## 3 Results and Discussion
### Properties in Hardened State  
#### 3.3.1 Flexural and Compressive Strength  
The resistance of a cement considers that of a normalized mortar mixed with siliceous sand, with a water/cement ratio equal to 0.5 [26]. The tests were carried out on three prismatic molds of 40 \(\times\) 40 \(\times\) 160 mm, completed with mortar, according to the standard. In all the tests, the strengths for one year are considered, starting with the flexural strength. Compared with standard cement, all of the additions show lower values than that relative to the OPC: the lowest value coincides with 20% substitution. Flexural strength measurements are achieved in all substitutions, lower than those of the OPC, but almost equal, after the reaction year, when the substitution is 10% waste, while the 20% waste substitution remains with lower values in all times studied, as seen in Figure 3.  
The particle size of the system also influences the development of resistances--these being higher the greater the reaction surface provided by the cement.  
The partial substitution of pozzolanic materials in the OPC generates a decrease in the resistance in the first curing ages, while in the long-term, they can reach (or even exceed) the strengths of the OPC. The hydrated calcium silicate 3 CaO 2 SiO\({}_{2}\) H\({}_{2}\)O (C-S-H gels) in its different forms and structures, is the main responsible for cohesion and resistance. Consequently, an increase in said product due to the pozzolanic reaction causes a gain in mechanical resistance in the medium- and long-term.  
The mortars to be obtained must be of the compression resistance class after setting 42.5 N (normal resistance) or 42.5 R (high initial resistance), with initial resistance values after 2 days, higher or equal to 10 MPa for 42.5 N and equal to or greater than 20 MPa at 42.5 R; then, after 28 days, reach values equal to or greater than 42.5 MPa, in both classes [28].  
Short-time compression values increase with the formation of amorphous C-S-H gels and when the concentration of portlandite decreases [44]. Setting time, mechanical strength, and shrinkage are related with higher mechanical strength, since it implies less shrinkage [45]. The elasticity modulus under compression increases as the percentage of cement substitution for siliceous materials is higher [40].  
Figure 3: Variation of the flexural strength for all specimens.  
Amorphous materials generate a strength gain at an early age due to the filler effect, which is immediate and facilitates the acceleration of cement hydration during the first day. The maximum effect occurs between 7 and 14 days for replacement percentages between 5% and 30%. After 14 days of curing, the strength gain is less [46].  
The incorporation of granite wastes in mortars does not modify the logarithmic trend that links composition and curing time, regardless of the percentage of waste substitution (10% or 20%) [47]. Figure 4 show the results when 10% waste is added: the compressive strength increases with time and, in all cases, exceeds the OPC value. However, there is a 20% waste substitution, and after 28 days of reaction, the trend changes and coincides with that proposed by [PERSON] et al. [17] in conventional mortars, and with results similar to those of [PERSON] et al. [48] and [PERSON] et al. [49], when studying sludge and calcareous materials, respectively, in the manufacturing of new cements. As shown in Figure 4, the highest values correspond to the PR-2 sample, although at the end of the time, the compressive strengths are equalized.  
[PERSON] [50] considers granite powder substitutions of different percentages (5% and 10%). The optimal addition is 10%, generating a positive effect on the tensile strength and without detecting changes in the chemical phases of the mixture with respect to the standard cement.