Influence of M w of LDPE and vinyl acetate content of EVA on the rheology of polymer modified asphalt

Asphalt binder was modified by low-density polyethylene (LDPE) and ethyl vinyl acetate (EVA) polymers to investigate the structure–property relationships of polymer-modified asphalt (PMA). The PMA was prepared in a high-shear blender at 160 °C. The optimum blending time (OBT) for each polymer was determined following a separate investigation. OBT was influenced by M_w, MWD, and polymer structure. The influence of M_w of LDPE and vinyl acetate (VA) content of EVA on PMAs was studied by rheological tools. Polymer modification improved the rheological properties of base asphalt. EVA–PMAs were found to be less temperature sensitive than LDPE-modified asphalts. LDPE modification increased flow activation energy (E_a) but EVA modification decreased E_a. Both VA content and M_w of LDPE have influenced the storage stability of PMAs. The low-temperature properties of PMAs and short ageing tests were not influenced by polymer type. On the other hand, the high-temperature properties of PMAs were strongly influenced by M_w of LDPE and VA content of EVA. Overall, EVA with low VA content showed the best temperature resistance to high- temperature deformations, the highest upper service temperature as well as the best storage stability.     

Effect of vinyl acetate content and silicate loading on EVA nanocomposites under shear and extensional flow

In this study, three EVAs (ethylene-vinyl acetate co-polymers) with different vinyl contents (VA) ranging from 9 wt% to 28 wt% (EVA9, EVA18 and EVA28) were melt blended with organo-clay to obtain polymer layered silicate nanocomposites. Filler intercalation and exfoliation were evidenced by X-ray diffraction. The melt state viscoelastic properties of EVA nanocomposites were studied to examine the influence of clay in altering the flow properties of these polymeric nanocomposites. The EVA18 and EVA28 nanocomposites exhibited remarkable difference in dynamic and steady shear properties compared to neat polymers. On the other hand, EVA9-5% nanocomposite did not exfoliate and exhibited rheological behaviour very similar to that of the neat polymer. Furthermore, the first normal stress difference was found to be dependent on the silicate loadings when measured at low shear stresses. The uniaxial extensional viscosity measurement indicated that the strain hardening was weaker in EVA nanocomposites compared to neat polymers. Environmental scanning electron (ESE)-microscopy elucidated a possible reason for reduced strain hardening in these systems.     

Thermoreversible gels in oil/EVA systems

In this work we investigate the gel formation of EVA/recycled motor oil systems as a route to obtain synthetic binders which could be used instead of natural bitumen, as well as mixed with natural bitumen to modify adequately its viscoelastic response. The EVA copolymer studied in this work has a vinyl acetate content of 18 wt% and solutions of EVA/motor oil have been prepared up to a concentration of 50 wt%. Dynamic viscoelastic frequency sweeps between 10⁻² Hz and 10² Hz have shown that above 3 wt%, at 25 °C, EVA/motor oil systems form gels. It has been possible to define an elastic equilibrium modulus, G_e, for each gel. The dependence of G_e on concentration has been compared with that of PVC/DOP and SBS/oil gels on the basis of the De Gennes model. Thermal stability of EVA/motor oil gels has also been analyzed, indicating that for the highest polymer concentrations gel point is above 80 °C. Received: 23 December 1999 Accepted: 13 June 2000     

The rheology of recycled EVA/LDPE modified bitumen

This paper describes linear viscoelasticity, at low and intermediate temperatures, and the flow behaviour, at high temperatures, of polymer modified bitumen (PMB) containing 5 and 9 wt% recycled EVA/LDPE. The relationship between flow behaviour and microstructure of the modified bitumen was also considered, by comparison of experiments carried out in capillary and rotational rheometers and photomicrographs taken using a microscopy system whilst the sample was being sheared. Blends of 60/70 penetration grade bitumen and waste plastic (EVA/LDPE) were processed in an open mixer using a four blade propeller. Rheological tests, differential scanning calorimetry (DSC) and microscopy showed that the bitumen performance was improved by adding the recycled polymer. As a consequence, the use of recycled EVA/LDPE in PMBs can be considered a suitable and interesting alternative from both an environmental and economical point of view. The experimental results also show that pure bitumen has shear-thinning characteristics. The blending of polymer into the bitumen modifies the melt processing characteristics of the blend, whilst the viscoelastic properties of the semi-solid composite are enhanced.This paper was presented at the first Annual European Rheology Conference (AERC) held in Guimarães, Portugal, September 11-13, 2003.     

