Theses and Dissertations

Issuing Body

Mississippi State University


Howard, Isaac L.

Committee Member

Truax, Dennis D.

Committee Member

Cooley, Larry Allen, Jr.

Committee Member

Brown, E. R.

Date of Degree


Document Type

Dissertation - Open Access


Civil Engineering

Degree Name

Doctor of Philosophy


James Worth Bagley College of Engineering


Department of Civil and Environmental Engineering


Asphalt binder modification is a common method of improving Hot-mix Asphalt (HMA) performance by enhancing mix properties and reducing or delaying three general HMA distress types: deformation (rutting and shoving), cracking (from repeated loads and low temperatures) and general deterioration (raveling and stripping). Since the early 1960’s, a common modified asphalt alternative has employed reclaimed rubber as an economical and environmental friendly method of recycling waste tires while improving asphalt physical and mechanical properties. Pavement network deterioration combined with increasing material costs makes polymer modification of asphalt binder desirable, with reclaimed rubber from waste tires being an attractive alternative which addresses performance, economics and environmental issues. The primary objective of this dissertation is to demonstrate the importance of proper processing of all types of modified bituminous binders, whether they be virgin (e.g. styrene-butadiene-styrene (SBS) or styrene-butadiene rubber (SBR)), post-consumer polymers (e.g. ground tire rubber (GTR)) or a combination (GTR plus SBS). To achieve this four secondary objectives were identified: 1) characterize GTR using thermo-gravimetric analysis (TGA), 2) improve processing of GTR modified binders, 3) improve testing and specifications of GTR modified binders and 4) evaluate mixes containing GTR modified binders. A simple efficient instrumental, TGA, method to analyze polymers in binary rubber compounds was developed to quantify the functional polymer content available in GTR. TGA analysis provides a better understanding of the general chemical characteristics of GTR used in modification of asphalt binders for production of asphalt paving mixtures. Results are presented from efforts to optimize GTR modified binder formulations with respect to how GTR loading, GTR particle size, processing temperature and asphalt cement source affect modified binder properties and ability to meet performance graded binder specifications. These results are the basis to establish recommended processing parameters for formulation and preparation of GTR modified asphalt binders. GTR modified binders were used in: dense graded asphalt (DGA), stone matrix asphalt (SMA) and open graded friction courses (OGFC) and compared to conventional asphalt cement and styrene-butadiene-styrene (SBS) modified asphalt binders. Mixture performance evaluation with respect to binder effectiveness as it relates to the three general HMA distress types.