Performance Characteristics of Nano-Modified Asphalt Mixtures

The growing need for high quality paving materials has aroused an increasing interest in innovative reinforcing agents, such as those characterized by nanometric dimensions. The experimental study presented in this paper focused on the use in asphalt mixtures of nanoclays and multiwall carbon nanotubes as bitumen modifiers. The performance characteristics of asphalt mixtures containing these nano-sized additives and those of a reference neat mixture were compared in a wide array of temperature and loading conditions. The testing program included the assessment of linear viscoelastic characteristics, anti-rutting potential and crack propagation resistance, by means of stiffness modulus, flow number and semi-circular bending tests, respectively. Results highlighted that both types of nano-additives have the potential to improve the performance properties of neat asphalt mixtures, with nanoclays yielding a superior reinforcing actio

Interferometric length metrology for the dimensional control of ultra-stable Ring Laser Gyroscopes

We present the experimental test of a method for controlling the absolute length of the diagonals of square ring laser gyroscopes. The purpose is to actively stabilize the ring cavity geometry and to enhance the rotation sensor stability in order to reach the requirements for the detection of the relativistic Lense-Thirring effect with a ground-based array of optical gyroscopes. The test apparatus consists of two optical cavities 1.32 m in length, reproducing the features of the ring cavity diagonal resonators of large frame He-Ne ring laser gyroscopes. The proposed measurement technique is based on the use of a single diode laser, injection locked to a frequency stabilized He-Ne/Iodine frequency standard, and a single electro-optic modulator. The laser is modulated with a combination of three frequencies allowing to lock the two cavities to the same resonance frequency and, at the same time, to determine the cavity Free Spectral Range (FSR). We obtain a stable lock of the two cavities to the same optical frequency reference, providing a length stabilization at the level of 1 part in $10^{11}$, and the determination of the two FSRs with a relative precision of 0.2 ppm. This is equivalent to an error of 500 nm on the absolute length difference between the two cavities

Effect of anti-icing chemicals on stripping of asphalt concrete mixtures for airport runway wearing courses

As part of a wider research project for the study and development of a system for the prediction, monitoring and management of meteorological winter emergencies in airports (Airport Weather Information System, AWIS), the experimental investigation reported in this paper focused on damage phenomena caused by antiicing chemicals on asphalt concrete mixtures for airport runway surface courses, with an emphasis placed upon stripping. Asphalt mixtures derived from the combination of aggregates of two different mineralogical types (basaltic and siliceous) and two bituminous binders (one neat bitumen and one SBS polymer modified binder). The testing program included determination of aggregate-binder affinity, indirect tensile strength and fracture properties. A potassium formate solution was employed as antiicer. Obtained results indicated that anti-icing treatments may promote stripping phenomena to an extent which depends on aggregate and binder typ

Experimental investigation on the use of waste elastomeric polymers for bitumen modification

The study described in this paper focused on the possible use of waste products coming from the production of styrene-butadiene rubber (SBR) and polybutadiene rubber (PBR), as bitumen modifiers. Modified binders containing these products were prepared in the laboratory with different polymer dosages and were thereafter subjected to the evaluation of empirical and rheological properties. For comparative purposes, the study also considered SBR and PBR products of premium quality. Ageing effects were also taken into account by means of proper laboratory simulations. Obtained results indicated that the two types of polymer (SBR and PBR) have completely different effects on the rheology and expected performance of the resulting modified binders. In particular, while the two polymers showed similar effects in terms of resistance to permanent deformation, the SBR products proved to be superior from the viewpoint of fatigue resistance. However, only minor differences were found when comparing the effects produced by premium quality and waste polymers. As a result of the experimental findings, it was concluded that the use of waste SBR polymers can be an attractive solution for the production of affordable modified binders

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

Modification of electronic surface states by graphene islands on Cu(111)

We present a study of graphene/substrate interactions on UHV-grown graphene islands with minimal surface contamination using \emph{in situ} low-temperature scanning tunneling microscopy (STM). We compare the physical and electronic structure of the sample surface with atomic spatial resolution on graphene islands versus regions of bare Cu(111) substrate. We find that the Rydberg-like series of image potential states is shifted toward lower energy over the graphene islands relative to Cu(111), indicating a decrease in the local work function, and the resonances have a much smaller linewidth, indicating reduced coupling to the bulk. In addition, we show the dispersion of the occupied Cu(111) Shockley surface state is influenced by the graphene layer, and both the band edge and effective mass are shifted relative to bare Cu(111).Comment: 12 pages, 3 figure

Testing of reclaimed asphalt model systems for the evaluation of the effectiveness of rejuvenators

This paper presents the results of a preliminary study on the use of a novel ap-proach for the evaluation of the effectiveness of rejuvenating agents used in as-phalt mixtures containing reclaimed asphalt (RA). Such an approach is based on the mechanical testing of model systems constituted by a single-sized RA materi-al, in its original state and after pretreatment with rejuvenators, compacted to a target volumetric condition. Model systems were prepared by making use of two rejuvenators and by also considering a reference combination of virgin binder and aggregates extracted from the RA. Tests were carried out for the evaluation of stiffness modulus and indirect tensile strength as a function of curing time. Ex-perimental results showed that the proposed approach can capture the changes occurring in the aged RA binder as a consequence of the effects induced by reju-venators. Quantification of the rejuvenating effects was carried out by analyzing recorded stiffness and strength variations, and by referring to a ductility tough-ness index, introduced to better describe stress-strain response after failure

Enrico VII, Dante e Pisa: a 700 anni dalla morte dell'imperatore e dalla Monarchia (1313-2013)

Atti del Convegno internazionale "Enrico VII, Dante e Pisa a 700 anni dalla morte dell'imperatore e dalla Monarchia (1313-2013) (Pisa-San Miniato, 24-26 ottobre 2013

CHARACTERIZATION OF CRUMB RUBBER FROM END-OF-LIFE TYRES FOR PAVING APPLICATIONS

Crumb rubber (CR) derived from grinding of end-of-life tyres (ELTs) may be successfully used as a bitumen modifier or as a supplementary component in the production of bituminous mixtures employed for the construction and maintenance of road pavements. However, CRs deriving from different sources and processes yield effects on performance under traffic loading and on gaseous emissions produced during laying on site which may change considerably depending upon their physical and chemical properties. In order to quantitatively assess the possible variability of CR characteristics, samples were taken from 9 Italian and 2 foreign ELT processing plants. Investigation activities included field surveys, during which plants were examined in detail, and laboratory tests, which focused on physical and chemical characterization of CR. Based on the analysis of available technical information and experimental data, it was possible to find relationships between the peculiar characteristics of treatment cycles and corresponding CR properties