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Prepared for
Texas Department of Transportation
Prepared by
Center for Transportation Infrastructure Systems
Product Number: 0-5566-P1
August 2010
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This manual was developed to aid in the identification of flexible pavement distress and
appropriate treatment at intersection. This document is a guideline that can be used in
the field by TxDOT Maintenance Section Supervisors and other TxDOT personnel in
evaluating Texas roadways. In many cases, Texas rural intersections are constructed
similar to the rest of the roadway with thin untreated flexible base and hot mix or a two-
course surface treatment. However, these intersection experience a different level of
distress compared to the rest of the roadway since it is subjected to different traffic
conditions. This guide allows users to identify the type of distress and level of severity
for each distress type. This guide summarized based on responses of a multi-district
survey within TxDOT, interviews with district personnel, observations of field
performance of various repair methods, and review of existing published guidelines and
manuals relevant to pavement maintenance and preservation.
Preface
This guideline was one of the product of Research Project 0-5566, “Strategies to
Improve and Preserve Flexible Pavement at Intersections” funded by Texas Department
of Transportation (TxDOT) in cooperation with the Federal Highway Administration. The
research was conducted by the Center for Transportation and Infrastructure Systems
(CTIS). Thanks is extended to many TXDOT personnel from the Districts of Abilene,
Atlanta, Austin, Brownwood, Bryan, Ft. Worth, Houston, Laredo, Lubbock, Lufkin,
Odessa, Paris, Pharr, San Antonio, Tyler. A special thanks to the initial project director
Mr. Stacy Crumby. Last but not least the project monitoring committee:
Acknowledgments
Pedro Alvarez, P.E.
Brett Haggerty, P.E.
Adriana Geiger
For more information, please contract Imad Abdallah, Center for Transportation
Infrastructure Systems, (915)747-6925, or ctis@utep.edu.
Prepared by:
Imad Abdallah
Soheil Nazarian
Center for Transportation Infrastructure Systems
The University of Texas at El Paso
500 west University Ave, M105
El Paso, TX 79968
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How to Use This Manual
This guideline is organized in a manner that makes it easy for identifying the appropriate
distress and appropriate remediation options.
The first part of the guideline references the common and the second portion of the
guideline provides appropriate treatments and or remediation strategies. For each
distress, a brief description is provided with a schematic where appropriate that illustrate
the distress based on the pavement condition. In addition, the possible causes and
appropriate treatment or rehabilitation alternatives are provided.
The second portion of the guide provides the treatment alternatives. In this section,
each treatment includes a brief description followed by illustration of the treatment
application. The typical values for traffic range, life expectancy, and unit price is
provided. Also, included in some cases are the advantages and limitation of each
treatment.
This guidebook should be used as a reference in the decision making with consideration
given to other factors and practices. These recommendations might not be applicable
to every situation.
This manual is under development and is only intended for review purposes.
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Common
Distresses at
Intersections
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Surface/Wear Rutting
Wear rutting, which is due to progressive loss of
coated aggregate particles from the pavement
surface and which is caused by combined
env ironmental and traffic inf luences (the rate at
which wear rutting develops may be accelerated
when winter ice control abrasives accumulate).
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SURFACE OR WEAR RUTTING
Description: Wear rutting, which is due to progressive loss of
coated aggregate particles from the pavement surface and which
is caused by combined environmental and traffic influences (the
rate at which wear rutting develops may be accelerated when
winter ice control abrasives accumulate).
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Mechanism: Excessive vertical compressive stresses on the
HMA surface causing non-recoverable permanent deformation in
the asphalt layer of a pavement structure. Surface rutting will be
classified to three levels of severity: a) Low severity is measured
less than 0.5 in., b) Medium severity is measured greater than or
equal to 0.5 in. and less than 1 in. and c) High severity is
measured greater than or equal to 1in.
Causes:
• Studded tires/chain action
• Compaction (density): Insufficient compaction of HMA layers
during construction. If it is not compacted enough initially, HMA
pavement may continue to densify under traffic loads.
• Raveling
• Traffic loading densification
Prevention: The use of quality design, quality aggregate and
quality liquid asphalt; durable hot-mix asphalt surface course with
sufficient asphalt cement content; Proper compaction during
construction; Adequate drainage.
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Structural Rutting
Structural rutting, which is due to the permanent
vertical deformation of the pavement structure
under repeated traffic loads and which is
essent ially a reflection of permanent
deformation w ithin the base and/or subgrade.
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STRUCTURAL RUTTING
Description: Structural rutting, which is due to the permanent
vertical deformation of the pavement structure under repeated
traffic loads and which is essentially a reflection of permanent
deformation within the base, subbase and/or subgrade. The layer
causing the rutting needs to be identified, and a full structural
analysis is often warranted. In general, the wider the rut is on the
surface, the deeper the problem layer. Conversely, the shallower
the rut is on the surface, the higher the probability the rut is in the
upper layer. NDT devices such as FWD and coring and DCP can
prove crucial to identifying the rut layer.
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Mechanism: Excessive vertical compressive stresses on the
HMA surface, base and subgrade soil causing non-recoverable
permanent deformation in one or all layers in the pavement
structure. Structural rutting will be classified to three levels of
severity: a) Low severity when less than 0.5 in., b) Medium
severity when greater than or equal to 0.5 in. and less than 1 in.
and c) High severity when greater than or equal to 1in.
Causes:

Poor drainage

Weak subgrade

Weak pavement structure

Excessive loading for pavement structure
Prevention: The use of quality design, quality aggregate and
quality liquid asphalt. Also adequate drainage is important to help
prevent this type of distress.
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Instability Rutting
Instability rutting, which is due to lateral
displacement of material within the pavement
layer and which occurs within the wheel paths
(instability rutting occurs when the structural
properties of the compacted pavement are
inadequate to resist the stresses imposed upon
the pavement, particularly by frequent repetitions
of high axle loads).
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INSTABILITY RUTTING
Description:
Instability rutting, which is due to lateral
displacement of material within the pavement layer and which
occurs within the wheel paths (instability rutting occurs when the
structural properties of the compacted pavement are inadequate
to resist the stresses imposed upon the pavement, particularly by
frequent repetitions of high axle loads).
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Causes: Weak asphalt concrete layer (weak aggregate structure,
excessive asphalt, cement or filler, improper asphalt cement
(binder) grade and/or moisture damage). Especially at
intersections and truck routes where the pavement is subjected to
heavy, slow-moving continuous traffic. There are also stop lines
where severe braking, standing, accelerating, turning, that can
attribute to lateral stresses.
Mechanism: Excessive vertical compressive stresses on the
HMA surface, base and subgrade soil causing non-recoverable
permanent deformation in the top layer of the pavement structure.
Instability rutting will be classified to three levels of severity: a)
Low severity when less than 0.5 in., b) Medium severity when
greater than or equal to 0.5 in. and less than 1 in. and c) High
severity when greater than or equal to 1in.
Prevention: The use of quality design, quality aggregate and
higher asphalt binder.
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Allig ator Cracking
Alligator Cracking is a series o f interconnected cracks
caused by fatigue failure of the HMA surface (or
stabi lized base) unde r repeated t raffic loading. In thin
pavements, cracking i nitiates at the bot tom of the HMA
layer where the tensile stress is the highest then
propagates to the surface as one or more longitudinal
cracks.
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FATIGUE OR ALLIGATOR CRACKING
Description: Series of interconnected cracks caused by fatigue
failure of the HMA surface (or stabilized base) under repeated
traffic loading. In thin pavements, cracking initiates at the bottom
of the HMA layer where the tensile stress is the highest then
propagates to the surface as one or more longitudinal cracks.
This is commonly referred to as “bottom-up” or “classical” fatigue
cracking. In thick pavements, the cracks most likely initiate from
the top in areas of high localized tensile stresses resulting from
tire-pavement interaction and asphalt binder aging (top-down
cracking). Alligator cracking in the wheel path is a load-
associated, fatigue type of failure for asphalt concrete. At these
locations, the evaluated pavement deflections will almost always
exceed the tolerable values indicating that rehabilitation is needed
to restore structural adequacy. Water should be prevented from
entering the structural section in this area especially, due to the
many cracks in a small area that will develop into a localized
failure.
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Mechanism: Repeated applications of tensile strain due to wheel
loading cause the initiation (and propagation) of a crack at the
bottom of the HMA layer. A secondary type of fatigue cracking is
that which occurs in thick HMA layers from the top-down. This
surface-initiated fatigue cracking is associated with the state of
stress directly below a tire and usually takes much longer to
appear than bottom-up cracking in thinner HMA layers. Alligator
cracking will be classified to three levels of severity. Please refer
to the picture below for a description of the severity level.
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Low Severity: Few
connecting cracks
with no spalling;
cracks are not
sealed.
Medium Severity:
Cracks forming
alligator pattern;
slightly spalled;
cracks maybe
sealed.
High Severity: Cracks
forming alligator
pattern very wide
spread; pieces are
loose cracks maybe
sealed; moderate to
severe spalling
Causes:
• Inadequate structure,
• Loss of base, subbase or subgrade support,
• Excessive air voids in HMA
• Asphalt cement properties (burnt binder)
• Stripping on the bottom of the HMA layer

