Investigation of performance parameters for hot -mix asphalt

Shangzhi Xiao, Purdue University

Abstract

This study presents partial findings of the Joint Transportation Research Program Project No. SPR-2644 project within which performance criteria were developed that incorporates both stiffness and strength properties of asphalt mixtures based on mechanical testing. Candidate strength and stiffness parameters were investigated and evaluated through extensive testing on eleven representative hot-mix asphalt mixtures used in Indiana with a wide range of traffic levels and geographic locations. Two types of mixtures (stone matrix asphalt mixtures and dense-graded mixtures) were studied. The investigation involved testing samples at four stages of construction, i.e., mixture design stage, production stage, placement stage and in-service stage. A novel method, called the composite specimen approach was developed and evaluated to provide with the possibility of obtaining the dynamic modulus :E*: of thin pavement cores. The relationship between :E*: and :G*: was investigated. Testing conditions for the indirect tensile strength test were linked to the conditions of the triaxial strength test, and verification was performed. Both linear and nonlinear analyses were performed on the triaxial data. It was concluded that :E*: and :G*: are not theoretically interchangeable, but estimation of stiffness through the Hirsch models was possible and was accurate for the purpose of practice. The composite specimen approach was found to be capable of measuring the dynamic modulus of thin pavement cores. Comparisons of the results from asphalt plant loose mixtures and raw material mixtures showed that the four-hour laboratory aging for mechanic testing prescribed by the current specifications were excessive. In addition, the analyses indicated that the specimens were subjected to significant aging even under cold storage in the laboratory environment. The nonlinearity of triaxial strength test existed, but the effect on the stability of HMA mixture was negligible. The correlation between the IDT strength and triaxial strength based on linear elastic theory and the Mohr-Coulomb failure criterion was found to be good for the asphalt plant loose mixtures. From the standpoint of practice, the effect of the friction angle on the HMA's stability was negligible and the cohesion could be estimated by the IDT strength test.

Degree

Ph.D.

Advisors

Pellinen, Purdue University.

Subject Area

Civil engineering

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