Nonlinear viscoelastic response of asphalt binders: An experimental study of the relaxation of torque and normal force in torsion

Development of normal stress in the direction perpendicular to the plane of shear is an important feature of the nonlinear viscoelastic behavior of asphalt binders. Here, we study the significance of this phenomenon with the help of stress-relaxation experiments in torsion. We conducted these experiments using a dynamic shear rheometer on an unmodified binder and polymer modified binder, at different temperatures and aging conditions. The results not only illustrate the nonlinearity of the behavior but also show certain distinctive characteristics of the relaxation behavior (torque relax faster than normal force) and it is seen that new constitutive models are required to predict such behavior.     

Rheology of carbon black suspensions. V. Heat-induced gelation and its reversibility

Linear viscoelastic properties of carbon black (CB) suspensions in a mixture of a rosin-modified phenol resin-type varnish (Varnish-1)/an alkyd resin-type varnish (Varnish-2), which exhibited a sol?Cgel transition on an increase in CB concentration, were investigated from 30°C to 80°C. The viscoelastic properties were reversible from 30°C to 60°C. In contrast, at temperatures above 60°C, the storage (G??) and loss (G??) moduli were irreversible and increased significantly with increasing temperature. This increase in the moduli is due to a change of the dispersion state to agglomerated state by heating. The agglomerated state was held, when the suspensions were lowered at 30°C. However, the G?? and G?? recovered to the original values upon shearing. This heat-induced gelation should be a universal feature for suspensions of weakly attractive particles. The temperature and shearing histories of the suspensions were discussed in relation to adsorption of polymeric component in the varnish on the CB particles.     

End-performance evaluation of thiourea-modified bituminous binders through viscous flow and linear viscoelasticy testing

Straight-run bitumens are no longer suitable in new asphalt mixtures. Consequently, the use of modified bitumens has become more important. In order to both improve binders’ mechanical properties and prevent it from phase separation whilst stored at high temperature, the paving industry is currently developing new modification routes based on reactive agents. This work studies the use of thiourea, which has proven to efficiently broaden the temperature interval over which the binder demonstrates an adequate performance. On the one hand, viscous flow and dynamic shear tests indicate an enhancement in the high in-service temperature strength, along with a reduced thermal susceptibility. On the other hand, results of dynamic flexural tests reveal a significant decrease in the binder glass transition temperature. Finally, the use of master curves and a further frequency/temperature conversion are proposed, in order to attain a suitable viscoelastic characterisation of bituminous binders at low temperatures.     

Micro Scale Tensile Behaviour of Thin Bitumen Films

The tensile behaviour of two types of viscoelastic bituminous films confined between mineral aggregates or steel as adherends, was investigated in the brittle and ductile regimes. Uniaxial specimens were fabricated employing a prototype set up allowing construction of micro-scale thin films and visualization of failure phenomena. The effect of key parameters, namely, temperature (23°C and −10°C), binder type (straight run and polymer modified), adherend type (stainless steel and mineral aggregate), and water conditioning were investigated sequentially. The results show that water sensitive aggregate-binder combinations in macro (150 mm diameter) and mega (in service) scales also displayed reduced tensile strength in the micro scale when water conditioned. At 23°C ductile failure and at −10°C brittle fracture were observed. At 23°C phenomena, such as formation of striations during tensile mechanical loading, void nucleation and growth, filamentation and large ductile flow before fracture could be witnessed. When using proper surface preparation procedures, in all types of specimen investigated at 23°C only cohesive failure and at −10°C predominantly adhesive-cohesive failure were found.     

