## 3 Use of SMA-MA Mixture--Case Study
### SMA-MA Protective Layer  
The protective layer was made of SMA-MA 8 mixture. The binder for the protective layer made of SMA-MA 8 mixture was chosen based on the properties of the bitumen and the mixture in which it was used, including low-temperature performance in particular. Three bitumens were considered: 50/70 paving grade bitumen and two medium modified bitumens, i.e.,: PMB 45/80-65 and PMB 65/105-60. The tested parameters of the bitumens included softening point, penetration at 5 \({}^{\circ}\)C and 25 \({}^{\circ}\)C, critical temperatures and stiffness modulus obtained from the BBR (Bending Beam Rheometer) test and elastic recovery. The low-temperature properties in the BBR test were determined on specimens aged according to Rolling Thin Film Oven Test (RTFOT) (EN 1267-1) and Pressure Aging Vessel (PAV) (EN 14769) at the following temperatures: \(-10\), \(-16\), \(-22\) and \(-28\)\({}^{\circ}\)C. The samples were subjected to a constant, controlled temperature for 60 min. and the values were read after 60 sec. of load application. The following parameters were determined in the tests:  
* Critical temperature (\(T(S)_{60}\)) at 300 MPa creep stiffness;
* Critical temperature at the value of m (\(T(m)_{60}\)) equal to 0.3;
* Stiffness of bitumen at the temperature of \(-16\)\({}^{\circ}\)C (\(S(T)_{-16}\)). The obtained properties of bitumens are compiled in Table 1.  
The Penetration index _lp_ was calculated from Equation (1), on the basis of the penetration values at 5 \({}^{\circ}\)C and 25 \({}^{\circ}\)C.  
\[I_{p}=\frac{20-500A}{1+50A} \tag{1}\]  
\[A=\frac{LogP(25^{\circ}C)-LogP(5^{\circ}C)}{20} \tag{2}\]  
Figure 13: Methyl methacrylate waterproofing layer on the Trasa Zamkowa bridge and SMA-MA 8 layer. The results from the tests of bituminous binders show that polymer-modified bitumens will be more appropriate for the production of SMA-MA mixtures. Based on the values of low-temperature stiffness S(T)-16, cracking resistance T(S)60 and stress relaxation ability T(m)60 polymer-modified bitumen PMB 65/105-60 was chosen. The elastic properties of both these modified bitumens and their rheological type are at a similar level. The parameters of 50/70 unmodified bitumen are worse, in particular in terms of low-temperature cracking. In the case of SMA-MA the choice of bitumen was also connected with the cracking resistance determined with the Thermal Stress Restrained Specim Test (TSRST) according to EN 12697-46 [51]. The equivalent failure temperatures of the tested mixtures are compiled in Table 2.  
PMB 65/105-60 (according to [52]) was the binder finally chosen for the production of the SMA-MA mixture, added at a rate of 9.1% (m/m). The gradation curve of aggregate in SMA-MA 8 mixture is displayed in Figure 14 below. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{1}{c}{**Type of Test**} & \multicolumn{1}{c}{**Standard**} & \multicolumn{3}{c}{**Result**} \\ \cline{3-5}  & & **50/70** & **PMB 45/80-65** & **PMB 65/105-60** \\ \hline Penetration (P) (100 g, 5 s) & 25 \({}^{\circ}\)C & EN 1426:2015-08 [46] & 62.1 & 63.2 & 74.0 \\ (\(\times\) 0.1 mm) & 5 \({}^{\circ}\)C & 10.5 & 11.5 & 14.3 \\ \hline Softening point (T\({}_{\text{RgB}}\)) (5 \({}^{\circ}\)C/min) [\({}^{\circ}\)C] & EN 1427:2015-08 [47] & 50.2 & 75.6 & 70.8 \\ \hline BBR bending beam test (\(-\)10, \(-\)16, \(-\)22, \(-\)28 \({}^{\circ}\)C) & T(S)\({}_{\text{60}}\) [\({}^{\circ}\)C] & \multirow{2}{*}{EN 14,771 [48]} & \(-\)16.6 & \(-\)18.6 & \(-\)20.8 \\ \cline{3-5}  & T(m)\({}_{\text{60}}\) [\({}^{\circ}\)C] & & \(-\)15.7 & \(-\)15.1 & \(-\)21.1 \\ \cline{3-5}  & S(T)\({}_{\text{16}}\) [MPa] & \multirow{2}{*}{EN 13,398 [49]} & 302 & 241 & 181 \\ \cline{3-5}  & & EN 13,398 [49] & 13 & 93 & 92 \\ \hline Penetration index (I\({}_{\text{P}}\)) [\(-\)] & EN 12591:2010 (Annex \(\quad\)A) [50] & 0.24 & 0.53 & 0.77 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Properties of 50/70 paving grade bitumen and two modified bitumens: PMB 45/80-65 and PMB 65/105-60.