No abstract

Asphalt mix durability is one of the most important aspects if looking on longer lifetime of pavement structures. It is influenced by several factors whereas one of the most important is moisture susceptibility and the quality of adhesion between bitumen binder and aggregateparticles. If the coating by the bitumen is not fully provided or is affected by strongly hydrophilic aggregate type which easier creates bonds with more polar water then it is immediately attacking the aggregate surface and leads to stripping effects – ongoing loss of bitumen-aggregate bonds, mix cohesion problems, etc. With respect to improve adhesion quality different additives (surfactants) are used, whereas two factors might be critical for them: 1) thermal stability of the additive used in bitumen stored for several days at elevated temperatures; 2) bitumen ageing and the effect on additive activity. Both aspects have been studied as a key objective of an ongoing research looking fora suitable laboratory procedure for simulating the thermal stability and assess the remaining activity of the additive. Further asphalt ageing impact on moisture susceptibility is evaluated by changed ratios of indirect tensile strength values for unaged and differently aged test specimens. Results for one type of mix and different aggregates with application of straight-run bitumen 50/70 and 4 different types of adhesion promoters are summarized in the paper.

Durability of pavement structures represents one of the most important aspects increasingly followed during last years. There are many reasons for this focus, most important are related to public budget constraints and the necessity to develop or rehabilitate road infrastructure. Since many years there has been a stress on using locally available resources which is for asphalt related mainly to the aggregates. On the other hand bitumen comes from a nonrenewable resource which is used to cover many demands of the world's society. To keep it simple, remaining byproduct is then classified as bitumen what has of course impact on its qualities as well. In case of asphalt pavements durability is related to water and frost resistance of the mix. The water can cause problems if adsorbed by the aggregates. This happens if hydrophilic aggregates are used and the coating by bitumen is not good. For these reasons different additives are used to improve coating and turn the hydrophilic state to a hydrophobic one. Plenty of solutions are available on the market sometimes making the decision for not easy to make a right choice. Since decades test methods have been developed to study durability aspects, adhesion or water susceptibility. In many countries like the Czech Republic simple methods are still used, often based only on observer's visual opinion and especially often qualifying only the status of a doped bitumen/mix when being produced. This is valid for all test methods defined in EN 12697-11 and similarly also in the national test method used in the Czech Republic. Based on this fact a research project was launched to ideally define a suitable test procedure for evaluating thermal stability and long-term activity of adhesion promoters if used in the bitumen and applied in a mix. This paper is describing how the test method was selected and evaluated, what are the principles the method is based on, if applicable only to the bitumen-aggregate coating quality or analyzing the water/water-frost impacts more. Results are given for the tests done and for assessment of different adhesion promoters. Test protocol is proposed at the end defining necessary conditions.