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

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

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

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

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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