# Recycling 3D Printed Concrete Waste for Normal Strength Concrete Production
## 2 Materials and Methods
### Mix Design  
Table 2 provides a comprehensive breakdown of mix designations and the respective percentages of different materials incorporated into the mix. In parallel, Table 3 offers a detailed presentation of the mix proportions measured in kg/m\({}^{3}\), accompanied by the fresh concrete density for various mixtures. The focal points of this study encompass three main parameters: (i) the type of aggregate (natural or recycled), with varying proportions, (ii) the  
Figure 5: Grading curve for 50% replacement ratio (1:1). Figure 6: Grading curve of aggregate. variation of water amount with constant cement content, and (iii) the strength class of the concrete, represented by C30/37 and C40/50. To systematically explore the impact of these parameters, ten concrete mixtures, each comprising four specimens, were carefully prepared. These mixtures encompass different aggregate replacement percentages and water amounts, tailored for the selected concrete strength classes. The mix designations outlined in Tables 2 and 3 utilize specific labels: 'C' for concrete, 'NA' for natural aggregates, and 'RA' for recycled aggregates. The numerical values following 'C' and 'RA' denote the cylindrical characteristic compressive strength in MPa at the age of 28 days and the percentage of recycled aggregate by weight in the total aggregate, respectively. The symbols 'w+' and 'w\(-\)' represent the utilization of additional water without superplasticizer and the use of superplasticizer with a reduced water amount compared to the reference mix to achieve the desired workability in the recycled concrete mix. This systematic nomenclature provides a clear and organized framework for understanding the composition and characteristics of each concrete mixture in the study. The primary source of natural coarse aggregate (NCA) is quartz gravel, with a minor fraction sourced from sand--this accounts for a maximum of 3%. River sand is employed as the natural fine aggregate. Recycled coarse and fine aggregates (RCA and RFA) are derived from crushed 3D-printed concrete waste. The water-cement (w/c) ratio is a pivotal factor with a direct impact on the properties and workability of concrete mixes. In light of this, we introduce different water-cement ratios (w/c) beyond those of the reference mixes. In the absence of a superplasticizer, determining the highest permissible w/c ratio becomes crucial, aligning with the natural workability of recycled concrete. Conversely, the introduction of a superplasticizer into \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Mix**} & **Mix** & \multicolumn{2}{c}{**Superplasticizer (1\%**} & \multicolumn{2}{c}{**Aggregate (\%)**} \\  & **Designation** & **w/c** & **of Binder)** & **NA** & **RA** \\ \hline Mix 1 & C40-RA0 & 0.41 & - & 100 & - \\ Mix 2 & C40-RA50 & 0.41 & 1 & 50 & 50 \\ Mix 3 & C40-RA50w+ & 0.51 & - & 50 & 50 \\ Mix 4 & C40-RA67 & 0.41 & 1 & 33 & 67 \\ Mix 5 & C40-RA67w\(-\) & 0.38 & 1 & 33 & 67 \\ Mix 6 & C30-RA0 & 0.51 & - & 100 & - \\ Mix 7 & C30-RA50 & 0.51 & 1 & 50 & 50 \\ Mix 8 & C30-RA50w+ & 0.70 & - & 50 & 50 \\ Mix 9 & C30-RA67 & 0.51 & 1 & 33 & 67 \\ Mix 10 & C30-RA67w\(-\) & 0.41 & 1 & 33 & 67 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mix designations and proportions of different ingredients. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Mix**} & \multirow{2}{*}{**Cement**} & \multirow{2}{*}{**River Sand**} & \multirow{2}{*}{**River Gravel**} & \multirow{2}{*}{**RA 1**} & \multirow{2}{*}{**Water**} & \multicolumn{2}{c}{**Superplasticizer**} & \multirow{2}{*}{**Fresh**} \\  & & & & & & **(1\% of Binder)** & **Density** \\ \hline C40-RA0 & 459 & 542 & 1206 & - & 188 & - & 2388 \\ C40-RA50 & 459 & 874 & - & 874 & 188 & 4.59 & 2236 \\ C40-RA50w+ & 459 & 874 & - & 874 & 234 & - & 2191 \\ C40-RA67 & 459 & 583 & - & 1165 & 188 & 4.59 & 2207 \\ C40-the mix presents another dimension. Superplasticizers, as chemical admixtures, enhance the workability of concrete without significantly altering the w/c ratio.