## 2 Materials and Methods
### Characterization of Cement Composites
#### 3.2.3 Microstructure Visualization--SEM  
Figure 8 shows SEM images of the mortars at 28 days and 90 days. The matrices and the matrix/sand interfaces enable the evaluation of the evolution of the material over time  
Figure 7: Compressive strength and bulk density (dispersed stars) (**a**) and hydration degree and hydrates contents (**b**) of 28-, 60-, and 90-day cured mortars. as well as the adhesion of the matrix to the sand grain. According to these images, the adhesion of the matrix to the sand grain evolves negatively from the reference to EURO15G, with interfacial transition zones of 0 \(\upmu\)m, 0.2-0.3 \(\upmu\)m, 0.3 \(\upmu\)m, and 0.5-1.4 \(\upmu\)m on average for the reference, EURO2G, EURO5G, and EURO15G, respectively. These values are the second argument that the compressive strength of mortars decreases as the nuclage concentration increases after the flocculation by polysaccharides, as shown in Figure 4.  
Figure 8: _Cont._  
The reference sample (A1 to B2) shows a densification of the matrix with the presence of microporosities at 28 days and their disappearance at 90 days. In images A1 and B1, there is a good distribution of Portlandite and CSH. In the vicinity of the sand grain, weakly polymerized CSH and Portlandite evolve at 90 days into an adhesive interface of CSH gel with Ca/Si between 1.2 and 2.2. The presence of mucilage in small quantities in the EURO2G images perfectly illustrates the impact of the polysaccharide on the cement  
Figure 8: SEM observations of 28- and 90-day mortars matrices and sand/matrix interface. Stars on the micrographs correspond to EDS targets and arrows point to characteristic mineral species ((**C2**) Magnification (M) = 1000; (**A1**,**A2**) M = 2500; (**F1**) M = 2600; (**B1**,**B2**,**C1**,**D1**,**E1**,**E2**,**F2**) M = 5000; (**D2**,**G1**,**G2**,**H1**,**H2**) M = 10,000). matrix. Image C1 shows a spherical geometric shape of CSH (Ca/Si of 2.6) surrounded by Portlandite that is particularly well ordered towards this sphere. This Portlandite organization is particularly visible and amplified on H1. This micrograph corresponds to a higher FM concentration, confirming the polysaccharides' influence on Portlandite structure. [PERSON] et al. [49] already observed this aligned arrangement of Portlandite because of polysaccharides. Image D1, despite the relatively long curing time, shows CSH and Portlandite forming, predominantly. The structure of the matrix remains particularly disordered and less dense than the reference. As far as the matrix around the sand grain is concerned, it consists mainly of Portlandite in the 28-day cure (C2), whereas in the 90-day cure, there is Portlandite and CSH at the same time (D2). The increase in mucilage concentration (Figure 8) induces more and more morphological changes, confirming the arguments presented earlier. Image E1 shows that mucilage appears to influence CSH morphology since all the points analyzed in this image have Ca/Si values ranging from 2.2 to 2.9. At 90 days (F1), the evolution is notable, with Portlandite and CSH present. The matrix remains less dense than the reference matrix (B1) at the same age. The matrix/sand interface consists of Portlandite, as in mortar with less FM (C2). Indeed, image E2 shows Portlandite in two forms: one with a Ca/Si of 8.8 (close to the sand grain) and a Portlandite probably in the process of forming CSH, with a drop in Ca/Si = 5.2 (at distance of 6 \(\upmu\)m from the sand grain). Finally, EURO15G shows significant carbonation (G1) not seen in the other samples. The matrix is filled with CaCO\({}_{3}\) at 28 days (G1), whereas in the 90-day cure, the matrix consists mainly of Ca(OH)\({}_{2}\), as the FM proportion is high. The observation of Ca(OH)\({}_{2}\) in the matrix of the 90-day cure, when at 28 days CaCO\({}_{3}\) was in the majority, has never been reported in the literature regarding low temperatures, but it is corroborated by Figure 7b showing that CaCO\({}_{3}\) disappears in favor of Ca(OH)\({}_{2}\).