## 4 Experimental Test Results
### Flexural Strength  
Figure 8a presents the average flexural strength of concrete samples at 28 days with the traditional mixture and the modified EMV mixtures. In addition, the relative strength ratios of the ERA series, ERB series, and ERR mix are depicted in Figure 8b-d, respectively, compared to the flexural strength of the control specimens (CNC). Compared to the remarkable drop in the compressive strength of as much as 24% in the ERA2 mix, the difference in the flexural strength was reduced to 16% in the ERA2 mix. Two studies explained [45; 46] that the flexural strength of RCA concrete is not greatly affected by the presence of RCA, compared to flexural behavior of NA concrete because of the interfacial bond and better mechanical interlocking resulting from rough-textured as well as angular RCA. This trend also  
Figure 7: [PERSON]’s modulus results of concrete samples.  
can be explained by the relation between flexural strength (modulus of rupture: MOR) and compressive strength. [PERSON] [47] suggested from his tests that the MOR of concrete to compressive strength is 14.5% with a compressive strength of 27.6 MPa and 12.8% with 41.4 MPa. However, test results in the ERB series show that the MOR to compression is about 18%, as shown in Table 4. Therefore, either ERB1 or ERB2 mix may be preferred for concrete pavements, where the pavement is loaded in bending.  
It is seen in Figure 8b,c that at the same water-cement ratio, slump, and air content, EMV mixtures with S = 1 (ERA1 and ERB1) have higher flexural strength than those with S = 2 (ERA2 and ERB2). The lower FA/a ratio of the ERA1 and ERB1 mixes, compared to the ERA2 and ERB2 mixes, contributed to higher flexural strength.  
Next, comparing test results between the ERA series (Figure 8b) and ERB series (Figure 8c), it was observed that flexural strength is decreased as RCA replacement content is increased. Hundred  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Mix-Id**} & \multicolumn{2}{c}{**Average Strength of Concrete (MPa)**} & \multicolumn{2}{c}{**Ratio (\%)**} \\ \cline{2-5}  & **Compression** & **Flexure** & **Split Tension** & **Flexure to Compression** & **Split Tension to Compression** \\ \hline CNC & 38.7 & 5.36 & 3.72 & 13.9 & 9.6 \\ ERA1 & 34.4 & 4.95 & 3.40 & 14.4 & 9.9 \\ ERA2 & 29.3 & 4.50 & 3.05 & 15.3 & 10.4 \\ ERB1 & 32.4 & 5.91 & 3.47 & 18.3 & 10.7 \\ ERB2 & 31.0 & 5.55 & 3.31 & 17.9 & 10.7 \\ ERB3 & 39.5 & 5.27 & 3.30 & 13.4 & 8.4 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Relation between compressive, flexural, and split tensile strength of concrete; Mix-Id: mixture identification.  
Figure 8: Flexural strength results of concrete samples (**a**) strength, (**b**) relative value of ERA series, (**c**) relative value of ERB series, and (**d**) relative value of ERB mix.  
percent of RCA was replaced in the ERA series, while only 50% RCA was replaced in the ERB series. Thus, the relative strength value of the ERB series (104-110%) is far greater than the ERA series (84-92%). It was pointed out by [PERSON] et al. [48] that failure through old residual mortar (here in ERA series) might result in lower flexural strength and a more irregular failure pattern.  
Test results in Figure 8d indicates that the flexural strength of the ERR mix is similar to that of the control CNC mix. The high quality of the RCA, which was produced from PC concrete sleepers, may be one of the main reasons for this.