## 3 Results and Discussion
### Matrix
Alkali-activated materials are usually characterized by significantly higher drying shrinkage and moisture loss than traditional OPC, up to six time higher which can result in cracking and loss of durability and serviceability in restrained elements [41]. The type of reactive powders and the type and content of alkaline activators play a pivotal role in determining the extent of the shrinkage [42]. To mitigate the free shrinkage, 2 wt% of CaO on reactive powders was added as additive in mortar mix design. Its reaction to give calcium hydroxide with a volume increase of around 90% provides an expansive strain that partially compensates the shrinkage of the alkali-activated mortars. To highlight and discuss the modifications induced by CaO on the free shrinkage and mass loss behavior of the matrix, a mortar with the same composition without CaO has been used as reference (identified as S2 KS7F2A1). As can be observed from Figure 9, the use of CaO lowers the overall free shrinkage from 2800 \(\mu\varepsilon\) to \(\approx\)1800 \(\mu\varepsilon\), with a reduction of about 35%. Figure 8: Capillary absorption vs. time. Figure 7: Flexural and compressive strength vs. curing days. CaO is effective in compensating shrinkage at early age and determines a variation of the shrinkage without modifying the moisture loss with time, as Figure 10 clearly shows. Furthermore, it can be observed in Figure 11 that CaO causes a change in the slope of the shrinkage-mass loss curve. Reference mortar is characterized by a viscous response, with an early significant shrinkage with low moisture loss. This behavior is often observed for AAM and can ascribed to the structural incorporation of alkali cations in C-A-S-H that determines a reduction in the stacking regularity of C-A-S-H layers and is responsible of their easier tendency to collapse and redistribute upon drying [43]. The reference matrix shrinkage-mass loss curve can be described in terms of two linear steps, as reported in Figure 11.  
Figure 10: Mortars’ weight loss vs. curing days. Figure 6.0 Mortars’ drying shrinkage vs. curing days. When CaO is added, the viscous response is reduced and only one linear trend between drying shrinkage and moisture loss is observed. Analogue behavior is experienced for OPC mortars [43]. Interestingly, the second linear step of the reference mortar linear and mortar admixed with CaO show similar slopes. In Table 3 the capillary water absorption, compressive strength and drying shrinkage of the alkali-activated mortar used in the present investigation are compared with the values of different available commercial mortars (a natural hydraulic lime and a cementitious mortar), obtained from their technical data sheets. As can be observed in Table 3, the measured capillary absorption value of the alkali-activated mortar falls within the range of values that occurs in commercial matrices. In particular, capillary  
Figure 6.1 Mortars’ drying shrinkage vs. weight loss. \begin{table}
\begin{tabular}{p{113.8 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline
**Matrix Type** & \begin{tabular}{c} **Capillary** \\ **Absorption** \\ **(EN 1015-18)** \\ **(kg/m\({}^{2}\).min\({}^{0.5}\))** \\ \end{tabular}  & \begin{tabular}{c} **Compressive** \\ **Strength (EN 1015-11)** \\ **(MPa)** \\ \end{tabular}  & \begin{tabular}{c} **Shrinkage** \\ **(EN 12617-4)** \\ **(\%)** \\ \end{tabular}  & \ \begin{tabular}{c} **Flexural** \\ **Strength** \\ **(EN 1015-11)** \\ **(MPa)** \\ \end{tabular}  & \begin{tabular}{c} **Tensile** \\ **Strength** \\ **(MPa)** \\ \end{tabular}  \\ \hline \multicolumn{5}{p{113.8 pt}}{Alkali-activated binder.} \\ Maximum dimension of aggregate: 1 mm. (present paper) & \(\approx\)0.27  & \(\approx\)33  & \(\approx\)0.18  & \(\approx\)5.5  & \(\approx\)2.4 [FOOTNOTE:5]Footnote 5: 5 absorption is comparable to the value reported for the Mineral-Natural Hydraulic Lime (NHL) mortar, which is the one provided by the manufacturer, to be coupled with the basalt textile used in the present investigation.