# Practical Application of Sustainable Road Structure: Mechanical and Environmental Approach
## 3 Materials, Testing Methods and Trial Sections  
### Materials Characteristics  
Considering the structure of an eco-friendly flexible pavement, three different materials and technology solutions were investigated for each layer. For the surface course, an asphalt mixture containing an alternative binder was examined. Lignin, as an energy production waste by-product, was used to partially replace crude-derived bitumen and polymers (due to intellectual property right (IPR) protection details regarding physical and chemical properties cannot be presented). For the binder and base courses, higher (30%) than the typical maximum observed in Polish road practice (20%, based on the internal project survey with construction companies) amount of reclaimed asphalt pavement (RAP) was applied for the production of new asphalt mixtures in regular asphalt mix plants. A typical asphalt plant without an extra RAP heating, such as double barrel system, was used. The entire production process was conducted without the need for major capital expenditure thanks to the use of a BIO-additive as an aid in the homogenization of the mixture. RAP was considered as a \"black rock\" in the asphalt mixture. Only surface activation by the incorporation of the BIO-additive without deep rejuvenation effect was assumed. The lower sub-base layer was composed of recycled aggregates derived from construction and demolition waste (CDW). Considering the equivalent compaction and load capacity of the CDW sub-base layer in relation to the reference solution (limestone subbase), CDW as the material was not mechanically tested in this study, but elastic modulus of its layer was calculated on the basis of FWD tests, as presented later in the paper.  
The main parts of the asphalt pavement structure are binder and base layers. The composition and properties of these layers are shown in Table 1.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Properties**} & \multicolumn{4}{c}{**Base Course AC 22**} & \multicolumn{4}{c}{**Binder Course AC 22**} \\ \cline{2-7}  & **Reference** & **Standard** & **APSE Experimental** & **Reference** & **Standard** & **APSE Experimental** \\  & **Mixture** & **Section** & **Section** & **Mixture** & **Section** & **Section** \\ \hline RAP content, & & & & & & \\ \% & & & & & & \\ \hline Bittumen type & 35/50 & 35/50 & \
\begin{tabular}{c} 35/50 \\ +2.5\% BIO \\ \end{tabular} & 35/50 & 35/50 &
\begin{tabular}{c} 35/50 \\ +2.5\% BIO \\ \end{tabular} \\ \hline Extracted binder, \% & 3.9 & 3.6 & 3.6 & 4.2 & 3.9 & 4.2 \\ \hline Bulk density, \(\rho_{\text{b}}\) (Mg/m\({}^{3}\)) & 2.478 & 2.473 & 2.478 & 2.472 & 2.458 & 2.490 \\ \hline Maximum density, \(\rho_{\text{m}}\) (Mg/m\({}^{3}\)) & 2.591 & 2.612 & 2.604 & 2.612 & 2.613 & 2.619 \\ \hline Air voids, V\({}_{\text{m}}\) (\%) & 4.4 & 5.3 & 4.8 & 4.8 & 5.9 & 4.9 \\ \hline Core air voids, \% & — & 5.0 & 4.5 & — & 5.5 & 5.0 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Composition and properties of base and binder courses layers.  
In relation to the BIO-additive, dual-function agent was used in accordance with the technology described in previous works [14; 15]. In this technology, it is assumed that in the first process stage liquefied bitumen with BIO origin additive occurs, which helps in homogenizing RAP in the asphalt mixture. When RAP is directly incorporated to the mixer, BIO-additive provides mixing and homogenizing support. In order to not reduce the binder's stiffness too much, in BIO-additive there are oxy-polymerization reactions that rebuild and restore bitumen stiffness over time. An oxy-polymerization reaction occurs in the binder as a result of the action of siccative that activates the polymerisation process [16; 17]. The reaction is time-limited and does not over stiffen the binder. The point is that, in mixtures where RAP bitumen is not activated or is only surface-activated to a small extent, this additive only supports the production process and does not long-term change the properties of the material.