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Technical Topics
Technical Topics is a periodic newsletter supplement aimed at providing a link
between innovative developments in technology and practical engineering applications.
Issues in PDF format are available below. Viewing them requires the free Acrobat Reader.
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2007
Recycling Asphalt Pavements—A Strategy Revisited
By Larry Santucci, PE, California LTAP Field Engineer, Technology Transfer Program,
and Pavement Specialist, Pavement Research Center,
Institute of Transportation Studies, University of California Berkeley
(12 pages, 1M)
Pavement recycling is a logical and practical
way to conserve our diminishing supply
of construction materials and to help
reduce the cost of preserving our existing
pavement network. When properly designed
and constructed, recycled pavements have
been found to perform as well as pavements
built with all new materials....
2006
Performance Graded (PG) Polymer Modified Asphalts in California
By Larry Santucci, PE, California LTAP Field Engineer, Technology Transfer Program,
and Pavement Specialist, Pavement Research Center,
Institute of Transportation Studies, University of California Berkeley
(8 pages, PDF, 1.4M download)
In January 2006, when the Performance Graded (PG) system for asphalt cements replaced the Aged Residue (AR) grading system formerly in use, four polymer modified Performance Based Asphalts (PBA) were retained for interim use until they could be replaced by PG polymer modified (PG-PM) grades. In 2006, a Caltrans-Industry task force examined the PBA grades and identified appropriate replacement polymer modified PG grades. The implementation date for replacing the PBA polymer modified asphalts with PG polymer modified asphalts is January 1, 2007....
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2005
Performance Graded (PG) Asphalts in California
By Larry Santucci, PE, California LTAP Field Engineer, Technology Transfer Program,
and Pavement Specialist, Pavement Research Center,
Institute of Transportation Studies, University of California Berkeley
(8 pages, PDF, 1.4M download)
The existing Aged Residue (AR) grading
system for asphalt cements currently
specified by the California Department
of Transportation (Caltrans) will be
replaced with the Performance Graded
(PG) system. The implementation date
is January 1, 2006, at which time
California will join the other 49 states
that have adopted some version of the
PG system over the past 10 to 12 years...
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2004
Foamed Asphalt Base Stabilization
By Don Raffaelli, PE, California LTAP Field Engineer
(8 pages, PDF, 412k download)
Foamed asphalt base stabilization is a
roadway recycling process in which all
of the pavement and some of the
underlying material is pulverized and
treated with a foamed asphalt additive
to produce an improved, stabilized
base. This status report presents lessons
learned from current usage in California
of the base stabilization process called
foamed asphalt, cold foamed asphalt or
expanded asphalt, hereafter referred to
as foamed asphalt...
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2002
Moisture Sensitivity of Asphalt Pavement
By Larry Santucci, P.E., LTAP Field Engineer
(PDF, 112k download)
The presence of water (or moisture)
often results in premature failure of
asphalt pavements in the form of isolated
distress caused by debonding of the
asphalt film from the aggregate surface
or early rutting/fatigue cracking due to
reduced mix strength. Moisture sensitivity
has long been recognized as an
important mix design consideration.
Francis Hveem (1), in 1940, realized
the importance of water resistance and
identified it along with consistency,
durability, and curing rate or setting as
the four critical engineering properties
that need to be determined in the selection
of quality asphalts for pavement
construction. A recent survey (2) of 55
state and federal highway agencies
showed that 87% of them test for moisture
sensitivity and 82% require some
type of treatment to resist moisture
damage. As the concept of perpetual
pavements and long life pavements
become more popular, engineers must
focus on how to minimize the detrimental
effects of moisture damage...
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2001
Rut Resistant Asphalt Pavements
By Larry Santucci, P.E., LTAP Field Engineer
(PDF - 756k download)
The three major distress conditions
affecting the performance of asphalt
pavements are permanent deformation
or rutting, fatigue or load associated
cracking, and low temperature or thermal
cracking.
In an earlier technical topics article
(1998), we examined the causes of
fatigue cracking and the importance of
good compaction during construction
to help minimize this type of distress.
In this article, we will examine the
causes and potential cures of asphalt
pavement rutting. Rutting on the
asphalt pavement surface generally
results from one of two conditions...
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1999
The Pothole Primer for Planners, Managers, and Public Officials
By Larry Santucci, P.E., LTAP Field Engineer
(PDF - 806k download)
While most of the travelling public
knows very little about the structure
of the streets and highways
they use to get to work or for
recreation, they are quite keenly
aware when the conditions of their
roads are inadequate. The common
failure in the road known as a
"pothole" brings the road to
everyone's attention and when the
public gets agitated, politicians are
soon to follow. Encounters with
potholes annoy the vehicle's occupants
and cause significant damage
and expensive repairs in the form
of tire wear, wheel alignments, and
structural fatigue. Pothole repair
isn't popular either, since it results
in lane closures, congestion and
more frustration for the traveling
public. Research at the University
of California has improved our
understanding about pothole
formation as well as techniques for
minimizing their formation and
streamlining their repair. Application
of this understanding will
result in better service to the
traveling public, longer lasting
repairs and more durability...
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1998
The Role of Compaction in the Fatigue Resistance of Asphalt Pavements
By Larry Santucci, P.E., LTAP Field Engineer
(PDF - 368 k download)
Fatigue or load associated cracking
was identified in the Strategic
Highway Research Program
(SHRP) as one of the primary
distress mechanisms affecting the
long term performance of asphalt
pavements. The other two major
distress conditions are permanent
deformation (rutting) and low
temperature cracking. Fatigue
cracking generally starts as a series
of short longitudinal cracks in areas
subjected to repeated wheel loadings.
With additional traffic, the
number of cracks increase and
interconnect into a typical "alligator"
crack pattern (Figure 1).
In an asphalt pavement structure
under load, the highest tensile
stresses normally occur on the
underside of the asphalt treated
layer, as shown in Figure 2. In
some circumstances, the tensile
stresses can be higher on the
pavement surface next to the wheel
load but this is generally the exception
rather than the rule. Fatigue
cracks initiate in these high tensile
stress zones and then gradually
propagate through the asphalt
treated layer of the pavement. One
way to reduce the potential for
fatigue cracking is to simply make
the asphalt pavement thicker to
reduce the magnitude of the tensile
stresses. However, it costs money
to build pavements thicker. Hence,
the challenge becomes how to build
more cost effective pavements that
are fatigue resistant...
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