Stripping of asphalt from aggregate (problems in an old
buried HMA layer)
• Layer debonding (poor construction practices)
• Accumulated damage
• Increase in loading
• Age hardening
• Construction deficiencies (poor joints, segregation)
• Poor drainage
• Excessive air voids in Hot Mix Asphalt Concrete
• Stripping of asphalt from aggregate
Prevention: The use of quality structural design and materials
during construction; Adequate drainage; Preventive maintenance
treatments as the pavement begins to age; Structural overlays
applied at the right time to increase the pavement strength.
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.
Block C racking
Block C racking is a pattern of cracks t hat divides the
pavement into approximately rectangu lar pieces. Rectangu lar
blocks range in size from approximately 0.1 square yard to 12
square yards. B lock cracking is generally not load-assoc iated
and us ually divides the pavement into approximately equal
size polygons or rectangular p ieces. It is main ly caused by
hardening and/or shr inkage of the asphalt and daily
temperature cycling.
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BLOCK CRACKING
Description: Pattern of cracks that divides the pavement into
approximately rectangular pieces. Rectangular blocks range in
size
from approximately 0.1 square yard to 12 square yards.
Block cracking is generally not load-associated and usually
divides the pavement into approximately equal size polygons or
rectangular pieces. It is mainly caused by hardening and/or
shrinkage of the asphalt and daily temperature cycling. However,
severe block cracking, where the size of the polygon is
approximately one or two feet, is usually the result of a structural
failure of the pavement when the asphalt concrete is placed over
treated bases such as cement treated base (CTB), lime treated
base (LTB), and lean concrete base (LCB). It can also occur
when an asphalt concrete (AC) overlay has been placed over old
Portland cement concrete (PCC) pavement. If the area is
localized, the pavement and base should be repaired. If the area
is extensive, the rehabilitation design should be sufficient to
remedy this type of failure. Block cracks are often greater than ¼
inch wide. Experience has shown that a minimum 4.2 in. AC
overlay is required when severe block cracking exists in the AC
over treated bases or AC over PCC.
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Mechanism: Shrinking and hardening of the asphalt due to age
and/or environment (temperature).
Block cracking will be
classified to three levels of severity: a) Low severity when width of
crack is less than 0.25 in., b) Medium severity when width of
crack is greater than or equal to 0.5 in. and less than 1 in. and c)
High severity when width of crack greater than or equal to 1in.
Causes:
• Asphalt binder aging
• Poor choice of asphalt binder in the mix design
• Aging and shrinking asphalt
• Shrinkage of stabilized layers (excess stabilizer)
• Frost action
• Heavy traffic
Prevention: The use of quality structural design and materials
during construction such as proper binder can help prevent block
cracking.
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Longi tudinal Cracking
Longi tudinal Cracking are cracks tha t are approximately
parallel to pavement centerline and are no t in the wheel path.
Longi tudinal cracks are non-load associated cracks. Location
within the lane (wheel path versus non -wheel path) is
signi ficant. A longitud inal crack in the wheel path is
considered a load-associated crack.
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LONGITUDINAL CRACKING
Description: Cracks that are approximately parallel to pavement
centerline and are not in the wheel path. Longitudinal cracks are
non-load associated cracks. Location within the lane (wheel path
versus non-wheel path) is significant. A longitudinal crack in the
wheel path is considered a load-associated crack.
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Mechanism: Poorly constructed paving joint, shrinkage of surface
layer due to temperature cycling or hardening of the asphalt.
Longitudinal cracking can be load or nonload related depending
on the location of the crack within the travel lane. Longitudinal
crack in the wheel path also refers to the initial stage of fatigue
(alligator) cracking. Longitudinal cracking due to thermal and/or
shrinkage will be considered under the transverse and block-
cracking categories. Longitudinal cracking will be classified to
three levels of severity: a) Low severity when width of crack is
less than 0.25 in., b) Medium severity when width of crack is
greater than or equal to 0.5 in. and less than 1 in. and c) High
severity when width of crack greater than or equal to 1in.
Causes:
• Structural deficiency
Load Associated
• Excessive air voids in Hot Mix Asphalt Concrete
• Asphalt cement properties
• Stripping of asphalt from aggregate
• Aggregate Gradation
• Construction deficiencies
• Volume change potential of foundation soil
Non Load Associated
• Slope stability of fill materials

Settlement of fill or in-place materials as a result of
increased loading
• Segregation due to laydown machine
• Poor joint Construction
• Other construction deficiencies
• Inadequate bonding
• Reflection cracks
• Heavy loads
Prevention: One means of preventing longitudinal cracking is
proper construction, especially of joints. Joints should be
constructed outside of the wheelpath so that they are only
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infrequently loaded. Joints in the wheelpath will general fail
prematurely.
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Transverse Cracking
Transverse Cracking are cracks that are predominately
perpendicular to pavement centerline and a re not located over
Portland cement concrete joints. Thermal cracking is typica lly
in th is category.
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TRANSVERSE CRACKING
Description: Cracks that are predominately perpendicular to
pavement centerline and are not located over Portland cement
concrete joints. Thermal cracking is typically in this category.
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Mechanism: Inadequate bonding between paving lanes due to
poor construction techniques (improper joint compaction),
shrinkage of asphalt surface due to low temperatures or
hardening of asphalt cement, or reflective cracks caused by
cracks below the surface. Transverse cracks caused by low
temperature are referred to as thermal cracks which are due to
contractive forces and restraint supplied by 1) friction on the
bottom of the HMA surface and 2) the continuity of the HMA layer
itself, that causes the tensile stress to build up to such a point that
it can exceed the tensile strength of the HMA layer thus initiating
cracking. Transverse cracking will be classified to three levels of
severity: a) Low severity when width of crack is less than 0.25 in.,
b) Medium severity when width of crack is greater than or equal to
0.5 in. and less than 1 in. and c) High severity when width of
crack greater than or equal to 1in.
Causes:
• Hardness of asphalt cement
• Stiffness of Hot Mix Asphalt Concrete
• Volume changes in base and subbase
• Poor base and soil properties
• Temperature changes
Prevention: The use of quality structural design and materials
during construction such as proper stabilization of the underlying
layers.
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Shov ing/Corrugation
Shoving is a form of plastic movement typified by r ipples
(corrugation) or an abrupt wave (shoving) across the pavement
surface. The distor tion i s perpendicular to the traffic direction.
Usually occurs at points where traff ic starts and s tops
(corrugation) or areas where HMA abuts a r igid ob ject (shoving).
This longitud inal d isplacement of the pavement surface is
generally caused by braking, turning or accelerating vehicles,
and i s usually located on hi lls or curves, or at intersections . It
also may have vertica l displacement.
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SHOVING
Description: Shoving is a form of plastic movement typified by
ripples (corrugation) or an abrupt wave (shoving) across the
pavement surface. The distortion is perpendicular to the traffic
direction. Usually occurs at points where traffic starts and stops
(corrugation) or areas where HMA abuts a rigid object (shoving).
This longitudinal displacement of the pavement surface is
generally caused by braking, turning or accelerating vehicles, and
is usually located on hills or curves, or at intersections. It also may
have vertical displacement. An unstable or tender mix primarily
causes shoving. It can take place during the compaction
operation or can occur later under traffic. They occur in asphalt
layers that lack stability. Lack of stability may be caused by a
mixture that is too rich in asphalt, has too high a proportion of fine
aggregate, has coarse or fine aggregate that is too round or too
smooth, or has asphalt cement that is too soft. It may also be due
to excessive moisture, contamination due to oil spillage, or lack of
aeration when placing mixes using liquid asphalt. The pavement
may have low tensile strength and delamination or may have
bleeding from too much asphalt in the mix. Removal of the
offending material is usually necessary.
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Mechanism: Plastic movement in the HMA surface layer caused
by traffic action on HMA with too much asphalt, too much fine
aggregate, or smoothed course aggregate. The distress usually
appears in localized areas and the deformation can be
longitudinal as well as vertical. Shoving will be classified to three
levels of severity. However quantifying the severity level is hard.
Please use the ride quality and engineering judgment as an
indicator of level of severity.
Causes:
• Unstable Mix
• Braking, stopping, accelerating traffic
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• Slippage between layers
• Poor interlayer bond
• Poor construction
• Heavy trucks
• Moisture damage
• Shrinkage of stabilized layers (too much stabilizer)
• Asphalt cement properties (burnt binder)
Prevention: The use of quality design, quality aggregate, quality
liquid asphalt, and quality construction is favorable. Also, a good
tack between layers helps reduce this type of distress.
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Raveling
Raveling is wearing away of the pavement surface in high-
quality hot mix asphalt concrete tha t may be caused by the
dislodging of aggregate particles (either from the edges
inward or the surface downward) and loss of asphalt b inder. It
is no rmally caused by lack of compaction, construction of a
th in lift dur ing c old weather, dirty or d isintegrating aggregate,
too l itt le asphalt in the mix, or overheating of the aspha lt mix.
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RAVELING
Description: Wearing away of the pavement surface in high-
quality hot mix asphalt concrete that may be caused by the
dislodging of aggregate particles (either from the edges inward or
the surface downward) and loss of asphalt binder. It is normally
caused by lack of compaction, construction of a thin lift during
cold weather, dirty or disintegrating aggregate, too little asphalt in
the mix, or overheating of the asphalt mix. Studded tires have
also been shown to contribute to raveling. Also, it could occur in
the middle of the lane where the oil that drips from the vehicles
strips the asphalt from the aggregate.
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Mechanism The result of a loss of adhesion between the asphalt
binder and the aggregate causing the loss of material from
pavement surface. For the purpose of the online expert system,
only the area of raveling in the distressed portion of the
intersection is required. The program internally proportions that
area with the total distressed area and based on that classifies
the severity of raveling. The program classifies reveling to three
levels of severity: a) Low severity when percent of the rated
surface area less than or equal to 15% is raveling, b) Medium
severity when percent of the rated surface area less than or equal
to 50% but greater than 10% is raveling, and c) High severity
when percent of the rated surface area greater than 50% is
raveling.
Causes:
• Low asphalt content
• Excessive air voids in Hot Mix Asphalt Concrete
• Hardening of asphalt
• Water susceptibility (stripping)
• Aggregate characteristics
• Hardness and durability of aggregate
• Improper compaction
• Lack of density
• Uneven mixture
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• QC of gradation
• Clay in gravel
• Aging pavement
• Binders oxidized
Prevention: Proper construction practices and quality control
such as achieving proper density during compaction to develop
sufficient cohesion within the HMA can help prevent raveling.
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Potholes
Potholes are localized failure areas which are usually caused
by weak base or subgrade
layers. Bowl-shaped hol es of
various sizes in the pavement surface. Holes in the pavement
generally started when small parts of an alligator-cracked area
are dislodged by traffic together with excessive water. Patch
the potholes pr ior to rehabilitation.
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POTHOLES
Description: Potholes are localized failure areas which are
usually caused by weak base or subgrade layers. Bowl-shaped
holes of various sizes in the pavement surface. Holes in the
pavement generally started when small parts of an alligator-
cracked area are dislodged by traffic together with excessive
water. Patch the potholes prior to rehabilitation.
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Mechanism: Traffic loads causing to pavement disintegrate
because of inadequate strength in one or more layers of the
pavement, usually accompanied by the presence of water.
Potholes will be classified to three levels of severity: a) Low
severity when one pothole is visible in the distressed area of the
intersection, b) Medium severity when two potholes are visible in
the distressed area of the intersection, and c) High severity when
more than 2 potholes are visible in the distressed area of the
intersection.
Causes:
• Excess moisture in subbase or subgrade
• Insufficient thickness
• Freeze/thaw
• Constant loading
Prevention: Proper construction and adequate bonding between
the HMA and base layer can reduce this failure. Also, the best
method of preventing potholes is to address distresses such as
alligator cracking before it becomes severe.
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Bleeding/Flushing
Flushing is excess bituminous binder in the mixture (and/or
low air void content) occurring on the pavement surface. It
may create a shiny, glass-like, reflective surface that may be
tacky to the touch. Usually found i n the wheel paths.
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FLUSHING OR BLEEDING
Description: Flushing is excess bituminous binder in the mixture
(and/or low air void content) occurring on the pavement surface. It
may create a shiny, glass-like, reflective surface that may be
tacky to the touch. Usually found in the wheel paths.
Mechanism: Excessive asphalt in the mix relative to the void
space in the mineral aggregate, therefore, the air voids in the mix
are too low and the excess asphalt is forced to the pavement
surface causing bleeding. For the purpose of the online expert
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system, only the area of bleeding or flushing in the distressed
portion of the intersection is required. The program internally
proportions that area with the total distressed area and based on
that classifies the severity of this distress. The program classifies
bleeding and or raveling to three levels of severity: a) Low
severity when percent of the rated surface area less than or equal
to 15% is bleeding, b) Medium severity when percent of the rated
surface area less than or equal to 50% but greater than 10% is
bleeding, and c) High severity when percent of the rated surface
area greater than 50% is bleeding.
Causes:
• High asphalt content
• Excessive densification of Hot Mix Asphalt Concrete during
construction or by traffic (low air void content)

