. Some have proposed to mill deeper, thin lift
level, single layer surface treatment, level again, and then overlay. This option is not practical for numerous
reasons.
1. Most small towns don't have enough total in-place pavement structure to increase mill depths.
Encountering sub-grade or granular base next to the curb where the original road was widened and
utilities were added during milling is common.
For example: 75 lbs/yd2 of leveling over the milled surface +3/4 inches of surface treatment+ 75 lbs/ yd2
of leveling over the surface treatment+ 165 lbs/yd2 of surface mix= 3 3/4 inches mill and inlay.
2. Even if adequate pavement structure were present, the additional cost for the milling, leveling, tack, and
traffic control would not be practical.
3. Since the surface treatment must be immediately leveled prior to traffic exposure to prevent stone loss/
vehicle damage, this option would not typically work in towns due to traffic constantly crossing/turning
on the un-compacted pavement surface.
Other issues to consider when using single surface treatment as a crack relief layer include the following:
1. This application has specific weather and seasonal limitation that pertain to its use. The use
of emulsion as the tack material is the most significant limiting factor involved with this
process. The contractor must wait until the emulsion is completely set prior to covering with
the asphaltic concrete leveling course. Recently, the Department experienced issues on a
project where the leveling over the surface treatment raveled after being exposed to traffic.
This material failure was attributed to saturated sub-grade and base material under a
moderately cracked roadway where the overnight temperatures were near freezing before
and immediately after paving. These factors resulted in the emulsified asphalt being unable
to cure and develop adequate strength to bond the aggregate particles. Additionally, the
pavement was under traffic shortly after paving which exacerbated the problem related to
the uncured asphalt emulsion.
Based on this experience and other similar occurrences, the specifications were revised. These revised
specifications are found on The Source "Sub-section 424.3.05.A Observing Seasonal and Weather
Limitations" and are summarized below:
• Ambient temperature has not been less than 50 °F (10 °C) for 48 hours immediately prior
to application.
• No forecast of ambient temperature less than 50 °F (10 °C) for 48 hours immediately
following application.
• Ambient temperature and road surface temperature is at least 60 °F (16 °C) and stable at
the time of application.
• No exceptions are permitted except as authorized by the Engineer. Do not apply asphalt
cement to a wet surface.
NOTE 1: When the relative humidity exceeds 80%, the ambient temperature exceeds 95
°F (35 °C), the pavement temperature exceeds 125 °F (52 °C) or the weather is windy or
overcast, application of bituminous surface treatment will be at the discretion of the
Engineer.
This change in weather and temperature requirement has resulted in helping make this process
very effective in preventing reflective cracking from the underlying pavements in non milled or
high volume traffic conditions. However, construction may be delayed during the fall and
winter months using this process even though the placement of the surface mix is allowed for
the current ambient air temperature.
2. This procedure, as with all applications of surface treatment, utilizes a chip spreader to place
the aggregate. It has often been observed that when the chip spreader stops between truck
exchanges, an overlap of aggregate results in a noticeable bump easily detectable when
measuring the smoothness quality using a Laser Road Profiler. If these overlapped areas are
addressed prior to leveling, this deficiency doesn't become an issue. However, smoothness
testing conducted on the leveling course on a number of recent projects indicates rougher
smoothness than the pre-construction original existing pavement.
3. Data compiled over the last few years on projects using this application indicates that
existing rutting is not improved. Rutting measurements taken on several projects before and
after the crack relief inlayer/leveling placement reveal that if existing rutting measures 1/2
inch or greater, the ruts reappear once the chip seal and leveling has been placed and
exposed to traffic.
Funding limitations over the last several years have resulted in decreased preventative maintenance and
resurfacing activities on Georgia's roadways. This loss of resurfacing and preventative maintenance has
resulted in more widespread and severe cracking of our asphalt pavements. Additionally, many of the
roadways needing crack relief are located in conditions already discussed as not suitable for GDOT's
method of using single surface treatment. Given this situation, it was decided to investigate alternate
cost and performance effective strategies to address reflective cracking concerns for the Department.
One method used to retard reflective cracking by the commercial industry in Georgia for a number of
years involves the placement of an open-graded type of mix prior to surfacing. This mix is relatively
similar to GDOT's "D" mix which was used on the interstate system as a drainage course for many
years. Basically, a fairly high air void inlayer (10-15%) is provided acting much like a single layer of
surface treatment that interrupts the crack from propagating any further. This application appears
extremely successful and widely used in the private sector; however, GDOT has never used the
process.
