# Design Procedures for Sustainable Structural Concretes Using Wastes and Industrial By-Products
## 4 Discussion  
### Fresh Behavior  
The EAFS aggregates significantly altered concrete fresh state behavior when compared to natural aggregates typically used in structural concrete design. This is most likely due to the increased water absorption by the EAFS aggregates and the lack of fine particles which may be clearly identified in the grading curves (Figure 1b). Compositions have been shown to be very sensitive to the process of mixing and to the \(w/p\) or \(w/c\) ratio, most likely due to the porous nature of the EAFS aggregates. The EAFS aggregates porosity leads to the gradual absorption of water during the mixing process, resulting in alterations of the fresh and hardened behavior. In this regard, it is important to adapt the mixing process in order to take the best advantage of the physical properties of EAFS aggregates. This problem extends to any other situation where alternative aggregates or ingredients are included in conventional concrete mixtures, mainly in the case of the incorporation of wastes or industrial by-products. As shown in Figure 9, EAFS concrete mixtures showed distinct behaviors, initially very different from REF1 and REF2. Figure 10 shows some of the results obtained for representative specimens during the slump test. The mixtures EAFS3A and 4 (Figure 10c), with a distribution modulus of 0.35, had a very dry behavior; therefore, it was decided to decrease the distribution modulus in the subsequent mixtures. It seems that the porous nature of EAFS requires a greater volumetric percentage of paste in the concrete, necessary \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{\(t_{1}\) (Days)} & \multicolumn{3}{c}{\(R_{\text{c65}}\) (kg\_year/m\({}^{5}\))} & \multicolumn{3}{c}{\(R_{\text{c65m}}\) (kg\_year/m\({}^{5}\))/CoV} \\ \cline{2-5}  & **REF2** & **EAFS8D1** & **FRC\_EAFS** & **REF2** & **EAFS8D1** & **FRC\_EAFS** \\ \hline
28 & 37.75 & 58.17 & 47.39 & & \\
56 & 75.51 & 64.92 & 51.44 & & \\
63 & 40.06 & 62.69 & 59.75 & & \\
70 & 41.92 & 55.73 & 62.82 & & \\
90 & 53.39 & 72.93 & 73.27 & & \\
122 & 51.70 & 72.59 & 71.69 & & \\
143 & 48.58 & 68.45 & 64.19 & 48.92/0.189 & 65.30/0.076 & 63.42/0.119 \\
149 & 49.94 & 68.74 & 60.58 & & \\
163 & 47.10 & 62.99 & 67.10 & & \\
170 & 43.87 & 64.22 & 63.85 & & \\
174 & 45.99 & 65.15 & 67.54 & & \\
186 & 51.28 & 67.01 & 71.46 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 20: Results of carbonation resistance, \(R_{\text{c65}}\), for the REF2 mixture and for the mixtures designed with EAFS and RTSF. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{\(t_{1}\) (Days)} & \multicolumn{3}{c}{\(X_{\text{1m}}\) (mm)} \\ \cline{2-3}  & **REF2** & **EAFS8D1** & **FRC\_EAFS** \\ \hline
28 & 19.12 & 15.41 & 17.07 \\
56 & 27.22 & 20.63 & 23.17 \\
63 & 27.85 & 22.26 & 22.80 \\
70 & 28.70 & 24.89 & 23.44 \\
90 & 28.83 & 24.67 & 24.61 \\
122 & 34.11 & 28.79 & 28.97 \\
143 & 38.10 & 32.10 & 33.15 \\
149 & 38.36 & 32.69 & 34.83 \\
163 & 41.31 & 35.72 & 34.61 \\
170 & 43.71 & 3 to cover the pores at the surface of the EAFS aggregates and lubricate the interparticle movement, in order to reach equivalent fresh behaviors. With the change from \(q\) = 0.35 to \(q\) = 0.25, the fluid behavior did not show great improvement, although workability seemed to show an improvement. With the decrease in the distribution modulus to 0.20 and 0.15, a remarkable improvement in fluidity was observed, giving these mixtures the best performance in terms of fresh behavior (Figure 10d,e), with the exception of EAFS2. EAFS2 was the only alternative mixture with \(q\) = 0.35 that showed a fresh behavior close to the expected one. This may be explained by the fact that the optimization procedure, in this case, resulted in a greater amount of fine sand, probably because the aggregate fractions selected generated an unbalance in the grading curve, that ended up being fully compensated with fine sand.