## 2 Materials and Methods  
Four different categories of materials used for repairing airport pavements have been examined in the study: bituminous emulsions, quick-hardening cement mortars, ordinary cement concretes, cold bituminous conglomerates, and an expanding resin (Table 1). Two bituminous emulsions have been tested:  
* E1 is an over-stabilized cationic emulsion composed of 60% styrene-butadiene-styrene (SBS)-modified bitumen. Table 2 lists technical characteristics of bitumen extracted from the emulsion. Its correct temperature use ranges from 5 and 80 \({}^{\circ}\)C; moreover, it contains structural regenerative additives, therefore it is suitable for cold state repairs. * E2 is a bicomponent modified, workable cold bitumen: it is useful for pavement maintenance when temperature ranges between 10 and 30 \({}^{\circ}\)C. Its maturity time is not more than 45 min after mixing the two components. Five quick-hardening cement mortars (see Table 1) have been tested:
* the first and second cement mortars are composed of a Portland cement respectively 32.5 (M1) and 42.5 (M2) compliant with the standard EN 197-1 [22]. Mortars have been mixed with a water/powder (w/p) ratio equal to 0.45;
* the third cement mortar (M3) is a one-component fast setting and hardening cement with silica fume mortar [23; 24; 25]. It is fibre reinforced, suitable for smoothing, filling, and repairing concrete surfaces. Its correct w/p ratio is 0.13. Its elastic modulus evaluated according to the standard EN 13412 [26] is 32.6 GPa. * the fourth cement mortar (M4) is a one-component fast setting and hardening cement mortar with graded aggregates. It is suitable for smoothing, filling, and repairing concrete surfaces; for thickness over 5 cm it is suitable for casting with 6/10 aggregates without segregation. Its correct w/p ratio is 0.125. Its elastic modulus evaluated according to the standard EN 13412 [26] is 32.6 GPa. \begin{table}
\begin{tabular}{c c} \hline \hline
**Category** & **Notation** \\ \hline \hline Bituminous emulsions & E1 \\  & E2 \\ \hline \hline \multirow{2}{*}{Cement mortars} & M1 \\  & M2 \\  & M3 \\ \hline \hline \multirow{2}{*}{Cement concretes} & M4 \\  & M5 \\ \hline \hline \multirow{2}{*}{Cold bituminous mixes} & B1 \\  & B2 \\  & B3 \\  & B4 \\ \hline \hline Expanding resin & R \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Materials examined in the study. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Characteristic** & **Value** & **Unit of Measure** \\ \hline \hline Penetration at 25 \({}^{\circ}\)C & 55 & dmm \\ Softening point & 62 & \({}^{\circ}\)C \\ [PERSON] breaking point & \(-\)16 & \({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Technical characteristics of bitumen extracted from the emulsion E1. * the fifth cement mortar (M5) is a thixotropic, non-shrink, fibre reinforced, fast setting and hardening hydraulic mortar with graded aggregates. It is suitable for filling and repairing concrete surfaces. Its correct w/p ratio is 0.22. Its elastic modulus evaluated according to the standard EN 13412 [26] is 22 GPa. Figure 4 compares the granulometry curves of M3 and M5. The cement mortars M3 and M5 have similar granulometric curve: both have over 33% percentage passing at 63 \(\upmu\)m, and over 98% percentage passing at 4 mm. Nevertheless, M5 has more fine content than M3, while it has less fine sand than M3: these differences explain the different w/p ratios above listed. Figure 5 compares the compressive strength of cement mortars M3, M4 and M5 whose time, temperature, and procedures for laying are compliant with those adopted for ordinary cement concrete. Compressive strength has been evaluated after maturity at 20 \({}^{\circ}\)C according to the standards: EN 12190 [27] for M3 and M4, and UNI EN 1015-11 for M5 [28]. Figure 4: Granulometry curve of M3 and M5. Figure 5: Compressive strength evolution of M3, M4 and M5. Figure 6 compares the flexural strength of cement mortars M3, M4 and M5.