Polymer modified asphalt binders

doi:10.1016/j.conbuildmat.2005.07.007

Construction and Building Materials

Volume 21, Issue 1, January 2007, Pages 66-72

https://doi.org/10.1016/j.conbuildmat.2005.07.007 Get rights and content

Abstract

This paper is a review of research that has been conducted on polymer modified binders over the last three decades. Polymer modification of asphalt binders has increasingly become the norm in designing optimally performing pavements, particularly in the United States, Canada, Europe and Australia. Specific polymers that have been used include rubber, SBR, SBS and Elvaloy^®. Specifications have been designed and pre-existing ones modified to capture the rheological properties of polymer modified binders. The elastic recovery test is good at determining the presence of polymers in an asphalt binder, but is less successful at predicting field performance of the pavement.

Introduction

The addition of polymers, chains of repeated small molecules, to asphalt has been shown to improve performance. Pavement with polymer modification exhibits greater resistance to rutting and thermal cracking, and decreased fatigue damage, stripping and temperature susceptibility. Polymer modified binders have been used with success at locations of high stress, such as intersections of busy streets, airports, vehicle weigh stations, and race tracks [1]. Polymers that have been used to modify asphalt include styrene–butadiene–styrene (SBS), styrene–butadiene rubber (SBR), Elvaloy^®, rubber, ethylene vinyl acetate (EVA), polyethylene, and others. Desirable characteristics of polymer modified binders include greater elastic recovery, a higher softening point, greater viscosity, greater cohesive strength and greater ductility [1], [2].

Section snippets

History, use, and benefits

Processes of asphalt modification involving natural and synthetic polymers were patented as early as 1843 [3]. Test projects were underway in Europe in the 1930s, and neoprene latex began to be used in North America in the 1950s [1]. In the late 1970s, Europe was ahead of the United States in the use of modified asphalts because the European use of contractors, who provided warranties, motivated a greater interest in decreased life cycle costs, even at higher initial costs. The high preliminary

Test methods

As discussed by King et al. in the 1999 Journal of the AAPT [1], there are several test methods that have been developed or altered for modified binders. Previously, both modified and unmodified binders alike were tested according to the same methods, supported by the Strategic Highway Research Program (SHRP). Bahia et al. in their 1998 article for the Journal of AAPT note, however, that this blanket testing method failed to test the extreme grades required by the new, modified binders,

Rubber

“Crumb rubber modifier” (CRM) and “asphalt-rubber” are terms that refer to applications in which ground recycled rubber and paving asphalt are combined [1]. Characteristics of asphalt–rubber are dependent on rubber type, asphalt composition, size of rubber crumbs, and time and temperature of reaction [1]. Usually, the rubber is recycled from used automotive tyres, which has the additional benefits of saving landfill space that would otherwise be occupied by tyres and reducing cost [1], [18].

Elastic recovery test

Elastic recovery (or elasticity) is the degree to which a substance recovers its original shape following application and release of stress. A degree of elastic recovery is desirable in pavement to avoid permanent deformation. “When a tire passes over a section of pavement, it is desirable for that pavement to have the ability to ‘give’, but it is equally important for it to recover to its original shape,” according to the Asphalt Institute website [32].

Conclusions

In the 1980s, polymer modified asphalts began to be used in the US and by 1997 all but three states were already using modified binders or intended to use them in the future and federal regulations supported their use. Pavements made with modified binders are more resistant to fatigue, thermal cracking, rutting, stripping, and temperature susceptibility than neat binders. Polymer modified binders tend to exhibit increased viscosity and elastic recovery, although penetration does not appear to

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