Samenvatting

The overriding purpose of the thesis research is to develop new design concepts for improved and sustainable asphalt mixes. To accomplish this goal, it became necessary to reach some prerequisite goals. Determining what a sustainable asphalt means, and how that ideal is connected with the field of asphalt mix production assumed a high degree of importance during the literature review conducted for this thesis. Related to that effort, it became necessary to reach an understanding about the main challenge posed in the road construction sector and how solution could be proffered. Thence, to proffer solution to this main challenge, a central question was proposed i.e. "How can an improved/high performance and eco-friendly asphalt mix be produced considering, sustainability and durability”?. This central question was split into sub questions, which provided working steps or method to the production of sustainable asphalt mixes. Once these fundamental steps were outlined, the research was able to commence.
To aid the production of sustainable mixes, five mix variants were developed to compare the relative characteristics of the mixes. The new asphalt mixes consisted of 80% “RAP” and 20% virgin materials according to the client specifications. To enable the production of mixes with 80% RAP, rejuvenators were introduced due to their ability to restore the properties of the aged bitumen present in the “RAP”. The method involved the production and testing procedure of 5 new asphalt mixes i.e. 1 Reference mix and 4 other mixes containing rejuvenators in accordance to the Standard NEN norm.
The choice of the most suitable mix was dependent on three main factors namely ; the Type Test result, sustainability (Eco Chain) and cost of the mix. The Type test result considered the relative characteristics of the asphalt mixes in regards to stiffness, fatigue and permanent deformation, while the mix sustainability was analyzed using EcoChain software considering the Life Cycle Analysis (LCA) data of materials and products used in the mix production. More so, the cost analysis of the 5 variants of the asphalt mixes were compared to determine the mix with the least cost in terms of production in the asphalt plant. With the results obtained from these factors, a Multi Criteria Analysis (MCA) was set up to make a conclusion on the most sustainable mix. In addition, it was realized that the ability to produce asphalt mixes with high “RAP” percentage is possible (80%) but there are technical challenges involved, which is as a result of the inability of the mineral aggregates in the mix to properly bind together. More so, producing a mix with 80% “RAP” in the asphalt plant is challenging because the capacity of production in tons/hour decreases as a result of heating and drying of a high “RAP” percentage, thence taking more time in the current facilities.
Furthermore, it was concluded that the undesired test results, was obtained because the bitumen content (%) derived from the “RAP” at the beginning of the research was incorrect. This is due to the fact that, the obtained bitumen content (%) at the beginning of the research was higher than the amount obtained at the end of the research, which was as a result of variation in the “RAP”. Conclusively, it was recommended that the “RAP” to be used in the production of the new mixes should be more consistent and under control in order to have more homogeneity in the asphalt mixes and also to avoid obtaining distinctive bitumen content. More so, it was concluded that to obtain better test results, more bitumen properties need to be known, which implies that only the R & B and Penetration Test is insufficient to determine the accurate bitumen content (%) in the “RAP”. Thence, an advanced DSR (Dynamic Shear Rheometer) test should be introduced to determine the additional properties of the aged bitumen from the “RAP”. This is because when considering the black rock behavior of aged bitumen, the AC “RAP” with highly aged bitumen acts like a rock and it is uncertain if the aged and virgin bitumen mix properly.