A rehabilitation project in downtown Millen, Georgia presented GDOT the opportunity for a test
section using this research appealing procedure. This project consisted of removing and replacing all of
the existing curb and gutter and extending out the parking areas adjacent to the travel lanes. This new
design required cross-section milling the asphalt pavement structure to the gutter. The existing roadbed
consisted of multiple lifts of sand asphalt and fine-graded mixes over the original concrete pavement. A
surface with very wide cracks and severe scabbing was the result of the milling operation (Photo 1 &
2).
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As Let, this project specified the inlay of 1-1/2-inch of 12.5 mm Superpave directly over the milled surface.
Inspection of the remaining pavement structure following milling operations, led GDOT's Area Office to
request assistance from this office. Solutions up to full removal and reconstruction were discussed; however,
limited funding (GDOT and City of Millen) eliminated this option. Finally, the option of an Open-Graded HMA
crack-relief interlayer was approached. The patching, leveling, and surface quantities available on this project in
conjunction with additional quantities available though an adjoining T-Grant project for downtown
beautifications were reviewed. It was determined that funding was available to place 75 lbs/yd2 of this interlayer
and 125 lbs/yd2 — 135 lbs/yd2 of surface mix over the total project area. This option was discussed with and
agreed to by the City and GDOT. Moreland Altebetti, who was responsible for the T-Grant fund distribution,
also agreed to this change.
It was also agreed that this application was favorable in assessing the effectiveness of this process by providing
GDOT the opportunity of evaluating this process under extreme conditions. The erratic profile of this project
presented the prospect to evaluate the leveling ability of this mix application as well as its crack relief
properties. It should be noted that this project also consisted of approximately 800-ft of two lane roadway
outside of the milled section(Photo 3).
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Photo 3
This section exhibited severe block cracking with no evidence of load related deficiencies. It extended from
Station 0+00 — 8+00 and was overlaid with an average of 60 - 65 lbs/yd2 of this inter.layer/leveling course
(Photo 4). Applying the process in this location provided an opportunity to evaluate this procedure over un-
milled surfaces that had not been crack sealed.
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Photo 4
The challenges associated with this project allowed for the evaluation of this process at various application rates
over the milled surface. A section from Station 8+50 — 24+75 was covered with an average application rate of
120 lbs/yd2. This section exhibited severe defects. The erratic profile resulting from the existing utilities;
allowed the placement of this mix as a leveling course ranging in placement depths from 2 inches to 1/2 inch
within a 100-ft area(observe the longitudinal joint in Photos 5 and 6). Additionally, the existing utilities as well
as parking areas provided an opportunity to see the acceptable hand work potential of this mix.
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An area of this project, outside of the newly constructed curb and gutter section referenced above, where a
significant portion of the mix wasn't necessary for leveling; allowed for the placement of an average of 70
lbs/yd2 (Photo 7 & 8).
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Photo 7, Before Interlayer
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Photo 8, After Interlayer
Conclusions
At this time the following findings are provided.
1. For this application, this mix appears to be an effective leveling tool. Being an Open-Graded HMA with
the benefit of stone on stone properties, as expected there is no evidence that the rutting/deformities
previously existing in the thicker areas have returned at this time. Additionally, at very thin lifts (< 1/2
inch)raveling has not been observed.
2. During the paving operation, traffic was continually crossing the hot mat with no apparent stone loss or
vehicle damage. This mix was produced using 4.5% PG 67-22 asphalt cement without the inclusion of
fiber and was not especially"sticky".
3. The final interlayer mat was exposed to traffic for a number of days prior to overlaying with the final
surface mix. This allowed the mat to be exposed to the stress of vehicle tires twisting and turning on the
mat within the parking areas and side street intersections. Prior to overlay, the mat was inspected for
stone loss and/or any related damage from the traffic. None was observed.
4. This mix, even when placed at thicker depths, appeared to be open and exhibited the expected high in-
place air voids. A water truck was used to evaluate this in several locations. Regardless of the spread
rate, the water dissipated through the mat; however, areas placed thinner did appear to filter through
faster.
This project will be evaluated monthly to determine if any reflective cracking is observed.
The following mixture information is provided for your information. This Open-Graded HMA crack interlayer
was produced incorporating 59 % #7 stone and 40 % # 89 stone with 1% hydrated lime at an AC content of
4.5%. The mix was produced at 260 degrees F. It was compacted using 2 static covers with a steel wheel roller.