# Effect of Characteristics of Different Types of Bauxite Clinker on Adhesion
## 3 Results and Discussion
### Aggregate-Bitumen Adhesion
#### 3.2.2 Surface Free Energy Theory  
The work of adhesion represents the energy required for an object to generate a new surface per unit area, and is evaluated by surface energy parameters [32]. In terms of asphalt and aggregate adhesion, two aspects of energy need to be considered: one is to overcome the adhesion of asphalt to itself, and the other is to overcome the adhesion between asphalt and aggregate interface. The adhesion between aggregate and asphalt was evaluated by the magnitude of work done in these two aspects. Table 9 shows the surface energy parameters of 60/80 pen asphalt and 30/60 pen asphalt. Higher values of \(ER_{1}\) and \(ER_{2}\) indicate that a sample has a better water stability. Table 11 shows that, for 60/80 pen asphalt, the order of \(ER_{1}\) and \(ER_{2}\) was: D \(>\) B \(>\) E \(>\) F \(>\) A \(>\) C. For 30/60 pen asphalt, the order was: B \(>\) E \(>\) F \(>\) C \(>\) A \(>\) D. The work of adhesion for 60/80 pen asphalt was: D \(>\) E \(>\) B \(>\) F \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Type** & \(r_{\text{S}}\) & \(r_{\text{S}}^{\text{LW}}\) & \(r_{\text{S}}^{\text{AB}}\) & \(r_{\text{S}}^{\text{+}}\) & \(r_{\text{s}}^{\text{-}}\) \\ \hline F & 25.73 & 14.66 & 11.07 & 0.685 & 44.76 \\ E & 31.98 & 18.20 & 13.78 & 1.048 & 45.30 \\ D & 16.42 & 12.36 & 4.058 & 0.035 & 117.6 \\ C & 23.83 & 14.61 & 9.224 & 0.734 & 28.98 \\ B & 24.28 & 14.72 & 9.562 & 0.349 & 65.50 \\ A & 25.48 & 14.92 & 10.56 & 0.707 & 39.41 \\ \hline \hline \end{tabular} \({}^{*}\) The six types of calcined bauxite are labeled A–F, with increasing Al\({}_{2}\)O\({}_{3}\) content.  
\end{table} 
Table 10: Surface energy parameters of aggregates. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Parameter Type of Asphal** & **F** & **E** & **D** & **C** & **B** & **A** \\ \hline Adsorption (mg/g) & 60/80 pen asphalt & 0.0077 & 0.0054 & 0.0077 & 0.0073 & 0.0065 & 0.0072 \\ Net adsorption (mg/g) & 60/80 pen asphalt & 0.0062 & 0.0040 & 0.0068 & 0.0050 & 0.0056 & 0.0056 \\ Stripping ratio (\%) & 60/80 pen asphalt & 20.18 & 25.93 & 12.29 & 31.13 & 14.41 & 21.78 \\ \hline \hline \end{tabular} \({}^{*}\) The six types of calcined bauxite are labeled A–F, with increasing Al\({}_{2}\)O\({}_{3}\) content.  
\end{table} 
Table 7: Asphal stripping rate. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Stripping Ratio (\%)** & **Adhesion Grade** & \multicolumn{3}{c}{**Description of Stripping**} \\ \hline \(\leq\)5 & 5 & Asphal membrane is in good condition and extremely little & \\  & & & stripping exists at the edge. & \\  & & & Asphal membrane is in good condition, and little stripping & \\
5–20 & 4 & Asphal membrane is in good condition, and little stripping & \\  & & & exists at the mineral aggregate surface. & \\
20–35 & 3 & Asphal membrane is partially stripped, and up to 20\% to 35\% & \\  & & & of the area in the mineral aggregate is exposed. & \\
35–60 & 2 & Large area of stripping in the asphalt membrane, and the & \\  & & & exposed area is 35\% to 60\% in the mineral aggregate. & \\ \(>\)60 & 1 & Most asphalt membrane is stripped, and the exposed area is & \\  & & & more than 60\% in the mineral aggregate. & \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Asphal adhesion grading index. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Type of Asphalt** & \(r_{a}\) & \(r_{a}^{LW}\) & \(r_{a}^{AB}\) & \(r_{a}^{\text{+}}\) & \(r_{a}^{\text{-}}\) \\ \hline
60/80 pen asphalt & 15.72 & 12.23 & 3.49 & 1.22 & 2.50 \\
30/60 pen asphalt & 22.11 & 17.78 & 4.33 & 0.83 & 5.64 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Surface energy parameters of asphalt. A \(>\) C. For 30/60 pen asphalt, is was: E \(>\) D \(>\) B \(>\) F \(>\) A \(>\) C. The stripping work for 60/80 pen asphalt followed the order: C \(>\) A \(>\) F \(>\) E \(>\) D \(>\) B. For 30/60 pen asphalt, it was D \(>\) C \(>\) A \(>\) F \(>\) E \(>\) B.