## 2 Materials and Methods  
### Fabricating and Characterizing the Samples  
The specimens were prepared by [27] using CP II E 40 RS Portland cement, water, fine sand as fine aggregate, gravels 0 (4.8 mm to 9.5 mm) and 1 (9.5 mm to 19 mm) as coarse aggregates, superplasticizer, EVA grains, and piassava fibers. The piassava fibers were extracted from Attalea funifera Martius plants, which are palm trees from Amazon forest and, mostly, from the southern region of Bahia, Brazil.  
The EVA aggregates were divided into two categories, according to diameter. Elements with diameters between 2.36 mm and 1.18 mm were designated coarse EVA (EG), and EVA aggregates with diameters less than 850 um were designated fine EVA (EF). The length adopted for the piassava fibers was a uniform 2 cm long. The superplasticizer used was the MaSterGlenium 54, in a content of 0.5% of the cement mass.  
The specimens were molded in cylindrical molds 100 mm in diameter and 200 mm in height, according to NBR 5738 [28].  
The mixture for the reference concrete (RC) was defined by the ABCP (Associacao Brasileira de Cimento Portland) method [29] as 1:1.70:0.98:2.41 with a 0.62 water/cement ratio. This RC has 44.2% gravel (coarse aggregate), while in the lightweight concrete, the non-conventional aggregates partially replace the gravel in volume values. All the other concrete constituents' values are preserved in all specimens.  
Table 1 lists the different concretes studied, with the acronyms and percentages used in the manufacture of the specimens. Table 2 lists the calculated percentages of gravel, EVA, and fiber considering the mix in each specimen type.  
Porosity Estimation  
The concrete mix defines the volumetric composition of the specimens but the porosity is caused by the air that is stuck inside the cementitious mass. For this reason, specimen porosity is usually estimated using standardized techniques in the construction industry. The porosities of the specimens analyzed in this study were obtained using water absorption method [27] and the calculated reference values in volume are shown in last column of Table 2.  
The porosity reference values measured in the samples with lightweight additives were higher than the porosity measured in the reference concrete (5.41%). This indicates a higher air retention associated with the addition of EVA and fiber. This finding was also supported by [30; 31], who reported porosities in standard concrete samples ranging between 2.5% and 6.2%. However, after the incorporation of lightweight aggregates, they  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & \multicolumn{4}{c}{**EVA Grain**} \\ \cline{3-6}  & & \multicolumn{2}{c}{**Thin EVA**} & \multicolumn{2}{c}{**Thick EVA**} \\ \hline Fiber & 0\% & 5\% & 15\% & 25\% & 15\% \\
0\% & CR & EF5 & EF15 & EF25 & EG15 \\
1\% & - & 1 EF5 & 1 EF15 & 1 EF25 & 1 EG15 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Acronyms used in this work for each concrete mixture and percentages in volume of gravel substitution for non-conventional aggregates.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Probe** & **EVA-Ref \%** & **Fiber-Ref (\%)** & **Gravel-Ref (\%)** & **Pore-Ref (\%)** \\ \hline CR & - & - & 44.2 & 5.41 \\ EF5 & 2.20 & - & 41.9 & 5.95 \\ EF15 & 6.60 & - & 37.6 & 8.98 \\ EF25 & 11.0 & - & 33.1 & 12.3 \\ EG15 & 6.60 & - & 37.5 & 11.2 \\
1 EF5 & 2.20 & 0.98 & 41.5 & 0.86 \\
1 EF15 & 6.60 & 0.98 & 37.2 & 15.3 \\
1 EF25 & 11.0 & 0.98 & 32.8 & 10.4 \\
1 EG15 & 6.60 & 0.98 & 37.2 & 7.20 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Reference volume percentages of each aggregate (gravel, EVA and fiber).  
observed values ranging from 4% to 15.28%. Similarly, other authors, such as [15], who analyzed similar samples, estimated the porosity ranging from 4.28% to 15.46%. Thus, the porosity results used in this study align with those reported in the literature, confirming an increase in concrete porosity resulting from the addition of light aggregates.