Study On The Influence Of Emulsification On The Properties Of SBS Modified Asphalts

In this work, the styrene-butadiene-styrene (SBS) modified asphalt emulsions wereprepared as SBS was pre-blended chemically with the asphalt prior to emulsification. On thebasis of base asphalt, emulsifier type and modifier type, the influences of emulsification onthe high-, low-temperature performance and temperature sensitivity, elastic recovery ability,thermal stability, micromorphology and microstructure of SBS modified asphalts were studied,by means of physical tests such as penetration, softening point, ductility at5℃, penetrationindex, elastic recovery, as well as fluorescence microscopy, differential scanning calorimetry(DSC) and fourier transform infrared (FT-IR) spectroscopy.By optimization of the technological conditions, the preferable process conditions andformula of SBS chemically modified asphalts were found. The sample was sheared for60minat a shearing rate of3000rpm and then it was put into the oven for complete swelling whenthe modifier and stabilizer contents are3%and0.265%respectively. In that case, thedispersion of SBS particles in Zhonghaiyou, Liaohe, Caltex and Qilu asphalts is quitedifferent, and most uniform dispersion can be observed in Caltex asphalt, which is morepreferable for emulsification. Under the favorable emulsification conditions, the modifiedasphalts were heated to160～170℃and the emulsifier solutions were heated to55℃.The physical properties of modified asphalts became inferior during emulsification, butthe microstructure is unchanged. The modified asphalt emulsions were prepared as fourmodified asphalts (prepared by the same modifier and different asphalts) emulsified by thesame emulsifier under the preferable process conditions. Compared to modified asphalt, itdisplays a decline in softening point, ductility at5℃, elastic recovery ability and storagestability for its corresponding emulsion residue. Changes for above mentioned properties arisefrom the aggregation of SBS particles that do not react with asphalt. Evidence about yellowgreen particles which mean size is far more than that of SBS particles in modified asphaltscan be verified on fluorescence microscope images. The DSC results indicate the totalabsorbed heat of modified asphalts increases slightly during emulsification, suggesting aslight decrease in thermal stability. However, FT-IR results suggest the cross-linking structurebetween asphalt and SBS molecules remains unchanged during emulsification, namely the microstructure of modified asphalt is invariable.Different emulsifiers have distinct effect on the modified asphalt. The modified asphaltemulsions were prepared as the same modified asphalt emulsified by three emulsifiers underthe preferable process conditions. It is found that amide and imidazoline emulsifiers (MA-1Mand RAI-44) played an agglomerative roll between asphalt molecules, which makes themodified asphalt physical properties improved substantially and the microstructure ofmodified asphalt remains unchanged. On the other hand, the emulsifier that mainly containsquaternary ammonium salts (JFQ-2) exerts an inhibiting action between the asphalt molecules,which results in a great decline in the physical properties of modified asphalt and even causesthe cross-linking state between SBS and asphalt molecules broken so that the microstructureof modified asphalt changes.The S/B block ratio and molecular structure of SBS have different effect on the physicalproperties and thermal behavior but no substantial influence on the microstructure of modifiedasphalts during emulsification. The modified asphalt emulsions were prepared as fourmodified asphalts (prepared by the same asphalt and different modifiers) emulsified by thesame emulsifier under the favorable process conditions. The conclusions can be drawnaccording to a series of relative tests. For three linear SBS modifiers with different S/B blockratio, the modified asphalt before and after emulsification displays the optimum physicalproperties and thermal stability when the S/B block ratio is30/70. It results from the SBS isfully swollen in asphalt so that the dispersion of SBS phase in asphalt phase is uniform andthe compact three-dimensional network is formed. On the other hand, for the SBS modifierswith the same S/B block ratio (30/70) and different molecular structure, the asphalt modifiedby the linear SBS before and after emulsification shows more preferable storage stability athigh temperature and compatibility than that modified by star SBS due to more uniformdispersion of linear SBS in asphalt. However, the latter represents better high temperatureproperty, temperature sensitivity and elastic recovery ability, which attribute to thecomplicated three-dimensional and branch structure in star SBS so that the SBS phase isdifficult to apart from asphalt phase after uniformly dispersed. Furthermore, themicrostructure of asphalt modified by the four various modifiers during emulsificationremains unchanged. And the cross-linking reaction is not complete between modifiers and asphalt molecules, revealing the cross-linking percentage between asphalt and modifiermolecules is from12%to27%, which have no harmful impact on the asphalt properties.The modified asphalts properties are extremely different if the modification method isdistinct. The properties of modified asphalt can be improved greatly by chemical modificationand less by physical modification. What’s more, the emulsion particles for the former areuniform, whereas the emulsion particles for the latter are substantially nonuniform with abroad range of particles and the particles tend to aggregate.