## 4 Discussion  
The overall effect of SAPs incorporation in cementitious materials highly depends on the SAPs properties. In this study, in house synthesized SAPs were used with tailored properties [39]. Firstly, different SAP particle sizes introduce different effects. For the same SAP concentration and w/c ratio, the larger the SAP particle size, the lower the determined strength was in means of flexural and compressive strength. This is directly correlated with the formation of larger SAP voids left behind in the cement structure when SAPs release the amount of water they absorbed during mixing [21]. The size of the SAPs used in this work laid in the submicron scale as shown in Figure 1c, whereas the particle sizes of SAPs tested by other researchers were several micrometers [8; 9; 10; 15; 18; 21; 23]. Additionally, SAPs chemical constitution triggers different behaviors in the cementitious matrix. As mentioned earlier, most commercially available SAPs are copolymeric networks based on acrylic acid or acrylamide that may or may not have been partially neutralized [10; 11; 14; 15; 17; 18; 20; 21; 23; 35] which present a low affinity with cement and as a result form large aggregates when incorporated in it. In this work, SAPs that have been tested had a hybrid organic core--inorganic shell structure. The introduction of an inorganic coating on the organic SAP core has been proposed by [PERSON] et al. (2019), via the encapsulation of the polymeric core with an inorganic CaO-SiO\({}_{2}\) shell via solution-gelation technique [31]. Other research groups have investigated the behavior of coated SAPs via the Wurster process but the compensation of the strength reduction achieved was only partial [9]. On the contrary, as indicated by the total porosity reduction and the fact that no mechanical strength degradation was determined with respect to flexural and compressive strength for the mortar/SAPs composite materials, the tailored SAPs in this work presented enhanced chemical affinity with the cementitious matrix. More specifically, due to the enhancement of the chemical affinity between SAPs and cement, large SAP agglomerates were not formed and as a result the size of the SAP voids (porosity) when water was released from their particles were smaller. Additionally, the limited water absorption capacity of the coated SAPs compared to the corresponding capacity of the uncoated particles also favored the size limitation of the SAP voids. The total porosity reduction in both cases of SAPs incorporation in mortars as shown in Table 3 indicates that:  
* SAPs were homogeneously dispersed in mortars due to enhanced chemical affinity with the cementitious matrix and  
Figure 12: Calculated morphometric parameters to evaluate the self-healing process of mortars. Percent object volume (**a**), connectivity density (**b**). The error bars refer to percent error. * SAPs promoted hydration reactions in the cement matrix, thus forming denser and consequently more durable structures, since stress inducing points (voids) in the cement matrix were smaller. This is coherent with the mechanical properties behavior discussed later. The slight flexural strength increment (-3%) of the mortar-SAPs specimens in comparison to the control specimens was evaluated taking into account as corroborating evidence the aforementioned porosity parameters and was attributed to the water absorbed by SAPs during the mixing process, which became available later during cement curing, thus promoting and accelerating hydration reactions. The space surrounding SAP particles was enriched with hydrated cement phases. As a result, mitigation of autogenous shrinkage and early age cracking were observed, while the densification of the cement microstructure led to the enhancement of the mortar/SAPs composites flexural strength [52; 54; 59; 8]. Moreover, compressive strength is considered a key concrete property since it is directly correlated with concrete quality.