## 2 Materials and Methods
### Solvent Preparation and Tests
The pH measured with a pH meter was 12.55 (water-concrete mixture), and the pH measured with pH test paper (water-concrete mixture and fresh concrete) was 12, in both cases at 22.2 \({}^{\circ}\)C.  
Since five different materials were tested (HI, ENG, ESD, GYP, and ABS), and three specimens were prepared per material, the amount of the solutions was determined accordingly. After determining the pH values, two solutions were prepared with NaOH powder. A 250 mL solution with pH 12.55 and a 500 mL solution with pH 12 were prepared. Based on the previous measurements, two solutions were made, one with a pH value of 12 and one with 12.55, since the values of the pH strip measurement were identical. The first solution was prepared from a mixture of 0.2 g NaOH powder and 500 mL ionized water and the second solution from a mixture of 0.355 g NaOH powder and 250 mL ionized water. Equations (1)-(4) show the calculations for the first solution (500 mL) preparation (where \(M_{NaOH}\) = 40.00 g/mol, the pH value of the NaOH solution is 12, and the pH of the powdered NaOH solvent is 14):  
\[\text{pOH1}=14-12=2 \tag{1}\]\[[\mathrm{OH}^{-}]_{1}=10^{-\mathrm{POH}1}=10^{-2}\ [\mathrm{mol}/\mathrm{L}]=0.01\ [ \mathrm{mol}/\mathrm{L}] \tag{2}\]  
\[n_{1}=0.01\ [\mathrm{mol}/\mathrm{L}]\ \times 0.5\ [\mathrm{L}]=0.005\ [ \mathrm{mol}] \tag{3}\]  
\[m_{1}=40.00\ [\mathrm{g}/\mathrm{mol}]\ \times 0.005\ [\mathrm{mol}]=0.2\ [ \mathrm{g}] \tag{4}\]  
Equations (5)-(8) show the calculations for the second solution (250 mL) preparation (where \(M_{\mathrm{NaOH}}\) = 40.00 g/mol, the pH value of the NaOH solution is 12.55, and the pH of the powdered NaOH solvent is 14):  
\[\mathrm{pOH2}=14-12.55=1.45 \tag{5}\]  
\[[\mathrm{OH}^{-}]_{2}=10^{-\mathrm{pOH2}}=10^{-1.45}\ [\mathrm{mol}/\mathrm{L}]=3.55\ \times 10^{-2}\ [\mathrm{mol}/\mathrm{L}] \tag{6}\]  
\[n_{2}=3.55\ \times 10^{-2}\ [\mathrm{mol}/\mathrm{L}]\ \times 0.25\ [ \mathrm{L}]=8.88\ \times 10^{-3}\ [\mathrm{mol}] \tag{7}\]  
\[m_{2}=40.00\ [\mathrm{g}/\mathrm{mol}]\times 8.88\ \times 10^{-3}\ [\mathrm{mol}]=0.355\ [ \mathrm{g}] \tag{8}\]  
The solutions were mixed in several steps. First, the solutes were weighed on an analytical balance of hundredths accuracy. This was followed by a preliminary dissolution, where about two-thirds of the total solvent was added to the solute. After the exothermic reaction, the solution was diluted to the appropriate amount, and finally, after stirring, the pH value was adjusted with the pH meter to the nearest hundredth of the pH of the concrete until it was set to a predetermined value of 12 and 12.55. After the preparations, the solutions were divided into five parts for 250 mL of pH 12.55 and ten parts for 500 mL of pH 12, so that 50 mL of solution was in measuring cups. Then, the 0.4 mm thin PLA samples were put into the solution and checked periodically after every 24 h for 28 days. With this experiment, the aim was to observe the behavior of PLA and ABS specimens with a size of 25.0 \(\times\) 0.4 \(\times\) 80.0 mm in an alkaline medium with the same pH as the concrete over the same time interval as the concrete curing time.