Determination of Asphalt Binder Creep Compliance Using Depth-Sensing Indentation

Asphalt binders are common construction materials, however due to time- and temperature- dependence, their mechanical properties are often difficult to characterize. Several standard tests methods exist to describe their complex behavior. This paper presents an exploratory feasibility study of a flat-tip indentation testing to analyze the linear viscoelastic properties of asphalt binders. Depth-sensing indentation testing has been extensively used to characterize the properties of many engineering materials, however the applications to asphalt binders are very limited. This paper presents a simple solution for the creep compliance in tension derived for flat-tipped indenter. This solution was verified with the Finite Element Analysis and then applied to the experimental results from the indentation testing performed on one typical unmodified asphalt binder. The testing was conducted at three different low temperatures and under three different creep load levels to verity the linearity of the response, and to evaluate the robustness and applicability of the indentation method. Furthermore, the creep compliance functions determined from the indentation testing were compared with a more traditional 3-point bending experiments. The results show that there is a non-uniform discrepancy between the two testing methods, most likely due to nonlinear behavior of the asphalt binder at higher temperatures and micro-damage of the binder samples at lower temperatures. Other possible sources of error between indentation and 3-point bending are problems determining the initial tip-specimen contact surface and possible tip-specimen adhesion. It is concluded that flat-tipped indentation at low temperatures should be performed at lower load levels to avoid excessive stress concentrations that leads to micro-damage and nonlinear response of asphalt binders. Alternatively, asphalt binders at low temperatures could be evaluated using different indenter geometries, such as spherical or pyramidal, using corresponding parameter interpretation procedures.     

Measurement of Temperature-Dependent Young’s Modulus at a Strain Rate for a Molding Compound by Nanoindentation

The mechanical properties of a molding compound on a packaged integrated circuit (IC) were measured by spherical nanoindentation using a 50 μm radius diamond tip. The molding compound is a heterogeneous material, consisting of assorted diameters of glass beads embedded in an epoxy. Statistical analysis was conducted to determine the representative volume element (RVE) size for a nanoindentation grid. Nanoindentation was made on the RVE to determine the effective viscoelastic properties. The relaxation functions were converted to temperature-dependent Young’s modulus at a given strain rate at several elevated temperatures. The Young’s modulus values at a given strain rate from nanoindentation were found to be in a good agreement with the corresponding data obtained from tensile samples at or below 90 °C. However, the values from nanoindentation were significantly lower than the data obtained from tensile samples when the temperature was near or higher than 110 °C, which is near the glass transition. The spatial distribution of the Young’s modulus at a given strain rate was determined using nanoindentation with a Berkovich tip. The spatial variation of the Young’s modulus at a given strain rate is due to the difference in nanoindentation sites (glass beads, epoxy or the interphase region). A graphical map made from an optical micrograph agrees reasonably well with the nanoindentation results.     

Creep response of bituminous mixtures—rheological model and microstructural interpretation

The main failure mechanisms of flexible pavements, such as low-temperature cracking, fatigue failure, and rutting are strongly influenced by the viscoelastic properties of asphalt. These viscoelastic properties originate from the thermorheological behavior of bitumen, the binder material of asphalt. In this paper, the bitumen behavior is studied by means of a comprehensive experimental program, allowing the identification of viscoelastic parameters of a power-law type creep model, indicating two time scales (short-term and long-term) within the creep deformation history of bitumen. Moreover, these characteristics of the creep deformation transfer towards bitumen-inclusion mixtures, as illustrated for mastic, consisting of bitumen and filler. For this purpose, the aforementioned power-law creep model is implemented into a micromechanical framework. Finally, the activation of the different creep mechanisms as a function of the loading rate is discussed, using viscoelastic properties obtained from both static and cyclic creep tests.     

