The role of Sulphur Polymer and Crumb Rubber additives in resistance against stripping of asphalt mixes

Premature failures are experienced in road pavements. Among the various failure modes, moisture damage is probably the most occurring distress in asphalt pavements. In fact, the continuous presence of water in asphalt layers weakens the bond between aggregate particles and bitumen, ending to stripping of mixes. With this regard, several parameters affect water damages to asphalt layers. Among these, aggregates type and source, bitumen type and grade, mixture design, construction practice, traffic volume, environment and the additive properties could be named as the most affecting parameters. In order to prevent stripping, one of the most effective methods is to use anti-stripping additives. Among the various additives, sulphur which is a byproduct of petroleum gas production industries, has been known to increase stiffness of bituminous mixes appreciably, provided that it is added properly and at right amounts. However, due to environmental drawbacks of this additive (i.e. emission of disturbing gases) and the too much stiffening effects that imparts to mixes, sulphur alone was banned to be used in road pavements for several decades. In the recent years, combined additives, consisting of sulphur and polymers have been produced and applied into asphalt mixes. These additives have shown to have less adverse environmental effects (i.e. reduced emission of gases such as ). The effects of these additive types is so that their sulphur component provides stiffness to mixes and their polymer portion imparts some flexibility to mixes and increase the adhesion properties of the mix binders. “ASTM D8” Standard Testing Method. In this research a locally produced sulphur polymer additive, named ‘Googas’, was used and applied in a continuously graded asphalt mix. This new product had lower emissions of gas, compared with the conventional sulphur mixes. In addition, it provided enhanced properties to mixes, compared with previously made sulphur alone containing mixes. In order to reduce the stiffness of mixes and provide these with more flexibility, CRM (Crumb Rubber Modifier) modified binders were used as the replacement of conventional penetration grade binder of mixes. CRM binders were prepared containing different amounts of crumb rubber. The preparation was carried out in the laboratory using a high shear rate mixer upon following The results showed that increased amounts of Googas sulphur polymer although resulted in increased compression strength, reduced the moisture resistance of mixes substantially. In fact, it was seen that when asphalt mixes were cooled to ambient temperatures, the sulphur tended to change from liquid into solid state, contributing little to bitumen adhesiveness. In contrast, mixes containing CRM binders alone, showed increased tensile properties, as indicated by increased ITS testing results. With analyzing the laboratory results, optimum amounts of the above two additives were determined. In fact, increased amounts of CRM resulted in increased tensile resistance of mixes (i.e. showing a gradual increasing trend). This was up to CRM’s of 18% to 20%. Further increases resulted in lower tensile strengths. Hence, optimized mixes were designed containing both CRM and sulphur polymer additives.