## 3 Results and Discussion
### Mechanical Properties  
#### 3.3.1 Experimental Results  
The values of the mechanical properties are plotted in Figure 20. The compression-related properties were determined at early ages and advanced ages apart from at 28 days. Splitting tensile and flexural strengths were also measured at 28 days.  
The trends displayed by all the mechanical properties with the content of RCWTB were similar except for Poisson's coefficient. Therefore, all of them decreased in an approximately linear way as the RCWTB amount increased. This performance is thought to be due to two aspects. First, the weak particles of polymers and balsa wood that were introduced within the SCC when RCWTB was used as a raw material. They created interfacial transition zones with low levels of adhesion to the cementitious matrix, which could have caused these particles to slide when loading, as found for other concrete types [76]. Furthermore, they could easily break when applying the load in those cases in which they exhibited a better adhesion to the cementitious matrix [56; 70]. Second, the large increase in the water/cement ratio as the RCWTB content was augmented to preserve self-compactability in terms of free flow without obstacles [11]. These trends were not affected by age, as the 7-day compressive strength and compression-related mechanical properties at 90 days exhibited equivalent trends. These aspects caused the \(W3.0\) mix not to show mechanical properties with values suitable for use in structural applications [77].  
GFRP fibers show optimal adhesion to the cementitious matrix due to the wedge effect created between the matrix and the fiberglass in the interfacial transition zone, which causes the cementitious matrix to break instead of slipping [76]. Nevertheless, the stitching effect of the GFRP fibers was largely counterbalanced by the two aspects mentioned in the previous paragraph. Thus, these fibers did not contribute to the improvement of the mechanical properties of SCC, unlike what was found in conventional-workability concrete [41]. Only Poisson's coefficient was positively affected by them, since their stitching effect limited the transverse deformability [39], causing this property to remain constant for all SCC mixes regardless of the RCWTB content.  
From the results of these mechanical properties, it can be concluded that it is necessary to develop an SCC design specifically aimed not only to achieve self-compacting properties when RCWTB is added, but to ensure that adequate mechanical behavior is achieved. The study of varying the content of superplasticizers [78], the use of filler to improve the density of the fresh cement paste and the mechanical strength when hardened [5], and the analysis of other possible ways of adding RCWTB as, for instance, an aggregate replacement [34], are strategies that can be applied in future research. Another possibility would be to obtain higher quality GFRP fibers as in other studies in the literature [39], or that those fibers were not mixed with weak particles of balsa wood and polymers. This may enable the addition of waste from wind-turbine blades to SCC to yield a better mechanical performance.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **\(p\)-Value** & **Pearson’s Correlation** & **Spearman’s Correlation** \\ \hline Yield stress & 0.0789 & \(-\)0.51 & \(-\)0.54 \\ Plastic viscosity & 0.0111 & +0.93 & +0.84 \\ \hline \hline \end{tabular}
\end{table}
Table 7: \(p\)-Values for the one-way ANOVA and correlations of the CFD simulations.