Temperature susceptibility of asphalt (soft asphalt at high
temperatures)
• Excess application of “fog” seal or rejuvenating materials
• Water susceptibility of underlaying asphalt stabilized layers
together with asphalt migration to surface
• Improper compaction
• High truck counts
• Insufficient cooling
Prevention: Good quality control practices during construction
(ensuring the asphalt content is within tolerable limits), achieving
proper density of the mix during compaction and proper mix
design can reduce the occurrence of bleeding.
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Common Remediation
Strategies
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Chip Seal
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CHIP SEAL
PRODUCT DESCRIPTION: A chip seal is a single thin
surface treatment constructed by spraying a bituminous
binding agent and immediately spreading and rolling a thin
aggregate cover. The bituminous binding agent can be
emulsified asphalt, cutback asphalt, or asphalt cement.
The aggregate used is a single-sized crushed aggregate
chip; the maximum chip size is most commonly 1/4 to 3/8
in., although larger chips have been used successfully on
roads with heavy truck traffic. The thickness of the
constructed chip seal layer is equal to the maximum size
of the aggregate chips used. Typical use of chip seal is for
road surfacing such as preventative maintenance
treatment for small cracks, bleeding, raveling, and loss of
surface friction. Chip seals are a widely used alternative
for surfacing low volume roads. They protect underlying
materials from water and erosion and provide a relatively
smooth riding surface. In general, chip seals provide an
economical and relatively durable surface that is safe
under normal weather and driving conditions. Chip seals
can also be placed over new or existing hot asphalt
concrete pavement to modify, maintain, or improve the
surface texture and friction properties and/or seal small
cracks.
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TRAFFIC RANGE: Typically AADT< 2,000 (AADT < 1000
when placed on aggregate base, and typical AADT< 2,000
when placed on existing HMA. Also, less than 15% of
truck volume is preferred).
LIFE EXPECTANCY: Up to 3 to 7 years.
UNIT PRICE: $0.80 to $1.25/yd2
APPEARANCE:
Immediately after placement, the chip
seal’s appearance is influenced by both the black
bituminous binder and the aggregate chip color. If the
chips are pre-coated, the chip seal will be black and will
not be characterized by the natural aggregate color. A chip
seal’s appearance can be modified with the careful
selection of colored aggregates and by the use of
pigments in the binding agent.
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ADVANTAGES: Can postpone the need for heavier
surface treatments or resurfacing for up to 3 years.
Improves surface friction, slows surface ravelling and
oxidation, corrects minor deformations and seals small
cracks, provide temporary cover for a base course until
the final asphalt courses can be placed.
LIMITATION:
Chip seals should not be applied to
pavements with majority of ruts greater than 0.5 in. deep.
Preventative maintenance includes periodic crack sealing.
Fog seals can be applied to extend the serviceable life of
chip seals. Loose chips can be windshield hazard.
LANE CLOSURE REQUIREMENTS: The roadway lane(s)
being constructed is closed during construction, so
adequate traffic control is needed. The chip seal surface
can be opened to traffic at lower speeds as soon as it is
constructed. Normal traffic speeds can be allowed once
the loose chips have been swept from the roadway
surface. Road surface striping may be performed after the
lane is opened.
APPLICATION: The bituminous binding agent is sprayed
onto the prepared working surface by the distributor; then,
the aggregate chips are spread onto the surface using an
aggregate spreader. After the aggregate chips are placed,
the surface is rolled with a pneumatic-tired roller to embed
and realign the aggregate chips in the binder. The surface
should be rolled before the binding agent begins to set.
The constructed surface should consist of a single layer of
aggregate chips with about two-thirds of the voids being
filled with the binding agent. The time available for rolling
before the binder hardens will depend on the type of
binding agent, binder temperature when it is placed, air
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temperature, and wind, but can range from several
minutes to several hours or more. Once the binding agent
has hardened, the road surface should be swept with a
mechanical broom to remove all loose chips from the
surface. A fog seal can be applied to the chip seal after
construction to improve the bonding of the chips to the
road surface. Provides an economical all-weather surface
for light to medium traffic (polymer-modified emulsions and
high quality aggregates should be used for higher traffic
volume applications). Must be applied to structurally sound
pavements.
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Crack Seal
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CRACK SEAL
PRODUCT DESCRIPTION: A crack sealing treatment is a
maintenance procedure for preventing pavement damage,
not a corrective measure for restoring the structural
integrity of damaged pavements. As such the timing of
application is vital to optimizing the benefits of crack
sealing treatment. In general, crack sealing is
recommended as soon as cracks have fully developed
when temperatures are moderately cold, such as during
the spring. Routing, cleaning and filling the crack with
sealant. Moisture infiltration is the primary cause of
pavement deterioration. Crack sealing prevents water and
debris from entering a crack. “Crack Filling” does not
involve routing and does not fully seal the crack. Proper
placement is important to ensure that the sealant
maintains its integrity as long as possible. Several
materials and techniques are available to do this work.
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TRAFFIC RANGE: Typically AADT < 4,000
LIFE EXPECTANCY: Up to 5 years
UNIT PRICE: Weight $.60-$1.00/Lb and Lane Mile $1000
-$4000
APPEARANCE: Immediately after placement, the crack
seal’s appearance is influenced by the type of sealant
material usually black in color.
ADVANTAGES: Prevents moisture and debris from
getting into cracks, prevents water damage to the
pavements structure, extends pavement life by 3 to 5
years.
LIMITATION: Crack seal is not suitable for high severity
cracking such as alligator cracking, which is usually
associated with structural deficiencies. Also, poor choice
of sealing and poor workmanship such as excessive use
of sealant and multiple uses of treatments over several
years can cause the sealant to separate. A sealant can
also separate from the sides of a crack if applied to a wet
crack surface, dirty crack surface, poor material finishing
technique.
Other examples are application of cold
sealant, insufficient material, rain during the application, or
application during cold weather.
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LANE CLOSURE REQUIREMENTS: The roadway lane(s)
being constructed are closed during construction, so
adequate traffic control is needed. Depending on the type
of sealant used and weather conditions, roads can be
opened to traffic one to twelve hours after placement.
Sealing can be performed one lane at a time.
APPLICATION: Use for cracks less than 1in. wide,
spaced uniformly along the pavement and with limited
edge deterioration. Use Crack Filling for older pavements
with wider, more random cracking. Best applied during
cool dry weather (32ºF - 60ºF) when cracks are almost
fully open.
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Fog Seal
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FOG SEAL
PRODUCT DESCRIPTION:
A fog seal is a light
application of emulsified asphalt diluted with water. Fog
seals were used extensively in the past to seal new
pavements immediately after construction. They often
performed poorly due to excessive slipperiness when wet
and bleeding during hot weather; these problems where
mainly due to excessive application rates or inappropriate
choice of seal materials. Currently, fog seals are
predominately used to enrich oxidized asphalt surfaces or
to seal very small cracks and surface voids. Fog seal use
is sometimes restricted on high volume roadways due to
concerns over reduced skid resistance and short life
expectancy; for high volume applications, a high degree of
construction experience and quality control is required.
Fog seals should not be used on roadway surfaces with
low skid resistance. Fog seals work best on coarse or
porous surfaces where the emulsified asphalt can
penetrate the surfacing. When applied to smooth, dense
surfacings, fog seals can lie on top of the existing surface
and create a slippery surface. Fog seals can extend the
life of roadway surfacings and can be used as a “holding”
strategy (i.e. delay the need for major maintenance or
rehabilitation). Fog seals are often used on newly
constructed chip seals to provide a uniform black color
and to minimize aggregate loss.
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TRAFFIC RANGE: Typically AADT<4000
LIFE EXPECTANCY: Up to 2 years
UNIT PRICE: $0.20 to $0.50/yd2
APPEARANCE: Immediately after placement, fog seals
are black. A fog seal’s appearance can be modified with
the use of pigments in the emulsified asphalt.
ADVANTAGES: Low initial cost; enriches oxidized asphalt
surfaces; seals small cracks.
LIMITATION: Fog seal may not be appropriate for winding
roads due to slipperiness. Fog seals can lower the skid
resistance of a surfacing and create a slippery surface if it
is applied too thick. No structural value; short life
expectancy; can reduce skid resistance.
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BENEFITS: Rejuvenates dry and brittle asphalt surfaces,
seals very small cracks and surface voids, slows the rate
of weathering and oxidation.
LANE CLOSURE REQUIREMENTS: The roadway lane(s)
being treated is closed during construction, so adequate
traffic control is needed. The fog seal surface can be
opened to traffic after the emulsified asphalt has set,
typically 1 to 3 hours, depending on the weather. Road
surface striping may be performed after the lane is
opened.
APPLICATION: The diluted emulsified asphalt is applied
cold with application temperatures ranging from 70° to
185°F. The diluted emulsified asphalt is sprayed onto the
prepared working surface by the distributor. Typical
application rates for the diluted emulsified asphalt are 0.10
to 0.15 gal/yd2. A uniform coverage of the fog seal should
be achieved for best performance. Use on structurally
sound pavements to improve surface conditions on
pavements showing signs of minor cracking, weathering,
or segregation.
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Micro Surfacing
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MICROSURFACING
PRODUCT DESCRIPTION: Microsurfacing, an enhanced
slurry seal, is composed of a mixture of polymer-modified
emulsified asphalt, dense-graded crushed fine aggregate,
mineral filler or other additives, and water. The main
difference between microsurfacing and slurry seals is that
microsurfacing can be placed with a thickness up to about
three times the size of the largest aggregate in the mix;
slurry seals are applied at the thickness of the largest
aggregate in the mix. High quality materials and careful
mix design are used to create a high-stability mix that is
quick-setting and can be placed at thicknesses up to 1.5
in. for rut filling. In addition to rut-filling, microsurfacing is
used as a preventative maintenance treatment for
roadways with bituminous surfacing. Preventative
maintenance or corrective treatment for minor surface
irregularities, small cracks less than 0.25 in. wide, rutting
(fill ruts up to 1.5 in. deep in one pass), raveling, bleeding,
and loss of surface friction and to improve ride quality.
When microsurfacing is used to address pavement rutting,
the cause of rutting should be established in advance.
Microsurfacing can rehabilitate rutting due to densification
but is not a solution for correcting rutting due to
inadequate structural capacity or high instability
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TRAFFIC RANGE: Typically AADT<4000 (also AADT >
400 is preferred)
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LIFE EXPECTANCY: Up to 7 years
UNIT PRICE: $2.60 to $3.30/yd2
APPEARANCE:
Microsurfacing is typically black in
appearance, similar to HMA. Microsurfacing’s color can be
modified by the use of pigments in the microsurfacing mix.
ADVANTAGES: High quality surface treatment; Excellent
skid resistance; Can rehabilitate instability rutting.
Improves surface friction, slows surface ravelling and
seals small cracks, improves ride quality and corrects
surface irregularities
LIMITATION:
Microsurfacing is less susceptible to
damage from snow plows than single chip seals or slurry
seals in snow plowing areas. Higher initial cost than some
other surface treatments; Specialty contractors required.
LANE CLOSURE REQUIREMENTS: The roadway lane(s)
being constructed are closed during construction, so
adequate traffic control is needed. Depending on the type
of emulsified asphalt used and weather conditions, roads
can usually be opened to straight rolling traffic about one
hour after placement. Road surface striping may be
performed after the lane is opened.
APPLICATION: It is important that any areas of base
failure be repaired before microsurfacing is applied. A tack
coat is usually not required unless the surface is extremely
dry and raveled or consists of concrete or brick. The
microsurfacing mix is automatically fed into a spreader box
attached to the rear of the equipment and applied to the
roadway. Microsurfacing is commonly applied at a rate of
20 to 30 lb/yd2 with a corresponding thickness of 0.4 to
0.6 in. Rolling or compaction is seldom required but may
be beneficial in areas of minimal traffic such as parking
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lots or airports. For high volume applications, two lifts of
microsurfacing can be placed, consisting of a leveling
layer and a surface layer. Used on stable pavements with
a sound base that have minor surface distresses such as
cracking, rutting, ravelling and roughness. Can be used to
correct rutting. Do not use on pavements showing
structural distress or pavement failure. Defect will quickly
reflect through new surface.
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Sand Seal
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SAND SEAL
PRODUCT DESCRIPTION: A sand seal is a thin asphalt
surface treatment constructed by spraying a bituminous
binding agent and immediately spreading and rolling a thin
fine aggregate (i.e. sand or screenings) cover. A sand seal
is basically the same as a chip seal except that finer
aggregate is used in the cover. The bituminous binding
agent can be an emulsified asphalt, cutback asphalt, or
asphalt cement. The maximum aggregate size is usually
smaller than No.10 sieve. Sand seals are often used in
areas where good sources of aggregate for chip seals are
not available.
TRAFFIC RANGE: Typically AADT < 2,000 and low
percentage of trucks volume
LIFE EXPECTANCY: Up to 3 years
UNIT PRICE: $0.50 to $1.25/yd2
APPEARANCE:
Immediately after placement, the sand
seal’s appearance is influenced by the black bituminous
binder and, to a lesser extent, by the sand color. A sand
seal’s appearance can be modified by the use of pigments
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in the asphalt cement, but would not normally be done
because of the short service life of the surfacing.
ADVANTAGES: Can enrich dry, weathered, or oxidized
surfaces and seal small cracks, and improve skid
resistance; can be used in aggregate poor areas.
LIMITATION: Sand seals can be damaged by snow plow
operations. Sand seals should not be applied to
pavements with a majority of ruts greater than 0.5 in.
deep. Sand seals, similar to other non-structural asphalt
surfacings, do not improve ride quality; ride quality is
mainly determined by the roughness of the underlying
layer. On a properly prepared application surface, a good
to very good ride quality can be achieved after
construction. Ride quality deteriorates over the serviceable
life. Use and experience varies by region; Not as durable
as chip seals.
LANE CLOSURE REQUIREMENTS: The roadway lane(s)
being constructed is closed during construction, so
adequate traffic control is needed. The sand seal surface
can be opened to traffic at lower speeds, typically 20 mph
maximum speed, as soon as it is constructed. Normal
traffic speeds can be allowed once the binder has set and
excess sand is swept from the roadway surface. Road
surface striping may be performed after the lane is
opened.
APPLICATION: The bituminous binding agent is sprayed
onto the prepared working surface by the distributor; then,
the fine aggregate is spread onto the surface using a sand
spreader. Typical application rates are 0.15 to 0.28
gal/yd2 for emulsified asphalt and 10 to 22 lb/yd2 for fine
aggregate. After the fine aggregate is placed, the surface
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is rolled with a pneumatic-tired roller. The set time for the
binder will depend on the type of binding agent, binder
temperature when it is placed, air temperature, and wind,
but can range from several minutes to several hours or
more. Once the binding agent has hardened, the road
surface should be swept with a mechanical broom to
remove all loose sand from the surface.
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Slurry Seal
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SLURRY SEAL
PRODUCT DESCRIPTION: Slurry seals are a cold-
mixed thin surface treatment constructed of a mixture
of emulsified asphalt, dense-graded crushed fine
aggregate, mineral filler or other additives, and water.
Slurry seals are applied at the thickness of the largest
aggregate in the mix. Slurry seals are used as a
protective or preventive maintenance technique for
paved surfaces or thin asphalt surface treatments;
slurry seals are applied to existing surfaces to seal
small cracks, correct minor surface irregularities, stop
raveling, improve ride quality, and improve friction
properties. Slurry seals have a smoother texture than
chip seals. Slurry seals may slightly improve the ride
quality of a previously paved roadway. However,
slurry seals will not mitigate significant defects
(rutting, depressions, severe cracking, etc.) in the
existing surface. Ride quality deteriorates over the
serviceable life.
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TRAFFIC RANGE: Typically AADT < 4000
LIFE EXPECTANCY: Up to 5 years
UNIT PRICE: $0.75 to $1.50/yd2
APPEARANCE:
Slurry seals have a black
appearance similar to HMA. A slurry seal’s color can
be modified by the use of pigments in the slurry mix,
but this is not normally done because of cost.
ADVANTAGES/BENEFITS:
Slurry seals provide
excellent initial skid resistance.
LIMITATION: Slurry seals are generally not used for
roadway gradients steeper than 8%. Slurry seals can
be damaged by snow plow operations. Slurry seals
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should not be applied to pavements with majority of
ruts greater than 0.5 in. deep.
LANE CLOSURE REQUIREMENTS: The roadway
lane(s) being constructed are closed during
construction, so adequate traffic control is needed.
Depending on the type of emulsified asphalt used and
weather conditions, roads can be opened to traffic
one to twelve hours after placement. Road surface
striping may be performed after the lane is opened.
APPLICATION: In general, once the slurry is mixed
by the slurry seal mixing machine, the mix is
automatically fed into a spreader box attached to the
rear of the equipment and applied to the roadway.
Rolling or compaction is seldom required but may be
desirable in low traffic areas such as parking lots and
airports.
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Ultra-Thin Wearing
Course
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Ultrathin Friction Course (Wearing
Course)
PRODUCT DESCRIPTION:
An ultra-thin friction
course is constructed of a thin layer of gap graded,
coarse aggregate hot mix asphalt concrete that
provides a smooth, durable, and skid-resistant
surface. The thin layer, typically 3/8 to 3/4 in. thick,
combines attributes of stone matrix asphalt and open
graded friction course asphalt mixes. The hot mix
asphalt layer is bound to the existing surface with a
polymer modified emulsion that is specifically
designed to seal the existing surface and bond the
new mix to the existing surface. Ultrathin friction
course can be used on asphalt or concrete
pavements as a preventative maintenance or surface
rehabilitation treatment. Ultrathin friction course
provides excellent skid resistance, reduced tire/road
noise, and reduced vehicle splash/spray. Ultrathin
friction course should be placed over a structurally
sound pavement with rut depths less than 0.5 in.,
minor to moderate cracking, and/or minor bleeding.
Because ultrathin friction course provides a high-
quality road surfacing, there is a tendency for road
usage to be higher and for drivers to exceed posted
speed limits.
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TRAFFIC RANGE: No limit (Preferred AADT > 1,000)
LIFE EXPECTANCY: Up to 10 to 12 years
UNIT PRICE: $3.50 to $4.00/yd2
APPEARANCE:
Immediately after placement,
ultrathin friction course is generally black with a very
smooth surface.
ADVANTAGES:
Very good ride quality after
construction. Ultrathin friction course provides
excellent skid resistance; reduces tire/road noise and
vehicle splash/ spray; provides a very durable riding
surface for high volume roads.
LIMITATION: Since the quantities of ultrathin friction
course are relatively small and the quality
requirements are very high, production from a mobile
asphalt plant would likely not be economical.
LANE CLOSURE REQUIREMENTS: The roadway
lane(s) being constructed are closed during
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construction, so adequate traffic control is needed.
The ultrathin friction course surface can be opened to
traffic within minutes of being placed. Road surface
striping may be performed before or after the lane is
opened.
