The colloidal structure of bitumen: Consequences on the rheology and on the mechanisms of bitumen modification

Morphology, rheology, and physical properties of polymer-modified asphalt binders

The main focus of this study was to obtain plant produced Reclaimed Asphalt Pavement (RAP) mixtures, to document the mixture production parameters and to evaluate the degree of blending between the virgin and RAP binders. The effect of mixture production parameters on the performance (in terms of stiffness, cracking, rutting, and moisture susceptibility) and workability of the mixtures was evaluated. Eighteen plant produced mixtures were obtained from three locations in the Northeast United States. RAP contents (zero to 40%) were varied and softer binders were used. The data and analysis illustrated that the degree of blending between RAP and virgin binders is a function of production parameters. The stiffness of the mixtures increased as the percentage of RAP increased, but not when the discharge temperatures of the mixtures were inconsistent. The cracking resistance was reduced as the percentage of RAP increased. The rutting and moisture damage resistance improved as the percentage of RAP in the mixture...

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Performance characteristics of plant produced high RAP mixtures

This paper describes the use of Black diagrams of complex modulus versus phase angle to detect the occurrence of inconsistencies in rheological data caused by testing irregularities and distinctive material properties. In general, conventional penetration grade bitumens can be classified as “thermo-rheologically simple” materials with their rheological properties being temperature and time equivalent provided that they are determined within the binder's linear viscoelastic region and by suitable testing procedures. In the paper, Black diagrams have been successfully used to identify compliance (testing) errors in rheological data associated with the inappropriate use of various dynamic shear rheometer spindle geometries. The results indicate that using a 25 mm diameter testing geometry at complex modulus values greater than 105 Pa leads to an overestimation of elastic response and an underestimation of binder stiffness. As Black diagrams do not require any manipulation of rheological data prior t...

Use of Black Diagrams to Identify Inconsistencies in Rheological Data

Modelling the linear viscoelastic rheological properties of bituminous binders

The research results in this report concern the characterization of physical properties of asphalt binders and the development of test procedures for aging and adhesion. Asphalt binders were shown to be linear viscoelastic materials at expected pavement strains. Test methods and models describing rheological behavior were developed with the assumption of linear behavior. A mathematical model that contains parameters that can be used to relate physical and chemical parameters was developed. The test methods and models allow the stiffness of asphalt binders to be characterized as a function of loading time and temperature with the dynamic shear rheometer at intermediate to upper pavement surface temperatures and with a newly developed bending beam rheometer at low temperatures, where thermal cracking is important. To characterize fracture properties, the project developed a direct tension test, in which failure strain, stress, and energy are determined as functions of loading time and temperature. Limited work on fatigue properties at low temperatures successfully related them to tensile properties. A new phenomenon, low-temperature physical hardening, was identified during the project. This phenomenon results in increased stiffness of the binder when it is held at a constant temperature at room temperature or below. The blister test for quantitative measurement of adhesion between asphalt binder and aggregate surfaces was found to be impractical. The investigation of various factors, including film thickness, aging temperature, the effect of oxygen versus air, and the effect of mineral surfaces, led to a new aging procedure for simulating in-service oxidative hardening of asphalt binders, which was adopted as part of the new Strategic Highway Research program (SHRP) binder specification.

Binder characterization and evaluation. volume 3: physical characterization

One of the primary objectives of the Strategic Highway Research Program (SHRP) is to develop performance-related specifications for asphalt cement. This paper describes the program of research that is being pursued by the authors to develop new or improved test methods and specification criteria that are suitable for the development of a performance-related specification for asphalt cement. This paper consists of six sections, each of which is relevant to the problem of developing more effective specifications for paving grade asphalts: (1) a review of asphalt rheology; (2) a brief discussion of the chemistry and microstructure of asphalt cement; (3) a review of the traditional methods of characterization; (4) a discussion of the shortcomings of current specifications; (5) a description of proposed test methods and specification framework; and (6) a final section in which the information presented in this paper is summarized, and a few important conclusions are made concerning the development of performance-related specifications for asphalt cement.

D W Christensen

Papers

Binder characterization and evaluation. volume 3: physical characterization

Physical properties of asphalt cement and the development of performance-related specifications