# Meta-Analysis of the Performance of Previous Concrete with Cement and Aggregate Replacements
## 5 Results and Discussion
### Aggregate Replacement in Previous Concrete
#### 5.3.2 Performance Evaluation  
Table 2 shows the type of replacement material for NA, the percentage of replacement, and the effect sizes for PC performance based on aggregate replacement. The mechanical performance of PC was generally inferior upon replacing NA with other aggregates such as RA. Out of the 11 effect sizes for bulk density, seven negative values were obtained, signifying a tendency for replaced aggregates to produce lighter-weight PC. This general decrease in bulk density may be attributed to the lower unit weight of the replaced aggregates as compared to that of NA [35; 56; 57]. Furthermore, out of the 14 and 10 effect sizes for compressive and flexural strengths, respectively, 8 and 6 negative effect sizes were obtained, signifying the inferior performance of PC with replaced aggregates. This is due to impurities, the porous nature of the replacement aggregates, and the weaker interfacial bond between the binding matrix and the aggregates [50; 55]. While RA replacement gave conflicting results, replacement with EAFS, SS, and CS improved the mechanical properties. Such enhancement is due to the stronger nature of these slag-based aggregates compared to NA, alongside the improved bond with the binding matrix because of their angular and irregular shape [44; 58; 59]. Alternatively, improved hydraulic performance was observed in PC with replaced aggregates as compared to NA-PC. Out of the 13 effect sizes for porosity and permeability, 9 and 10 positive effect sizes were obtained, respectively, indicating a general improvement  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Reference**} & \multirow{2}{*}{**Type**} & \multirow{2}{*}{**Percentage**} & \multicolumn{3}{c}{**Mechanical Properties**} & \multicolumn{3}{c}{**Hydraulic Properties**} & \multicolumn{1}{c}{**Durability**} \\ \cline{3-10}  & & & **Bulk** & **Compressive** & **Tensile** & **Flexural** & **Porosity** & **Permeability** & **Abrasion** \\  & & & **Density** & **Strength** & **Strength** & **Strength** & **Strength** & **Strength** & **Strength** \\ \hline
[17] & RA & \(50\%\) & \(-2.8\) & \(-2.0\) & \(-250.0\) & \(-3.0\) & \(3.0\) & \(3.0\) & \(-10.0\) \\  & & \(100\%\) & \(-1.8\) & \(-0.5\) & \(0.0\) & \(-3.8\) & \(3.0\) & \(2.0\) & \(-9 in this performance with aggregate replacement. The replaced aggregates are more porous than NA, thus producing a more porous and permeable PC [50; 52; 55]. However, such an increase in hydraulic performance was not necessarily associated with a decrease in mechanical properties. In fact, this was the case for PC mixes with aggregates replaced by SS, EAFS, and CS, and occasionally by RA. Meanwhile, only one study examined the impact of NA replacement by RA on the durability properties. Despite having a negative effect size, the results are inconclusive due to insufficient data. The results in Table 2 are further analyzed in Figure 8 using fixed-effect pooled \(d\) values. It can be observed that there is no significant change in mechanical and hydraulic performance with aggregate replacement, except for tensile strength, which was improved. Indeed, the \(d\) values (black box) ranged between \(-1\) and \(+1.5\). The durability properties were not included in the analysis due to limited available data. Conclusively, despite the negative effect of aggregate replacements in PC, especially RA, the mechanical performance of PC with aggregate replacement appeared to be similar to that of NA-based PC, with an improvement in hydraulic performance. Variation in the performance of PC based on aggregate replacement was further analyzed with box and whisker plots, as shown in Figure 9. The aggregates considered were NA, IWA, and RA (including recycled coarse and fine aggregates). Correspondingly, the medians of NA-based PC, IWA-based PC, and RA-based PC for compressive strength were approximately 13.1, 20.3, and 10.1 MPa. The respective medians for tensile strength were 1.4, 2.8, and 0.8 MPa, while those for flexural strength were 2.5, 3.6, and 1.9 MPa, respectively.