Dynamic rheological properties of a fumed silica grease

The thermo-rheological characteristics of a fumed silica lubricating grease in linear and nonlinear oscillatory experiments have been investigated. The material rheological behavior represents a soft solid being thermo-rheologically complex. There is an abnormal temperature dependency in the range of ??10 to 10 °C which is related to the phase transition of the base oil. The dynamic moduli data in linear viscoelastic envelop (LVE) have been modeled using mode-coupling theory (MCT) in the whole temperature range. Two main relaxation mechanisms can be identified through linear and nonlinear viscoelastic properties related to interaction of the primary particle and its neighbor particles as well as a slow relaxation process which represents the escape of this particle from its “cage”. Finally, it is demonstrated that the dominant yielding process in large amplitude oscillatory experiments can be explained based on either particle cage rupture (consistent with MCT framework) or particle “hopping” out of its cage proposed in soft glassy rheology (SGR) model. It will be discussed that the governing mechanism depends on the applied frequency.     

The Effect of Grain Size on Deformation and Failure of Ti<Subscript>2</Subscript>AlC MAX Phase under Thermo-Mechanical Loading

An experimental investigation was performed to analyze the effects of grain size on the quasi-static and dynamic behavior of Ti₂AlC. High-density Ti₂AlC samples of three different grain sizes were densified using Spark Plasma Sintering and Pressureless sintering. A servo-hydraulic testing machine equipped with a vertical split furnace, and SiC pushrods, was used for the quasi-static experiments. Also, a Split Hopkinson Pressure Bar (SHPB) apparatus and an induction coil heating system were used for the dynamic experiments. A series of experiments were conducted at temperatures ranging from 25 °C to 1100 °C for strain rates of 10^?4 s^?1 and 400 s^?1. The results show that under quasi-static loading the specimens experience a brittle failure for temperatures below Brittle to Plastic Transition Temperature (BPTT) of 900–1000 °C and large deformation at temperatures above the BPTT. During dynamic experiments, the specimens exhibited brittle failure, with the failure transitioning from catastrophic failure at lower temperatures to graceful failure (softening while bearing load) at higher temperatures, and with the propensity for graceful failure increasing with increasing grain size. The compressive strengths of different grain sizes at a given temperature can be related to the grain length by a Hall-Petch type relation.     

Temperature Dependent Viscoelastic Properties of Polymers Investigated by Small-Scale Dynamic Mechanical Analysis

The temperature-dependent viscoelastic properties of polymers were investigated by small-scale dynamic mechanical analysis in the range of −100°C to 200°C. The polymers tested included glassy polymer (atactic polystyrene), semicrystalline polymer (high-density polyethylene) and rubbery polymer (polyisobutylene). The small-scale dynamic mechanical analyses were performed by using a flat-tip indenter with an oscillating displacement of amplitude 36 nm. The force amplitude and phase angle were measured, from which the storage modulus E′ and loss tangent tanδ were calculated. The results obtained from indentation experiments are consistent with those obtained from conventional dynamic mechanical analyzer (DMA). It is thus demonstrated that the indentation technique can quantitatively measure the temperature-dependent viscoelastic properties of polymers at small dimensions.     

Thermo-viscoelastic and viscoplastic behavior of high-density polyethylene

Observations are reported on high-density polyethylene in uniaxial tensile tests with constant strain rates and relaxation tests at various temperatures ranging from 25 to 90 °C. A constitutive model is derived for the nonlinear viscoelastic and viscoplastic behavior of semi-crystalline polymers at three-dimensional deformations. Adjustable parameters in the stress–strain relations are found by fitting the experimental data. It is demonstrated that (i) the model correctly approximates the observations and (ii) material parameters are independent of strain rate and change consistently with temperature.     

Sur le caractère thermo-extensif de la surface de charge d'un sol non saturéOn the thermo-extensive nature of the yield surface for an unsaturated soil

A study of temperature influence on the yield surface for one unsaturated soil at constant suction is presented. Mechanical consolidation tests are realized at different temperatures on clayey silty sand. A specific triaxial apparatus for unsaturated soils with temperatures included between 30 °C and 60 °C is used. Experimental results show without ambiguity a thermo-extensive nature of the yield surface. The physical interpretation proposed calls for microscopic considerations on the menisci capillary evolution according to temperature and suction. To cite this article: F. Jamin et al., C. R. Mecanique 332 (2004).     

