Effect of Graphene Nanoplatelets (GNPs) on Fatigue Properties of Asphalt Mastics

To investigate the effect of graphene on the fatigue properties of base asphalt mastics, graphene nanoplatelets (GNPs)-modified asphalt mastics and base asphalt mastics were prepared. A dynamic shear rheometer (DSR) was used to conduct the tests in the stress-controlled mode of a time-sweep test. The results showed that GNPs can improve the fatigue life of asphalt mastic. Under a stress of 0.15 MPa, the average fatigue life growth rate (ω¯) was 17.7% at a filler-asphalt ratio of 0.8, 35.4% at 1.0, and 45.2% at 1.2; under a stress of 0.2 MPa, the average fatigue life growth rate (ω¯) was 17.9% at a filler-asphalt ratio of 0.8, 25.6% at 1.0, and 38.2% at 1.2. The growth value (ΔT) of fatigue life of GNPs-modified asphalt mastics increased correspondingly with the increase of filler–asphalt ratio, the correlation coefficient R2 was greater than 0.95, and the growth amount showed a good linear relationship with the filler–asphalt ratio. In the range of 0.8~1.2 filler–asphalt ratio, the increase of mineral powder can improve the fatigue life of asphalt mastics, and there is a good linear correlation between filler–asphalt ratio and fatigue life. The anti-fatigue mechanism of GNPs lies in the interaction between GNPs and asphalt, as well as its own lubricity and thermal conductivity.

Nanoclay Migration and the Rheological Response of PBAT/LDPE Blends

Blends of a poly(butylene adipate-co-terephthalate) (PBAT) and a low density polyethylene (LDPE) (80 wt%/20 wt%) were prepared through a twin screw extruder while incorporating 3 wt% Cloisite 30B (C30B) nanoclay that possessed a much higher affinity with PBAT. The blends were processed through three melt mixing strategies: ( i) direct mixing of all three components, (ii) mixing C30B and PBAT followed by mixing with LDPE, and (iii) mixing C30B and LDPE followed by mixing with PBAT. The rheological properties of each system were determined in small amplitude oscillatory shear (SAOS) experiments. The migration of C30B nanoparticles from the LDPE minor phase towards the PBAT matrix was then monitored in the blend nanocomposites prepared through strategy (iii) via SAOS time sweep experiments. It was firstly understood that the C30B migration could be detected during time sweep SAOS experiments. The migration time was observed to be frequency dependent due to the smaller length scales probed at larger frequencies. Such migration occurred even faster when the SAOS time sweep experiments were conducted at a higher temperature due to the viscosity reduction.

Preparation and characterization of oleogels with tallow and partially hydrolyzed tallow as organogelators

The aim of this study was to evaluate the organogelation potential of tallow fat (TF) and partially hydrolyzed tallow fat (HTF) against saturated monoglyceride (MG) and a saturated monoglyceride + diglyceride mixture (MDG) as the organogelators. TF itself created oleogel at a 30% addition level, while HTF, MG and MDG oleogels were prepared at 10% addition levels. Fatty acid composition data showed that the oleogel of HTF (HTFO) was quite similar to those of MG and MDG oleogels. Solid fat content, free fatty acidity and peroxide values were found to be in acceptable ranges for HTFO. Thermal properties, crystal morphology and X-ray diffraction patterns were also evaluated. Rheological analyses indicated that all oleogels had higher storage modulus (G´) than loss modulus (G´´). The time-sweep test showed that after applying higher shear rates, the gels re-formed at rest. Further, all oleogels maintained their gelled consistency until around 54 °C. The results suggest that HTF could be a cheap, efficient, fast melting, safe and readily available organogelator.

Aplicação de parâmetro de resistência à fadiga para ligantes asfálticos baseado na mecânica da fratura elástico-linear

Ensaios e parâmetros de fadiga para ligantes asfálticos foram desenvolvidos como alternativas ao parâmetro G*.sind, mas também apresentam limitações. Estudos recentes indicaram que o índice de tolerância ao dano por fadiga (af) do ensaio Linear Amplitude Sweep (LAS) se mostrou ineficiente para caracterizar alguns asfaltos modificados. Uma abordagem baseada na Mecânica da Fratura Elástico-Linear (MFEL) se mostrou efetiva para analisar os dados do ensaio LAS, inclusive nos casos em que não foi possível determinar o índice af. Neste trabalho, o parâmetro de tolerância à fadiga baseado na MFEL (aMFEL) foi avaliado quanto à aplicabilidade e representação do comportamento à fadiga. Os índices aMFEL, af e FFL (fator de fadiga do ligante) foram comparados quanto à aplicabilidade em ensaios realizados com seis ligantes asfálticos (dois puros e quatro modificados) em três temperaturas. O índice aMFEL pôde ser obtido em um maior número de casos que o índice af, indicando maior aplicabilidade do índice baseado na MFEL em relação ao índice af. O FFL apresentou a maior aplicabilidade dentre os três índices analisados. O aMFEL apresentou boa correlação com o af e com o FFL, porém o aMFEL e o af não apresentaram correlação significativa com o parâmetro Np20 do ensaio Time Sweep (TS). Dentre os índices aMFEL, af e FFL, o FFL foi o que apresentou maior correlação com o Np20.

ASPHALT FATIGUE MODELING IN CONSTANT STRAIN TIME SWEEP TESTS BASED ON DISSIPATED ENERGY APPROACHES

This paper aims to develop asphalt binder fatigue models by time sweep tests under constant strain. By investigating of the fatigue life in neat and modified asphalts under linear and nonlinear viscoelastic responses, results were analyzed in terms of strain levels, asphalt kind and additive content. The dissipated energy and dissipated energy ratio concepts were utilized to develop the phenomenological models for estimating fatigue lives of asphalt binders. Results showed that the dissipated energy ratio based equations give relatively identical fatigue models irrespective of the strain level or asphalt binder type. Moreover, statistical analyses were performed to investigate the contribution of each parameter in the fatigue model prediction. A comparison was made between fatigue life predictions by means of traditional and energy based methods. Results proved that the fatigue life prediction models based on the concept of dissipated energy ratio follow a similar trend.

Enhancement of the Temporal Resolution of Fluorescent Signals Acquired by the Confocal Microscope

Here, we describe a method of acquisition of fast fluorescent signals with the help of the laser scanning confocal microscope (LSCM). Our method permits an increase in the temporal resolution of acquired signals. The method is based on LSCM recordings of fast fluorescent signals with the shortest achievable time sweep, which are performed with the help of a proprietary algorithm. A series of recordings is made in multiple steps; at each step, the fluorescent signal is incremented by a time interval smaller than the time sweep of the frame of LSCM. The size of the increment determines the achievable time resolution. The convolution of the recorded images results in a signal with the temporal resolution determined by the chosen time increment. This method was applied to register the change in fluorescence (calcium transient) of calcium dye preloaded into peripheral nerve endings by electrical stimulation of the motor nerve. Calculated parameters of the calcium transient were identical to the parameters obtained earlier with the help of a high-speed camera and photodiode. We conclude that the method described here can be applied for the registration of fast fluorescent signals by LSCM with a high spatial and temporal resolution.