Factors influencing asphalt compactibility and its relation to asphalt rutting performance

[摘要] ENGLISH ABSTRACT: This thesis covers the factors affecting compactibility of hot mix asphalt including gradation,filler/binder ratios, binder types, binder content, polymer modification, temperature, volumetricproperties etc. The study is not limited to compactibility as the property measured, but also onthe influence of these factors on the mix's capacity to resist permanent deformation or rutting.An experimental design was used with a variety of the above factors being included.Laboratory analysis of the mixes as well as accelerated pavement testing of different mix typesusing the one-third scale Model Mobile Load Simulator (MMLS3) was carried out. Theanalysis assists in identification of the factors that influence both compactibility and rutresistance, those influencing the one but not the other, and those factors having no significantinfluence. The compactibility of the mixes has been analysed in terms of voids in the mix at aspecific binder content and compaction level. Special consideration was given to thecharacterisation of the filler and filler/binder system of some mixes.It was found that gradation of a mix has a significant influence on compaction and the ruttingperformance. High filler/binder ratios were found to be the critical factors influencing thecompactibility of the wearing course mixes investigated, but based on the limited testsperformed, the reduction of the filler/binder ratios for improved compactibility did notsignificantly increase rutting under accelerated pavement testing.As expected, the binder type has a significant influence on the rutting resistance as well ascompactibility. In addition, an increase in binder content facilitated compaction, but decreasedrutting resistance.Polymer modification considerably improved the rutting resistance of a standard mix under thesame loading conditions. Although some modifiers may improve rutting resistance, it requireshigher compaction temperatures.The addition of the antistripping agent Gripper L decreased the rutting, aggregate stripping andalso the rate of rutting of the Quartzite LAMBS mix that result from the stripping failuremechanism. Low densities can lead to considerable rutting and moisture damage, especiallywhen a moisture susceptible aggregate is used.In terms of compactibility as evaluated with the Superpave Gyratory Compactor, it appears thatthere exists a temperature window in which compaction can be achieved, but in terms ofrutting; even a small deviation in temperature can influence rutting results significantly. Thecontrol of the temperature during testing is critical if meaningful comparisons betweendifferent mixes with regard to rutting performance are to be made.Linear elastic and finite element analysis has been performed to ascertain whether differentspecimen geometries would influence the stress distribution within the specimen, andsubsequently the rutting results. It was found that the geometry of test specimens has aninfluence on the stress distribution within the specimens, which can influence the permanentdeformation results. The briquette specimens tested in the laboratory also yielded higher ruttingresults for the same mix tested in the field. It is therefore important to use specimens that aremost representative of field conditions

[发布机构] Stellenbosch University