## 4 Discussion
Nevertheless, it must be clarified that the determined value of each measurement set highly depends on a variety of parameters namely the w/c, additives incorporation and curing conditions, i.e., humidity levels and temperature profiles. Curing conditions can affect drastically the compressive strength of a cementitious material. More specifically, compressive strength degradation has been correlated with low moisture levels during the first day of curing or high temperatures in the initial curing state which is responsible for lower quality hydration products [52]. Furthermore, w/c ratios used in mortars formulation have also been directly correlated with the voids formed in the concrete matrix and consequently with their mechanical strength. More specifically, increased w/c ratios have been known to lead to increased voids in the cementitious matrix and thus to the degradation of mechanical properties [1]. The w/c ratio used in this work (0.5) is high compared to the corresponding ratios examined by other research groups. For example the w/c ratios in cementitious composites with SAPs were 0.30-0.35 in the research of [PERSON] et al. [8], 0.40 and 0.50 in the research of [PERSON] et al. [9], 0.30, 0.40, 0.50 in the research of [PERSON] et al. [10], 0.35, 0.40 and 0.50 in the research of [PERSON] et al. [15] and 0.40 in the research of [PERSON] [54]. Nonetheless, since the effective w/c ratio is not the same as the total w/c ratio, when SAPs are incorporated in mortars, excess of water must be added to counterbalance the amount of water absorbed by SAPs. Considering the dosage of SAPs used in this work (1 and 2% bwoc) the high w/c ratio of 0.50 was chosen. The w/c ratio chosen combined with the curing conditions of the mortar specimens and notably, low moisture during the first day after casting as well as low temperature during the 28 days specimen curing the value of the compressive strength of the control specimens was calculated below 52.5 MPa. In literature, it is often reported that cementitious materials containing SAPs show poorer compressive performance compared to the corresponding materials without SAPs during all curing periods and for SAPs dosages even lower than those examined in this work, while this behavior became more pronounced for increased SAPs dosages. [1; 7; 9; 10; 15; 17]. On the contrary, in this work compressive strength was not influenced by the SAPs incorporation in mortars. The relationship between the determined flexural and compressive strength for the mortar specimens as depicted in Figure 6 was also indicative of the fact that SAPs incorporation in the mortars affected flexural and compressive strength in a similar manner and that their incorporation did not negatively influence the mortar microstructure and hence the mortar strength was not degraded [53; 54]. According to the results in Table 3, the percentage of total porosity was reduced by 0.5% and 2.5% in the cases of mortar-SAPs-1 and mortar-SAPs-2, respectively. Moreover, the percentage of open porosity was also reduced in the case of mortar-SAPs-2 compared to mortar-reference by 0.5%. Open porosity represents the pores which are in direct contact with the specimen environment thus allowing humidity and/or other harmful factors (e.g., corrosive factors) to penetrate the bulk of the specimen and cause the material deterioration. As a result, the open porosity reduction in cementitious materials promotes their mechanical integrity and their sustainability. Additionally, as shown in Figure 7, the size of the pores in the mortar-reference specimens was greater than that of the mortar-SAPs-1 and mortar-SAPs-2 specimens, while the smallest pores were recorded in the case of mortar-SAPs-2. The pore sizes in the mortar-reference specimens showed a wide distribution ranging from 9 to almost 500 \(\upmu\)m. On the contrary, the pore sizes in mortar specimens in which SAPs had been incorporated showed a narrower distribution ranging from 9 to 333 \(\upmu\)m and from 9 to 171 \(\upmu\)m for mortar-SAPs-1 and mortar-SAPs-2, respectively.