doi:10.1016/j.conbuildmat.2007.12.005 
Copyright © 2007 Elsevier Ltd All rights reserved.
Influence of surface area and size of crumb rubber on high temperature properties of crumb rubber modified binders
Junan Shena, c, 
, 
, Serji Amirkhanianb, Feipeng Xiaob and Boming Tangc
aDepartment of Construction Management and Civil Engineering, Georgia Southern University, P.O. Box 8047, Statesboro, GA 30460-8047, United States
bDepartment of Civil Engineering, Clemson University, Clemson, SC 29634-0911, United States
cChongqing Jiaotong University, No. 66 Xuefudadao, Nanan District, Chongqing 400074, PR China
Received 30 March 2006;
revised 4 December 2007;
accepted 10 December 2007.
Available online 29 January 2008.
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Abstract
There are many variables of crumb rubber modifier (CRM) and asphalt binder, affecting the interaction of the CRM with the binder when crumb rubber modified binder (CRM binder) is produced. In this study, the influence of the surface area of CRM blends on the high temperature properties, i.e., the complex modulus (G*), the phase angle and high temperature grade of the CRM binders was investigated. To this end, the surface areas of CRM particles were measured using the BET (Brunauer, Emmett and Teller) tester, while weighted average particle size of CRM blends was calculated based on their graduations and then used as a size index. High temperature properties of CRM binders were measured using Dynamic Shear Rheometer (DSR) test. A total of 108 CRM binders were produced using different combinations of these variables. Results observed from this study indicated: (1) the surface area of the ambient CRM was twice as large as that of the cryogenic one, leading to a much higher G* and phase angle of the CRM binders; (2) the phase angle and G* were affected by both the surface area and average size; however, the average size is the predominating factor; and (3) ambient CRM binders were produced about 3 °C in high temperature grade higher than cryogenic CRM binders.
Keywords: Surface area; BET; CRM binder; High temperature; DSR
Fig. 1. Phase angle versus surface area of ambient blends.
Fig. 2. Phase angle versus surface area of cryogenic blends.
Fig. 3. Phase angle versus average size of ambient blends.
Fig. 4. Phase angle versus average size of cryogenic blends.
Fig. 5. G* versus average size of ambient blends.
Fig. 6. G* versus average size of cryogenic blends.
Fig. 7. G* versus surface area of ambient blends.
Fig. 8. G* versus surface area of cryogenic blends.
Fig. 9. High temperature grades of modified binders (base binder PG64–22).
Table 1.
CRM binders produced
Table 2.
Properties of the three base binders
Table 3.
Gradations (retained, %) of the 6 CRM blends used
Table 4.
Surface area of the ambient CRM for various mesh sizes (n = 3)
Table 5.
Surface area of the cryogenic CRM for various mesh sizes (n = 3)
Table 6.
Total surface area of the 6 blends
Table 7.
Average size of the 6 CRM blends (μm)
Table 8.
Surface area (cm2/g) of the CRM per gram of CRM binders
Table 9.
Regression of the DSR parameters with average diameter (D) and surface area (A)
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