Process rheokinetics and microstructure of recycled EVA/LDPE-modified bitumen

Knowledge of the kinetics of the manufacturing process of polymer–bitumen blends is of great interest because it provides information on the behaviour of the binder at different stages of the mixing operation, which is useful for the establishment of the optimum processing conditions, involving temperature and operation time. The purpose of this research was to study the evolution of the rheological properties and microstructure of a polymer-modified bitumen during its processing. A 60/70-penetration grade bitumen and recycled EVA/LDPE were mixed under different processing conditions. Measurements of the evolution of viscosity with time, at different temperatures and agitation speeds, were carried out with an experimental device known as ‘rheomixer’, that is, a helical ribbon impeller inside a mixing vessel coupled with the transducer and motor of a conventional rheometer. Under the experimental conditions selected (within the laminar region, Re<10), temperature is the most important processing variable. Hence, low agitation speeds and a processing temperature of around 180°C should be chosen for bitumen modification with the polymer used.     

Analysis of biaxial-fatigue damage at elevated temperatures

Two-level cumulative-damage fatigue tests were conducted on tubular 304 stainless-steel specimen under biaxial-strain conditions at elevated temperatures. Effects of temperature, biaxiality and sequence of straining were investigated. The experimental results are forwarted with a new approach that utilizes the Miner cumulative-damage rule. This approach has shown that fatigue damage at elevated temperatures of 538°C (1000°F) and 649°C (1200°F) accelerates and decelerates as a result of time of exposure to a given loading sequence. The effect of biaxiality is shown through the behavior of the material under axial and shear-strain components. The axial (tensile) strain component has shown to be the severest detrimental damaging component when compared to a shear-strain component. A damage mechanism emerges from the interaction of temperature and loading sequence. Its significance can be observed only when a certain life ratio has been exhausted.     

Rheology and structural changes of plasticized zeins in the molten state

Zeins, storage proteins from maize, are suitable for making biobased thermoplastic materials. The rheological behavior of a commercial zein plasticized with 20 w% glycerol was studied in the molten state by steady-state flow experiments in extrusion conditions and oscillatory rheometry. For low residence times, a shear-thinning viscoelastic behavior was observed, with G″ exceeding G′. After 300 s at 130 °C, the complex viscosity |η ^?|?=?7?×?10³ ω ^?0.46 was found to be similar to that of thermoplastic polymer melts used in fused deposition modeling. However, the ratio between the exponents of the power laws describing G′(ω) and G″(ω) did not meet the typical value of 2 for entangled polymer melts. Moreover, for longer residence times, the viscosity increased and a gelation phenomenon was observed with a crossing over of G′(ω) and G″(ω). Gel times ranged from 6000 s at 120 °C to 1700 s at 150 °C. The evolution of the macromolecular structure assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and high-performance size exclusion chromatography suggested that this gelation phenomenon involves various types of covalent and non-covalent cross-links. Disulfide bonds played a significant role in gelation kinetics despite a very low cysteine residue content in the protein primary structure (about 1 mol%). These results suggested that plasticized zeins initially behave like a low-viscosity non-entangled polymer melt, before cross-linking progressively led to a continuous network.     

Temperature and rate effects on stable crack growth in a particulate composite material

In this study, edge cracked sheet specimens made from polybutadiene rubber embedded with hard particles were used in crack propagation tests. Crack propagation tests were conducted under two crosshead speeds (2.54 mm/min and 12.7 mm/min) at three temperatures (−53.9°C, 22.2°C and 73.9°C). The experimental data were analyzed and the crack growth resistance curves and the crack growth rate versus the Mode I stress intensity factor were plotted. Based on these experimental results, the effects of temperature and loading rate on the crack growth behavior were investigated and the results are discussed.