APPLICATION: Cracks in the surfacing to be covered
should be sealed or repaired before ultrathin friction
course is placed. The polymer modified emulsified
asphalt membrane and thin asphalt layer are placed
in one pass using a special asphalt paver, specially
designed for ultrathin friction course placement. The
emulsified asphalt is sprayed onto the prepared
surface by the machine and the asphalt concrete
layer is placed immediately after the emulsified
asphalt. The paving machine has a special
combination tamping barvibratory equipment that
compacts and levels the surfacing layer after it has
been applied. Once the ultrathin friction course has
been placed, a steel drum roller is used to seat the
asphalt concrete overlay into the emulsified asphalt
membrane layer.
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Cold In-Place Recycling
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COLD IN-PLACE RECYCLING
PRODUCT DESCRIPTION: In-Place Recycling is an
in situ process used to recycle 100% of an existing
asphalt concrete pavement to construct a new asphalt
concrete layer. Cold In-Place Recycling (CIR) is the
rehabilitation of asphalt pavements without the
application of heat during the recycling process. In the
CIR process, the existing asphalt is cold milled, mixed
with about 1.5 to 2.0 percent of emulsified asphalt,
and then placed on the road and compacted. The CIR
material requires about 1 week of curing. The depth of
treatment is typically 2 to 4 in. but 5 to 6 in. is also
possible. Chemical additives (i.e., lime, cement, fly
ash, etc.) are sometimes used to decrease the initial
cure time (i.e. promote a more rapid strength gain)
and also increase the ultimate strength of the
material. New aggregate can also be added to the
CIR, not exceeding 25% by weight of RAP, to improve
the characteristics of the mix or to address a prior
flushing problem. CIR is commonly overlaid with
HMA; however, on low volume roads, slurry seals,
chip seals, or other surface treatments are used. As
CIR depth is limited, it is not suitable for fixing
problems with lower asphalt courses or granular
base/subbase. Pavements with major or extensive
structural deficiencies (severe alligator cracking and
severe structural rutting) are not good candidates for
CIR. Asphalt pavements in poor structural condition
are not considered to be suitable candidates for CIR
treatment. If the pavement exhibits localized structural
failures, full depth repairs including granular base and
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subbase may be required, as well as providing
efficient surface and subsurface drainage. One of the
major advantages of CIR is the mitigation of reflective
cracking; in order to achieve this, at least 70 % of the
asphalt pavement thickness needs to be treated.
TRAFFIC RANGE: AADT < 2000. Also, less than
10% truck traffic is preferred especially at
intersections.
LIFE EXPECTANCY: Varies from 2 to 20 years
UNIT PRICE: ($3.50 to $4.00/yd2) for 3 in. recycling
depth
APPEARANCE: Immediately after placement, CIR is
generally black with a smooth surface.
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ADVANTAGES:
In situ process; Recycles existing
HMA; Reduces energy requirements. Uses 100%
existing aggregates and asphalt, mitigates reflective
cracking, corrects cross fall and longitudinal grades of
existing pavements.
LIMITATION: Not typically used as surface course;
Experienced personnel and equipment required;
Construction weather limitations; Will not remove full
depth cracking in original HMA.
LANE CLOSURE REQUIREMENTS: The roadway
lane(s) being constructed are closed during
construction, so adequate traffic control is needed.
The CIR surface can be opened to traffic during the
curing period but heavy traffic should be avoided.
When the CIR is cured, the roadway lane(s) must be
closed for the surface course application.
APPLICATION: CIR is an in situ process. In the CIR
process, a portion of the existing pavement is milled
typically to a depth of 2 to 4 inches. The reclaimed
material is thoroughly mixed with emulsified asphalt
and recycling agent to restore the properties of the
asphalt binder in the mix. In the modified CIR
process, new aggregates are also added. The
resulting mixture is then placed back on the pavement
as the base/binder course, with new wearing course
placed later. Densification of the CIR mixes typically
requires more compactive effort than conventional
HMA and large pneumatic-tired rollers and vibratory
steel drum rollers are used. Well compacted CIR
mixes could have 9 to 14% Voids in Total Mix (VTM).
Rolling with a steel roller several days after initial
compaction (re-rolling) is used to remove minor
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consolidation in the wheel paths. The compacted CIR
layers must be cured for a period of about 1 to 2
weeks of good weather before the wearing course is
placed.
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Hot In-Place Recycling
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HOT IN-PLACE RECYCLING
PRODUCT DESCRIPTION:
The Hot In-Place
Recycling (HIR) process consists of (1) heating and
softening the existing asphalt pavement so it can be
scarified or hot rotary milled to the specified depth, (2)
mixing the loosened asphalt pavement with a
recycling (rejuvenating) agent and possibly additional
virgin asphalt and (3) placing and compacting the
mixture with conventional hot mix asphalt paving
equipment. This process is called heater-scarification
(or reshaping). In the HIR repaving process, heater-
scarification is simultaneously combined with an
overlay of HMA. When additional materials are
needed to recycle the pavement, such as mineral
aggregate or virgin hot mix asphalt concrete, the
remixing process is used. Typical treatments depths
range from 0.75 to 2 in. HIR is usually surfaced with a
hot mix asphalt concrete overlay or chip seal, but is
sometimes used as a surface course on low volume
roads. The typical HIR process requires a minimum of
3 in. of existing asphalt pavement. Detailed pavement
evaluation is required before designing the HIR
pavement rehabilitation. The evaluation should
include visual condition survey and evaluation of
pavement structural condition, using the Falling
Weight Deflectometer (FWD) for instance. If required
strengthening is less than 0.75 in. of HMA, the
pavement can be treated with remixing or repaving. If
required strengthening is greater than 0.75 in. of
HMA, but less than 2 in., the repaving process can be
used. HIR is not suitable if required strengthening is
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greater than 2 in. of HMA. The pavement to be HIR
treated should be relatively homogenous. If surface
treatments, crack sealants, etc. are present, they
should be removed. Large patches may require their
own specific mix designs.
sealants, etc. are
present, they should be removed. Large patches
may require their own specific mix designs.
TRAFFIC RANGE: Typically AADT < 4000
LIFE EXPECTANCY: Up to 8 years
UNIT PRICE: $2.00/yd2
APPEARANCE: Immediately after placement, HIR is
generally black with a very smooth surface.
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ADVANTAGES/BENEFITS: In situ process; recycles
in-place HMA; Reduces energy requirements.
Provides new waterproof surface, slows surface
ravelling, seals small cracks, improves ride quality
and corrects surface irregularities, improves surface
friction.
LIMITATION: Specialized equipment required; only
recycles a maximum of 2 in. of existing HMA.
LANE CLOSURE REQUIREMENTS: The roadway
lane being constructed is closed during construction,
so adequate traffic control is needed. The HIR surface
can be opened to traffic as soon as the HIR has
cooled and construction equipment is cleared from
the roadway.
APPLICATION: There are three sub-categories within
HIR:
heater-scarification
(also called surface
recycling);
remixing; and repaving. Heater-
scarification is the process in which softening of the
asphalt pavement surface is achieved with heat from
a series of pre-heating and heating units. The heated
and softened surface layer is then scarified to a
predetermined depth, a recycling (rejuvenating) agent
is added, the loose recycled material is thoroughly
mixed, and then placed with a standard paver screed.
The depth of treatment typically ranges from 0.5 to
0.75 in., although treatments as deep as 2 in. have
been used. No new aggregate or HMA are added in
the heater-scarification process. Remixing is the HIR
process in which the existing asphalt pavement is
heated, softened, scarified, and new aggregate, new
asphalt binder, recycling agent, and/or new HMA is
added and the resultant blend is thoroughly mixed.
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The recycled mix is then placed and compacted in
one layer. The remixing process is used when the
existing asphalt pavement requires significant
modification. The recycled mix is usually left as the
wearing course, although chip seal or HMA overlay
are sometimes placed as a separate operation.
Treatment depth is 1 to 2 in. Repaving combines the
heater-scarification or remixing process with the
placement of an ‘integral’ overlay of new HMA. The
recycled mix and new HMA overlay are compacted
together. The thickness of the HMA wearing course
ranges from 0.75 to 2 in.
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Hot Mix Overlay
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HOT MIX OVERLAY
PRODUCT DESCRIPTION: Hot asphalt concrete
pavement is a high quality pavement material that is
hot mixed at a plant and then hot laid. Hot asphalt
concrete pavement is composed of a carefully
designed blend of coarse and fine aggregate and
mineral filler with asphalt cement as a binder. The
asphalt mix proportions need to be designed to suit
the particular application. The asphalt cement grade
needs to be selected based on service temperature
ranges and traffic volumes. A high stability mix should
be used for heavy industrial loading conditions (i.e.
slow moving trucks, frequent braking, etc.). Mixture
criteria should be tailored for the conditions of use.
The grade of asphalt cement needs to be selected
based on service temperature ranges and traffic
volumes. In a hot mix overlay, a layer of hot mix is
placed over existing pavement. Thin overlays are at
least 1.5 in. thick if conventional asphalt is used but
thinner overlays can be laid with specialized mixes.
The most common rehabilitation technique (as
opposed to preventive maintenance technique) is a
similar form of hot mix overlay. Commonly known as
“Shave and Pave”, the process involves the
contractor milling and replacing up to 3 in. asphalt.
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TRAFFIC RANGE: No limit
LIFE EXPECTANCY: Up to 12 years
UNIT PRICE: $30 to $40/ton
APPEARANCE:
Immediately after placement, hot
asphalt concrete pavement is generally black with a
very smooth surface. Conventional hot asphalt
concrete pavement’s appearance can be modified
with the careful selection of colored aggregates, by
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the use of pigments in the asphalt cement, and by
inclusion of a coarser aggregate in the hot asphalt
concrete pavement.
ADVANTAGES: Provided high quality aggregates are
used in the asphalt concrete mix, HMA provides good
to excellent skid resistance. Provides new waterproof
surface, mitigates surface raveling, seals small
cracks, improves ride quality and corrects surface
irregularities, improves surface friction.
LIMITATION: Asphalt concrete plant is needed in the
area; quality aggregate source is required.
LANE CLOSURE REQUIREMENTS: The roadway
lane(s) being constructed are closed during
construction, so adequate traffic control is needed.
The hot asphalt concrete pavement surface can be
opened to traffic as soon as the hot asphalt concrete
pavement has cooled and construction equipment is
cleared from the roadway. Road surface striping may
be performed before or after the lane is opened.
APPLICATION: Upon arrival at the site, the asphalt
concrete mixture is transferred from the haul vehicles
into
the paver hopper, spread onto the prepared
working surface by the paver, and leveled by a screed
at the rear of the asphalt paver. The HMA is then
rolled with compaction equipment to achieve the
required density. The compaction process should be
completed before the asphalt binder stiffens to the
point where additional compactive effort will damage
the pavement mat, which generally occurs between a
temperature of about 185 °F and 300 °F, depending
on the asphalt binder. The time available for
compaction before the mix has cooled will depend on
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the mix temperature when it is placed, layer
thickness, air temperature, and wind, but can range
from several minutes to more than 30 minutes. Do not
use on pavements showing structural distress or
pavement failure. Defects will quickly reflect through
the new surface.
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Hot Mix Asphalt with
RAP
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HMA
with
RECLAIMED ASPHALT
PAVEMENT (RAP)
PRODUCT DESCRIPTION: Recycled hot asphalt
concrete pavement is HMA that contains a mixture of
virgin asphalt binder and aggregate combined with
cold milled HMA from old pavement structures. This
cold milled product is generally referred to as
Reclaimed Asphalt Product or Pavement (RAP).
Recycled HMA mixtures typically can contain up to
30% by mass of cold milled HMA (RAP), although
higher amounts can be used depending on the
proposed use. Surface course mixtures generally will
use less or no recycled HMA, and binder courses will
use more. The asphalt mix proportions need to be
designed to suit the particular application.
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TRAFFIC RANGE: Typically AADT < 4000. However,
a high stability mix should be used for high traffic
volumes and for heavy industrial loading conditions
(i.e. slow moving trucks, frequent braking, etc.)
LIFE EXPECTANCY: Up to 15 years
UNIT PRICE: $25 to $35/ton for recycled HMA
APPEARANCE:
Immediately after placement,
recycled HMA is generally black with a very smooth
surface. Where a pigmented HMA is desired, RAP
should not be added to the mix since it would
introduce an unknown aggregate type and the old
asphalt binder may compromise the effectiveness of
the pigment. Recycled HMA could still be used for the
binder course.
ADVANTAGES/BENEFITS:
Recycles old HMA;
provides a use for cold milling product; high quality
surfacing.
LIMITATION: Adversely affects the quality of HMA
when used in too high a proportion. Many agencies
prohibit the use of RAP in wearing course mixes and
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strictly limit the proportion allowed in base course
layers. Mix quality becomes more difficult to control as
the RAP content increases.
LANE CLOSURE REQUIREMENTS: The roadway
lane(s) being constructed are closed during
construction, so adequate traffic control is needed.
The recycled HMA surface can be opened to traffic as
soon as it has cooled and construction equipment is
cleared from the roadway. Road surface striping may
be performed before or after the lane is opened.
APPLICATION: In general, upon arrival at the site,
the asphalt concrete mixture is transferred from the
haul vehicles into the paver hopper, spread onto the
prepared working surface by the paver, and leveled
by a screed at the rear of the asphalt paver. The
recycled HMA is then rolled with compaction
equipment to achieve the required density. The
compaction process should be completed before the
asphalt binder stiffens to a point where additional
compactive effort will damage the mat. Typically, this
range is from 300 °F down to 185 °F. This
temperature range may not apply to modified binders.
Experience has shown that the compaction process
may continue to temperatures below 185 °F when
modified binders have been used. The time available
for compaction before the mix has cooled will depend
on the mix temperature when it is placed, layer
thickness, air temperature, and wind, but can range
from several minutes to more than 30 minutes.
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Hot Mix Asphalt with
Shingles
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HMA with RECYCLED ASPHALT
SHINGLES (RAS)
PRODUCT DESCRIPTION: Hot-Mix Asphalt (HMA) is
the most common process to which shingles can be
added. Waste shingles are ground and screened to
produce 0.5 in. pieces for batch plants, or 0.25in.
pieces for continuous feed plants. The ground
shingles are usually fed into and mixed with the
aggregate before adding the virgin asphalt binder.
RAS reduces the amount of asphalt binder needed for
HMA. Asphalt Shingles can be used as a subbase in
road construction, for temporary roads, driveways and
parking lots, or to minimize dust on rural and unpaved
roads.
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TRAFFIC RANGE: No limit
LIFE EXPECTANCY: Up to 10 years.
UNIT PRICE: $0.50 to $3.30 per ton of HMA
APPEARANCE: Immediately after placement, RAS is
generally black with a very smooth surface.
ADVANTAGES:
There may be an immediate
economic benefit due to asphalt reclamation. Plants
produce fiberglass-based shingles, which are
approximately 20% asphalt. AC is approximately 6%
asphalt. So a small percentage of shingles (e.g., 5%
by weight of aggregate) can displace a large
percentage of asphalt binder (approximately 20%).
Other economic factors include recyclers' tipping fees,
costs to grind the shingles, price of virgin asphalt, and
transportation costs. Another benefit may be
improved pavement performance. Because the
asphalt used in shingles is harder than pavement
asphalt, the pavement benefits may include improved
resistance to rutting, increased stability, decrease in
temperature susceptibility, improved compaction, and
improved “rideability” index.
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LIMITATION:
The main disadvantage is the
availability of processing plants. Adversely affects the
quality of mix when used in too high a proportion.
Also, mix quality becomes more difficult to control as
the RAP content increases.
LANE CLOSURE REQUIREMENTS: The roadway
lane(s) being constructed are closed during
construction, so adequate traffic control is needed.
The RAS surface can be opened to traffic as soon as
it has cooled and construction equipment is cleared
from the roadway.
APPLICATION: However, in general, upon arrival at
the site, the asphalt concrete mixture is transferred
into the paver hopper, spread onto the prepared
working surface by the paver, and leveled by a screed
at the rear of the asphalt paver. The RAS mix is then
rolled with compaction equipment to achieve the
required density. The compaction process should be
completed before the asphalt binder stiffens to a point
where additional compactive effort will damage the
mat. The time available for compaction before the mix
has cooled will depend on the mix temperature when
it is placed, layer thickness, air temperature, and
wind, but can range from several minutes to more
than 30 minutes.
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Portland Cement
Concrete Overlay
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PORTLAND CEMENT CONCRETE
OVERLAY
PRODUCT DESCRIPTION:
Portland cement
concrete pavement (PCCP) is a mixture of aggregate,
cementitious material, and water that forms a rigid,
paved surfacing. Additives are used to help with
production and paving and to improve durability.
Typical additives include air entraining admixture,
water reducing agents, and supplementary
cementitious materials (e.g. fly ash, ground blast
furnace slag, silica fume, and calcinated clay).
Concrete pavements are designed and constructed
as
plain concrete, or as common in Texas as
continuously reinforced. PCCP have very good
performance characteristics with respect to strength,
durability, and ride quality.
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TRAFFIC RANGE: No limit (Preferred for high traffic
volume and high percentage of truck traffic).
LIFE EXPECTANCY: Life expectancy varies
depending on construction materials used,
environmental conditions, and traffic volumes. Typical
PCCP design life is 30 to 40 years.
UNIT PRICE: $100 to $135/yd3
APPEARANCE:
PCCP typically has a smooth
surface texture and light gray color. The appearance
can be influenced by aggregate type and source, so
visual aesthetics can be improved by using select
aggregates, when available. Surface appearance can
also be modified by using pigments or stains to color
the concrete or finishing techniques to change the
surface texture. Special treatments are available to
remove some of the cement paste and expose the
PCC aggregate.
ADVANTAGES: Long life; very good ride quality; low
maintenance requirements.
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LIMITATION: High initial cost; initial construction is
time and labor intensive.
LANE CLOSURE REQUIREMENTS: The roadway
lane(s) being constructed is closed during
construction and curing, so adequate traffic control is
needed. Normal traffic loads can be allowed on the
PCCP surface after initial curing and once an
adequate PCC strength is reached, typically after 7 or
14 days. High strength PCC can be used to achieve
design concrete strengths faster, so the road
surfacing can be opened to traffic sooner, as soon as
eight hours after placement. Road surface striping
may be performed after the lane is opened.
APPLICATION: The concrete mix is discharged from
mixing trucks and placed using automatic screeds or
hand troweled. On large projects, continuous slip form
concrete pavers can be used; if automatic dowel
inserters are used, they should be checked to ensure
proper placement and functioning of the equipment.
The concrete is consolidated with vibrators to
increase density and reduce voids. Thermal
expansion joints are constructed at predetermined
intervals. The concrete should be cured in place for 4
to 7 days or until a minimum strength is achieved,
depending on exposure conditions. To facilitate
curing, curing compounds can be applied, wet burlap
can be used, or insulated sheets in low ambient
temperatures can be used. Control joints must be
saw-cut/formed before the stress in the concrete
exceeds the strength to minimize random cracking.
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Page 139Top


