Measurement of the viscoelastic properties of bituminous materials using an oscillating needle technique

An embedded oscillating needle is used to measure the dynamic viscoelastic properties of a stiff bituminous material. A Micro-Fourier Rheometer was used to cause the embedded needle to undergo pseudorandom small amplitude oscillations in the axial direction with measurement of the instantaneous resistance force. The phase and magnitude of the force signal are used to calculate the storage and loss moduli. A theoretical framework for this technique is developed from the Mindlin solution coupled with slender body theory, and the correspondence principle of linear viscoelasticity. Experiments are performed on neat bitumen binders as well as mixtures of glass spheres in bitumen; the results show that the presence of the glass spheres dramatically increases the viscoelastic response functions. The results agree reasonably well with those obtained using the parallel plate squeezing mode. Received: 31 March 1999 Accepted: 14 July 1999     

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.     

Sulfur modified bitumen: A new binder

Summary Bitumen is modified after a treatment with 2% sulfur, at 160°C. It is more plastic consecutive to a variation of the nature of the interactions between asphaltene molecules.Composites prepared with this bitumen and silica present dynamic viscoelastic properties obeying the time-temperature-interfacial parameter equivalence principles, evidenced previously. However, the domains of applicability of these principles are more restricted.With 11 figures     

Theory of multiphase mixtures—A thermomechanical formulation

The paper presents a theory of mixtures with the nonzero interfacial area between the constituents of the mixture. The conservation laws are physically motivated by utilizing a volume averaging procedure and by the definition of a mapping transformation. It is shown that the theory constructed in this manner is consistent with the theory of mixtures with a vanishingly small interfacial area and that a second law of thermodynamics can be assigned for each phase of the mixture. The conservation laws are examined for invariance properties with the principle of the material frame indifference, and a particular constitutive assumption is discussed. Also presented in the paper are the conservation laws in the integral form and the jump conditions for the singular surfaces in the multiphase mixture.     

Rheological properties of polyacrylates used as synthetic road binders

Most adhesives and binders, including bitumen for asphalt mixture production, are presently produced from petrochemicals after the refining of crude oil. The fact that crude oil reserves are a finite resource means that in the future, it may become necessary to produce these materials from alternative and probably renewable sources. Suitable resources of this kind may include polysaccharides, plant oils and proteins. This paper deals with the synthesis of polymer binders from monomers that could, in future, be derived from renewable resources. These binders consist of polyethyl acrylate (PEA) of different molecular weight, polymethyl acrylate (PMA) and polybutyl acrylate (PBA), which were synthesised from ethyl acrylate, methyl acrylate and butyl acrylate, respectively, by atom transfer radical polymerisation. The rheological properties of these binders were determined by means of oscillatory testing using a dynamic shear rheometer and combinations of stress/strain, temperature and frequency sweeps. The results indicate that PEA can be produced to have rheological properties similar to that of ‘soft’ 100/150 penetration grade bitumen, PMA with similar rheological properties to that of ‘hard’ 10/20 penetration grade bitumen, while PBA, due to its highly viscous nature and low dynamic moduli, cannot be used on its own as a binder. The synthetic polymers were found to be thermo-rheologically simple, and the shift factors, used to produce the dynamic moduli master curves, were found to fit an Arrhenius function.     

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.     

Rheology and microstructure of asphalt binders

The viscous and linear viscoelastic properties of different asphalt binders have been analyzed in this paper. Thus, an unmodified bitumen, a polymer-modified (SBS) bitumen, a commercial synthetic binder, and two model synthetic binders with different polymer (SBS) concentrations have been studied. The mechanical spectra of these binders are quite different, mainly influenced by SBS concentration. Thus, up to three regions may be observed for a synthetic binder with high polymer concentration. The temperature dependence of the zero-shear-rate-limiting viscosity is described by an Arrhenius-like equation, in a temperature range that depends on binder composition. These results have been discussed taking into account the development of a polymer-rich phase in SBS-modified bitumen and model synthetic binders. Received: 6 February 2000 Accepted: 8 August 2000     

Saint-Venant decay rates for a non-homogeneous isotropic mixture of elastic solids in anti-plane shear

The purpose of this research is to investigate the influence of material inhomogeneity on the decay of Saint-Venant end effects in anti-plane shear deformations of linear isotropic mixtures of elastic solids. The work is motivated by the recent research activity on functionally graded materials (FGMs), i.e. materials with spatially varying properties tailored to satisfy particular engineering applications. The spatial decay of solutions of a boundary value problem with variable coefficients on a semi-infinite strip is investigated. The results may be interpreted in terms of a Saint-Venant principle for anti-plane shear deformations of linear isotropic mixtures of elastic solids.     

Bitumen/polyethylene blends: using m-LLDPEs to improve stability and viscoelastic properties

The stability and the rheological properties of blends of a 60/70 penetration-grade bitumen with conventional HDPEs and metallocene catalysed LLDPEs (m-LLDPE) are investigated. Considerably better stability results are obtained using m-LLDPEs instead of conventional polyethylenes, allowing one to avoid phase separation of the emulsion-like system during storage at high temperature. Thermodynamical interaction between bitumen and polyethylene is discarded as a cause of the observed difference, because the solubility parameter is practically the same for all the investigated polyethylenes. The result is explained on the basis of the lower melt elasticity of m-LLDPEs (attributed to their narrow molecular weight distribution), which facilitates the drop breakup during mixing process. The modification of bitumen with any of the m-LLDPEs considered in this work gives a new material with considerably improved viscoelastic properties.     

An empirical constitutive model for complex glass-forming liquids using bitumen as a model material

While extensive research efforts have been devoted to understand the dynamics of chemically and structurally simple glass-forming liquids (SGFLs), the viscoelasticity of chemically and structurally complex glass-forming liquids (CGFLs) has received only little attention. This study explores the rheological properties of CGFLs in the vicinity of the glass transition. Bitumen is selected as the model material for CGFLs due to its extremely complex chemical composition and microstructure, fast physical aging and thermorheological simplicity, and abundant availability. A comprehensive rheological analysis reveals a significant broadening of the glass transition dynamics in bitumen as compared to SGFLs. In particular, the relaxation time spectrum of bitumen is characterized by a broad distribution of long relaxation modes. This observation leads to the development of a new constitutive equation, named the broadened power-law spectrum model. In this model, the wide distribution of long relaxation times is described by a power-law with positive exponent and a stretched exponential cut-off, with parameter β serving as a measure of the broadness of the distribution. This characteristic shape of the bitumen spectrum is attributed to the heterogeneous freezing of different molecular components of bitumen, i.e., to the coexistence of liquid and glassy micro-phases. Furthermore, as this type of heterogeneous glass transition behavior can be considered as a general feature of complex glass-forming systems, the broadened power-law spectrum model is expected to be valid for all types of CGFLs. Examples of the applicability of this model in various complex glass-forming systems are given.