Pavement Preservation Journal - Fall 2017 - 35

EMULSIONS FOR THIN
BONDED OVERLAYS
Ultrathin bonded overlays (UTBOs) also
called ultrathin bonded wearing courses
(UTBWCs), ultrathin bonded asphalt surfaces (UBASs), and ultrathin asphalt concrete surfacings (UTACSs)-are constituted
of a heavy application of polymer modified
asphalt emulsion, followed by an ultrathin (0.5 to 1.0-in.), polymer modified,
gap-graded hot mix asphalt layer, both
applied by the same machine.
An ultrathin bonded overlay is a highperformance wearing course for preventive maintenance or new construction, and
is used over both asphalt and concrete
pavements. The emulsion application rate
is 0.13 to 0.30 gal. per sq. yd., according
to the Preservation Toolbox developed
by FP2 Inc.
Ultrathin bonded overlays need polymer modification. Today, the most common
types of emulsions used for conventional
paving bond coats include slow-setting
grades of emulsion such as SS-1, SS-1h,
CSS-1, and CSS-1h and the rapid-setting
grades of emulsion such as RS-1, RS-2 and
CRS-1 or CRS-1h. However, these emulsions
are not polymer modified, as is generally
required for ultrathins. For them, a common
modified emulsion used is a (C)RS-2H PM.
California DOT (Caltrans) defines its
bonded wearing courses "a gap- or opengraded, ultra-thin hot-mix asphalt mixture applied over a thick polymer modified
asphalt emulsion membrane," to quote the
agency. "The emulsion membrane seals the
existing surface and produces high binder
content at the interface of the existing roadway surface and the gap- or open-graded
mix, all in one pass."
In addition to enhancing friction, such
gap-graded and open-graded mixes

IMAGE CREDIT: WIRTGEN AMERICA INC.

and type of surfactant used, along with
other variables, controls properties of the
emulsion critical to performance in the
field application.
For example, emulsifiers affect the
"break" time following placement on a road,
in which the water evaporates, leaving the
residual asphalt behind. Asphalt emulsions
partially are categorized as rapid setting
(RS), medium setting (MS), slow setting (SS)
and quick setting (QS) emulsions.

Spray bars on paver of Las Vegas Paving Corp. place asphalt emulsion bond coat in advance of
ultrathin bonded overlay

provide an open surface texture to allow
rain water to flow through the surface,
reducing tire spray, eliminating ponding,
and suppressing noise at the tire/pavement
interface. They represent one version of a
porous asphalt pavement.
Such bonded wearing courses are
primarily used in high-traffic areas as a
surface treatment over hot mix asphalt
or portland cement concrete pavements.
They are placed over structurally sound
pavements as a maintenance treatment
but may also be used in new construction and rehabilitation projects as the final
wearing course.
In a bonded wearing course like those
specified by Caltrans, the polymer modified asphalt emulsion membrane seals
the existing pavement while bonding the
gap-graded or open-graded mix to the
surface. The thicker nature of the "membrane" allows it to "wick" upwards into

the mix, filling voids in the aggregate
and creating an interlayer of high cohesion that does not delaminate or bleed, if
applied correctly.
ROLE OF SPRAY PAVER
Ultrathin bonded overlays are placed with
a dedicated spray paver. From an onboard
tank, this specialized piece of equipment
sprays the bond coat directly ahead of the
screed placing the thin overlay.
Spray pavers combine the functions of
a distributor truck, typically placing bond
coat and high-performance polymer modified thin overlay in a single pass. In this
case the bond or tack coat will be polymer
modified as well, with application at rates
of 0.08 to 0.20 gal. per sq. yd. residual,
according to The Asphalt Institute.
As no bond coat is placed in front of the
paver, traffic, road workers and pedestrians can move freely in front of the process
Fall 2017 | PAVEMENT PRESERVATION JOURNAL

35



Table of Contents for the Digital Edition of Pavement Preservation Journal - Fall 2017

