This document discusses how crumb rubber properties affect the performance of crumb rubber modified (CRM) asphalt binders. It outlines the objectives to examine the effects of crumb rubber properties on CRM binder performance using standard test procedures. The document then discusses crumb rubber, describing that it is derived from scrap tires and can be produced through ambient or cryogenic grinding methods. It also summarizes the key properties of CRM binders related to handling and pumping, resistance to permanent deformation, and resistance to thermal cracking. The conclusions indicate that crumb rubber increases binder viscosities and modifies failure temperatures in asphalt, and that the extent of modification depends on factors like base binder properties and crumb rubber properties

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Effects of Crumb Rubber Properties on
CRM Binder Performance
Carl Thodesen

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Outline
 Introduction
 Objectives
 Crumb Rubber
 CRM Binder Properties
 Conclusions

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Introduction: Scrap Tire Problem
 Scrap tires generated in U.S. (2005): 300x106
 Scrap tire generation: 1 tire/person/year
 Environmental dangers: Tire fires and runoff
 Social dangers: Breeding ground for mosquitoes
 Reduced landfill space
 Tire disposal: non sustainable practice
 Wasted resources

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CRM Binder

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Introduction: Solution
 Approximately 28% of all scrap tires used in construction
materials are used within the field of civil engineering
 Incorporation of crumb rubber with asphalt binder to produce
crumb rubber modified (CRM) binder
 CRM asphalt meets many of the specifications of conventional
modified asphalts
 CRM asphalt include improved resistance to permanent
deformation, fatigue cracking, and thermal cracking.
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Overhead View of Plant Site
Hot Plant Oil Tank
Virgin Oil Tank
Hot Mix Plant
Blending Unit
Bag House
Reaction Tank
Generator

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Field Binder Testing
 After Reaction Time Is
Complete (30, 45, 60
Minutes)
 Binder sample taken and
checked for viscosity
 Target: 1,500 – 4,000 cP
(Centipoise) @ 350° F

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Crumb Rubber Reaction

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Crumb Rubber Reaction

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Outline
 Introduction
 Objectives
 Crumb Rubber
 CRM Binder Properties
 Conclusions

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Objectives
 Discuss nature of variability within crumb rubber
 Examine effects of crumb rubber properties on CRM binder
performance using SHRP testing procedures, and
 Determine which properties of crumb rubber play the biggest
role in specific binder performance parameter.

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Objectives
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CRM Binder
Grinding
Concentration
Gradation

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US Modified binder use
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0 %
25 %
50 %
75 %
100 %
PG 58-22 PG 58-28 PG 58-34 PG 64-22 PG 64-28 PG 70-22 PG 70-28 PG 76-22 PG 76-28
%Statesreportinuse
2005 2006

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Outline
 Introduction
 Objectives
 Crumb Rubber
 CRM Binder Properties
 Conclusions

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Crumb Rubber
 Derived from the grinding of scrap tires
 Generally produced using two methods:
 Ambient
 Cryogenic
 Fine powder like substance
 Some properties depend on grinding method
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Crumb Rubber
Cryogenic at 30 x
magnification
Ambient at 30 x
magnification

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Outline
 Introduction
 Objectives
 Crumb Rubber
 CRM Binder Properties
 Conclusions

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CRM Binder Properties: SHRP Properties
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CRM Binder Properties
 Handling and Pumping
 Resistance to Permanent Deformation
 Resistance to Thermal Cracking

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Handling and Pumping
 Rotational Viscometer
 Viscosity limits set

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Handling and Pumping
 Particle Size

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Handling and Pumping
 Morphology

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Resistance to Permanent Deformation

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Resistance to Permanent Deformation
 Particle Size
Testing at 64oC

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Resistance to Permanent Deformation
 Morphology

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Resistance to Thermal Cracking

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Resistance to Thermal Cracking
 Particle Size
10% CRM

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Resistance to Thermal Cracking
 Morphology

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Outline
 Introduction
 Objectives
 Crumb Rubber
 CRM Binder Properties
 Conclusions

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Conclusions
 The addition of crumb rubber to binder:
 Raises the upper failure temperature
 Decreases lower failure temperature
 Increases viscosities
 Extent of modification dependent on:
 Base binder properties
 Crumb rubber properties
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Conclusions
 Ambient CRM binder viscosity is typically higher than that of
cryogenic CRM binder.
 As concentration increases the effect of the crumb rubber becomes
more defined.
 Particle size (0.18 – 0.85 mm) plays a small role in establishing
the binder viscosity
 Increases in the crumb rubber concentration consistently
produced higher G*/sinδ values,
 Particle size (0.18 – 0.85 mm) was not seen to play a statistically
significant effect on the rutting susceptibility of the CRM binder.
 Ambient CRM binders produced significantly higher failure
temperatures than cryogenic CRM binders.

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Conclusions
 As particle fineness (0.18 – 0.85 mm) increased so too did the
resistance to thermal cracking.
 Ambient and cryogenic grinding procedures produced statistically
similar CRM binders with respect to thermal cracking.
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Future work
 Studded tyre issues?
 Relevance of high end PG grade to predicting rutting in
Norway?
 Suitability with Norwegian asphalt mixes?
 More research necessary to evaluate suitability in Norway
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Questions?

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 Tayebali, A. A., Vyas, B. B., & Malpass, G. A. (1990). Effect of
Crumb Rubber Particle Size and Concentration on Performance
Grading of Rubber Modified Asphalt Binders. ASTM Special
Technical Publication , 30-47.
 Bahia, H. U., & Davies, R. (1996). Factors Controlling the Effect
of Crumb Rubber on Critical Properties of Asphalt Binders.
Journal of the Association of Asphalt Paving Technologists , 64,
130-162.
 Bahia, H. U., & Davis, R. (1994). Effect of Crumb Rubber
Modifiers (CRM) on Performance Related properties of Asphalt
Binders. Journal of the Association of Asphalt Paving
Technologists , 63, 414-449.
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