Experimental Evaluation and Modeling of Physical Hardening in Asphalt Binders

The research described in this paper deals with the experimental evaluation and modeling of physical hardening in asphalt binders. The term physical hardening refers to a reversible phenomenon occurring at low temperatures that causes time-dependent changes in viscoelastic properties. The experimental approach, followed to quantitatively assess physical hardening, was based on flexural creep tests carried out by means of the Bending Beam Rheometer at various temperatures and conditioning times. The results obtained confirmed that hardening phenomena have a significant influence on the creep response of asphalt binders, to an extent that can be quantitatively assessed by referring to the appropriate rheological parameters and by applying the loading time–conditioning time superposition principle. The experimental data were fitted to a mechanical model proposed in the literature (composed of a single Kelvin–Voigt element) and thereafter to an improved model (with two Kelvin–Voigt elements in series). Both models were assessed in terms of their prediction accuracy. The improved model was found to better describe physical hardening effects in the case of both short- and long-term conditioning. Practical implications of the study were finally highlighted by referring to possible ranking criteria to be introduced in acceptance procedures for the comparative evaluation of asphalt binders.

Electro Physical Hardening of Non Metallic Composite Materials in Additive Technology

The analysis of the prospects for the use of additive technologies in the production of aerospace equipment has been performed. It is shown that one of the main problems of implementation of these technologies in the main production is the lack of strength and endurance of 3D printing objects. The influence of electro physical effects of varying intensity on the strength properties of the objects from powder materials, formed by 3D printing has been researched. It is found that the electromagnetic field of medium intensity of the investigated range causes an increase in the flexural strength of the plates made of powder Zp130 impregnated with cyanoacrylate Z-Bond TM90, not less than 38%. Thus, a 24% decrease in pore size and reduction in their dispersion by almost 30% is noticed. It is shown that the composite material structure becomes denser with a large number of connections between the agglomerates. The increase in the number of connections, and the increased uniformity of the structure after the electrophysical influence is one of the mechanisms to improve the strength of 3D printed objects exposed to electro-physical influence.

Characterization of granite and limestone powders for use as fillers in bituminous mastics dosage

This paper discusses the importance of studies on materials known as fillers from different mineral origins, used in asphalt mixes, specifically in the formulation of mastics. The research was carried out on samples of limestone and granite rock filler and asphalt binder (50/70). The samples were evaluated through semiquantitative chemical analyses by X-ray fluorescence, granulometry by low angle laser emission, scanning electron microscopy, softening point tests, penetration tests, and aggregate-asphalt binder and aggregate-mastic adhesion tests. The results highlighted convergent trends, indicating that the active behavior of the fillers in the mastic formulation is not related to the size of the particles, but rather to their form, surface texture, specific surface area and mineralogical nature, allowing the filler activity concept to be divided into two components: physical (hardening) and chemical (adhesion).