Ultra-Thin Whitetopping
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WHITETOPPING
PRODUCT DESCRIPTION:
Whitetopping is a
pavement rehabilitation technique that involves
construction of a Portland cement concrete (PCC)
overlay or inlay on top of hot asphalt concrete
pavement (HMA). Three different types of
whitetopping are commonly used in construction:
conventional whitetopping, thin whitetopping, and
ultrathin whitetopping (UTW). Conventional
whitetopping is a PCC overlay or inlay, typically at
least 8 in. thick, placed over HMA. Conventional
whitetopping does not rely on bonding with the HMA
layer and no special treatment of the HMA layer is
required. Thin and ultrathin whitetopping rely on bond
development between the PCC overlay or inlay and
the existing HMA; by creating a bond between the two
layers, the existing HMA layer provides significant
structural support and allows for the whitetopping
overlay thickness to be reduced. Thin whitetopping
typically has a thickness of 4 to 8 in. UTW typically
has a thickness of 2 to 4 in. For thin and ultrathin
whitetopping, joint spacing is reduced compared to
conventional whitetopping. Whitetopping is not
recommended for applications where the existing
asphalt concrete is badly deteriorated or when
substantial portions of the asphalt concrete have to be
removed during rehabilitation.
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TRAFFIC RANGE: No limit (Preferred for high traffic
volume and high percentage of truck traffic).
LIFE EXPECTANCY: Average 5 to 15 years
UNIT PRICE: ($13.00 to $16.00/yd2)
APPEARANCE: Whitetopping typically has a smooth
surface texture and light gray color. The close spacing
of sawn joints, as close as 2 ft., in the ultrathin
whitetopping, produces a distinctly different surface
appearance from conventional PCCP. The
appearance can be influenced by aggregate type and
source, so visual aesthetics can be improved by using
select aggregates, when available. ADVANTAGES:
Whitetopping provides very good ride quality after
construction. Whitetopping requires relatively little
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preventative maintenance. Joints may require periodic
joint resealing. When high quality aggregates are
used, whitetopping provides very good initial skid
resistance. The use of lower quality aggregates leads
to aggregate polishing at the surface that can reduce
the skid resistance over time. Durable; Good ride
quality; Excellent skid resistance.
LIMITATION: High initial cost. Whitetopping should
also be avoided when the asphalt concrete has
material problems, such as asphalt stripping.
LANE CLOSURE REQUIREMENTS: The roadway
lane being constructed is closed during construction
and curing, so adequate traffic control is needed.
Normal traffic loads can be allowed on the
whitetopping surface after initial curing and once an
adequate PCC strength is reached, typically after
about 3 days. High strength PCC can be used to
achieve design concrete strengths faster, so the road
surfacing can be opened to traffic sooner, as soon as
eight hours after placement. Road surface striping
may be performed after the lane is opened.
APPLICATION: Prior to PCC placement, cold milling
of the existing asphalt concrete surface is required for
thin and ultrathin whitetopping. The milled surface
should be thoroughly cleaned of loose material prior
to PCC placement to ensure a good bond between
the overlay and the milled surface. Whitetopping
placement is similar to conventional PCCP. The
concrete mix is discharged from mixing trucks and
placed using vibrating screeds or hand troweled. On
large projects, continuous slip form concrete pavers
can be used. The concrete is consolidated with
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vibrators to increase density and reduce voids. Load
transfer across joints is provided by aggregate
interlock, or by the installation of dowel bars, for
heavier traffic loading. In general, whitetopping is built
using plain, unreinforced concrete. However, the use
of fiber reinforcement can allow longer joint spacing to
be utilized. The surface can be textured to improve
skid resistance. The concrete should be cured in
place for 4 to 7 days, depending on exposure
conditions. To facilitate curing, curing compounds can
be applied, or wet burlap can be used, or insulated
sheets in low ambient temperatures. The joints can be
formed by sawing, tooling, or by using inserts. Sawing
within 4 to 12 hours of concrete placement is the most
common method for joint construction.
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Full -Depth Reclamation
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FULL DEPTH RECLAMATION (FDR)
PRODUCT DESCRIPTION: Full Depth Reclamation
(FDR) is a rehabilitation technique in which the full
thickness of the asphalt pavement and predetermined
portion of the underlying materials (base, and
sometimes, subbase) are uniformly pulverized and
blended to provide an upgraded, homogenous base
material. The reclaimed layer is then compacted to
provide a uniform platform for the subsequent asphalt
base course or surface course. FDR is an in situ
process without the addition of heat. Stabilizing
additives can be applied to enhance the properties of
the reclaimed layer. FDR with bituminous and
chemical stabilization are covered in detail in separate
product summaries. The structural support of the
pulverized in situ pavement materials can be
enhanced by the addition of granular materials such
as virgin aggregates, reclaimed granular materials,
crushed/reclaimed PCC, or reclaimed asphalt
pavement (RAP). These additional granular materials
can improve gradation deficiencies and drainage
characteristics of the compacted base. Typical FDR
equipment can in situ process up to 5 to 6 inches of
existing asphalt. Where existing asphalt thickness is
greater than this, prior cold milling is required. Where
there is extensive hot mix patching, the variation in
asphalt thickness can pose construction problems for
the FDR operation. Pulverized pavement will perform
as an unbound granular surface and can be used for
temporary construction traffic without additional
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surfacing, but is not generally suitable for use as a
permanent surfacing.
TRAFFIC RANGE: No limit.
LIFE EXPECTANCY: Up to 10 years
UNIT PRICE: ($1.70 to $3.30/yd2), for a typical 8 inch
processing depth.
APPEARANCE: The pulverized pavement resulting
from FDR is generally not left exposed. The
appearance is similar to a dark aggregate base
material, with the asphalt coated particles visible on
close examination.
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ADVANTAGES/BENEFITS:
In situ process; reuses
existing base material; less expensive than other FDR
alternatives because no additive is used.
LIMITATION: Lower quality material than stabilized
FDR materials; some virgin aggregate base is
generally needed to permit fine grading prior to
paving.
LANE CLOSURE REQUIREMENTS: The roadway
lane being constructed is closed during construction,
so adequate traffic control is needed. The FDR
surface can generally be opened to temporary traffic
as soon as construction is complete and construction
equipment is cleared from the roadway.
APPLICATION:
In general, pulverization may be
limited to the existing asphalt concrete or may also
include a predetermined depth of the underlying
granular material. Additional granular material, RAP
or crushed PCC can also be added. The initial
shaping of the roadway after pulverization and
blending is performed with a motor grader. This is
then followed with initial compaction using large
pneumatic-tired or vibratory drum rollers and final
compaction and shaping to achieve the required
longitudinal profile and cross–slope. A chip seal or
overlay can be placed as soon as the specified
compaction is achieved.
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Rolle r Compacted
Concrete
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Page 153Top


