## 4 Experimental Results
\begin{table}
\begin{tabular}{l c c c c c c c c c c c c c} \hline \hline  & & & & & & & & & & & & & & & & & \\ \hline T [\({}^{\circ}\)C] & 50 & 50 & 50 & 60 & 60 & 60 & 70 & 70 & 70 & 80 & 80 & 80 \\ \(\tau\) [MPa] & 0.1 & 3.2 & 10 & 0.1 & 3.2 & 10 & 0.1 & 3.2 & 10 & 0.1 & 3.2 & 10 \\ \(\alpha\) [-] & 0.498 & 0.471 & - & 0.387 & 0.0001 & - & 0.984 & 0.945 & - & 0.999 & n.a. * & - \\ b\({}_{1}\) [1] & 215.2 & 271.2 & - & 104.8 & 0.0006 & - & 3.145 & 343.1 & - & 0.062 & n.a. * & - \\ b\({}_{2}\) [-] & 5.056 & 4.688 & - & 0.748 & 0.666 & - & 0.187 & 0.154 & - & 0.205 & n.a. * & - \\ SSE R\({}^{2}\) & 0.999 & 0.998 & - & 0.994 & 0.977 & - & 0.990 & 0.826 & - & 0.986 & n.a. * & - \\ \hline \multicolumn{10}{c}{**MAS-L**} \\ \hline T [\({}^{\circ}\)C] & 50 & 50 & 50 & 60 & 60 & 60 & 70 & 70 & 70 & 80 & 80 & 80 \\ \(\tau\) [MPa] & 0.1 & 3.2 & 10 & 0.1 & 3.2 & 10 & 0.1 & 3.2 & 10 & 0.1 & 3.2 & 10 \\ \(\alpha\) [-] & 0.784 & 0.536 & 0.414 & 0.668 & 0.203 & 0.188 & 0.951 & 0.617 & 0.0001 & 0.991 & 0.990 & n.a. * \\ b\({}_{1}\) [1] & 460.1 & 1398 & 2468 & 31.18 & 1026 & 2691 & 38.85 & 1252 & 0.048 & 4.941 & 70.25 & n.a. * \\ b\({}_{2}\) [-] & 26.68 & 24.73 & 15.96 & 3.768 & 3.748 & 2.285 & 1.005 & 0.9043 & 0.548 & 0.332 & 0.265 & n.a. * \\ SSE R\({}^{2}  
In general, a progressive increase of \(\alpha\) parameters should be expected when the viscosity started to prevail (e.g., at higher test temperatures). Similarly, at fixed temperature and stress level, stiffer materials should present lower \(\alpha\) values. In reality, such hypothetical behaviors were not clearly observed; in this regard, as reported by other researchers [36], a combined evaluation of all parameters (\(\alpha\), \(b_{1}\), \(b_{2}\)) could explain this experimental finding (elasticity/viscosity predominance is affected by \(\alpha\) but also by \(b_{1}\) and \(b_{2}\)). In particular, the relative contribution given by the springpot to the overall deformation seemed higher than that of the dashpot. Otherwise, it is worth noting that \(b_{1}\) and \(b_{2}\) were sensibly reduced when increasing \(T\), and this indicated the general weakening of material performance (i.e., higher strain accumulation as already observed by lower \(R_{\%}\) and greater \(J_{nr}\)). The stress dependency was then assessed considering the coefficients of each material at fixed temperature: in this case, the decrease of \(\alpha\) and \(b_{2}\), together with the increase of \(b_{1}\), illustrate behaviors reversed towards the spring case. Otherwise, it must be considered that, at high stress levels (at least higher than 0.1 kPa), secondary non-linear effects could influence the global visco-elastic response of materials [38]. Comparing _MOR-S_ with _MOR-L_ (reference), the inclusion of harder steel slag mainly influenced \(b_{1}\) parameter related to stiffness. Given the mathematical complexity of the proposed model, a further analysis of MSCR experimental data was performed with the objective of describing the creep-recovery phase. To this aim, two physical parameters were considered, studying the evolutive behavior of the strain during each test cycle. For the initial creep phases (1 s duration), quasi-linear time-strain relationships were identified. Therefore, for a given material, temperature, and stress, a unique average creep-slope (\(s\)) was calculated as the average of the creep slopes of each of the ten cycles. Similarly, a univocal parameter was calculated averaging the ten recovery phases (9 s duration): this was referred to as the delay (\(d\)) related to the time needed to develop an established amount of deformation within the cycle. Parameter \(d\) was thus identified as time passing from the load removal (1 s) to the beginning of a linear time-strain relationship (Figure 7). This linear recovery phase was determined by checking the gradient of punctual creep slopes below a fixed tolerance value of 0.0005 %/s.