# Effect of Aggregate Size on Recycled Aggregate Concrete under Equivalent Mortar Volume Mix Design
## 2 Materials and Methods  
### Materials  
Ordinary Portland cement corresponding to Korean Standards (KS) Type I [36] was used. Density and specific surface area of the OPC were 3.14 g/cm\({}^{3}\) and 3550 cm\({}^{2}\)/g, respectively.  
Natural crushed granite aggregate produced in the quarry was used as NA. For natural fine aggregate (NFA), natural siliceous river sand with round and smooth particles was used. The specific gravity and water absorption were 2.53 and 0.91%, respectively.  
Two types of RCAs (RCA1 and RCA2) with a nominal maximum aggregate size of 25 mm were selected from the RCA processing plant: RCA1 from a concrete road and RCA2 from unknown sources. As a result of visual inspection, no foreign substances other than aggregate, mortar, and concrete were found in the RCAs. The RCAs were transferred to the laboratory in ton bags, and were classified by size (9.5, 13, 19, and 25 mm) to evaluate material properties for each size. Water absorption and specific gravity were performed as per KS F2503 [37]. The aggregates used in the study are shown in Figure 1 and the material characteristics are summarized in Table 1. The average specific gravity and water absorption of RCA1 were 2.41 and 5.28%, and for RCA2 of 2.53 and 2.54%, respectively.  
Concrete preparation using the EMV mix design method requires quantification of residual mortar attached to RCA. The residual mortar content was determined by the mechanical and chemical stress method developed by [PERSON] et al. [38]. RCA samples of individual size fractions were prepared for this experiment, and the sample mass was approximately 2000 g for the 19-25 mm size fraction and 1000 g for the remaining size fractions. RCA samples dried in an oven at 110 \({}^{\circ}\)C for 24 h were weighed (M1) and immersed in sodium sulfate solution for 24 h. While immersed in sodium sulfate solution, the RCA samples were subjected to a total of five cycles of freezing at \(-\)17 \({}^{\circ}\)C for 16 h and thawing at 80 \({}^{\circ}\)C for 8 h. After the last cycle, the solution was drained and the samples were washed with water. The RCA smaller than 4.75 mm was removed. After that, the washed and sieved samples were placed in an oven to dry and then weighed (M2). The  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Aggregate**} & \multirow{2}{*}{**Size (mm)**} & \multicolumn{2}{c}{**Water Absorption (\%)**} & \multirow{2}{*}{**Specific Gravity**} & \multirow{2}{*}{**RMC (\%)**} \\ \hline NA & 4.75–19 & 0.95 & 2.66 & - \\ \hline \multirow{4}{*}{RCA1} & 19–25 & 4.20 & 2.46 & 21.7 \\  & 13–19 & 4.83 & 2.44 & 27.7 \\  & 9.5–13 & 5.48 & 2.39 & 32.2 \\  & 4.75–9.5 & 6.61 & 2.36 & 32.8 \\  & Average & 5.28 & 2.41 & 28.6 \\ \hline \multirow{4}{*}{RCA2} & 19–25 & 2.62 & 2.52 & 10.8 \\  & 13–19 & 2.23 & 2.55 & 8.9 \\ \cline{1-1}  & 9.5–13 & 2.45 & 2.54 & 13.7 \\ \cline{1-1}  & 4.75–9.5 & 2.86 & 2.52 & 14.5 \\ \cline{1-1}  & Average & 2.54 & 2.53 & 12.0 \\ \hline NFA & 0–4.75 & 0.91 & 2.53 & - \\ \hline \hline \end{tabular}
\end{table}
Table 1: Physical properties of coarse and fine aggregates.  
Figure 1: Natural and recycled aggregates used in the study. (**a**) NA; (**b**) RCA1; (**c**) RCA2.  
quantity of residual mortar was determined by Equation (1) as residual mortar content (RMC).  
\[\text{RMC }(\%)=[(\text{M1 }-\text{M2})/\text{M1}]\times 100 \tag{1}\]  
As seen in Table 1, a residual mortar content can be significantly different depending on the actual RCA source and probably also the way of crushing (28.6% for RCA1 and 12.0% for RCA2). However, the same trend was found for both samples with regard to the relationship between grain size and the amount of residual mortar: a higher residual mortar content was in the small particle size RCA, resulting in higher water absorption and lower specific gravity. Similar results have been reported in [39; 40]. This may be because the RCA of a small fraction contained the residual mortar that fell off the concrete mass during the RCA production.