ROLLER COMPACTED CONCRETE
PRODUCT DESCRIPTION:
Roller compacted
concrete (RCC) is constructed of zero-slump (i.e. very
stiff) concrete using traditional asphalt paving
equipment. RCC does not require steel reinforcing,
joints, dowel bars, or forms. RCC possesses most of
the benefits of conventional Portland cement concrete
pavement (PCCP), but has a lower cost and shorter
construction time. RCC has mainly been used in low-
speed, heavy-duty pavement applications. Roller
compacted concrete can be designed to support a
wide range of traffic loading conditions; it is frequently
used for heavy duty industrial pavements. RCC is
normally limited to low speed traffic applications with
speeds less than about 35 mph. RCC can be used for
medium to high speed applications if high density
paving machines are used or a surface treatment is
applied to improve smoothness and skid resistance.
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TRAFFIC RANGE: No limit (Preferred AADT over
2000, and low speed with traffic less than 35 mph).
LIFE EXPECTANCY: Up to 20 to 30 years
UNIT PRICE: $46 to $59/yd3
APPEARANCE: RCC has a relatively rough texture
and appearance and light gray color. The surface
color can be modified using pigments or stains to
color the RCC.
ADVANTAGES/BENEFITS: In general, RCC requires
relatively little preventative maintenance. Cracking
has little impact on RCC performance. For large
cracks, periodic crack sealing may be required.
LIMITATION: Compaction and moisture content are
critical components in successful RCC construction
projects and should be monitored closely.
Construction defects are generally difficult to repair.
Mix designs and trial mixes should be prepared in
advance of construction.
LANE CLOSURE REQUIREMENTS: The roadway
lane(s) being constructed is closed during
construction, so adequate traffic control or temporary
traffic diversion is needed. In some instances, the
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RCC surface has been opened to light traffic as soon
as it is constructed. Normal traffic loads can be
allowed on the RCC surface after initial curing and
once an adequate RCC strength is reached, typically
after 7 days. Road surface striping may be performed
after the lane is opened.
APPLICATION: In general, RCC is placed using an
asphalt concrete paver. After placement, the RCC is
compacted using a smooth drum vibratory roller.
Vibratory compaction can be followed by several
passes of a rubber tire roller to smooth out any
surface voids or fissures. RCC placement and
compaction generally must occur within 45 to 90
minutes after the point that water is initially added to
the mixture at the plant. Moist curing is used on most
projects after RCC placement, normally for a
minimum of 7 days. A water truck or irrigation
sprinkler system is used to keep the RCC surface
moist with a fine mist. A thin asphalt surface treatment
can be applied to the RCC surface to prevent
moisture loss during curing.
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Stabiliza tion
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Page 159Top


