A comparison of indices used to evaluate asphalt-filler interactions

Abstract

Based on the physicochemical reactions between asphalt and filler, the structural asphalt film is formed. The interaction can significantly affect the strength of structural asphalt film and the mechanical properties of asphalt mastic. The strength of asphalt-filler interaction is hard to intuitively characterize. Hence, we need the index to evaluate the ability of interaction. To select the optimum evaluation index to characterize filler-asphalt interactions, we compared the rationality and reliability of six interaction indices (Palierne C, complex shear modulus coefficient ΔG*, Einstein coefficient ΚE, complex viscosity coefficient Δη*, Ziegel-B and Luis Ibrarra-A). This comparison was based on the complex modulus, phase angle and viscosity of asphalt mastics manufactured from four asphalt binders and nine mineral fillers comprising different fractions of filler volume. Comparing the sensitivity of the evaluation indices to changes in asphalt performance, filler type, and filler volume fraction, respectively, the complex shear modulus coefficient index (ΔG*), Einstein coefficient (KE) and complex viscosity coefficient (Δη*) of the filler volume fraction is the dominant factor, and as the filler volume fraction increases, the values of the indices increase. This observation of interaction indices growing with filler volume fraction is inconsistent with the physical–chemical interactions between asphalt and filler. Therefore, these indices cannot be applied to evaluate the filler-asphalt physical–chemical interactions. When the filler volume fraction changes from 0.23 to 0.68, the range of Palierne C index values is 0.84 ∼ 1.42. The higher the filler volume fraction, the smaller the Palierne C value. When the filler volume fraction is below 0.53, the Palierne C varies little. This changing rule of Palierne C is consistent with the adsorbed asphalt layer theory. Hence, Palierne C was ultimately selected as the optimum interaction index based on the relationship between adsorbed asphalt layer on mineral filler and filler volume fraction. We applied Palierne C to evaluate the interaction between different asphalts and mineral fillers.We used the Palierne C index to analyze the effects of asphalt, filler type and filler volume fraction on the asphalt-filler interaction. The results showed that SBS modified asphalt had the greatest effect on the filler-asphalt interaction, followed by high viscosity modified asphalt, SK 90 matrix asphalt, and finally, KL70 matrix asphalt. We also found that although the filler-asphalt interaction increases as the proportion of cement and hydrated lime increases, the cement and hydrated lime demonstrated an insignificant effect on the interaction. The effects of the hydrated lime-asphalt interaction were stronger than that of cement. The higher the filler volume fraction, the lower the value of Palierne C.Finally, gray system theory was used to analyze the correlation between the asphalt-filler interaction and the composition of filler and asphalt. The correlation degrees of the Palierne C index with filler composition were MgO > GaO > K2O > Fe2O3 > SiO2 > AL2O3 > P2O5 > MnO > Na2O > Ga(OH)2 > TiO2. Results indicate that the filler composition has a stronger effect on the filler-asphalt interaction than the asphalt composition. This result is consistent with previous research. The filler particles absorb the polar composition of asphalt, and the reactions occur between the filler alkaline group and the asphalt acid group. The results showed that the composition of MgO and GaO fillers most significantly affected the filler-asphalt interaction. And this conclusion further confirms the feasibility of using the Palierne C index to evaluate the filler-asphalt interaction.