# Sustainable Concrete with Recycled Aggregate from Plastic Waste: Physical-Mechanical Behavior
## 2 Materials and Methods  
For the process of obtaining the recycled fine aggregate, PET waste was used (Figure 1c), which was crushed to a maximum particle size of 0.475 cm (No. 4 mesh) and a minimum size of 0.015 cm (No. 100 mesh). The particle size curve was adjusted using a partial crushing process that allowed for a grain distribution similar to natural sand and within the limits of the regulations [52]. The recycled coarse aggregate came from thermoplastic paint residues used in horizontal signage for pavement construction (Figure 1a). TP residues resemble artificial rocks, with surface hardness and color variability. These rocks were mechanically crushed with a demolition hammer and then manually crushed until reaching sizes that complied with ASTM C33 regulations and were consistent with the sizes of natural coarse aggregate. No. 4 mesh (0.475 cm) was considered the lower limit, and the 1\" mesh (2.54 cm) was the upper limit. The cement used for the mixtures was Ordinary Portland Cement, strength class 30 (CPO 30), corresponding to type 1 according to ASTM C150 [53]. The coarse and fine natural aggregates used were limestone from the Metropolitan Area of Monterrey. The maximum nominal size for the gravel was 3/4\". The basic physical properties were obtained for both the natural and recycled aggregates (Table 2), which allowed for the design of the mixtures. Figure 1: (a) Crushed TP waste, (b) TP coarse aggregate, and (c) PET fine aggregate. The recycled coarse and fine aggregates were adjusted to the natural gravel and sand granularometries to ensure proper distribution in the new concrete mixes. Although this procedure was considered adequate for preparing the mixes, it leads to increased environmental impact due to the higher consumption of energy required to screen the aggregates. Therefore, when developing an industrial process, the extent to which the screening process can be considered adequate must be established. Once the aggregates were characterized, the mixtures were designed following the ACI 211.1 methodology for mixture design [58]. The volume percentages of the RPAs corresponding to each mixture varied due to the difference between the densities of the recycled and natural aggregates, both for fine and coarse aggregates. A w/c ratio of 0.48, a design strength of 35 MPa, and a slump of 10 cm were used. Eight mixtures were prepared in total: one conventional (CON); three that replaced the fine aggregate with PET sand in percentages of 5% (PES), 9% (PE9), and 14% (PE14), keeping the natural coarse aggregates constant; and four that replaced the natural coarse aggregate with thermoplastic paint (TP) gravel in percentages of 5% (TP5), 10% (TP10), 15% (TP15), and 20% (TP20), keeping the natural fine aggregates constant. \begin{table}
\begin{tabular}{c c c c c c} \hline
**PROPERTY** & **REGULATIONS** & **CNA** & **CRPA** & **FNA** & **FRPA** \\ \hline Density & ASTM C128/C127 [54,55] & 2.69 & 2.01 & 2.62 & 1.14 \\ Absorption (\%) & ASTM C128/C127 [54,55] & 0.53 & 6.09 & 2.41 & NA \\ Dry compact volumetric weight & & & & & \\ (kg/m\({}^{3}\)) & ASTM C29 [56] & 1565.5 & 1182 & & NA \\ Fineess modulus & ASTM C33 [52] & \multicolumn{2}{c}{NA} & \multicolumn{2}{c}{2.4} \\ Resistance to & ASTM C131 [57] & 23.2 & 42.8 & NA \\ degradation (\%) & \multicolumn{2}{c}{ASTM C33 [52]} & \multicolumn{2}{c}{See Figure 2} \\ \hline \end{tabular}
\begin{tabular}{c c c c} \hline \hline \multicolumn{4}{c}{CNA: coarse natural aggregate. CRPA: coarse recycled plastic aggregate. FNA: fine natural aggregate. FRPA: fine recycled plastic aggregate.} \\ \hline \end{tabular}
\end{table} 
Table 2: Basic physical properties of natural and recycled aggregates. Figure 2: Particle size curves: (**a**) fine aggregate; (**b**) coarse aggregate. In Mexico, the complementary technical standards for the design and construction of concrete structures limit the use of recycled fine aggregates and only allow the addition of up to 20% recycled coarse aggregates from concrete waste [51].