Stiffening Effect Of Filler Research Articles

Micromechanics prediction of dynamic modulus for asphalt mastic considering filler distribution characteristic: A new perspective

This study aims to provide a new perspective into the consideration of filler distribution characteristic in micromechanical modeling of asphalt mastic through combining fractal microstructure. To do this, three viscoelastic micromechanical models were improved by the preliminarily combination between micromechanical equivalence and fractal statistic principles. Particle size distribution (PSD) of filler was tested by a laser particle size analyzer. Asphalt mastics with different filler concentrations were fabricated. Dynamic shear moduli of asphalt and asphalt mastics was tested by a dynamic shear rheometer. The PSD of the circles intercepted by the plane and dimensionless area of the intercepted asphalt matrix were analyzed. The dynamic shear modulus ratio of asphalt mastic to binder were calculated based on the improved models. The effects of various parameters on the distribution of the ratio were investigated. Results show that the shifted R-R distribution function is capable of capturing the PSD of filler. The dimensionless area increases with increasing dimensionless diameter, but decreases with increasing filler volume fraction. The shear modulus ratio shows a three-stage reduction trend with dimensionless diameter, replying that the shear modulus of asphalt mastic appears as a random distribution in space. Meanwhile, the spatial distribution is influenced by filler volume fraction and thus there has difference between the stiffening effects of filler on various local regions in asphalt mastic. Poisson’s ratio of binder plays an enhanced role in the stiffening effect of filler, which is affected by the spatial locations within asphalt mastic. Modulus and Poisson’s ratio of limestone filler and modulus of binder have little effect on the distribution of the shear modulus ratio. The combination of micromechanical modeling and fractal characteristic is capable of determining the spatial distribution characteristic of effective properties for asphalt mastic. The local homogenization of asphalt mastic in terms of the modulus and its influence on properties of asphalt mixture should be focused on and conducted in future.

Microstructural and rheological analysis of fillers and asphalt mastics

Pavements are made of different grades of mineral aggregates and organic binder. The aggregates are sorted in different sizes and different amount which are mixed together with bitumen. The finest mineral fraction (d<0.063 mm) is called filler. This component has an important role in asphalt mixture - it fills the gaps between the aggregates and if mixed with bitumen (which is called asphalt mastics) it sticks the larger particles together. Particle size, microstructure and surface properties of fillers highly affect the cohesion with bitumen, therefore the aim of our research was to investigate the microstructure of mineral fillers (limestone, dolomite) which are used in Hungarian road constructions with the use of different techniques (particle size distribution, scanning electronmicroscopy tests, mercury intrusion porosimetry, BET specific surface tests, determination of hydrophobicity). After the tests of fillers, asphalt mastics were prepared and rheological examinations were obtained. These examinations served to observe the interaction and the effect of fillers. The stiffening effect of fillers and the causes of rutting were also investigated. Based on our results, it can be stated that particle size, hydrophobic properties and the amount of fillers highly affect the rheological properties of mastics.

Viscoelastic Analysis of Asphalt Mastic Based on Micromechanics

In this study, the stiffening effect of fillers on asphalt binders was characterized through micromechanics and rheology methods. The dynamic shear rheometer (DSR) was used to measure viscoelastic properties of asphalt mastic. Mechanical volume filling effects and additional interacting mechanisms within mastic systems are discussed on the basis of micromechanics-rheology model to predict the complex shear modulus of asphalt mastic from the measured mastic data. It is observed that the phase angle ranges from 88.8o to 89.0o, does not significantly change due to limestone fillers addition. The analytical model prediction of complex shear modulus based on the dynamic shear modulus can be used. Using the nonlinear regression, the Einstein coefficient KE is 4.22, 5.09 and 7.44 for asphalt mixed with limestone, cement and hydrated lime, respectively. Beside, the SEM results explain why the mastic system with hydrated lime shows the highest KE. The behavior of hydrated lime fillers filled mastics is probably due to physico–chemical interaction, which can be validated by further research.

Modelling of Asphalt Mastic in Terms of Filler-Bitumen Interaction

ABSTRACT Many studies have focused on modelling the stiffening effect of mineral filler on asphalt binder. However, the interaction between both constituents was always a challenge to address. Current European as well as North American specifications includes limits on stiffening effects of fillers that are mostly empirically driven and hard to include in a mixture design process. This study offers a model that allows estimation of stiffening effects based on primary binder and filler properties. This study builds on a conceptual model provided in an earlier publication for understanding the mechanism by which the filler stiffens the asphalt mastic. The model hypothesizes that change of mastic complex modulus with filler content follows two phases; a diluted phase and a concentrated phase. In the diluted phase, the stiffening effect of the filler on the binder follows a linear filling trend where interaction between filler and binder is minimal. On the other hand the effect of the filler departs from the linear trend once its concentration enters the concentrated phase. The deviation from the linear trend indicates the start of the significant interaction between the filler particles and the asphalt binder. In this study a model is proposed for the effect of mineral filler on asphalt binder complex modulus at given temperature and frequency. The model is defined using three main parameters, (a) Initial Stiffening Rate, (b) Terminal stiffening rate, and (c) Critical filler concentration. The results presented in this study provide measurable filler and binder properties that can be used to estimate these three parameters, which are indicators of the mineral filler interaction with asphalt binder. The model provides an effective tool to determine the role of basic filler and binder physical and chemical properties on the overall complex modulus of the mastic.