STABILIZATION (CEMENT, LIME, FLY
ASH, EMULSION)
PRODUCT DESCRIPTION:
Cement: Full Depth
Reclamation (FDR) with cement additive is a
rehabilitation technique in which the full thickness of
the asphalt pavement and predetermined portion of
the underlying materials (base, and sometimes,
subbase) are uniformly pulverized and blended with a
chemical additive to provide an upgraded,
homogenous base material. The reclaimed layer is
then compacted to provide a uniform platform for the
subsequent asphalt base course or surface course.
FDR is an in situ process without the addition of heat.
Chemical stabilization such as Portland cement is a
good stabilizer to enhance the properties of the
reclaimed layer.
Lime: Lime can be obtained in the form of quicklime
or hydrated lime. Lime can be used to stabilize clay
soils and submarginal base materials (i.e. clay-gravel,
caliche, etc.). When added to clay soils, lime reacts
with water in the soil and reduces the soil’s water
content. The lime also causes ion exchange within the
clay, resulting in flocculation of the clay particles. This
reaction changes the soil structure and reduces the
plasticity of the soil. These changes will increase soil
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workability and can increase the soil strength and
stiffness. In the long term, calcium hydroxide in the
water reacts with the silicates and aluminates
(pozzolans) in the clay to form cementitious bonds
that further increase the soil strength. Lime works
best for clayey soils, especially those with moderate
to high plasticity (plasticity index greater than 15).
Lime does not work well with silts and granular
materials because the pozzolanic reaction does not
occur due to a lack of sufficient aluminates and
silicates in these materials. For lime to effectively
stabilize silts or granular materials, pozzolanic
admixtures (i.e. fly ash) should be used in addition to
lime. For soils with high sulfate contents, lime
stabilization is generally not recommended.
Fly Ash: Fly ash is a residue of coal combustion that
occurs at power generation plants throughout the
United States. Fly ash can be used to lower the water
content of soils, reduce shrink-swell potential,
increase workability, and increase soil strength and
stiffness. Two types of fly ash can be used to stabilize
soils: Class C and Class F. Both classes of fly ash
contain pozzolans, but Class C fly ash is rich in
calcium that allows it to be self-cementing. Class F fly
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ash requires an activation agent (e.g. lime or cement)
for a pozzolanic reaction to occur and create
cementitious bonds within the soil. For fly ashes with
greater than 10% sulfates, high initial strengths have
been observed for fly ash stabilized materials, but the
durability of the stabilized material may be reduced.
Fly ash stabilization is often used as a construction
expedient when wet soil conditions are present and
weather conditions or time constraints prevent the
contractor from processing the soil to dry it out. Fly
ash is also used to reduce the shrink/swell potential of
clay soils.
Emulsion: An emulsion is a suspension of small
globules of one liquid in a second liquid with which the
first will not mix. The two liquids that comprise an
asphalt emulsion are asphalt and water. Since oil and
water do not mix well, an asphalt emulsion contains
an emulsifier which prevents the separation of the two
liquids. Unlike hot mix, emulsion is used as part of a
cold process where no heating of either the aggregate
or the emulsion is required.
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TRAFFIC RANGE: No limit
LIFE EXPECTANCY: CEMENT: up to 15 years
UNIT PRICE: Cement: ($3.30 to $5.90/yd2), Lime:
($1.30 to $2.00/yd2), Fly Ash: ($2.10 to $3.80/yd2),
Emulsion: ($4.20 to $6.70/yd2). These prices are for
a mixing depth of 8 in.
APPEARANCE: The pulverized pavement resulting
from stabilization is generally not left exposed.
Cement: Cement stabilization does not significantly
alter the appearance of a soil/aggregate material. The
appearance will be of a soil/aggregate surface with
the overall color determined by the material type and
source. However, the cement-stabilized subgrade and
base layers are typically not visible once the roadway
is constructed. Lime: Lime stabilization does not
significantly alter the appearance of a soil/aggregate
material. The appearance will be of a soil/aggregate
surface with the overall color determined by the
material type and source.
However, the lime-
stabilized material is typically covered with a wearing
surface.
Fly Ash: Fly ash stabilization does not
significantly alter the appearance of a soil/aggregate
material. The appearance will be of a soil/aggregate
surface with the overall color determined by the
material type and source. However, the fly ash-
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stabilized material is typically covered with a wearing
surface. Emulsion: The appearance of the asphalt
stabilized base is darker than conventional aggregate
base material, but lighter than HMA. It presents a
stabilized surface with a relatively rough finish.
ADVANTAGES/BENEFITS:
In situ process;
Increases strength of soil/aggregate layer; widely
available; Reuses existing base materials; widely
available. In addition for Lime, construction is
expedient for wet soil conditions. As for Fly ash, it’s
an effective use of a waste byproduct of the coal
combustion power industry. Finally, asphalt emulsion
provides various benefits to a recycled base mixture.
It helps to increase cohesion and load bearing
capacity of a mix. It also helps in rejuvenating and
softening the aged binder in the existing asphalt
material. Aside from the structural gains by the newly
stabilized base, there are other benefits to using
emulsion as well.
LIMITATION:
Cement: Higher initial costs; with
excessive dosages of cementitious additive, layer
may become brittle and incompatible with flexible
surfacing.
Lime: Clay particles required in
soil/aggregate; quicklime is highly reactive. Fly ash:
Potential leaching of heavy metals; Limited availability
in some areas.
Emulsion: Full depth emulsion
stabilization should not be used during cold and/or
rainy weather. Also, when stabilizing
granular/recycled asphalt product in-place, mixing
should be limited to the depth of the granular material
to prevent subgrade soils from being introduced into
the mix. With asphalt emulsion stabilization, traffic will
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have to run on the stabilized surface until curing is
complete. A surfacing layer applied before the
completion of the curing period will be prone to
debonding from the stabilized layer.
LANE CLOSURE REQUIREMENTS: The roadway
lane being constructed is closed during construction,
so adequate traffic control is needed. The FDR
surface with stabilization additive can be opened to
temporary traffic after an initial curing period of 12 to
24 hours. Truck traffic is not allowed until the riding
surface is placed unless approved by the contracting
officer.
APPLICATION: Cement: However, in general, new
construction projects where aggregate must be
hauled to the site, the cement can be mixed with the
aggregate before transporting to site. This method
provides the most uniform mixing. Alternatively, if the
soil/aggregate is in place, the cement is uniformly
applied to the existing granular material. Additional
granular material, RAP or crushed PCC can also be
added. The initial shaping of the roadway after the
stabilizing additive has been added and mixed by the
reclaimer, is performed with a motor grader. This is
then followed with initial compaction using large
pneumatic-tired or vibratory drum rollers. Final
compaction and shaping to the required longitudinal
profile and cross–slope is followed by a curing period.
The compacted surface should be sprayed with water
again to ensure that enough water is provided for
cement hydration. Initially moist curing is required to
avoid excessive shrinkage cracking. This is followed
by a period of intermediate curing when excessive
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drying of the mix is prevented by the use of a
bituminous seal coat. The intermediate curing period
is typically seven days. Heavy vehicles should be kept
off the stabilized road during the curing period. A chip
seal or hot mix asphalt concrete overlay is placed at
the end of the curing period.
Lime: The lime is uniformly applied to the existing
surface and water is sprayed on the surface. A rotary
mixer is then used to mix the lime, soil, and water
together. If water can be added by the rotary mixer
during processing, this approach is recommended.
Enough water should be added to raise the soil
moisture content to 3% above optimum moisture
content, to allow for hydration of the lime. Subgrade
soils are usually treated to a depth of 8 in. For deeper
mixing and stabilization, the material should be mixed
and compacted in 8 in. lifts. Once mixed, the loose
surface is graded and compacted. For lime
stabilization, the lime treated soil must be given time
for the chemical reactions to change the material, or
for the soil to “mellow”; the mellowing period is
typically 1 to 7 days. After the mellowing period is
over, the soil should be remixed, graded, and
compacted. For drying or soil modification, mellowing
is not usually required. Avoid construction during
heavy rain or snow events and when the soil is
frozen. Warm temperatures are required for the
chemical reactions to occur between the lime and soil;
therefore, the air temperature should be above 40 ºF
for soil stabilization applications.
Fly Ash: The fly ash is uniformly applied to the
existing surface and water is sprayed on the surface.
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A rotary mixer or disc is then used to mix the fly ash,
soil, and water together. If water can be added by the
rotary mixer during processing, this approach is
recommended. Maximum strengths are obtained
when the moisture content is 0 to 7 percent below the
optimum water content, depending on the material
being treated. Subgrade soils are usually treated to a
depth of 8 in. For deeper mixing and stabilization, the
material should be mixed and compacted in 8 in. lifts.
Once mixed, the loose surface is graded and
compacted. Delays in compaction can result in lower
maximum strengths for the stabilized material.
Therefore, construction specifications often require
that mixing, grading, and compaction must be finished
within 2 hours of fly ash spreading.
Emulsion: The emulsion is transferred from a
transport truck to the reclaimer on site. This reclaimer
pumps the emulsion from the delivery truck and
meters the emulsion through a spray bar with nozzles
into the mixing chamber. This chamber encloses the
milling head, which simultaneously mills through the
road and mixes the base material with the asphalt
emulsion. Slightly behind the road reclaimer, the fully
processed base material is ready for breakdown
rolling by a pad foot roller, which is then followed by a
motor grader to trim the pad marks. The motor grader
is then followed by a pneumatic roller and a steel
drum roller for final compaction. This process serves
as a uniform stable foundation for a suitable wearing
course which can typically be opened to traffic the
same day and the final surface is placed on in two to
seven days. Since curing time is a major factor for the
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performance of an asphalt emulsion-treated base
course, time delays in the field while construction is
going on can be a major contributing factor to the
performance of the newly constructed road.
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Protocol for Data
Collection
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Protocol for Data Collection at Intersection in Texas
1. Purpose
The main objective of Research Project 0-5566, “Strategies to
Improve and Preserve Flexible Pavement at Intersections,” is to
understand the mechanisms of intersection pavement failures and
determine the best practices to minimize the failures at existing
intersection pavements. One of the outcomes of this project is an
online expert system that provides strategies for remediation
alternatives at intersections.
This online expert system has not been fully implemented with
actual field data on actual projects. However, field data from
various sites in several Districts have been used in the
development of the expert system. As part of the online system, a
pavement evaluation module is incorporated to examine and
identify the predominant distresses. For that reason, the primary
purpose of establishing this protocol is to be able to assist in field
testing and to help in gathering the necessary information for the
expert system.
2. Strategy
For each intersection, the following information should be
identified to assist in identifying the predominant distress:
1. Planning

