## 3 Results and Discussion
### Influence of the Cement Volume Reduction  
A comparative analysis for the compressive strength evolution is shown in Figure 3. These are classified by concrete types (PC-45 (Figure 3a) and RC-30 (Figure 3b)) in order to clarify the influence of the different cement content, and also to avoid a possible influence of the accelerator additive which is only included in RC-30 mixtures. For the mixtures compared, the additive rate was kept constant between the different cement steps in each concrete type, either in volume or in binder proportion. Figure 3 first seems to suggest that a reduction in the cement volume will entail a proportional fall in compressive strength, such that the evolution of strength is maintained approximately constant at the different measured ages. Thus, this proportional fall in compressive strength may be statistically evidenced, obtaining a degree of correlation of R\({}^{2}=-0.98\) for both situations. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline  & \ \begin{tabular}{c} **Cement** \\ **(kg)** \\ \end{tabular}  & \multicolumn{3}{c}{\(\mathbf{W_{\text{ef}}/C}\)} & \multicolumn{3}{c}{\(\mathbf{f_{\text{c}}\) (MPa)}} & \multicolumn{3}{c}{\(\mathbf{\%\ f_{\text{c}}\) (Ref 28 D) (MPa)}} & \multicolumn{3}{c}{ \begin{tabular}{c} **Cost** \\ **(EUR/m3)** \\ \end{tabular}  } \\ \cline{3-13}  & & & **24 h** & **3 d** & **7 d** & **28 d** & **24 h** & **3 d** & **7 d** & **28 d** & \\ \hline PC-45 & 420 & 0.34 & 51.3 & 59.4 & 62.8 & 71.3 & 71.9 & 83.3 & 88.1 & 100 & 56.7 \\ PC-45-360 & 360 & 0.39 & 42.4 & 49.1 & 53.9 & 64.2 & 66.0 & 76.5 & 84.0 & 100 & 48.0 \\ PC-45-360- & 360 & 0.37 & 41.2 & 51.2 & 59.4 & 65.4 & 63.0 & 78.3 & 90.8 & 100 & 55.1 \\ \(1\%\)\(\_\)nano & 360 & 0.48 & 31.5 & 40.6 & 44.2 & 55.5 & 56.8 & 73.2 & 79.6 & 100 & 45.7 \\ PC-45-300- & 300 & 0.38 & 38.3 & 48.5 & 52.0 & 65.8 & 58.2 & 73.7 & 79.0 & 100 & 48.2 \\ \(\text{plast\_{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_}{\_} & & & & & & \\ RC-30 & 360 & 0.43 & 36.9 & 51.0 & 58.9 & 66.2 & 55.7 & 77.0 & 89.0 & 100 & 53.3 \\ RC-30-Accl\_\_x0 & 360 & 0.41 & 30. However, this hypothetical cement volume-strength interaction must be considered incorrect since it is typically deduced by comparison between mixtures with significantly different cementitious matrices, which did not actually obtain the same volume of effective mixing water, and thus yielded a different effective W\({}_{\text{ef}}\)/C ratio. Thus, if PC-45-300 and PC-45-300-plast_x2 mixtures (dosages with same cement volume but different W\({}_{\text{ef}}\)/C ratio) are now compared and also compared with PC-45-360 (with +60 kg of cement but same W\({}_{\text{ef}}\)/C ratio as PC-45-300-plast_x2), the results (Figure 4a) show that the mixtures with a similar W\({}_{\text{ef}}\)/C ratio reach a similar final compressive strength (\(f_{\text{c28 4}}\): 65.8 y 64.2 MPa) despite the difference of 60 kg in cement volume. However, both mixtures with the same cement volume show different strength levels (\(f_{\text{c28 4}}\): 55.5 y 65.8 MPa), with the values being higher for the mix with lower effective W\({}_{\text{ef}}\)/C ratio (Figure 4a). These results corroborate that the real strength level for any concrete mix is actually influenced by the W\({}_{\text{ef}}\)/C relation, which is consistent with the findings of [PERSON] [46], and not by the total cement volume, as can be wrongly deducted from Figure 3. This aspect is commonly misrepresented in many recommendations (different concrete manufacturers and in some concrete manufacture technical recommendations).