President's Message
FP2 Marks Silver Anniversary
ARRA, FP2 Preservation Proponents Assault Capitol Hill
Neglected Rural Roads Drag on Economy
Early NCAT Results Favor Preservation
Perservation Partnerships: Southeast PPP Ponders Early Treatment Failures; Midwest PPP Meets in Michigan
Texas Contractor Upgrades Performance
Asphalt Emulsion Bond Coats Optimize UTBO, Thinlay Performance
Student Studies Sustainable Chip Seals
Pavement Preservation Journal - Fall 2017 - Intro
Pavement Preservation Journal - Fall 2017 - cover1
Pavement Preservation Journal - Fall 2017 - cover2
Pavement Preservation Journal - Fall 2017 - 3
Pavement Preservation Journal - Fall 2017 - 4
Pavement Preservation Journal - Fall 2017 - 5
Pavement Preservation Journal - Fall 2017 - 6
Pavement Preservation Journal - Fall 2017 - 7
Pavement Preservation Journal - Fall 2017 - 8
Pavement Preservation Journal - Fall 2017 - President's Message
Pavement Preservation Journal - Fall 2017 - FP2 Marks Silver Anniversary
Pavement Preservation Journal - Fall 2017 - 11
Pavement Preservation Journal - Fall 2017 - 12
Pavement Preservation Journal - Fall 2017 - 13
Pavement Preservation Journal - Fall 2017 - 14
Pavement Preservation Journal - Fall 2017 - 15
Pavement Preservation Journal - Fall 2017 - 16
Pavement Preservation Journal - Fall 2017 - ARRA, FP2 Preservation Proponents Assault Capitol Hill
Pavement Preservation Journal - Fall 2017 - 18
Pavement Preservation Journal - Fall 2017 - 19
Pavement Preservation Journal - Fall 2017 - 20
Pavement Preservation Journal - Fall 2017 - 21
Pavement Preservation Journal - Fall 2017 - 22
Pavement Preservation Journal - Fall 2017 - Neglected Rural Roads Drag on Economy
Pavement Preservation Journal - Fall 2017 - 24
Pavement Preservation Journal - Fall 2017 - 25
Pavement Preservation Journal - Fall 2017 - 26
Pavement Preservation Journal - Fall 2017 - Early NCAT Results Favor Preservation
Pavement Preservation Journal - Fall 2017 - 28
Pavement Preservation Journal - Fall 2017 - Perservation Partnerships: Southeast PPP Ponders Early Treatment Failures; Midwest PPP Meets in Michigan
Pavement Preservation Journal - Fall 2017 - 30
Pavement Preservation Journal - Fall 2017 - 31
Pavement Preservation Journal - Fall 2017 - 32
Pavement Preservation Journal - Fall 2017 - Texas Contractor Upgrades Performance
Pavement Preservation Journal - Fall 2017 - Asphalt Emulsion Bond Coats Optimize UTBO, Thinlay Performance
Pavement Preservation Journal - Fall 2017 - 35
Pavement Preservation Journal - Fall 2017 - 36
Pavement Preservation Journal - Fall 2017 - 37
Pavement Preservation Journal - Fall 2017 - 38
Pavement Preservation Journal - Fall 2017 - 39
Pavement Preservation Journal - Fall 2017 - 40
Pavement Preservation Journal - Fall 2017 - 41
Pavement Preservation Journal - Fall 2017 - 42
Pavement Preservation Journal - Fall 2017 - Student Studies Sustainable Chip Seals
Pavement Preservation Journal - Fall 2017 - 44
Pavement Preservation Journal - Fall 2017 - 45
Pavement Preservation Journal - Fall 2017 - 46
Pavement Preservation Journal - Fall 2017 - cover3
Pavement Preservation Journal - Fall 2017 - cover4
http://www.nxtbook.com/naylor/FPPQ/FPPQ0318
http://www.nxtbook.com/naylor/FPPQ/FPPQ0218
http://www.nxtbook.com/naylor/FPPQ/FPPQ0118
http://www.nxtbook.com/naylor/FPPQ/FPPQ0417
http://www.nxtbook.com/naylor/FPPQ/FPPQ0317
http://www.nxtbook.com/naylor/FPPQ/FPPQ0217
http://www.nxtbook.com/naylor/FPPQ/FPPQ0117
http://www.nxtbook.com/naylor/FPPQ/FPPQ0416
http://www.nxtbook.com/naylor/FPPQ/FPPQ0316
http://www.nxtbook.com/naylor/FPPQ/FPPQ0216
http://www.nxtbook.com/naylor/FPPQ/FPPQ0116
http://www.nxtbook.com/naylor/FPPQ/FPPQ0415
http://www.nxtbook.com/naylor/FPPQ/FPPQ0315
http://www.nxtbook.com/naylor/FPPQ/FPPQ0215
http://www.nxtbook.com/naylor/FPPQ/FPPQ0115
http://www.nxtbook.com/naylor/FPPQ/FPPQ0414
http://www.nxtbook.com/naylor/FPPQ/FPPQ0314
http://www.nxtbook.com/naylor/FPPQ/FPPQ0214
http://www.nxtbook.com/naylor/FPPQ/FPPQ0114
http://www.nxtbook.com/naylor/FPPQ/FPPQ0413
http://www.nxtbook.com/naylor/FPPQ/FPPQ0313
http://www.nxtbook.com/naylor/FPPQ/FPPQ0213
http://www.nxtbook.com/naylor/FPPQ/FPPQ0113
http://www.nxtbook.com/nxtbooks/naylor/FPPQ0412
http://www.nxtbook.com/nxtbooks/naylor/FPPQ0312
http://www.nxtbook.com/nxtbooks/naylor/FPPQ0212
http://www.nxtbook.com/nxtbooks/naylor/FPPQ0112
http://www.nxtbook.com/nxtbooks/naylor/FPPQ0411
http://www.nxtbook.com/nxtbooks/naylor/FPPQ0311
http://www.nxtbook.com/nxtbooks/naylor/FPPQ0211
http://www.nxtbook.com/nxtbooks/naylor/FPPQ0111
http://www.nxtbook.com/nxtbooks/naylor/FPPQ0410
http://www.nxtbook.com/nxtbooks/naylor/FPPQ0310
http://www.nxtbook.com/nxtbooks/naylor/FPPQ0210
http://www.nxtbook.com/nxtbooks/naylor/FPPQ0110
http://www.nxtbook.com/nxtbooks/naylor/FPPQ0409
http://www.nxtbook.com/nxtbooks/naylor/FPPQ0309
http://www.nxtbook.com/nxtbooks/naylor/FPPQ0209
http://www.nxtbook.com/nxtbooks/naylor/FPPQ0109
http://www.nxtbookMEDIA.com