As-built pavement sections

Traffic Information
2. Field Testing

Visual Survey

Nondestructive Testing

Destructive Testing
3. Planning
Before evaluating the intersection, it is crucial to identify the layer
thicknesses at the intersection for each lane. Other information
that is beneficial is the following:
1. Type of hot mix,
2. Type of base and subgrade
3. Stabilized layers and stabilization agents (additives)
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4. Geometry of the intersection.
Although not all of this information is directly used as input into the
expert system, it is valuable to know the type of material and
thickness that makeup the pavement. This can help in deciding
the type and extent of field testing necessary.
Aside from the pavement information, the traffic information is also
necessary. Traffic information can be requested from
Transportation Planning and Programming Division of TxDOT.
More specific, the AADT and traffic volume are very important to
the remediation strategies at intersections. The AADT is used as
an input to the expert system to help support the best strategies
for a particular intersection. .
4. Testing
Two types of testing are suggested. The first is a condition survey.
Identify the lane that shows the most distress to minimize time and
cost. The information on identifying distress is based on TxDOT
Raters Manual and the Distress Identification Manual for the Long-
Term Pavement Performance Program from the Federal Highway
Administration. This information is used as input in the expert
system to assist in identifying the three most predominant
distresses.
First, estimate the length of the problematic area using a
measuring wheel or a similar device. Proceed to record the type
of distresses and severity (supported with photographs) along the
length of the problematic area. The dominant distresses relevant
to intersection are shown in Figure 1 and are provided in the first
section of this guide:
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Figure 1- Snapshot of the Condition Survey Module in the
Expert System
As part of the visual survey, distress measurements need to be
carried for each distress identified. Please follow the information
provided under each distress type to quantify the distress and
level of severity. For example, if rutting is prevalent, the type of
rutting, such as: a) surface rutting, b) instability rutting and c)
structural rutting, needs to be identified. The next step is to
estimate the severity of rutting. In the case of rutting, there are
three levels of severity: a) low severity is measured less than 0.5
in., b) medium severity is measured greater than or equal to 0.5 in.
and less than 1 in. and c) high severity is measured greater than
or equal to 1in.
In most cases a visual distress survey is not enough to identify the
predominant distress especially if it is a structural problem. If more
investigation is needed, nondestructive and destructive testing
should be considered. The most common tests consists of the
following:
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-
Falling Weight Deflectometer (FWD)
Non Destructive Testing
-
Ground Penetrating Radar (GPR)
-
Portable Seismic Pavement Analyzer (PSPA)
-
Trenching or Coring
Destructive Testing
-
Dynamic Cone Penetrometer (DCP)
Non Destructive Testing
The main reason for field testing is to document the layer(s) that
have experienced excessive distress to isolate the layer(s) that
contributed to the predominant distress, and to obtain field data for
evaluating the structural capacity of the pavement. Several tools
are available to TXDOT personnel that can be used for this effort.
A quick summary of each method and how it should be carried out
at intersections is provided next. Also, it is important to note that
each intersection has different considerations and priorities and
not all the tools listed should be used at each intersection.
However, if as was done in the sites investigated during this
research effort, f several of these devices can be used without
much delay to traffic if the data collection is well-coordinated
ahead of time. Well-coordinated field testing should not take much
more than a standard project-level FWD-testing.
The FWD is the main structural strength test indicator for TXDOT
and can be used for structural evaluation of the pavement. The
deflections from the FWD can help identify weakness in the
pavement layers. Also, the backcalculated moduli based on FWD
can be used check and verify the design modulus of each layer.
FWD
Data Collection:
For each site, the following steps will be carried out:
1. Walk the site and identify the main lanes for testing (lane that is
most distressed). Also, select the most representative line for
testing. In most cases, the inner of outer wheel path are good
representation of the most distressed area of the pavement.
2. For typical intersections, it is important to test the areas outside
the intersection as a comparative tool. This means areas
several hundred feet before and and/or after the intersection
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where traffic is not impacted by the constraints at the
intersection. This helps compare pavement response close to
the intersection with those away from it to determine if the
distress is caused at the intersection or the problem is wide
spread throughout the roadway. The number of test points is
not crucial, but an average of 25 to 30 points is sufficient to
allow for proper diagnoses.
3. Set up traffic control if needed. The testing can be performed
using either moving traffic control or closing one lane
(whichever is more suitable for that intersection). (Important:
document all surface distresses in the comment sections of the
FWD tests and monitor the temperature of the hot mix asphalt.)
4. Follow typical project level FWD testing setup with four drops at
each point
Data reduction:
The deflections from the FWD tests are then used to determine the
structural condition index (SCI, is defined as the difference in the
first two deflections from the FWD, d0-d1) and the base curvature
index (BCI is defined as the difference in the second and third
deflections from the FWD, d1-d2). Measured deflections can also
be used to backcalculate pavement layer moduli. The SCI, BCI
and moduli of the layers can be used as input in the the expert
system as a screening tool to determine structural weakness in
underlying layer.
The GPR is another device that assists in identifying subsurface
conditions of flexible pavements rapidly. GPR provides information
especially with regards to the uniformity of the thickness of the hot
mix asphalt and base. This can be used to verify design thickness
and identify rutting in the base and or subgrade layer. Although the
GPR thickness profile is not used as direct input in the expert
system, a representative value of the layer thickness in an input
into the tool.
GPR
The data collection for GPR is easy and requires no traffic control
as the GPR collects data without impeding on traffic and at the
rate of the posted speed. The data collected from the GPR can be
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reduced with ColorMap and Pavecheck. Pavecheck allows users
to simultaneously view GPR, FWD, and Video of the site.
The PSPA is another nondestructive device that is available to
TxDOT and can be used to test layer moduli of the top layer. In
cases where the top layer needs to be checked the PSPA could
be utilized for that effort. Similar to the FWD the PSPA can be
used to check and verify the design modulus of the top layer.
PSPA
If the FWD is used at the same time, the test points for the PSPA
can be identical. If only the PSPA is to be used, then the same
data collection process described for the FWD can be followed.
The data reduction process for the PSPA is straight forward and
the layer moduli can be easily obtained.
Trenching and
coring although destructive provide absolute
verification of the structure of the pavement. Both methods require
traffic control and patching once complete. Trenching operation
provides viable information especially when structural rutting is
suspect. Figure 2 is taken from the TxDOT pavement Design
manual for illustration purposes. Since many District staff do not
favor trenching especially at intersections, coring can be used as
an alternative. Based on our experience, collecting five cores
across the lane is quite valuable. The recommended locations of
the cores are: inner edge, inside wheel path, center, outside wheel
path, and outer edge. Figure 3 depicts a set of cores that were
collected from one of the sites investigated under the project. The
cores show the variation in thickness from the center core to the
cores taken at the wheel path. 4-inch diameter cores are sufficient
to identify any potential structural distress. It is recommended that
a set of five cores be taken close to the intersection and another
set away from the intersection. The two sets of cores can be used
to determine whether the distress is localized at the intersection or
is extended further in the roadway.
Trenching and Coring
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Figure 2 – Trench as part of a Forensic study to Identify
Structural Rutting
Figure 3 - Coring operation for a Core Profile across a
Pavement Section
DCP serves as a good verification tool for the FWD especially
when sublayers are stabilized. Two sets of DCP testing should be
conducted at the intersection. One location should be located at
the starting location of the FWD away from the intersection and
one set close to the intersection. It is recommended that each set
consist of at least three tests for repeatability. The results of DCP
can produce the layer thickness and moduli based on the change
in penetration rate and established correlation respectively. Both
these parameters can be used in the expert system as a screening
tool to determine structural weakness in underlying layer.
DCP
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Remediation
Strategies for
Common Distress
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The remediation matrix in Table 1 is the summary matrix of
the online expert system. The frequency bars reflect the
frequency of strategies for each distress. This is based on
the number of transportation agencies and TxDOT District
surveys utilized in this research project. For each cell, the
frequency bars is normalized to represent the frequency of
experts that recommend a certain remediation for a particular
distress. Also, for each cell, the color of the cell reflects the
appropriateness of the remediation strategy for a particular
distress.
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Table 1 – Matrix of Appropriate Remediation Strategies for Distress of
Flexible Pavements at Intersections
C
h
ip
S
e
a
ls
C
r
ack S
eal
Fog S
e
a
l
M
ic
r
o
S
.
S
an
d
S
eal
S
l
u
r
r
y S
eal
U
T
W
C
C
o
ld
In
-
P
la
c
e
H
o
t
In
-
P
la
c
e
H
o
t
M
i
x A
sp
h
al
t
HM
A w
i
t
h
RAP
HM
A w
i
t
h
RAS
P
C
C
O
ver
l
ay
W
T
FD
R
RCC
S
t
a
b
.
L
M
H
L
M
H
L
M
H
L
M
H
L
M
H
L
M
H
L
M
H
L
M
H
L
M
H
Appropriate
Not recommended
May be appropreiate
Not a candidate (or no information provided)
Summary of
Frequency of
Remediation
Strategies
Maintenance
Rehabilitation
Surface
Rutting
Structural
Rutting
Instability
Rutting
Potholes
Bleeding or
Fl
hi
Alligator
Cracking
Block
Cracking
Shoving
Long.
Cracking
Transverse
Cracking
Raveling